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Pollock HS, Rutt CL, Cooper WJ, Brawn JD, Cheviron ZA, Luther DA. Equivocal support for the climate variability hypothesis within a Neotropical bird assemblage. Ecology 2024; 105:e4206. [PMID: 37950619 DOI: 10.1002/ecy.4206] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/09/2023] [Revised: 07/03/2023] [Accepted: 10/05/2023] [Indexed: 11/13/2023]
Abstract
The climate variability hypothesis posits that an organism's exposure to temperature variability determines the breadth of its thermal tolerance and has become an important framework for understanding variation in species' susceptibilities to climate change. For example, ectotherms from more thermally stable environments tend to have narrower thermal tolerances and greater sensitivity to projected climate warming. Among endotherms, however, the relationship between climate variability and thermal physiology is less clear, particularly with regard to microclimate variation-small-scale differences within or between habitats. To address this gap, we explored associations between two sources of temperature variation (habitat type and vertical forest stratum) and (1) thermal physiological traits and (2) temperature sensitivity metrics within a diverse assemblage of Neotropical birds (n = 89 species). We used long-term temperature data to establish that daily temperature regimes in open habitats and forest canopy were both hotter and more variable than those in the forest interior and forest understory, respectively. Despite these differences in temperature regime, however, we found little evidence that species' thermal physiological traits or temperature sensitivity varied in association with either habitat type or vertical stratum. Our findings provide two novel and important insights. First, and in contrast to the supporting empirical evidence from ectotherms, the thermal physiology of birds at our study site appears to be largely decoupled from local temperature variation, providing equivocal support for the climate variability hypothesis in endotherms. Second, we found no evidence that the thermal physiology of understory forest birds differed from that of canopy or open-habitat species-an oft-invoked, yet previously untested, mechanism for why these species are so vulnerable to environmental change.
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Affiliation(s)
- Henry S Pollock
- Department of Natural Resources and Environmental Sciences, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Cameron L Rutt
- Department of Biology, George Mason University, Fairfax, Virginia, USA
- American Bird Conservancy, The Plains, Virginia, USA
| | | | - Jeffrey D Brawn
- Department of Natural Resources and Environmental Sciences, University of Illinois Urbana-Champaign, Urbana, Illinois, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
| | - David A Luther
- Department of Biology, George Mason University, Fairfax, Virginia, USA
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2
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Schweizer RM, Romero A, Tobalske BW, Semenov GA, Carling MD, Rice AM, Taylor SA, Cheviron ZA. Thermal acclimation in a non-migratory songbird occurs via changes to thermogenic capacity, but not conductance. J Exp Biol 2023; 226:jeb245208. [PMID: 37680181 DOI: 10.1242/jeb.245208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2022] [Accepted: 09/01/2023] [Indexed: 09/09/2023]
Abstract
Thermoregulatory performance can be modified through changes in various subordinate traits, but the rate and magnitude of change in these traits is poorly understood. We investigated flexibility in traits that affect thermal balance between black-capped chickadees (Poecile atricapillus) acclimated for 6 weeks to cold (-5°C) or control (23°C) environments (n=7 per treatment). We made repeated measurements of basal and summit metabolic rates via flow-through respirometry and of body composition using quantitative magnetic resonance of live birds. At the end of the acclimation period, we measured thermal conductance of the combined feathers and skins. Cold-acclimated birds had a higher summit metabolic rate, reflecting a greater capacity for endogenous heat generation, and an increased lean mass. However, birds did not alter their thermal conductance. These results suggest that chickadees respond to cold stress by increasing their capacity for heat production rather than increasing heat retention, an energetically expensive strategy.
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Affiliation(s)
- Rena M Schweizer
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Abimael Romero
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Bret W Tobalske
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Georgy A Semenov
- Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80302, USA
| | - Matt D Carling
- Zoology and Physiology, University of Wyoming, Laramie, WY 82071, USA
| | - Amber M Rice
- Department of Biological Sciences, Lehigh University, Bethlehem, PA 18015, USA
| | - Scott A Taylor
- Ecology and Evolutionary Biology, University of Colorado, Boulder, CO 80302, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
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3
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Wilsterman K, Moore EC, Schweizer RM, Cunningham K, Good JM, Cheviron ZA. Adaptive structural and functional evolution of the placenta protects fetal growth in high-elevation deer mice. Proc Natl Acad Sci U S A 2023; 120:e2218049120. [PMID: 37307471 DOI: 10.1073/pnas.2218049120] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2022] [Accepted: 04/06/2023] [Indexed: 06/14/2023] Open
Abstract
Environmental hypoxia challenges female reproductive physiology in placental mammals, increasing rates of gestational complications. Adaptation to high elevation has limited many of these effects in humans and other mammals, offering potential insight into the developmental processes that lead to and protect against hypoxia-related gestational complications. However, our understanding of these adaptations has been hampered by a lack of experimental work linking the functional, regulatory, and genetic underpinnings of gestational development in locally adapted populations. Here, we dissect high-elevation adaptation in the reproductive physiology of deer mice (Peromyscus maniculatus), a rodent species with an exceptionally broad elevational distribution that has emerged as a model for hypoxia adaptation. Using experimental acclimations, we show that lowland mice experience pronounced fetal growth restriction when challenged with gestational hypoxia, while highland mice maintain normal growth by expanding the compartment of the placenta that facilitates nutrient and gas exchange between gestational parent and fetus. We then use compartment-specific transcriptome analyses to show that adaptive structural remodeling of the placenta is coincident with widespread changes in gene expression within this same compartment. Genes associated with fetal growth in deer mice significantly overlap with genes involved in human placental development, pointing to conserved or convergent pathways underlying these processes. Finally, we overlay our results with genetic data from natural populations to identify candidate genes and genomic features that contribute to these placental adaptations. Collectively, these experiments advance our understanding of adaptation to hypoxic environments by revealing physiological and genetic mechanisms that shape fetal growth trajectories under maternal hypoxia.
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Affiliation(s)
- Kathryn Wilsterman
- Division of Biological Sciences, University of Montana, Missoula, MT 59812
- Department of Biology, Colorado State University, Fort Collins, CO 80521
| | - Emily C Moore
- Division of Biological Sciences, University of Montana, Missoula, MT 59812
| | - Rena M Schweizer
- Division of Biological Sciences, University of Montana, Missoula, MT 59812
| | - Kirksey Cunningham
- Division of Biological Sciences, University of Montana, Missoula, MT 59812
| | - Jeffrey M Good
- Division of Biological Sciences, University of Montana, Missoula, MT 59812
- Wildlife Biology Program, University of Montana, Missoula, MT 59812
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT 59812
- Wildlife Biology Program, University of Montana, Missoula, MT 59812
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4
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Schweizer RM, Ivy CM, Natarajan C, Scott GR, Storz JF, Cheviron ZA. Gene regulatory changes underlie developmental plasticity in respiration and aerobic performance in highland deer mice. Mol Ecol 2023. [PMID: 37073620 DOI: 10.1111/mec.16953] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2022] [Revised: 03/27/2023] [Accepted: 04/03/2023] [Indexed: 04/20/2023]
Abstract
Phenotypic plasticity can play an important role in the ability of animals to tolerate environmental stress, but the nature and magnitude of plastic responses are often specific to the developmental timing of exposure. Here, we examine changes in gene expression in the diaphragm of highland deer mice (Peromyscus maniculatus) in response to hypoxia exposure at different stages of development. In highland deer mice, developmental plasticity in diaphragm function may mediate changes in several respiratory traits that influence aerobic metabolism and performance under hypoxia. We generated RNAseq data from diaphragm tissue of adult deer mice exposed to (1) life-long hypoxia (before conception to adulthood), (2) post-natal hypoxia (birth to adulthood), (3) adult hypoxia (6-8 weeks only during adulthood) or (4) normoxia. We found five suites of co-regulated genes that are differentially expressed in response to hypoxia, but the patterns of differential expression depend on the developmental timing of exposure. We also identified four transcriptional modules that are associated with important respiratory traits. Many of the genes in these transcriptional modules bear signatures of altitude-related selection, providing an indirect line of evidence that observed changes in gene expression may be adaptive in hypoxic environments. Our results demonstrate the importance of developmental stage in determining the phenotypic response to environmental stressors.
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Affiliation(s)
- Rena M Schweizer
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
| | - Catherine M Ivy
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | | | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
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5
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Pollock HS, Lamont D, MacDonald SE, Spence AR, Brawn JD, Cheviron ZA. Widespread Torpor Use in Hummingbirds from the Thermally Stable Lowland Tropics. Physiol Biochem Zool 2023; 96:119-127. [PMID: 36921271 DOI: 10.1086/722477] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/03/2022]
Abstract
AbstractTorpor, the temporary reduction of metabolic rate and body temperature, is a common energy-saving strategy in endotherms. Because of their small body size and energetically demanding life histories, hummingbirds have proven useful for understanding when and why endotherms use torpor. Previous studies of torpor in hummingbirds have been largely limited to tropical montane species or long-distance migrants that regularly experience challenging thermal conditions. Comparatively little is known, however, about the use of torpor in hummingbirds of the lowland tropics, where relatively high and stable year-round temperatures may at least partially negate the need for torpor. To fill this knowledge gap, we tested for the occurrence of torpor in tropical lowland hummingbirds (n=37 individuals of six species) from central Panama. In controlled experimental conditions simulating the local temperature regime, all six species used torpor to varying degrees and entered torpor at high ambient temperatures (i.e., ≥28°C), indicating that hummingbirds from the thermally stable lowland tropics regularly use torpor. Torpor reduced overnight mass loss, with individuals that spent more time in torpor losing less body mass during temperature experiments. Body mass was the best predictor of torpor depth and duration among and within species-smaller species and individuals tended to use torpor more frequently and enter deeper torpor. Average mass loss in our experiments (∼8%-10%) was greater than that reported in studies of hummingbirds from higher elevation sites (∼4%). We therefore posit that the energetic benefits accrued from torpor may be limited by relatively high nighttime temperatures in the lowland tropics, although further studies are needed to test this hypothesis.
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Beckman EJ, Vargas Campos W, Benham PM, Schmitt CJ, Cheviron ZA, Witt CC. Selection on embryonic haemoglobin in an elevational generalist songbird. Biol Lett 2022; 18:20220105. [PMCID: PMC9554719 DOI: 10.1098/rsbl.2022.0105] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Animals developing at high elevation experience a suite of environmental challenges, most notably the low partial pressure of oxygen (PO2) in ambient air. In low PO2, bird species with high-elevation ancestry consistently demonstrate higher hatching success than lowland counterparts, suggesting highland birds are adapted to restricted O2 (hypoxia) in early development. Haemoglobin (Hb), the critical oxygen-transport protein, is a likely target of PO2-related selection across ontogeny since Hb isoforms expressed at distinct developmental stages demonstrate different O2 affinities. To test if Hb function is under PO2-related selection at different ontogenetic stages, we sampled a songbird, the hooded siskin (Spinus magellanicus), across two approximately 4000 m elevational transects. We sequenced all of the loci that encode avian Hb isoforms, and tested for signatures of spatially varying selection by comparing divergence patterns in Hb loci to other loci sampled across the genome. We found strong signatures of diversifying selection at non-synonymous sites in loci that contribute to embryonic (απ, βH) and definitive (βA) Hb isoforms. This is the first evidence for selection on embryonic haemoglobin in high-elevation Neoaves. We conclude that selection on Hb function at brief, but critical stages of ontogeny may be a vital component to high elevation adaptation in birds.
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Affiliation(s)
- Elizabeth J. Beckman
- Museum of Southwestern Biology and Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA,Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, CA 94720, USA
| | - Walter Vargas Campos
- Centro de Ornitología y Biodiversidad, Calle Sta. Rita 105, Oficina 202, Santiago de Surco, Lima, Perú
| | - Phred M. Benham
- Museum of Southwestern Biology and Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA,Museum of Vertebrate Zoology and Department of Integrative Biology, University of California, Berkeley, CA 94720, USA
| | - C. Jonathan Schmitt
- Museum of Southwestern Biology and Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA,Department of Organismic and Evolutionary Biology and Museum of Comparative Zoology, Harvard University, Cambridge, MA 02138, USA
| | | | - Christopher C. Witt
- Museum of Southwestern Biology and Department of Biology, University of New Mexico, Albuquerque, NM 87131, USA
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7
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Yu JJ, Non AL, Heinrich EC, Gu W, Alcock J, Moya EA, Lawrence ES, Tift MS, O'Brien KA, Storz JF, Signore AV, Khudyakov JI, Milsom WK, Wilson SM, Beall CM, Villafuerte FC, Stobdan T, Julian CG, Moore LG, Fuster MM, Stokes JA, Milner R, West JB, Zhang J, Shyy JY, Childebayeva A, Vázquez-Medina JP, Pham LV, Mesarwi OA, Hall JE, Cheviron ZA, Sieker J, Blood AB, Yuan JX, Scott GR, Rana BK, Ponganis PJ, Malhotra A, Powell FL, Simonson TS. Time Domains of Hypoxia Responses and -Omics Insights. Front Physiol 2022; 13:885295. [PMID: 36035495 PMCID: PMC9400701 DOI: 10.3389/fphys.2022.885295] [Citation(s) in RCA: 4] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2022] [Accepted: 05/24/2022] [Indexed: 02/04/2023] Open
Abstract
The ability to respond rapidly to changes in oxygen tension is critical for many forms of life. Challenges to oxygen homeostasis, specifically in the contexts of evolutionary biology and biomedicine, provide important insights into mechanisms of hypoxia adaptation and tolerance. Here we synthesize findings across varying time domains of hypoxia in terms of oxygen delivery, ranging from early animal to modern human evolution and examine the potential impacts of environmental and clinical challenges through emerging multi-omics approaches. We discuss how diverse animal species have adapted to hypoxic environments, how humans vary in their responses to hypoxia (i.e., in the context of high-altitude exposure, cardiopulmonary disease, and sleep apnea), and how findings from each of these fields inform the other and lead to promising new directions in basic and clinical hypoxia research.
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Affiliation(s)
- James J. Yu
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Amy L. Non
- Department of Anthropology, Division of Social Sciences, University of California, San Diego, La Jolla, CA, United States,*Correspondence: Amy L. Non, Tatum S. Simonson,
| | - Erica C. Heinrich
- Division of Biomedical Sciences, School of Medicine, University of California, Riverside, CA, United States
| | - Wanjun Gu
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States,Herbert Wertheim School of Public Health and Longevity Sciences, University of California, San Diego, La Jolla, CA, United States
| | - Joe Alcock
- Department of Emergency Medicine, University of New Mexico, Albuquerque, MX, United States
| | - Esteban A. Moya
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Elijah S. Lawrence
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Michael S. Tift
- Department of Biology and Marine Biology, College of Arts and Sciences, University of North Carolina Wilmington, Wilmington, NC, United States
| | - Katie A. O'Brien
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States,Department of Physiology, Development and Neuroscience, Faculty of Biology, School of Biological Sciences, University of Cambridge, Cambridge, ENG, United Kingdom
| | - Jay F. Storz
- School of Biological Sciences, College of Arts and Sciences, University of Nebraska-Lincoln, Lincoln, IL, United States
| | - Anthony V. Signore
- School of Biological Sciences, College of Arts and Sciences, University of Nebraska-Lincoln, Lincoln, IL, United States
| | - Jane I. Khudyakov
- Department of Biological Sciences, University of the Pacific, Stockton, CA, United States
| | | | - Sean M. Wilson
- Lawrence D. Longo, MD Center for Perinatal Biology, Loma Linda, CA, United States
| | | | | | | | - Colleen G. Julian
- School of Medicine, University of Colorado Anschutz Medical Campus, Aurora, CO, United States
| | - Lorna G. Moore
- Division of Reproductive Sciences, Department of Obstetrics and Gynecology, Aurora, CO, United States
| | - Mark M. Fuster
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Jennifer A. Stokes
- Department of Kinesiology, Southwestern University, Georgetown, TX, United States
| | - Richard Milner
- San Diego Biomedical Research Institute, San Diego, CA, United States
| | - John B. West
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Jiao Zhang
- Department of Medicine, UC San Diego School of Medicine, San Diego, CA, United States
| | - John Y. Shyy
- Department of Medicine, UC San Diego School of Medicine, San Diego, CA, United States
| | - Ainash Childebayeva
- Department of Archaeogenetics, Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany
| | - José Pablo Vázquez-Medina
- Department of Integrative Biology, College of Letters and Science, University of California, Berkeley, Berkeley, CA, United States
| | - Luu V. Pham
- Division of Pulmonary and Critical Care Medicine, Department of Medicine, School of Medicine, Johns Hopkins Medicine, Baltimore, MD, United States
| | - Omar A. Mesarwi
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - James E. Hall
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Zachary A. Cheviron
- Division of Biological Sciences, College of Humanities and Sciences, University of Montana, Missoula, MT, United States
| | - Jeremy Sieker
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Arlin B. Blood
- Department of Pediatrics Division of Neonatology, School of Medicine, Loma Linda University, Loma Linda, CA, United States
| | - Jason X. Yuan
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Graham R. Scott
- Department of Pediatrics Division of Neonatology, School of Medicine, Loma Linda University, Loma Linda, CA, United States
| | - Brinda K. Rana
- Moores Cancer Center, UC San Diego, La Jolla, CA, United States,Department of Psychiatry, UC San Diego, La Jolla, CA, United States
| | - Paul J. Ponganis
- Center for Marine Biotechnology and Biomedicine, La Jolla, CA, United States
| | - Atul Malhotra
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Frank L. Powell
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States
| | - Tatum S. Simonson
- Division of Pulmonary, Critical Care and Sleep Medicine, Department of Medicine, School of Medicine, University of California, San Diego, La Jolla, CA, United States,*Correspondence: Amy L. Non, Tatum S. Simonson,
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8
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Ivy CM, Velotta JP, Cheviron ZA, Scott GR. Genetic variation in HIF-2α attenuates ventilatory sensitivity and carotid body growth in chronic hypoxia in high-altitude deer mice. J Physiol 2022; 600:4207-4225. [PMID: 35797482 DOI: 10.1113/jp282798] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/03/2022] [Accepted: 06/27/2022] [Indexed: 11/08/2022] Open
Abstract
KEY POINTS High-altitude natives of many species have experienced natural selection on the gene encoding HIF-2α, Epas1, including high-altitude populations of deer mice. HIF-2α regulates ventilation and carotid body growth in hypoxia, so the genetic variants in Epas1 in high-altitude natives may underlie evolved changes in control of breathing. Deer mice from controlled crosses between high- and low-altitude populations were used to examine the effects of Epas1 genotype on an admixed genomic background. The high-altitude variant was associated with reduced ventilatory chemosensitivity and carotid body growth in chronic hypoxia, but had no effects on haematology. The results help us better understand the genetic basis for the unique physiological phenotype of high-altitude natives. ABSTRACT The gene encoding HIF-2α, Epas1, has experienced a history of natural selection in many high-altitude taxa, but the functional role of mutations in this gene are still poorly understood. We investigated the influence of the high-altitude variant of Epas1 in North American deer mice (Peromyscus maniculatus) on control of breathing and carotid body growth during chronic hypoxia. We created hybrids between high- and low-altitude populations of deer mice to disrupt linkages between genetic loci so physiological effects of Epas1 alleles (Epas1H and Epas1L , respectively) could be examined on an admixed genomic background. In general, chronic hypoxia (4 weeks at 12 kPa O2 ) enhanced ventilatory chemosensitivity (assessed as the acute ventilatory response to hypoxia), increased total ventilation and arterial O2 saturation during progressive poikilocapnic hypoxia, and increased haematocrit and blood haemoglobin content across genotypes. However, effects of chronic hypoxia on ventilatory chemosensitivity were attenuated in mice that were homozygous for the high-altitude Epas1 allele (Epas1H/H ). Carotid body growth and glomus cell hyperplasia, which was strongly induced in Epas1L/L mice in chronic hypoxia, was not observed in Epas1H/H mice. Epas1 genotype also modulated the effects of chronic hypoxia on metabolism and body temperature depression in hypoxia, but had no effects on haematological traits. These findings confirm the important role of HIF-2α in modulating ventilatory sensitivity and carotid body growth in chronic hypoxia, and show that genetic variation in Epas1 is responsible for evolved changes in the control of breathing and metabolism in high-altitude deer mice. Abstract figure legend ventilation and carotid body growth in hypoxia, so we investigated the role genetic variants in Epas1 in highaltitude deer mice on the control of breathing. In the lab, hybrids between high- and lowaltitude populations of deer mice were created to disrupt linkages between genetic loci so physiological effects of Epas1 alleles (Epas1H and Epas1L, respectively) could be examined on an admixed genomic background. The high-altitude variant was associated with reduced ventilatory chemosensitivity and carotid body growth after 4 weeks of chronic hypoxia, compared to mice homozygous for the low-altitude allele (Epas1LL). These results help us better understand the genetic basis for the unique physiological phenotype of high-altitude natives. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Catherine M Ivy
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada
| | - Jonathan P Velotta
- Department of Biological Sciences, University of Denver, Denver, CO, 80210, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, 59812, USA
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada
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9
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Ivy CM, Wearing OH, Natarajan C, Schweizer RM, Gutiérrez-Pinto N, Velotta JP, Campbell-Staton SC, Petersen EE, Fago A, Cheviron ZA, Storz JF, Scott GR. Correction: Genetic variation in haemoglobin is associated with evolved changes in breathing in high-altitude deer mice. J Exp Biol 2022; 225:275664. [PMID: 35686596 DOI: 10.1242/jeb.244608] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
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10
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Ivy CM, Wearing OH, Natarajan C, Schweizer RM, Gutiérrez-Pinto N, Velotta JP, Campbell-Staton SC, Petersen EE, Fago A, Cheviron ZA, Storz JF, Scott GR. Genetic variation in haemoglobin is associated with evolved changes in breathing in high-altitude deer mice. J Exp Biol 2022; 225:273749. [PMID: 34913467 PMCID: PMC8917448 DOI: 10.1242/jeb.243595] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/23/2021] [Accepted: 12/09/2021] [Indexed: 01/21/2023]
Abstract
Physiological systems often have emergent properties but the effects of genetic variation on physiology are often unknown, which presents a major challenge to understanding the mechanisms of phenotypic evolution. We investigated whether genetic variants in haemoglobin (Hb) that contribute to high-altitude adaptation in deer mice (Peromyscus maniculatus) are associated with evolved changes in the control of breathing. We created F2 inter-population hybrids of highland and lowland deer mice to test for phenotypic associations of α- and β-globin variants on a mixed genetic background. Hb genotype had expected effects on Hb-O2 affinity that were associated with differences in arterial O2 saturation in hypoxia. However, high-altitude genotypes were also associated with breathing phenotypes that should contribute to enhancing O2 uptake in hypoxia. Mice with highland α-globin exhibited a more effective breathing pattern, with highland homozygotes breathing deeper but less frequently across a range of inspired O2, and this difference was comparable to the evolved changes in breathing pattern in deer mouse populations native to high altitude. The ventilatory response to hypoxia was augmented in mice that were homozygous for highland β-globin. The association of globin variants with variation in breathing phenotypes could not be recapitulated by acute manipulation of Hb-O2 affinity, because treatment with efaproxiral (a synthetic drug that acutely reduces Hb-O2 affinity) had no effect on breathing in normoxia or hypoxia. Therefore, adaptive variation in Hb may have unexpected effects on physiology in addition to the canonical function of this protein in circulatory O2 transport.
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Affiliation(s)
- Catherine M. Ivy
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1,Author for correspondence ()
| | - Oliver H. Wearing
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1
| | | | - Rena M. Schweizer
- Divison of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | | | - Jonathan P. Velotta
- Divison of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Shane C. Campbell-Staton
- Department of Ecology and Evolutionary Biology, University of California, Los Angeles, CA 90095, USA
| | - Elin E. Petersen
- Department of Biology, Aarhus University, 8000 Aarhus C, Denmark
| | - Angela Fago
- Department of Biology, Aarhus University, 8000 Aarhus C, Denmark
| | - Zachary A. Cheviron
- Divison of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Jay F. Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
| | - Graham R. Scott
- Department of Biology, McMaster University, Hamilton, ON, Canada, L8S 4K1
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11
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Schweizer RM, Jones MR, Bradburd GS, Storz JF, Senner NR, Wolf C, Cheviron ZA. Broad Concordance in the Spatial Distribution of Adaptive and Neutral Genetic Variation across an Elevational Gradient in Deer Mice. Mol Biol Evol 2021; 38:4286-4300. [PMID: 34037784 PMCID: PMC8476156 DOI: 10.1093/molbev/msab161] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
When species are continuously distributed across environmental gradients, the relative strength of selection and gene flow shape spatial patterns of genetic variation, potentially leading to variable levels of differentiation across loci. Determining whether adaptive genetic variation tends to be structured differently than neutral variation along environmental gradients is an open and important question in evolutionary genetics. We performed exome-wide population genomic analysis on deer mice sampled along an elevational gradient of nearly 4,000 m of vertical relief. Using a combination of selection scans, genotype-environment associations, and geographic cline analyses, we found that a large proportion of the exome has experienced a history of altitude-related selection. Elevational clines for nearly 30% of these putatively adaptive loci were shifted significantly up- or downslope of clines for loci that did not bear similar signatures of selection. Many of these selection targets can be plausibly linked to known phenotypic differences between highland and lowland deer mice, although the vast majority of these candidates have not been reported in other studies of highland taxa. Together, these results suggest new hypotheses about the genetic basis of physiological adaptation to high altitude, and the spatial distribution of adaptive genetic variation along environmental gradients.
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Affiliation(s)
- Rena M Schweizer
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | - Matthew R Jones
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
- Southwest Biological Science Center, U.S. Geological Survey, Flagstaff, AZ, USA
| | - Gideon S Bradburd
- Ecology, Evolution, and Behavior Program, Department of Integrative Biology, Michigan State University, East Lansing, MI, USA
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA
| | - Nathan R Senner
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
- Department of Biological Sciences, University of South Carolina, Columbia, SC, USA
| | - Cole Wolf
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
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12
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Abstract
Residence at high altitude is consistently associated with low birthweight among placental mammals. This reduction in birthweight influences long-term health trajectories for both the offspring and mother. However, the physiological processes that contribute to fetal growth restriction at altitude are still poorly understood, and thus our ability to safely intervene remains limited. One approach to identify the factors that mitigate altitude-dependent fetal growth restriction is to study populations that are protected from fetal growth restriction through evolutionary adaptations (e.g., high altitude-adapted populations). Here, we examine human gestational physiology at high altitude from a novel evolutionary perspective that focuses on patterns of physiological plasticity, allowing us to identify 1) the contribution of specific physiological systems to fetal growth restriction and 2) the mechanisms that confer protection in highland-adapted populations. Using this perspective, our review highlights two general findings: first, that the beneficial value of plasticity in maternal physiology is often dependent on factors more proximate to the fetus; and second, that our ability to understand the contributions of these proximate factors is currently limited by thin data from altitude-adapted populations. Expanding the comparative scope of studies on gestational physiology at high altitude and integrating studies of both maternal and fetal physiology are needed to clarify the mechanisms by which physiological responses to altitude contribute to fetal growth outcomes. The relevance of these questions to clinical, agricultural, and basic research combined with the breadth of the unknown highlight gestational physiology at high altitude as an exciting niche for continued work.
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Affiliation(s)
- Kathryn Wilsterman
- Division of Biological Sciences, University of Montana, Missoula, Montana
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana
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13
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Velotta JP, Robertson CE, Schweizer RM, McClelland GB, Cheviron ZA. Adaptive Shifts in Gene Regulation Underlie a Developmental Delay in Thermogenesis in High-Altitude Deer Mice. Mol Biol Evol 2021; 37:2309-2321. [PMID: 32243546 DOI: 10.1093/molbev/msaa086] [Citation(s) in RCA: 14] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022] Open
Abstract
Aerobic performance is tied to fitness as it influences an animal's ability to find food, escape predators, or survive extreme conditions. At high altitude, where low O2 availability and persistent cold prevail, maximum metabolic heat production (thermogenesis) is an aerobic performance trait that is closely linked to survival. Understanding how thermogenesis evolves to enhance survival at high altitude will yield insight into the links between physiology, performance, and fitness. Recent work in deer mice (Peromyscus maniculatus) has shown that adult mice native to high altitude have higher thermogenic capacities under hypoxia compared with lowland conspecifics, but that developing high-altitude pups delay the onset of thermogenesis. This finding suggests that natural selection on thermogenic capacity varies across life stages. To determine the mechanistic cause of this ontogenetic delay, we analyzed the transcriptomes of thermoeffector organs-brown adipose tissue and skeletal muscle-in developing deer mice native to low and high altitude. We demonstrate that the developmental delay in thermogenesis is associated with adaptive shifts in the expression of genes involved in nervous system development, fuel/O2 supply, and oxidative metabolism pathways. Our results demonstrate that selection has modified the developmental trajectory of the thermoregulatory system at high altitude and has done so by acting on the regulatory systems that control the maturation of thermoeffector tissues. We suggest that the cold and hypoxic conditions of high altitude force a resource allocation tradeoff, whereby limited energy is allocated to developmental processes such as growth, versus active thermogenesis, during early development.
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Affiliation(s)
| | | | - Rena M Schweizer
- Division of Biological Sciences, University of Montana, Missoula, MT
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14
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Faber JE, Storz JF, Cheviron ZA, Zhang H. High-altitude rodents have abundant collaterals that protect against tissue injury after cerebral, coronary and peripheral artery occlusion. J Cereb Blood Flow Metab 2021; 41:731-744. [PMID: 32703056 PMCID: PMC7983333 DOI: 10.1177/0271678x20942609] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 06/03/2020] [Accepted: 06/22/2020] [Indexed: 12/22/2022]
Abstract
Collateral number/density varies widely in brain and other tissues among strains of Mus musculus mice due to differences in genetic background. Recent studies have shown that prolonged exposure to reduced atmospheric oxygen induces additional collaterals to form, suggesting that natural selection may favor increased collaterals in populations native to high-altitude. High-altitude guinea pigs (Cavia) and deer mice (Peromyscus) were compared with lowland species of Peromyscus, Mus and Rattus (9 species/strains examined). Collateral density, diameter and other morphometrics were measured in brain where, importantly, collateral abundance reflects that in other tissues of the same individual. Guinea pigs and high-altitude deer mice had a greater density of pial collaterals than lowlanders. Consistent with this, guinea pigs and highlander mice evidenced complete and 80% protection against stroke, respectively. They also sustained significantly less ischemia in heart and lower extremities after arterial occlusion. Vessels of the circle of Willis, including the communicating collateral arteries, also exhibited unique features in the highland species. Our findings support the hypothesis that species native to high-altitude have undergone genetic selection for abundant collaterals, suggesting that besides providing protection in obstructive disease, collaterals serve a physiological function to optimize oxygen delivery to meet oxygen demand when oxygen is limiting.
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Affiliation(s)
- James E Faber
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- Curriculum in Neuroscience, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
- McAllister Heart Institute, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | - Hua Zhang
- Department of Cell Biology and Physiology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
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15
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Brekke TD, Moore EC, Campbell-Staton SC, Callahan CM, Cheviron ZA, Good JM. X chromosome-dependent disruption of placental regulatory networks in hybrid dwarf hamsters. Genetics 2021; 218:6168998. [PMID: 33710276 DOI: 10.1093/genetics/iyab043] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2020] [Accepted: 02/16/2021] [Indexed: 11/14/2022] Open
Abstract
Embryonic development in mammals is highly sensitive to changes in gene expression within the placenta. The placenta is also highly enriched for genes showing parent-of-origin or imprinted expression, which is predicted to evolve rapidly in response to parental conflict. However, little is known about the evolution of placental gene expression, or if divergence of placental gene expression plays an important role in mammalian speciation. We used crosses between two species of dwarf hamsters (Phodopus sungorus and Phodopus campbelli) to examine the genetic and regulatory underpinnings of severe placental overgrowth in their hybrids. Using quantitative genetic mapping and mitochondrial substitution lines, we show that overgrowth of hybrid placentas was primarily caused by genetic differences on the maternally inherited P. sungorus X chromosome. Mitochondrial interactions did not contribute to abnormal hybrid placental development, and there was only weak correspondence between placental disruption and embryonic growth. Genome-wide analyses of placental transcriptomes from the parental species and first- and second-generation hybrids revealed a central group of co-expressed X-linked and autosomal genes that were highly enriched for maternally biased expression. Expression of this gene network was strongly correlated with placental size and showed widespread misexpression dependent on epistatic interactions with X-linked hybrid incompatibilities. Collectively, our results indicate that the X chromosome is likely to play a prominent role in the evolution of placental gene expression and the accumulation of hybrid developmental barriers between mammalian species.
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Affiliation(s)
- Thomas D Brekke
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA.,School of Natural Sciences, Bangor University, Bangor, LL57 2UW, UK
| | - Emily C Moore
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA
| | - Shane C Campbell-Staton
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA.,Department of Ecology and Evolutionary Biology; Institute for Society and Genetics, University of California, Los Angeles, Los Angeles, CA, USA
| | - Colin M Callahan
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA
| | - Jeffrey M Good
- Division of Biological Sciences, The University of Montana, Missoula, MT 59812, USA
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16
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Abstract
Population genomic studies of humans and other animals at high altitude have generated many hypotheses about the genes and pathways that may have contributed to hypoxia adaptation. Future advances require experimental tests of such hypotheses to identify causal mechanisms. Studies to date illustrate the challenge of moving from lists of candidate genes to the identification of phenotypic targets of selection, as it can be difficult to determine whether observed genotype-phenotype associations reflect causal effects or secondary consequences of changes in other traits that are linked via homeostatic regulation. Recent work on high-altitude models such as deer mice has revealed both plastic and evolved changes in respiratory, cardiovascular, and metabolic traits that contribute to aerobic performance capacity in hypoxia, and analyses of tissue-specific transcriptomes have identified changes in regulatory networks that mediate adaptive changes in physiological phenotype. Here we synthesize recent results and discuss lessons learned from studies of high-altitude adaptation that lie at the intersection of genomics and physiology.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska 68588, USA;
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812, USA;
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17
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Mahalingam S, Cheviron ZA, Storz JF, McClelland GB, Scott GR. Chronic cold exposure induces mitochondrial plasticity in deer mice native to high altitudes. J Physiol 2020; 598:5411-5426. [PMID: 32886797 PMCID: PMC8329962 DOI: 10.1113/jp280298] [Citation(s) in RCA: 27] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2020] [Accepted: 09/01/2020] [Indexed: 12/21/2022] Open
Abstract
KEY POINTS Small mammals native to high altitude must sustain high rates of thermogenesis to cope with cold. Skeletal muscle is a key site of shivering and non-shivering thermogenesis, but the importance of mitochondrial plasticity in cold hypoxic environments remains unresolved. We examined high-altitude deer mice, which have evolved a high capacity for aerobic thermogenesis, to determine the mechanisms of mitochondrial plasticity during chronic exposure to cold and hypoxia, alone and in combination. Cold exposure in normoxia or hypoxia increased mitochondrial leak respiration and decreased phosphorylation efficiency and OXPHOS coupling efficiency, which may serve to augment non-shivering thermogenesis. Cold also increased muscle oxidative capacity, but reduced the capacity for mitochondrial respiration via complex II relative to complexes I and II combined. High-altitude mice had a more oxidative muscle phenotype than low-altitude mice. Therefore, both plasticity and evolved changes in muscle mitochondria contribute to thermogenesis at high altitude. ABSTRACT Small mammals native to high altitude must sustain high rates of thermogenesis to cope with cold and hypoxic environments. Skeletal muscle is a key site of shivering and non-shivering thermogenesis, but the importance of mitochondrial plasticity in small mammals at high altitude remains unresolved. High-altitude deer mice (Peromyscus maniculatus) and low-altitude white-footed mice (P. leucopus) were born and raised in captivity, and chronically exposed as adults to warm (25°C) normoxia, warm hypoxia (12 kPa O2 ), cold (5°C) normoxia, or cold hypoxia. We then measured oxidative enzyme activities, oxidative fibre density and capillarity in the gastrocnemius, and used a comprehensive substrate titration protocol to examine the function of muscle mitochondria by high-resolution respirometry. Exposure to cold in both normoxia or hypoxia increased the activities of citrate synthase and cytochrome oxidase. In lowlanders, this was associated with increases in capillary density and the proportional abundance of oxidative muscle fibres, but in highlanders, these traits were unchanged at high levels across environments. Environment had some distinct effects on mitochondrial OXPHOS capacity between species, but the capacity of complex II relative to the combined capacity of complexes I and II was consistently reduced in both cold environments. Both cold environments also increased leak respiration and decreased phosphorylation efficiency and OXPHOS coupling efficiency in both species, which may serve to augment non-shivering thermogenesis. These cold-induced changes in mitochondrial function were overlaid upon the generally more oxidative phenotype of highlanders. Therefore, both plasticity and evolved changes in muscle mitochondria contribute to thermogenesis at high altitudes.
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Affiliation(s)
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA
| | | | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, ON, Canada
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18
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Pollock HS, Brawn JD, Cheviron ZA. Heat tolerances of temperate and tropical birds and their implications for susceptibility to climate warming. Funct Ecol 2020. [DOI: 10.1111/1365-2435.13693] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- Henry S. Pollock
- Department of Natural Resources and Environmental Sciences University of Illinois at Urbana‐Champaign Champaign IL USA
| | - Jeffrey D. Brawn
- Department of Natural Resources and Environmental Sciences University of Illinois at Urbana‐Champaign Champaign IL USA
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19
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Stager M, Senner NR, Tobalske BW, Cheviron ZA. Body temperature maintenance acclimates in a winter-tenacious songbird. J Exp Biol 2020; 223:jeb221853. [PMID: 32376710 DOI: 10.1242/jeb.221853] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2020] [Accepted: 05/04/2020] [Indexed: 12/16/2022]
Abstract
Flexibility in heat generation and dissipation mechanisms provides endotherms the ability to match their thermoregulatory strategy with external demands. However, the degree to which these two mechanisms account for seasonal changes in body temperature regulation is little explored. Here, we present novel data on the regulation of avian body temperature to investigate how birds alter mechanisms of heat production and heat conservation to deal with variation in ambient conditions. We subjected dark-eyed juncos (Junco hyemalis) to chronic cold acclimations of varying duration and subsequently quantified their metabolic rates, thermal conductance and ability to maintain normothermia. Cold-acclimated birds adjusted traits related to both heat generation (increased summit metabolic rate) and heat conservation (decreased conductance) to improve their body temperature regulation. Increases in summit metabolic rate occurred rapidly, but plateaued after 1 week of cold exposure. In contrast, changes to conductance occurred only after 9 weeks of cold exposure. Thus, the ability to maintain body temperature continued to improve throughout the experiment, but the mechanisms underlying this improvement changed through time. Our results demonstrate the ability of birds to adjust thermoregulatory strategies in response to thermal cues and reveal that birds may combine multiple responses to meet the specific demands of their environments.
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Affiliation(s)
- Maria Stager
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Nathan R Senner
- Department of Biological Sciences, University of South Carolina, Columbia, SC 29208, USA
| | - Bret W Tobalske
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
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20
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Abstract
Endotherms defend their body temperature in the cold by employing shivering (ST) and/or non-shivering thermogenesis (NST). Although NST is well documented in mammals, its importance to avian heat generation is unclear. Recent work points to a prominent role for the sarco/endoplasmic reticulum Ca2+ ATPase (SERCA) in muscular NST. SERCA's involvement in both ST and NST, however, posits a tradeoff between these two heat-generating mechanisms. To explore this tradeoff, we assayed pectoralis gene expression of adult songbirds exposed to chronic temperature acclimations. Counter to mammal models, we found that cold-acclimated birds downregulated the expression of sarcolipin (SLN), a gene coding for a peptide that promotes heat generation by uncoupling SERCA Ca2+ transport from ATP hydrolysis, indicating a reduced potential for muscular NST. We also found differential expression of many genes involved in Ca2+ cycling and muscle contraction and propose that decreased SLN could promote increased pectoralis contractility for ST. Moreover, SLN transcript abundance negatively correlated with peak oxygen consumption under cold exposure (a proxy for ST) across individuals, and higher SLN transcript abundance escalated an individual's risk of hypothermia in acute cold. Our results therefore suggest that SLN-mediated NST may not be an important mechanism of-and could be a hindrance to-avian thermoregulation in extreme cold.
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Affiliation(s)
- Maria Stager
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
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21
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Tate KB, Wearing OH, Ivy CM, Cheviron ZA, Storz JF, McClelland GB, Scott GR. Coordinated changes across the O 2 transport pathway underlie adaptive increases in thermogenic capacity in high-altitude deer mice. Proc Biol Sci 2020; 287:20192750. [PMID: 32429808 PMCID: PMC7287372 DOI: 10.1098/rspb.2019.2750] [Citation(s) in RCA: 30] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2019] [Accepted: 04/24/2020] [Indexed: 01/19/2023] Open
Abstract
Animals native to the hypoxic and cold environment at high altitude provide an excellent opportunity to elucidate the integrative mechanisms underlying the adaptive evolution and plasticity of complex traits. The capacity for aerobic thermogenesis can be a critical determinant of survival for small mammals at high altitude, but the physiological mechanisms underlying the evolution of this performance trait remain unresolved. We examined this issue by comparing high-altitude deer mice (Peromyscus maniculatus) with low-altitude deer mice and white-footed mice (P. leucopus). Mice were bred in captivity and adults were acclimated to each of four treatments: warm (25°C) normoxia, warm hypoxia (12 kPa O2), cold (5°C) normoxia or cold hypoxia. Acclimation to hypoxia and/or cold increased thermogenic capacity in deer mice, but hypoxia acclimation led to much greater increases in thermogenic capacity in highlanders than in lowlanders. The high thermogenic capacity of highlanders was associated with increases in pulmonary O2 extraction, arterial O2 saturation, cardiac output and arterial-venous O2 difference. Mechanisms underlying the evolution of enhanced thermogenic capacity in highlanders were partially distinct from those underlying the ancestral acclimation responses of lowlanders. Environmental adaptation has thus enhanced phenotypic plasticity and expanded the physiological toolkit for coping with the challenges at high altitude.
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Affiliation(s)
- Kevin B. Tate
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
- Department of Biology, Texas Lutheran University, Seguin, TX 78155, USA
| | - Oliver H. Wearing
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Catherine M. Ivy
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
| | - Zachary A. Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Jay F. Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
| | | | - Graham R. Scott
- Department of Biology, McMaster University, Hamilton, ON L8S 4K1, Canada
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22
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DuBay SG, Wu Y, Scott GR, Qu Y, Liu Q, Smith JH, Xin C, Hart Reeve A, Juncheng C, Meyer D, Wang J, Johnson J, Cheviron ZA, Lei F, Bates J. Life history predicts flight muscle phenotype and function in birds. J Anim Ecol 2020; 89:1262-1276. [PMID: 32124424 DOI: 10.1111/1365-2656.13190] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/10/2019] [Accepted: 12/19/2019] [Indexed: 11/30/2022]
Abstract
Functional traits are the essential phenotypes that underlie an organism's life history and ecology. Although biologists have long recognized that intraspecific variation is consequential to an animals' ecology, studies of functional variation are often restricted to species-level comparisons, ignoring critical variation within species. In birds, interspecific comparisons have been foundational in connecting flight muscle phenotypes to species-level ecology, but intraspecific variation has remained largely unexplored. We asked how age- and sex-dependent demands on flight muscle function are reconciled in birds. The flight muscle is an essential multifunctional organ, mediating a large range of functions associated with powered flight and thermoregulation. These functions must be balanced over an individual's lifetime. We leveraged within- and between-species comparisons in a clade of small passerines (Tarsiger bush-robins) from the eastern edge of the Qinghai-Tibet Plateau. We integrated measurements of flight muscle physiology, morphology, behaviour, phenology and environmental data, analysing trait data within a context of three widespread, adaptive life-history strategies-sexual dichromatism, age and sex-structured migration, and delayed plumage maturation. This approach provides a framework of the selective forces that shape functional variation within and between species. We found more variation in flight muscle traits within species than has been previously described between species of birds under 20 g. This variation was associated with the discovery of mixed muscle fibre types (i.e. both fast glycolytic and fast oxidative fibres), which differ markedly in their physiological and functional attributes. This result is surprising given that the flight muscles of small birds are generally thought to contain only fast oxidative fibres, suggesting a novel ecological context for glycolytic muscle fibres in small birds. Within each species, flight muscle phenotypes varied by age and sex, reflecting the functional demands at different life-history stages and the pressures that individuals face as a result of their multi-class identity (i.e. species, age and sex). Our findings reveal new links between avian physiology, ecology, behaviour and life history, while demonstrating the importance of demographic-dependent selection in shaping functional phenotypic variation.
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Affiliation(s)
- Shane G DuBay
- Committee on Evolutionary Biology, University of Chicago, Chicago, IL, USA.,Integrative Research Center, Field Museum of Natural History, Chicago, IL, USA
| | - Yongjie Wu
- Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, China
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Yanhua Qu
- Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing, China
| | - Qiao Liu
- Institute of Mountain Hazards and Environment, Chinese Academy of Sciences, Chengdu, China
| | - Joel H Smith
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
| | - Chao Xin
- Laboratory of Molecular Evolution and Molecular Phylogeny, College of Life Sciences, Shannxi Normal University, Xi'an, China
| | - Andrew Hart Reeve
- Biosystematics Section, Natural History Museum of Denmark, University of Copenhagen, Copenhagen, Denmark
| | - Chen Juncheng
- Key Laboratory of Bio-resources and Eco-environment of Ministry of Education, College of Life Sciences, Sichuan University, Chengdu, China
| | - Dylan Meyer
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
| | - Jing Wang
- Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Jacob Johnson
- Department of Ecology and Evolution, University of Chicago, Chicago, IL, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | - Fumin Lei
- Key Laboratory of Zoological Systematics and Evolution, Institute of Zoology, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - John Bates
- Integrative Research Center, Field Museum of Natural History, Chicago, IL, USA
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23
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Benham PM, Cheviron ZA. Population history and the selective landscape shape patterns of osmoregulatory trait divergence in tidal marsh Savannah sparrows (Passerculus sandwichensis). Evolution 2019; 74:57-72. [DOI: 10.1111/evo.13886] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/29/2019] [Revised: 10/12/2019] [Accepted: 11/02/2019] [Indexed: 12/23/2022]
Affiliation(s)
- Phred M. Benham
- Division of Biological SciencesUniversity of Montana Missoula Montana 59812
- Current Address: Museum of Vertebrate ZoologyUniversity of California Berkeley 3101 Valley Life Sciences Building Berkeley CA 94720‐3160
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24
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Schweizer RM, Velotta JP, Ivy CM, Jones MR, Muir SM, Bradburd GS, Storz JF, Scott GR, Cheviron ZA. Physiological and genomic evidence that selection on the transcription factor Epas1 has altered cardiovascular function in high-altitude deer mice. PLoS Genet 2019; 15:e1008420. [PMID: 31697676 PMCID: PMC6837288 DOI: 10.1371/journal.pgen.1008420] [Citation(s) in RCA: 41] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2019] [Accepted: 09/13/2019] [Indexed: 11/19/2022] Open
Abstract
Evolutionary adaptation to extreme environments often requires coordinated changes in multiple intersecting physiological pathways, but how such multi-trait adaptation occurs remains unresolved. Transcription factors, which regulate the expression of many genes and can simultaneously alter multiple phenotypes, may be common targets of selection if the benefits of induced changes outweigh the costs of negative pleiotropic effects. We combined complimentary population genetic analyses and physiological experiments in North American deer mice (Peromyscus maniculatus) to examine links between genetic variation in transcription factors that coordinate physiological responses to hypoxia (hypoxia-inducible factors, HIFs) and multiple physiological traits that potentially contribute to high-altitude adaptation. First, we sequenced the exomes of 100 mice sampled from different elevations and discovered that several SNPs in the gene Epas1, which encodes the oxygen sensitive subunit of HIF-2α, exhibited extreme allele frequency differences between highland and lowland populations. Broader geographic sampling confirmed that Epas1 genotype varied predictably with altitude throughout the western US. We then discovered that Epas1 genotype influences heart rate in hypoxia, and the transcriptomic responses to hypoxia (including HIF targets and genes involved in catecholamine signaling) in the heart and adrenal gland. Finally, we used a demographically-informed selection scan to show that Epas1 variants have experienced a history of spatially varying selection, suggesting that differences in cardiovascular function and gene regulation contribute to high-altitude adaptation. Our results suggest a mechanism by which Epas1 may aid long-term survival of high-altitude deer mice and provide general insights into the role that highly pleiotropic transcription factors may play in the process of environmental adaptation.
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Affiliation(s)
- Rena M. Schweizer
- Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America
- * E-mail:
| | - Jonathan P. Velotta
- Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America
| | - Catherine M. Ivy
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Matthew R. Jones
- Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America
| | - Sarah M. Muir
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Gideon S. Bradburd
- Ecology, Evolutionary Biology, and Behavior Graduate Group, Department of Integrative Biology, Michigan State University, East Lansing, Michigan, United States of America
| | - Jay F. Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska, United States of America
| | - Graham R. Scott
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Zachary A. Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana, United States of America
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Walsh J, Benham PM, Deane‐Coe PE, Arcese P, Butcher BG, Chan YL, Cheviron ZA, Elphick CS, Kovach AI, Olsen BJ, Shriver WG, Winder VL, Lovette IJ. Genomics of rapid ecological divergence and parallel adaptation in four tidal marsh sparrows. Evol Lett 2019; 3:324-338. [PMID: 31388443 PMCID: PMC6675146 DOI: 10.1002/evl3.126] [Citation(s) in RCA: 22] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2019] [Accepted: 06/22/2019] [Indexed: 12/12/2022] Open
Abstract
Theory suggests that different taxa having colonized a similar, challenging environment will show parallel or lineage-specific adaptations to shared selection pressures, but empirical examples of parallel evolution in independent taxa are exceedingly rare. We employed comparative genomics to identify parallel and lineage-specific responses to selection within and among four species of North American sparrows that represent four independent, post-Pleistocene colonization events by an ancestral, upland subspecies and a derived salt marsh specialist. We identified multiple cases of parallel adaptation in these independent comparisons following salt marsh colonization, including selection of 12 candidate genes linked to osmoregulation. In addition to detecting shared genetic targets of selection across multiple comparisons, we found many novel, species-specific signatures of selection, including evidence of selection of loci associated with both physiological and behavioral mechanisms of osmoregulation. Demographic reconstructions of all four species highlighted their recent divergence and small effective population sizes, as expected given their rapid radiation into saline environments. Our results highlight the interplay of both shared and lineage-specific selection pressures in the colonization of a biotically and abiotically challenging habitat and confirm theoretical expectations that steep environmental clines can drive repeated and rapid evolutionary diversification in birds.
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Affiliation(s)
- Jennifer Walsh
- Fuller Evolutionary Biology ProgramCornell Laboratory of OrnithologyIthacaNew York14850
- Department of Ecology and Evolutionary BiologyCornell UniversityIthacaNew York14853
| | - Phred M. Benham
- Division of Biological SciencesUniversity of MontanaMissoulaMontana59812
| | - Petra E. Deane‐Coe
- Fuller Evolutionary Biology ProgramCornell Laboratory of OrnithologyIthacaNew York14850
- Department of Ecology and Evolutionary BiologyCornell UniversityIthacaNew York14853
| | - Peter Arcese
- Department of Forest and Conservation SciencesUniversity of British ColumbiaVancouverBritish ColumbiaT6T1Z4Canada
| | - Bronwyn G. Butcher
- Fuller Evolutionary Biology ProgramCornell Laboratory of OrnithologyIthacaNew York14850
- Department of Ecology and Evolutionary BiologyCornell UniversityIthacaNew York14853
| | | | | | - Chris S. Elphick
- Ecology and Evolutionary BiologyUniversity of ConnecticutStorrsConnecticut06269
| | - Adrienne I. Kovach
- Department of Natural Resources and the EnvironmentUniversity of New HampshireDurhamNew Hampshire03824
| | - Brian J. Olsen
- School of Biology and EcologyUniversity of MaineOronoMaine04469
| | - W. Gregory Shriver
- Department of Entomology and Wildlife EcologyUniversity of DelawareNewarkDelaware19716
| | | | - Irby J. Lovette
- Fuller Evolutionary Biology ProgramCornell Laboratory of OrnithologyIthacaNew York14850
- Department of Ecology and Evolutionary BiologyCornell UniversityIthacaNew York14853
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26
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Storz JF, Cheviron ZA, McClelland GB, Scott GR. Evolution of physiological performance capacities and environmental adaptation: insights from high-elevation deer mice ( Peromyscus maniculatus). J Mammal 2019; 100:910-922. [PMID: 31138949 DOI: 10.1093/jmammal/gyy173] [Citation(s) in RCA: 39] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2018] [Accepted: 12/14/2018] [Indexed: 12/14/2022] Open
Abstract
Analysis of variation in whole-animal performance can shed light on causal connections between specific traits, integrated physiological capacities, and Darwinian fitness. Here, we review and synthesize information on naturally occurring variation in physiological performance capacities and how it relates to environmental adaptation in deer mice (Peromyscus maniculatus). We discuss how evolved changes in aerobic exercise capacity and thermogenic capacity have contributed to adaptation to high elevations. Comparative work on deer mice at high and low elevations has revealed evolved differences in aerobic performance capacities in hypoxia. Highland deer mice have consistently higher aerobic performance capacities under hypoxia relative to lowland natives, consistent with the idea that it is beneficial to have a higher maximal metabolic rate (as measured by the maximal rate of O2 consumption, VO2max) in an environment characterized by lower air temperatures and lower O2 availability. Observed differences in aerobic performance capacities between highland and lowland deer mice stem from changes in numerous subordinate traits that alter the flux capacity of the O2-transport system, the oxidative capacity of tissue mitochondria, and the relationship between O2 consumption and ATP synthesis. Many such changes in physiological phenotype are associated with hypoxia-induced changes in gene expression. Research on natural variation in whole-animal performance forms a nexus between physiological ecology and evolutionary biology that requires insight into the natural history of the study species.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | | | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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27
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Velotta JP, Cheviron ZA. Remodeling Ancestral Phenotypic Plasticity in Local Adaptation: A New Framework to Explore the Role of Genetic Compensation in the Evolution of Homeostasis. Integr Comp Biol 2019; 58:1098-1110. [PMID: 30272147 DOI: 10.1093/icb/icy117] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Phenotypic plasticity is not universally adaptive. In certain cases, plasticity can result in phenotypic shifts that reduce fitness relative to the un-induced state. A common cause of such maladaptive plasticity is the co-option of ancestral developmental and physiological response systems to meet novel challenges. Because these systems evolved to meet specific challenges in an ancestral environment (e.g., localized and transient hypoxia), their co-option to meet a similar, but novel, stressor (e.g., reductions in ambient pO2 at high elevation) can lead to misdirected responses that reduce fitness. In such cases, natural selection should act to remodel phenotypic plasticity to suppress the expression of these maladaptive responses. Because these maladaptive responses reduce the fitness of colonizers in new environments, this remodeling of ancestral plasticity may be among the earliest steps in adaptive walks toward new local optima. Genetic compensation has been proposed as a general form of adaptive evolution that leads to the suppression of maladaptive plasticity to restore the ancestral trait value in the face of novel stimuli. Given their central role in the regulation of basic physiological functions, we argue that genetic compensation may often be achieved by modifications of homeostatic regulatory systems. We further suggest that genetic compensation to modify homeostatic systems can be achieved by two alternative strategies that differ in their mechanistic underpinnings; to our knowledge, these strategies have not been formally recognized by previous workers. We then consider how the mechanistic details of these alternative strategies may constrain their evolution. These considerations lead us to argue that genetic compensation is most likely to evolve by compensatory physiological changes that safeguard internal homeostatic conditions to prevent the expression of maladaptive portions of conserved reaction norms, rather than direct evolution of plasticity itself. Finally, we outline a simple experimental framework to test this hypothesis. Our goal is to stimulate research aimed at providing a deeper mechanistic understanding of whether and how phenotypic plasticity can be remodeled following environmental shifts that render ancestral responses maladaptive, an issue with increasing importance in our current era of rapid environmental change.
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Affiliation(s)
- Jonathan P Velotta
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
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Benham PM, Cheviron ZA. Divergent mitochondrial lineages arose within a large, panmictic population of the Savannah sparrow (Passerculus sandwichensis). Mol Ecol 2019; 28:1765-1783. [PMID: 30770598 DOI: 10.1111/mec.15049] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/22/2018] [Revised: 02/06/2019] [Accepted: 02/12/2019] [Indexed: 12/24/2022]
Abstract
Unusual patterns of mtDNA diversity can reveal interesting aspects of a species' biology. However, making such inferences requires discerning among the many alternative scenarios that could underlie any given mtDNA pattern. Next-generation sequencing methods provide large, multilocus data sets with increased power to resolve unusual mtDNA patterns. A mtDNA-based phylogeography of the Savannah sparrow (Passerculus sandwichensis) previously identified two sympatric, but divergent (~2%) clades within the nominate subspecies group and a third clade that consisted of birds sampled from northwest Mexico. We revisited the phylogeography of this species using a population genomic data set to resolve the processes leading to the evolution of sympatric and divergent mtDNA lineages. We identified two genetic clusters in the genomic data set corresponding to (a) the nominate subspecies group and (b) northwestern Mexico birds. Following divergence, the nominate clade maintained a large, stable population, indicating that divergent mitochondrial lineages arose within a panmictic population. Simulations based on parameter estimates from this model further confirmed that this demographic history could produce observed levels of mtDNA diversity. Patterns of divergent, sympatric mtDNA lineages are frequently interpreted as admixture of historically isolated lineages. Our analyses reject this interpretation for Savannah sparrows and underscore the need for genomic data sets to resolve the evolutionary mechanisms behind anomalous, locus-specific patterns.
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Affiliation(s)
- Phred M Benham
- Division of Biological Sciences, University of Montana, Missoula, Montana
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana
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29
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Wilde LR, Wolf CJ, Porter SM, Stager M, Cheviron ZA, Senner NR. Botfly infections impair the aerobic performance and survival of montane populations of deer mice,
Peromyscus maniculatus rufinus. Funct Ecol 2019. [DOI: 10.1111/1365-2435.13276] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Affiliation(s)
- Luke R. Wilde
- Division of Biological Sciences University of Montana Missoula Montana
| | - Cole J. Wolf
- Division of Biological Sciences University of Montana Missoula Montana
| | - Stephanie M. Porter
- College of Veterinary Medicine and Biomedical Sciences Colorado State University Fort Collins Colorado
| | - Maria Stager
- Division of Biological Sciences University of Montana Missoula Montana
| | | | - Nathan R. Senner
- Division of Biological Sciences University of Montana Missoula Montana
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30
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Velotta JP, Ivy CM, Wolf CJ, Scott GR, Cheviron ZA. Maladaptive phenotypic plasticity in cardiac muscle growth is suppressed in high-altitude deer mice. Evolution 2018; 72:2712-2727. [PMID: 30318588 DOI: 10.1111/evo.13626] [Citation(s) in RCA: 34] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2018] [Revised: 09/12/2018] [Accepted: 09/19/2018] [Indexed: 12/19/2022]
Abstract
How often phenotypic plasticity acts to promote or inhibit adaptive evolution is an ongoing debate among biologists. Recent work suggests that adaptive phenotypic plasticity promotes evolutionary divergence, though several studies have also suggested that maladaptive plasticity can potentiate adaptation. The role of phenotypic plasticity, adaptive, or maladaptive, in evolutionary divergence remains controversial. We examined the role of plasticity in evolutionary divergence between two species of Peromyscus mice that differ in native elevations. We used cardiac mass as a model phenotype, since ancestral hypoxia-induced responses of the heart may be both adaptive and maladaptive at high-altitude. While left ventricle growth should enhance oxygen delivery to tissues, hypertrophy of the right ventricle can lead to heart failure and death. We compared left- and right-ventricle plasticity in response to hypoxia between captive-bred P. leucopus (representing the ancestral lowland condition) and P. maniculatus from high-altitude. We found that maladaptive ancestral plasticity in right ventricle hypertrophy is reduced in high-altitude deer mice. Analysis of the heart transcriptome suggests that changes in expression of inflammatory signaling genes, particularly interferon regulatory factors, contribute to the suppression of right ventricle hypertrophy. We found weak evidence that adaptive plasticity of left ventricle mass contributes to evolution. Our results suggest that selection to suppress ancestral maladaptive plasticity plays a role in adaptation.
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Affiliation(s)
- Jonathan P Velotta
- Division of Biological Sciences, University of Montana, Missoula, Montana, 59812
| | - Catherine M Ivy
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Cole J Wolf
- Division of Biological Sciences, University of Montana, Missoula, Montana, 59812
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana, 59812
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31
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Beckman EJ, Benham PM, Cheviron ZA, Witt C. Detecting introgression despite phylogenetic uncertainty: The case of the South American siskins. Mol Ecol 2018; 27:4350-4367. [DOI: 10.1111/mec.14795] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2017] [Revised: 05/21/2018] [Accepted: 05/23/2018] [Indexed: 12/25/2022]
Affiliation(s)
- Elizabeth J. Beckman
- Division of Biological Sciences University of Montana Missoula Montana
- Department of Biology and Museum of Southwestern Biology University of New Mexico Albuquerque New Mexico
| | - Phred M. Benham
- Division of Biological Sciences University of Montana Missoula Montana
| | | | - Christopher C. Witt
- Department of Biology and Museum of Southwestern Biology University of New Mexico Albuquerque New Mexico
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32
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Senner NR, Stager M, Verhoeven MA, Cheviron ZA, Piersma T, Bouten W. High-altitude shorebird migration in the absence of topographical barriers: avoiding high air temperatures and searching for profitable winds. Proc Biol Sci 2018; 285:rspb.2018.0569. [PMID: 30051848 DOI: 10.1098/rspb.2018.0569] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/13/2018] [Accepted: 06/05/2018] [Indexed: 02/05/2023] Open
Abstract
Nearly 20% of all bird species migrate between breeding and nonbreeding sites annually. Their migrations include storied feats of endurance and physiology, from non-stop trans-Pacific crossings to flights at the cruising altitudes of jetliners. Despite intense interest in these performances, there remains great uncertainty about which factors most directly influence bird behaviour during migratory flights. We used GPS trackers that measure an individual's altitude and wingbeat frequency to track the migration of black-tailed godwits (Limosa limosa) and identify the abiotic factors influencing their in-flight migratory behaviour. We found that godwits flew at altitudes above 5000 m during 21% of all migratory flights, and reached maximum flight altitudes of nearly 6000 m. The partial pressure of oxygen at these altitudes is less than 50% of that at sea level, yet these extremely high flights occurred in the absence of topographical barriers. Instead, they were associated with high air temperatures at lower altitudes and increasing wind support at higher altitudes. Our results therefore suggest that wind, temperature and topography all play a role in determining migratory behaviour, but that their relative importance is context dependent. Extremely high-altitude flights may thus not be especially rare, but they may only occur in very specific environmental contexts.
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Affiliation(s)
- Nathan R Senner
- Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700, CC, Groningen, The Netherlands .,Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA
| | - Maria Stager
- Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA
| | - Mo A Verhoeven
- Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700, CC, Groningen, The Netherlands
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, 32 Campus Drive, Missoula, MT 59812, USA
| | - Theunis Piersma
- Conservation Ecology Group, Groningen Institute for Evolutionary Life Sciences, University of Groningen, PO Box 11103, 9700, CC, Groningen, The Netherlands.,NIOZ Royal Netherlands Institute for Sea Research, Department of Coastal Systems, Utrecht University, PO Box 59, 1790, AB Den Burg, Texel, The Netherlands
| | - Willem Bouten
- Computational Geo-Ecology, Institute for Biodiversity and Ecosystem Dynamics, University of Amsterdam, Sciencepark 904, 1098, XH Amsterdam, The Netherlands
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33
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Williams CM, Ragland GJ, Betini G, Buckley LB, Cheviron ZA, Donohue K, Hereford J, Humphries MM, Lisovski S, Marshall KE, Schmidt PS, Sheldon KS, Varpe Ø, Visser ME. Understanding Evolutionary Impacts of Seasonality: An Introduction to the Symposium. Integr Comp Biol 2018; 57:921-933. [PMID: 29045649 DOI: 10.1093/icb/icx122] [Citation(s) in RCA: 52] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Seasonality is a critically important aspect of environmental variability, and strongly shapes all aspects of life for organisms living in highly seasonal environments. Seasonality has played a key role in generating biodiversity, and has driven the evolution of extreme physiological adaptations and behaviors such as migration and hibernation. Fluctuating selection pressures on survival and fecundity between summer and winter provide a complex selective landscape, which can be met by a combination of three outcomes of adaptive evolution: genetic polymorphism, phenotypic plasticity, and bet-hedging. Here, we have identified four important research questions with the goal of advancing our understanding of evolutionary impacts of seasonality. First, we ask how characteristics of environments and species will determine which adaptive response occurs. Relevant characteristics include costs and limits of plasticity, predictability, and reliability of cues, and grain of environmental variation relative to generation time. A second important question is how phenological shifts will amplify or ameliorate selection on physiological hardiness. Shifts in phenology can preserve the thermal niche despite shifts in climate, but may fail to completely conserve the niche or may even expose life stages to conditions that cause mortality. Considering distinct environmental sensitivities of life history stages will be key to refining models that forecast susceptibility to climate change. Third, we must identify critical physiological phenotypes that underlie seasonal adaptation and work toward understanding the genetic architectures of these responses. These architectures are key for predicting evolutionary responses. Pleiotropic genes that regulate multiple responses to changing seasons may facilitate coordination among functionally related traits, or conversely may constrain the expression of optimal phenotypes. Finally, we must advance our understanding of how changes in seasonal fluctuations are impacting ecological interaction networks. We should move beyond simple dyadic interactions, such as predator prey dynamics, and understand how these interactions scale up to affect ecological interaction networks. As global climate change alters many aspects of seasonal variability, including extreme events and changes in mean conditions, organisms must respond appropriately or go extinct. The outcome of adaptation to seasonality will determine responses to climate change.
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Affiliation(s)
- Caroline M Williams
- Department of Integrative Biology, University of California, 3040 Valley Life Sciences Building, Berkeley, CA 94705, USA
| | - Gregory J Ragland
- Department of Integrative Biology, University of Colorado, Denver, CO, USA
| | - Gustavo Betini
- Department of Integrative Biology, University of Guelph, Guelph, Ontario, Canada
| | - Lauren B Buckley
- Department of Biology, University of Washington, Seattle, WA, USA
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
| | | | - Joe Hereford
- Department of Ecology and Evolution, University of California, Davis, CA, USA
| | - Murray M Humphries
- Department of Natural Resource Sciences, McGill University, Quebec, Canada
| | - Simeon Lisovski
- Department of Neurobiology, Physiology and Behavior, University of California, Davis, CA, USA
| | | | - Paul S Schmidt
- Department of Biology, University of Pennsylvania, Philadelphia, PA, USA
| | - Kimberly S Sheldon
- Department of Ecology and Evolutionary Biology, University of Tennessee, Knoxville, TN, USA
| | - Øystein Varpe
- Department of Arctic Biology, The University Centre in Svalbard, Longyearbyen, Norway.,Akvaplan-niva, Fram Centre, Tromsø, Norway
| | - Marcel E Visser
- Department of Animal Ecology, Netherlands Institute of Ecology (NIOO-KNAW), P.O. Box 50, 6700 AB Wageningen, The Netherlands
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34
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Cheviron ZA, Swanson DL. Comparative Transcriptomics of Seasonal Phenotypic Flexibility in Two North American Songbirds. Integr Comp Biol 2018; 57:1040-1054. [PMID: 29095984 DOI: 10.1093/icb/icx118] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Phenotypic flexibility allows organisms to reversibly alter their phenotypes to match the changing demands of seasonal environments. Because phenotypic flexibility is mediated, at least in part, by changes in gene regulation, comparative transcriptomic studies can provide insights into the mechanistic underpinnings of seasonal phenotypic flexibility, and the extent to which regulatory responses to changing seasons are conserved across species. To begin to address these questions, we sampled individuals of two resident North American songbird species, American goldfinch (Spinus tristis) and black-capped chickadee (Poecile atricapillus) in summer and winter to measure seasonal variation in pectoralis transcriptomic profiles and to identify conserved and species-specific elements of these seasonal profiles. We found that very few genes exhibited divergent responses to changes in season between species, and instead, a core set of over 1200 genes responded to season concordantly in both species. Moreover, several key metabolic pathways, regulatory networks, and gene functional classes were commonly recruited to induce seasonal phenotypic shifts in these species. The seasonal transcriptomic responses mirror winter increases in pectoralis mass and cellular metabolic intensity documented in previous studies of both species, suggesting that these seasonal phenotypic responses are due in part to changes in gene expression. Despite growing evidence of muscle nonshivering thermogenesis (NST) in young precocial birds, we did not find strong evidence of upregulation of genes putatively involved in NST during winter in either species, suggesting that seasonal modification of muscular NST is not a prominent contributor to winter increases in thermogenic capacity for adult passerine birds. Together, these results provide the first comprehensive overview of potential common regulatory mechanisms underlying seasonally flexible phenotypes in wild, free-ranging birds.
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Affiliation(s)
- Z A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - D L Swanson
- Department of Biology, University of South Dakota, Vermillion, SD 57069, USA
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35
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Campbell‐Staton SC, Bare A, Losos JB, Edwards SV, Cheviron ZA. Physiological and regulatory underpinnings of geographic variation in reptilian cold tolerance across a latitudinal cline. Mol Ecol 2018; 27:2243-2255. [DOI: 10.1111/mec.14580] [Citation(s) in RCA: 33] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/28/2016] [Revised: 01/11/2018] [Accepted: 01/16/2018] [Indexed: 12/26/2022]
Affiliation(s)
| | - Anna Bare
- University of Illinois Champaign‐Urbana Illinois
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36
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Barve S, Dhondt AA, Mathur VB, Cheviron ZA. Life-history characteristics influence physiological strategies to cope with hypoxia in Himalayan birds. Proc Biol Sci 2017; 283:rspb.2016.2201. [PMID: 27903874 DOI: 10.1098/rspb.2016.2201] [Citation(s) in RCA: 23] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2016] [Accepted: 11/02/2016] [Indexed: 12/18/2022] Open
Abstract
Hypobaric hypoxia at high elevation represents an important physiological stressor for montane organisms, but optimal physiological strategies to cope with hypoxia may vary among species with different life histories. Montane birds exhibit a range of migration patterns; elevational migrants breed at high elevations but winter at low elevations or migrate further south, while high-elevation residents inhabit the same elevation throughout the year. Optimal physiological strategies to cope with hypoxia might therefore differ between species that exhibit these two migratory patterns, because they differ in the amount time spent at high elevation. We examined physiological parameters associated with blood-oxygen transport (haemoglobin concentration and haematocrit, i.e. the proportion of red blood cells in blood) in nine species of elevational migrants and six species of high-elevation residents that were sampled along a 2200 m (1000-3200 m) elevational gradient. Haemoglobin concentration increased with elevation within species regardless of migratory strategy, but it was only significantly correlated with haematocrit in elevational migrants. Surprisingly, haemoglobin concentration was not correlated with haematocrit in high-elevation residents, and these species exhibited higher mean cellular haemoglobin concentration than elevational migrants. Thus, alternative physiological strategies to regulate haemoglobin concentration and blood O2 carrying capacity appear to differ among birds with different annual elevational movement patterns.
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Affiliation(s)
- S Barve
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA .,Wildlife Institute of India, Chandrabani, Uttarakhand, India
| | - A A Dhondt
- Department of Ecology and Evolutionary Biology, Cornell University, Ithaca, NY, USA
| | - V B Mathur
- Wildlife Institute of India, Chandrabani, Uttarakhand, India
| | - Z A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
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Tate KB, Ivy CM, Velotta JP, Storz JF, McClelland GB, Cheviron ZA, Scott GR. Circulatory mechanisms underlying adaptive increases in thermogenic capacity in high-altitude deer mice. ACTA ACUST UNITED AC 2017; 220:3616-3620. [PMID: 28839010 DOI: 10.1242/jeb.164491] [Citation(s) in RCA: 52] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2017] [Accepted: 08/18/2017] [Indexed: 01/08/2023]
Abstract
We examined the circulatory mechanisms underlying adaptive increases in thermogenic capacity in deer mice (Peromyscus maniculatus) native to the cold hypoxic environment at high altitudes. Deer mice from high- and low-altitude populations were born and raised in captivity to adulthood, and then acclimated to normoxia or hypobaric hypoxia (simulating hypoxia at ∼4300 m). Thermogenic capacity [maximal O2 consumption (V̇O2,max), during cold exposure] was measured in hypoxia, along with arterial O2 saturation (SaO2 ) and heart rate (fH). Hypoxia acclimation increased V̇O2,max by a greater magnitude in highlanders than in lowlanders. Highlanders also had higher SaO2 and extracted more O2 from the blood per heartbeat (O2 pulse=V̇O2,max/fH). Hypoxia acclimation increased fH, O2 pulse and capillary density in the left ventricle of the heart. Our results suggest that adaptive increases in thermogenic capacity involve integrated functional changes across the O2 cascade that augment O2 circulation and extraction from the blood.
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Affiliation(s)
- Kevin B Tate
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada.,School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
| | - Catherine M Ivy
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada
| | - Jonathan P Velotta
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE 68588, USA
| | - Grant B McClelland
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, ON, L8S 4K1, Canada
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Campbell-Staton SC, Cheviron ZA, Rochette N, Catchen J, Losos JB, Edwards SV. Winter storms drive rapid phenotypic, regulatory, and genomic shifts in the green anole lizard. Science 2017; 357:495-498. [DOI: 10.1126/science.aam5512] [Citation(s) in RCA: 152] [Impact Index Per Article: 21.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/19/2016] [Accepted: 07/05/2017] [Indexed: 12/23/2022]
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Scott GR, Ivy CM, Tate KB, Velotta JP, Schweizer RM, Cheviron ZA. High‐altitude Adaptation and Hypoxia Signaling in Deer Mice. FASEB J 2017. [DOI: 10.1096/fasebj.31.1_supplement.1075.2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Affiliation(s)
| | | | - Kevin B. Tate
- Department of BiologyMcMaster UniversityHamiltonONCanada
- Department of BiologyTruman State UniversityKirksvilleMO
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Lau DS, Connaty AD, Mahalingam S, Wall N, Cheviron ZA, Storz JF, Scott GR, McClelland GB. Acclimation to hypoxia increases carbohydrate use during exercise in high-altitude deer mice. Am J Physiol Regul Integr Comp Physiol 2017; 312:R400-R411. [PMID: 28077391 DOI: 10.1152/ajpregu.00365.2016] [Citation(s) in RCA: 40] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2016] [Revised: 12/13/2016] [Accepted: 01/05/2017] [Indexed: 12/24/2022]
Abstract
The low O2 experienced at high altitude is a significant challenge to effective aerobic locomotion, as it requires sustained tissue O2 delivery in addition to the appropriate allocation of metabolic substrates. Here, we tested whether high- and low-altitude deer mice (Peromyscus maniculatus) have evolved different acclimation responses to hypoxia with respect to muscle metabolism and fuel use during submaximal exercise. Using F1 generation high- and low-altitude deer mice that were born and raised in common conditions, we assessed 1) fuel use during exercise, 2) metabolic enzyme activities, and 3) gene expression for key transporters and enzymes in the gastrocnemius. After hypoxia acclimation, highland mice showed a significant increase in carbohydrate oxidation and higher relative reliance on this fuel during exercise at 75% maximal O2 consumption. Compared with lowland mice, highland mice had consistently higher activities of oxidative and fatty acid oxidation enzymes in the gastrocnemius. In contrast, only after hypoxia acclimation did activities of hexokinase increase significantly in the muscle of highland mice to levels greater than lowland mice. Highland mice also responded to acclimation with increases in muscle gene expression for hexokinase 1 and 2 genes, whereas both populations increased mRNA expression for glucose transporters. Changes in skeletal muscle with acclimation suggest that highland mice had an increased capacity for the uptake and oxidation of circulatory glucose. Our results demonstrate that highland mice have evolved a distinct mode of hypoxia acclimation that involves an increase in carbohydrate use during exercise.
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Affiliation(s)
- Daphne S Lau
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Alex D Connaty
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Sajeni Mahalingam
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Nastashya Wall
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, Montana; and
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska
| | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
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Velotta JP, Jones J, Wolf CJ, Cheviron ZA. Transcriptomic plasticity in brown adipose tissue contributes to an enhanced capacity for nonshivering thermogenesis in deer mice. Mol Ecol 2016; 25:2870-86. [PMID: 27126783 DOI: 10.1111/mec.13661] [Citation(s) in RCA: 31] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2015] [Revised: 03/04/2016] [Accepted: 04/01/2016] [Indexed: 01/08/2023]
Abstract
For small mammals living at high altitude, aerobic heat generation (thermogenesis) is essential for survival during prolonged periods of cold, but is severely impaired under conditions of hypobaric hypoxia. Recent studies in deer mice (Peromyscus maniculatus) reveal adaptive enhancement of thermogenesis in high- compared to low-altitude populations under hypoxic cold stress, an enhancement that is attributable to modifications in the aerobic metabolism of muscles used in shivering. However, because small mammals rely heavily on nonshivering mechanisms for cold acclimatization, we tested for evidence of adaptive divergence in nonshivering thermogenesis (NST) under hypoxia. To do so, we measured NST and characterized transcriptional profiles of brown adipose tissue (BAT) in high- and low-altitude deer mice that were (i) wild-caught and acclimatized to their native altitude, and (ii) born and reared under common garden conditions at low elevation. We found that NST performance under hypoxia is enhanced in wild-caught, high-altitude deer mice, a difference that is associated with increased expression of coregulated genes that influence several physiological traits. These traits include vascularization and O2 supply to BAT, brown adipocyte proliferation and the uncoupling of oxidative phosphorylation from ATP synthesis in the generation of heat. Our results suggest that acclimatization to hypoxic cold stress is facilitated by enhancement of nonshivering heat production, which is driven by regulatory plasticity in a suite of genes that influence intersecting physiological pathways.
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Affiliation(s)
- Jonathan P Velotta
- Department of Animal Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61081, USA
| | - Jennifer Jones
- Department of Animal Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61081, USA
| | - Cole J Wolf
- Department of Animal Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61081, USA
| | - Zachary A Cheviron
- Department of Animal Biology, University of Illinois at Urbana-Champaign, Urbana, IL, 61081, USA
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Tuttle EM, Bergland AO, Korody ML, Brewer MS, Newhouse DJ, Minx P, Stager M, Betuel A, Cheviron ZA, Warren WC, Gonser RA, Balakrishnan CN. Divergence and Functional Degradation of a Sex Chromosome-like Supergene. Curr Biol 2016; 26:344-50. [PMID: 26804558 DOI: 10.1016/j.cub.2015.11.069] [Citation(s) in RCA: 186] [Impact Index Per Article: 23.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2015] [Revised: 10/12/2015] [Accepted: 11/25/2015] [Indexed: 11/18/2022]
Abstract
A major challenge in biology is to understand the genetic basis of adaptation. One compelling idea is that groups of tightly linked genes (i.e., "supergenes" [1, 2]) facilitate adaptation in suites of traits that determine fitness. Despite their likely importance, little is known about how alternate supergene alleles arise and become differentiated, nor their ultimate fate within species. Herein we address these questions by investigating the evolutionary history of a supergene in white-throated sparrows, Zonotrichia albicollis. This species comprises two morphs, tan and white, that differ in pigmentation and components of social behavior [3-5]. Morph is determined by alternative alleles at a balanced >100-Mb inversion-based supergene, providing a unique system for studying gene-behavior relationships. Using over two decades of field data, we document near-perfect disassortative mating among morphs, as well as the fitness consequences of rare assortative mating. We use de novo whole-genome sequencing coupled with population- and phylogenomic data to show that alternate supergene alleles are highly divergent at over 1,000 genes and that these alleles originated prior to the split of Z. albicollis from its sister species and may be polymorphic in Z. albicollis due to a past hybridization event. We provide evidence that the "white" allele may be degrading, similar to neo-Y/W sex chromosomes. We further show that the "tan" allele has surprisingly low levels of genetic diversity yet does not show several canonical signatures of recurrent positive selection. We discuss these results in the context of the origin, molecular evolution, and possible fate of this remarkable polymorphism.
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Affiliation(s)
- Elaina M Tuttle
- Department of Biology and The Center for Genomic Advocacy, Indiana State University, 600 Chestnut Street, Terre Haute, IN 47809, USA.
| | - Alan O Bergland
- Department of Biology, Stanford University, 371 Serra Mall, Stanford, CA 94305-5020, USA
| | - Marisa L Korody
- Department of Biology and The Center for Genomic Advocacy, Indiana State University, 600 Chestnut Street, Terre Haute, IN 47809, USA
| | - Michael S Brewer
- Department of Biology, East Carolina University, Howell Science Complex, Greenville, NC 27858, USA
| | - Daniel J Newhouse
- Department of Biology, East Carolina University, Howell Science Complex, Greenville, NC 27858, USA
| | - Patrick Minx
- McDonnell Genome Institute, Washington University School of Medicine, 4444 Forest Park Avenue, Campus Box 8501, St. Louis, MO 63108, USA
| | - Maria Stager
- Department of Animal Biology, School of Integrative Biology, University of Illinois, Urbana-Champaign, IL 61801, USA
| | - Adam Betuel
- Department of Biology and The Center for Genomic Advocacy, Indiana State University, 600 Chestnut Street, Terre Haute, IN 47809, USA
| | - Zachary A Cheviron
- Department of Animal Biology, School of Integrative Biology, University of Illinois, Urbana-Champaign, IL 61801, USA
| | - Wesley C Warren
- McDonnell Genome Institute, Washington University School of Medicine, 4444 Forest Park Avenue, Campus Box 8501, St. Louis, MO 63108, USA
| | - Rusty A Gonser
- Department of Biology and The Center for Genomic Advocacy, Indiana State University, 600 Chestnut Street, Terre Haute, IN 47809, USA
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Abstract
Recent studies of indigenous human populations at high altitude have provided proof-of-principle that genome scans of DNA polymorphism can be used to identify candidate loci for hypoxia adaptation. When integrated with experimental analyses of physiological phenotypes, genome-wide surveys of DNA polymorphism and tissue-specific transcriptional profiles can provide insights into actual mechanisms of adaptation. It has been suggested that adaptive phenotypic evolution is largely mediated by cis-regulatory changes in genes that are located at integrative control points in regulatory networks. This hypothesis can be tested by conducting transcriptomic analyses of hypoxic signaling pathways in conjunction with experimental measures of vascular oxygen supply and metabolic pathway flux. Such studies may reveal whether the architecture of gene regulatory networks can be used to predict which loci (and which types of loci) are likely to be "hot spots" for adaptive physiological evolution. Functional genomic studies of deer mice (Peromyscus maniculatus) demonstrate how the integrated analysis of variation in tissue-specific transcriptomes, whole-animal physiological performance, and various subordinate traits can yield insights into the mechanistic underpinnings of high-altitude adaptation.
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Affiliation(s)
- Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, NE, USA.
| | - Zachary A Cheviron
- Division of Biological Sciences, University of Montana, Missoula, MT, USA
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Scott GR, Elogio TS, Lui MA, Storz JF, Cheviron ZA. Adaptive Modifications of Muscle Phenotype in High-Altitude Deer Mice Are Associated with Evolved Changes in Gene Regulation. Mol Biol Evol 2015; 32:1962-76. [PMID: 25851956 DOI: 10.1093/molbev/msv076] [Citation(s) in RCA: 82] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
At high-altitude, small mammals are faced with the energetic challenge of sustaining thermogenesis and aerobic exercise in spite of the reduced O2 availability. Under conditions of hypoxic cold stress, metabolic demands of shivering thermogenesis and locomotion may require enhancements in the oxidative capacity and O2 diffusion capacity of skeletal muscle to compensate for the diminished tissue O2 supply. We used common-garden experiments involving highland and lowland deer mice (Peromyscus maniculatus) to investigate the transcriptional underpinnings of genetically based population differences and plasticity in muscle phenotype. We tested highland and lowland mice that were sampled in their native environments as well as lab-raised F1 progeny of wild-caught mice. Experiments revealed that highland natives had consistently greater oxidative fiber density and capillarity in the gastrocnemius muscle. RNA sequencing analyses revealed population differences in transcript abundance for 68 genes that clustered into two discrete transcriptional modules, and a large suite of transcripts (589 genes) with plastic expression patterns that clustered into five modules. The expression of two transcriptional modules was correlated with the oxidative phenotype and capillarity of the muscle, and these phenotype-associated modules were enriched for genes involved in energy metabolism, muscle plasticity, vascular development, and cell stress response. Although most of the individual transcripts that were differentially expressed between populations were negatively correlated with muscle phenotype, several genes involved in energy metabolism (e.g., Ckmt1, Ehhadh, Acaa1a) and angiogenesis (Notch4) were more highly expressed in highlanders, and the regulators of mitochondrial biogenesis, PGC-1α (Ppargc1a) and mitochondrial transcription factor A (Tfam), were positively correlated with muscle oxidative phenotype. These results suggest that evolved population differences in the oxidative capacity and capillarity of skeletal muscle involved expression changes in a small suite of coregulated genes.
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Affiliation(s)
- Graham R Scott
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Todd S Elogio
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Mikaela A Lui
- Department of Biology, McMaster University, Hamilton, ON, Canada
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln
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Abstract
ABSTRACT
Small temperate birds reversibly modify their aerobic performance to maintain thermoregulatory homeostasis under seasonally changing environmental conditions and these physiological adjustments may be attributable to changes in the expression of genes in the underlying regulatory networks. Here, we report the results of an experimental procedure designed to gain insight into the fundamental mechanisms of metabolic flexibility in the dark-eyed junco (Junco hyemalis). We combined genomic transcriptional profiles with measures of metabolic enzyme activities and whole-animal thermogenic performance from juncos exposed to four 6-week acclimation treatments that varied in temperature (cold, 3°C; warm, 24°C) and photoperiod (short day, 8 h light:16 h dark; long day, 16 h light:8 h dark). Cold-acclimated birds increased thermogenic capacity compared with warm-acclimated birds, and this enhanced performance was associated with upregulation of genes involved in muscle hypertrophy, angiogenesis, and lipid transport and oxidation, as well as with catabolic enzyme activities. These physiological changes occurred over ecologically relevant timescales, suggesting that birds make regulatory adjustments to interacting, hierarchical pathways in order to seasonally enhance thermogenic capacity.
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Affiliation(s)
- Maria Stager
- Department of Animal Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - David L. Swanson
- Department of Biology, University of South Dakota, Vermillion, SD 57069, USA
| | - Zachary A. Cheviron
- Department of Animal Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
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Lui MA, Mahalingam S, Patel P, Connaty AD, Ivy CM, Cheviron ZA, Storz JF, McClelland GB, Scott GR. High-altitude ancestry and hypoxia acclimation have distinct effects on exercise capacity and muscle phenotype in deer mice. Am J Physiol Regul Integr Comp Physiol 2015; 308:R779-91. [PMID: 25695288 DOI: 10.1152/ajpregu.00362.2014] [Citation(s) in RCA: 86] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2014] [Accepted: 02/15/2015] [Indexed: 01/14/2023]
Abstract
The hypoxic and cold environment at high altitudes requires that small mammals sustain high rates of O2 transport for exercise and thermogenesis while facing a diminished O2 availability. We used laboratory-born and -raised deer mice (Peromyscus maniculatus) from highland and lowland populations to determine the interactive effects of ancestry and hypoxia acclimation on exercise performance. Maximal O₂consumption (V̇o(2max)) during exercise in hypoxia increased after hypoxia acclimation (equivalent to the hypoxia at ∼4,300 m elevation for 6-8 wk) and was consistently greater in highlanders than in lowlanders. V̇o(2max) during exercise in normoxia was not affected by ancestry or acclimation. Highlanders also had consistently greater capillarity, oxidative fiber density, and maximal activities of oxidative enzymes (cytochrome c oxidase and citrate synthase) in the gastrocnemius muscle, lower lactate dehydrogenase activity in the gastrocnemius, and greater cytochrome c oxidase activity in the diaphragm. Hypoxia acclimation did not affect any of these muscle traits. The unique gastrocnemius phenotype of highlanders was associated with higher mRNA and protein abundances of peroxisome proliferator-activated receptor γ (PPARγ). Vascular endothelial growth factor (VEGFA) transcript abundance was lower in highlanders, and hypoxia acclimation reduced the expression of numerous genes that regulate angiogenesis and energy metabolism, in contrast to the observed population differences in muscle phenotype. Lowlanders exhibited greater increases in blood hemoglobin content, hematocrit, and wet lung mass (but not dry lung mass) than highlanders after hypoxia acclimation. Genotypic adaptation to high altitude, therefore, improves exercise performance in hypoxia by mechanisms that are at least partially distinct from those underlying hypoxia acclimation.
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Affiliation(s)
- Mikaela A Lui
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Sajeni Mahalingam
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Paras Patel
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Alex D Connaty
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Catherine M Ivy
- Department of Biology, McMaster University, Hamilton, Ontario, Canada
| | - Zachary A Cheviron
- School of Integrative Biology, University of Illinois, Urbana, Illinois; and
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln, Nebraska
| | | | - Graham R Scott
- Department of Biology, McMaster University, Hamilton, Ontario, Canada;
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Jones MR, Cheviron ZA, Carling MD. Spatially variable coevolution between a haemosporidian parasite and the MHC of a widely distributed passerine. Ecol Evol 2015; 5:1045-60. [PMID: 25798222 PMCID: PMC4364819 DOI: 10.1002/ece3.1391] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2014] [Revised: 12/03/2014] [Accepted: 12/12/2014] [Indexed: 12/12/2022] Open
Abstract
The environment shapes host-parasite interactions, but how environmental variation affects the diversity and composition of parasite-defense genes of hosts is unresolved. In vertebrates, the highly variable major histocompatibility complex (MHC) gene family plays an essential role in the adaptive immune system by recognizing pathogen infection and initiating the cellular immune response. Investigating MHC-parasite associations across heterogeneous landscapes may elucidate the role of spatially fluctuating selection in the maintenance of high levels of genetic variation at the MHC. We studied patterns of association between an avian haemosporidian blood parasite and the MHC of rufous-collared sparrows (Zonotrichia capensis) that inhabit environments with widely varying haemosporidian infection prevalence in the Peruvian Andes. MHC diversity peaked in populations with high infection prevalence, although intra-individual MHC diversity was not associated with infection status. MHC nucleotide and protein sequences associated with infection absence tended to be rare, consistent with negative frequency-dependent selection. We found an MHC variant associated with a ∽26% decrease in infection probability at middle elevations (1501-3100 m) where prevalence was highest. Several other variants were associated with a significant increase in infection probability in low haemosporidian prevalence environments, which can be interpreted as susceptibility or quantitative resistance. Our study highlights important challenges in understanding MHC evolution in natural systems, but may point to a role of negative frequency-dependent selection and fluctuating spatial selection in the evolution of Z. capensisMHC.
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Affiliation(s)
- Matthew R Jones
- Department of Zoology and Physiology, Berry Biodiversity Conservation Center, University of Wyoming 1000 E. University Ave., Dept. 4304, Laramie, Wyoming, 82071
| | - Zachary A Cheviron
- Department of Animal Biology, School of Integrative Biology, University of Illinois Urbana-Champaign 505 South Goodwin Ave., Urbana, Illinois, 61801
| | - Matthew D Carling
- Department of Zoology and Physiology, Berry Biodiversity Conservation Center, University of Wyoming 1000 E. University Ave., Dept. 4304, Laramie, Wyoming, 82071
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Natarajan C, Hoffmann FG, Lanier HC, Wolf CJ, Cheviron ZA, Spangler ML, Weber RE, Fago A, Storz JF. Intraspecific polymorphism, interspecific divergence, and the origins of function-altering mutations in deer mouse hemoglobin. Mol Biol Evol 2015; 32:978-97. [PMID: 25556236 PMCID: PMC4379404 DOI: 10.1093/molbev/msu403] [Citation(s) in RCA: 83] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/12/2022] Open
Abstract
Major challenges for illuminating the genetic basis of phenotypic evolution are to identify causative mutations, to quantify their functional effects, to trace their origins as new or preexisting variants, and to assess the manner in which segregating variation is transduced into species differences. Here, we report an experimental analysis of genetic variation in hemoglobin (Hb) function within and among species of Peromyscus mice that are native to different elevations. A multilocus survey of sequence variation in the duplicated HBA and HBB genes in Peromyscus maniculatus revealed that function-altering amino acid variants are widely shared among geographically disparate populations from different elevations, and numerous amino acid polymorphisms are also shared with closely related species. Variation in Hb-O2 affinity within and among populations of P. maniculatus is attributable to numerous amino acid mutations that have individually small effects. One especially surprising feature of the Hb polymorphism in P. maniculatus is that an appreciable fraction of functional standing variation in the two transcriptionally active HBA paralogs is attributable to recurrent gene conversion from a tandemly linked HBA pseudogene. Moreover, transpecific polymorphism in the duplicated HBA genes is not solely attributable to incomplete lineage sorting or introgressive hybridization; instead, it is mainly attributable to recurrent interparalog gene conversion that has occurred independently in different species. Partly as a result of concerted evolution between tandemly duplicated globin genes, the same amino acid changes that contribute to variation in Hb function within P. maniculatus also contribute to divergence in Hb function among different species of Peromyscus. In the case of function-altering Hb mutations in Peromyscus, there is no qualitative or quantitative distinction between segregating variants within species and fixed differences between species.
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Affiliation(s)
| | - Federico G Hoffmann
- Department of Biochemistry, Molecular Biology, Entomology, and Plant Pathology, Mississippi State University Institute for Genomics, Biocomputing and Biotechnology, Mississippi State University
| | - Hayley C Lanier
- Department of Zoology and Physiology, University of Wyoming at Casper
| | - Cole J Wolf
- Department of Animal Biology, School of Integrative Biology, University of Illinois, Urbana-Champaign
| | - Zachary A Cheviron
- Department of Animal Biology, School of Integrative Biology, University of Illinois, Urbana-Champaign
| | | | - Roy E Weber
- Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Angela Fago
- Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln
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Jones MR, Cheviron ZA, Carling MD. Variation in positively selected major histocompatibility complex class I loci in rufous-collared sparrows (Zonotrichia capensis). Immunogenetics 2014; 66:693-704. [DOI: 10.1007/s00251-014-0800-7] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/18/2014] [Accepted: 08/25/2014] [Indexed: 11/25/2022]
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Cheviron ZA, Natarajan C, Projecto-Garcia J, Eddy DK, Jones J, Carling MD, Witt CC, Moriyama H, Weber RE, Fago A, Storz JF. Integrating evolutionary and functional tests of adaptive hypotheses: a case study of altitudinal differentiation in hemoglobin function in an Andean Sparrow, Zonotrichia capensis. Mol Biol Evol 2014; 31:2948-62. [PMID: 25135942 DOI: 10.1093/molbev/msu234] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
In air-breathing vertebrates, the physiologically optimal blood-O2 affinity is jointly determined by the prevailing partial pressure of atmospheric O2, the efficacy of pulmonary O2 transfer, and internal metabolic demands. Consequently, genetic variation in the oxygenation properties of hemoglobin (Hb) may be subject to spatially varying selection in species with broad elevational distributions. Here we report the results of a combined functional and evolutionary analysis of Hb polymorphism in the rufous-collared sparrow (Zonotrichia capensis), a species that is continuously distributed across a steep elevational gradient on the Pacific slope of the Peruvian Andes. We integrated a population genomic analysis that included all postnatally expressed Hb genes with functional studies of naturally occurring Hb variants, as well as recombinant Hb (rHb) mutants that were engineered through site-directed mutagenesis. We identified three clinally varying amino acid polymorphisms: Two in the α(A)-globin gene, which encodes the α-chain subunits of the major HbA isoform, and one in the α(D)-globin gene, which encodes the α-chain subunits of the minor HbD isoform. We then constructed and experimentally tested single- and double-mutant rHbs representing each of the alternative α(A)-globin genotypes that predominate at different elevations. Although the locus-specific patterns of altitudinal differentiation suggested a history of spatially varying selection acting on Hb polymorphism, the experimental tests demonstrated that the observed amino acid mutations have no discernible effect on respiratory properties of the HbA or HbD isoforms. These results highlight the importance of experimentally validating the hypothesized effects of genetic changes in protein function to avoid the pitfalls of adaptive storytelling.
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Affiliation(s)
- Zachary A Cheviron
- Department of Animal Biology, School of Integrative Biology, University of Illinois, Urbana-Champaign School of Biological Sciences, University of Nebraska, Lincoln
| | | | | | - Douglas K Eddy
- Department of Animal Biology, School of Integrative Biology, University of Illinois, Urbana-Champaign
| | - Jennifer Jones
- Department of Animal Biology, School of Integrative Biology, University of Illinois, Urbana-Champaign
| | | | - Christopher C Witt
- Department of Biology, University of New Mexico Museum of Southwestern Biology, University of New Mexico
| | | | - Roy E Weber
- Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Angela Fago
- Zoophysiology, Department of Bioscience, Aarhus University, Aarhus, Denmark
| | - Jay F Storz
- School of Biological Sciences, University of Nebraska, Lincoln
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