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Tan A, St. John M, Chau D, Clair C, Chan H, Holzman R, Martin CH. Multiple performance peaks for scale-biting in an adaptive radiation of pupfishes. bioRxiv 2023:2023.12.22.573139. [PMID: 38187684 PMCID: PMC10769438 DOI: 10.1101/2023.12.22.573139] [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] [Subscribe] [Scholar Register] [Indexed: 01/09/2024]
Abstract
The physical interactions between organisms and their environment ultimately shape their rate of speciation and adaptive radiation, but the contributions of biomechanics to evolutionary divergence are frequently overlooked. Here we investigated an adaptive radiation of Cyprinodon pupfishes to measure the relationship between feeding kinematics and performance during adaptation to a novel trophic niche, lepidophagy, in which a predator removes only the scales, mucus, and sometimes tissue from their prey using scraping and biting attacks. We used high-speed video to film scale-biting strikes on gelatin cubes by scale-eater, molluscivore, generalist, and hybrid pupfishes and subsequently measured the dimensions of each bite. We then trained the SLEAP machine-learning animal tracking model to measure kinematic landmarks and automatically scored over 100,000 frames from 227 recorded strikes. Scale-eaters exhibited increased peak gape and greater bite length; however, substantial within-individual kinematic variation resulted in poor discrimination of strikes by species or strike type. Nonetheless, a complex performance landscape with two distinct peaks best predicted gel-biting performance, corresponding to a significant nonlinear interaction between peak gape and peak jaw protrusion in which scale-eaters and their hybrids occupied a second performance peak requiring larger peak gape and greater jaw protrusion. A bite performance valley separating scale-eaters from other species may have contributed to their rapid evolution and is consistent with multiple estimates of a multi-peak fitness landscape in the wild. We thus present an efficient deep-learning automated pipeline for kinematic analyses of feeding strikes and a new biomechanical model for understanding the performance and rapid evolution of a rare trophic niche.
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Affiliation(s)
- Anson Tan
- Department of Integrative Biology, University of California, Berkeley
- Museum of Vertebrate Zoology, University of California, Berkeley
| | | | - Dylan Chau
- Department of Integrative Biology, University of California, Berkeley
- Museum of Vertebrate Zoology, University of California, Berkeley
| | - Chloe Clair
- Department of Integrative Biology, University of California, Berkeley
- Museum of Vertebrate Zoology, University of California, Berkeley
| | | | - Roi Holzman
- School of Zoology, Tel Aviv University, Eilat, Israel
- Inter-University Institute for Marine Sciences, Eilat, Israel
| | - Christopher H. Martin
- Department of Integrative Biology, University of California, Berkeley
- Museum of Vertebrate Zoology, University of California, Berkeley
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Palominos MF, Muhl V, Richards EJ, Miller CT, Martin CH. Jaw size variation is associated with a novel craniofacial function for galanin receptor 2 in an adaptive radiation of pupfishes. Proc Biol Sci 2023; 290:20231686. [PMID: 37876194 PMCID: PMC10598438 DOI: 10.1098/rspb.2023.1686] [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] [Subscribe] [Scholar Register] [Received: 07/28/2023] [Accepted: 10/02/2023] [Indexed: 10/26/2023] Open
Abstract
Understanding the genetic basis of novel adaptations in new species is a fundamental question in biology. Here we demonstrate a new role for galr2 in vertebrate craniofacial development using an adaptive radiation of trophic specialist pupfishes endemic to San Salvador Island, Bahamas. We confirmed the loss of a putative Sry transcription factor binding site upstream of galr2 in scale-eating pupfish and found significant spatial differences in galr2 expression among pupfish species in Meckel's cartilage using in situ hybridization chain reaction (HCR). We then experimentally demonstrated a novel role for Galr2 in craniofacial development by exposing embryos to Garl2-inhibiting drugs. Galr2-inhibition reduced Meckel's cartilage length and increased chondrocyte density in both trophic specialists but not in the generalist genetic background. We propose a mechanism for jaw elongation in scale-eaters based on the reduced expression of galr2 due to the loss of a putative Sry binding site. Fewer Galr2 receptors in the scale-eater Meckel's cartilage may result in their enlarged jaw lengths as adults by limiting opportunities for a circulating Galr2 agonist to bind to these receptors during development. Our findings illustrate the growing utility of linking candidate adaptive SNPs in non-model systems with highly divergent phenotypes to novel vertebrate gene functions.
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Affiliation(s)
- M. Fernanda Palominos
- Department of Integrative Biology, University of California, 3101 Valley Life Sciences Building, Berkeley, CA 94720, USA
- Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720, USA
| | - Vanessa Muhl
- Department of Integrative Biology, University of California, 3101 Valley Life Sciences Building, Berkeley, CA 94720, USA
- Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720, USA
| | - Emilie J. Richards
- Department of Ecology, Evolution, and Behavior, University of Minnesota, Minneapolis, MN, USA
| | - Craig T. Miller
- Department of Molecular & Cell Biology, University of California, Berkeley, CA, USA
| | - Christopher H. Martin
- Department of Integrative Biology, University of California, 3101 Valley Life Sciences Building, Berkeley, CA 94720, USA
- Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720, USA
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3
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Palominos MF, Muhl V, Richards EJ, Miller CT, Martin CH. Jaw size variation is associated with a novel craniofacial function for galanin receptor 2 in an adaptive radiation of pupfishes. bioRxiv 2023:2023.06.02.543513. [PMID: 37333213 PMCID: PMC10274624 DOI: 10.1101/2023.06.02.543513] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/20/2023]
Abstract
Understanding the genetic basis of novel adaptations in new species is a fundamental question in biology that also provides an opportunity to uncover new genes and regulatory networks with potential clinical relevance. Here we demonstrate a new role for galr2 in vertebrate craniofacial development using an adaptive radiation of trophic specialist pupfishes endemic to San Salvador Island in the Bahamas. We confirmed the loss of a putative Sry transcription factor binding site in the upstream region of galr2 in scale-eating pupfish and found significant spatial differences in galr2 expression among pupfish species in Meckel's cartilage and premaxilla using in situ hybridization chain reaction (HCR). We then experimentally demonstrated a novel function for Galr2 in craniofacial development and jaw elongation by exposing embryos to drugs that inhibit Galr2 activity. Galr2-inhibition reduced Meckel's cartilage length and increased chondrocyte density in both trophic specialists but not in the generalist genetic background. We propose a mechanism for jaw elongation in scale-eaters based on the reduced expression of galr2 due to the loss of a putative Sry binding site. Fewer Galr2 receptors in the scale-eater Meckel's cartilage may result in their enlarged jaw lengths as adults by limiting opportunities for a postulated Galr2 agonist to bind to these receptors during development. Our findings illustrate the growing utility of linking candidate adaptive SNPs in non-model systems with highly divergent phenotypes to novel vertebrate gene functions.
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Affiliation(s)
- M Fernanda Palominos
- Department of Integrative Biology, University of California, Berkeley
- Museum of Vertebrate Zoology, University of California, Berkeley
| | - Vanessa Muhl
- Department of Integrative Biology, University of California, Berkeley
- Museum of Vertebrate Zoology, University of California, Berkeley
| | - Emilie J Richards
- Department of Ecology, Evolution, and Behavior, University of Minnesota
| | - Craig T Miller
- Department of Molecular & Cell Biology, University of California, Berkeley
| | - Christopher H Martin
- Department of Integrative Biology, University of California, Berkeley
- Museum of Vertebrate Zoology, University of California, Berkeley
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4
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Norland S, Saele Ø, Rønnestad I. Developmental stages of the ballan wrasse from first feeding through metamorphosis: Cranial ossification and the digestive system. J Anat 2022; 241:337-357. [PMID: 35638267 PMCID: PMC9296024 DOI: 10.1111/joa.13686] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [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: 01/05/2022] [Revised: 04/26/2022] [Accepted: 04/26/2022] [Indexed: 11/29/2022] Open
Abstract
We have described six developmental stages for the ballan wrasse, from the first feeding until the juvenile stage, supported by specific descriptions of cranial ossification, maturation of the digestive tract, and growth-correlated stages. The initial formation and development of bones are closely linked to the functional anatomical structures required for the mechanics of its feeding behavior and ingestion, particularly the jaws and branchial regions involved in opening the mouth and capturing food particles. The overall ontogeny of the cranial structure compares to that of other teleosts. The cranial ossification of the ballan wrasse skull and the development of its dentary apparatus-first pharyngal teeth and later oral teeth-is linked to the development of the digestive system and to their feeding habits, from preying on zooplankton to feeding on crustaceans and invertebrates on rocks and other substrates. As ballan wrasse is a nibbler, eating small meals, the digestive tract is short compared to the length of the fish; there is no stomach or peptic digestion and also no distinctive bulbus and pyloric ceca. The liver and exocrine pancreas and their outlets terminating in the lumen of the most anterior part of the intestine are important in the digestive process and develop with a larger volume than that in gastric teleosts, relative to the digestive system.
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Affiliation(s)
- Sissel Norland
- Department of Biological Sciences, University of Bergen, Bergen, Norway
| | - Øystein Saele
- National Institute of Nutrition and Seafood Research, Bergen, Norway
| | - Ivar Rønnestad
- Department of Biological Sciences, University of Bergen, Bergen, Norway
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Patton AH, Richards EJ, Gould KJ, Buie LK, Martin CH. Hybridization alters the shape of the genotypic fitness landscape, increasing access to novel fitness peaks during adaptive radiation. eLife 2022; 11:e72905. [PMID: 35616528 PMCID: PMC9135402 DOI: 10.7554/elife.72905] [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] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2021] [Accepted: 04/14/2022] [Indexed: 12/30/2022] Open
Abstract
Estimating the complex relationship between fitness and genotype or phenotype (i.e. the adaptive landscape) is one of the central goals of evolutionary biology. However, adaptive walks connecting genotypes to organismal fitness, speciation, and novel ecological niches are still poorly understood and processes for surmounting fitness valleys remain controversial. One outstanding system for addressing these connections is a recent adaptive radiation of ecologically and morphologically novel pupfishes (a generalist, molluscivore, and scale-eater) endemic to San Salvador Island, Bahamas. We leveraged whole-genome sequencing of 139 hybrids from two independent field fitness experiments to identify the genomic basis of fitness, estimate genotypic fitness networks, and measure the accessibility of adaptive walks on the fitness landscape. We identified 132 single nucleotide polymorphisms (SNPs) that were significantly associated with fitness in field enclosures. Six out of the 13 regions most strongly associated with fitness contained differentially expressed genes and fixed SNPs between trophic specialists; one gene (mettl21e) was also misexpressed in lab-reared hybrids, suggesting a potential intrinsic genetic incompatibility. We then constructed genotypic fitness networks from adaptive alleles and show that scale-eating specialists are the most isolated of the three species on these networks. Intriguingly, introgressed and de novo variants reduced fitness landscape ruggedness as compared to standing variation, increasing the accessibility of genotypic fitness paths from generalist to specialists. Our results suggest that adaptive introgression and de novo mutations alter the shape of the fitness landscape, providing key connections in adaptive walks circumventing fitness valleys and triggering the evolution of novelty during adaptive radiation.
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Affiliation(s)
- Austin H Patton
- Department of Integrative Biology, University of California, BerkeleyBerkeleyUnited States
- Museum of Vertebrate Zoology, University of California, BerkeleyBerkeleyUnited States
| | - Emilie J Richards
- Department of Integrative Biology, University of California, BerkeleyBerkeleyUnited States
- Museum of Vertebrate Zoology, University of California, BerkeleyBerkeleyUnited States
| | - Katelyn J Gould
- Department of Biology, University of North CarolinaChapel HillUnited States
| | - Logan K Buie
- Department of Biology, University of North CarolinaChapel HillUnited States
| | - Christopher H Martin
- Department of Integrative Biology, University of California, BerkeleyBerkeleyUnited States
- Museum of Vertebrate Zoology, University of California, BerkeleyBerkeleyUnited States
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Richards EJ, Martin CH. We get by with a little help from our friends: shared adaptive variation provides a bridge to novel ecological specialists during adaptive radiation. Proc Biol Sci 2022; 289:20220613. [PMID: 35611537 PMCID: PMC9130792 DOI: 10.1098/rspb.2022.0613] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [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: 11/19/2022] Open
Abstract
Adaptive radiations involve astounding bursts of phenotypic, ecological and species diversity. However, the microevolutionary processes that underlie the origins of these bursts are still poorly understood. We report the discovery of an intermediate C. sp. ‘wide-mouth’ scale-eating ecomorph in a sympatric radiation of Cyprinodon pupfishes, illuminating the transition from a widespread algae-eating generalist to a novel microendemic scale-eating specialist. We first show that this ecomorph occurs in sympatry with generalist C. variegatus and scale-eating specialist C. desquamator on San Salvador Island, Bahamas, but is genetically differentiated, morphologically distinct and often consumes scales. We then compared the timing of selective sweeps on shared and unique adaptive variants in trophic specialists to characterize their adaptive walk. Shared adaptive regions swept first in both the specialist desquamator and the intermediate ‘wide-mouth’ ecomorph, followed by unique sweeps of introgressed variation in ‘wide-mouth’ and de novo variation in desquamator. The two scale-eating populations additionally shared 9% of their hard selective sweeps with the molluscivore C. brontotheroides, despite no single common ancestor among specialists. Our work provides a new microevolutionary framework for investigating how major ecological transitions occur and illustrates how both shared and unique genetic variation can provide a bridge for multiple species to access novel ecological niches.
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Affiliation(s)
- Emilie J Richards
- Department of Integrative Biology, University of California, Berkeley, CA, USA.,Museum of Vertebrate Zoology, University of California, Berkeley, CA, USA
| | - Christopher H Martin
- Department of Integrative Biology, University of California, Berkeley, CA, USA.,Museum of Vertebrate Zoology, University of California, Berkeley, CA, USA
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Richards EJ, McGirr JA, Wang JR, St John ME, Poelstra JW, Solano MJ, O'Connell DC, Turner BJ, Martin CH. A vertebrate adaptive radiation is assembled from an ancient and disjunct spatiotemporal landscape. Proc Natl Acad Sci U S A 2021; 118:e2011811118. [PMID: 33990463 PMCID: PMC8157919 DOI: 10.1073/pnas.2011811118] [Citation(s) in RCA: 17] [Impact Index Per Article: 5.7] [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] [Indexed: 12/30/2022] Open
Abstract
To investigate the origins and stages of vertebrate adaptive radiation, we reconstructed the spatial and temporal histories of adaptive alleles underlying major phenotypic axes of diversification from the genomes of 202 Caribbean pupfishes. On a single Bahamian island, ancient standing variation from disjunct geographic sources was reassembled into new combinations under strong directional selection for adaptation to the novel trophic niches of scale-eating and molluscivory. We found evidence for two longstanding hypotheses of adaptive radiation: hybrid swarm origins and temporal stages of adaptation. Using a combination of population genomics, transcriptomics, and genome-wide association mapping, we demonstrate that this microendemic adaptive radiation of novel trophic specialists on San Salvador Island, Bahamas experienced twice as much adaptive introgression as generalist populations on neighboring islands and that adaptive divergence occurred in stages. First, standing regulatory variation in genes associated with feeding behavior (prlh, cfap20, and rmi1) were swept to fixation by selection, then standing regulatory variation in genes associated with craniofacial and muscular development (itga5, ext1, cyp26b1, and galr2) and finally the only de novo nonsynonymous substitution in an osteogenic transcription factor and oncogene (twist1) swept to fixation most recently. Our results demonstrate how ancient alleles maintained in distinct environmental refugia can be assembled into new adaptive combinations and provide a framework for reconstructing the spatiotemporal landscape of adaptation and speciation.
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Affiliation(s)
- Emilie J Richards
- Department of Integrative Biology, University of California, Berkeley, CA 94720
- Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720
| | - Joseph A McGirr
- Department of Environmental Toxicology, University of California, Davis, CA 95616
| | - Jeremy R Wang
- Department of Genetics, University of North Carolina, Chapel Hill, NC 27514
| | - Michelle E St John
- Department of Integrative Biology, University of California, Berkeley, CA 94720
- Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720
| | - Jelmer W Poelstra
- Molecular and Cellular Imaging Center, Ohio State University, Columbus, OH 43210
| | - Maria J Solano
- Department of Biology, University of North Carolina, Chapell Hill, NC 27514
| | | | - Bruce J Turner
- Department of Biological Sciences, Virginia Polytechnic Institute and State University, Blacksburg, VA 24601
| | - Christopher H Martin
- Department of Integrative Biology, University of California, Berkeley, CA 94720;
- Museum of Vertebrate Zoology, University of California, Berkeley, CA 94720
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8
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McGirr JA, Martin CH. Few Fixed Variants between Trophic Specialist Pupfish Species Reveal Candidate Cis-Regulatory Alleles Underlying Rapid Craniofacial Divergence. Mol Biol Evol 2021; 38:405-423. [PMID: 32877534 PMCID: PMC7826174 DOI: 10.1093/molbev/msaa218] [Citation(s) in RCA: 13] [Impact Index Per Article: 4.3] [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: 02/07/2023] Open
Abstract
Investigating closely related species that rapidly evolved divergent feeding morphology is a powerful approach to identify genetic variation underlying variation in complex traits. This can also lead to the discovery of novel candidate genes influencing natural and clinical variation in human craniofacial phenotypes. We combined whole-genome resequencing of 258 individuals with 50 transcriptomes to identify candidate cis-acting genetic variation underlying rapidly evolving craniofacial phenotypes within an adaptive radiation of Cyprinodon pupfishes. This radiation consists of a dietary generalist species and two derived trophic niche specialists-a molluscivore and a scale-eating species. Despite extensive morphological divergence, these species only diverged 10 kya and produce fertile hybrids in the laboratory. Out of 9.3 million genome-wide SNPs and 80,012 structural variants, we found very few alleles fixed between species-only 157 SNPs and 87 deletions. Comparing gene expression across 38 purebred F1 offspring sampled at three early developmental stages, we identified 17 fixed variants within 10 kb of 12 genes that were highly differentially expressed between species. By measuring allele-specific expression in F1 hybrids from multiple crosses, we found that the majority of expression divergence between species was explained by trans-regulatory mechanisms. We also found strong evidence for two cis-regulatory alleles affecting expression divergence of two genes with putative effects on skeletal development (dync2li1 and pycr3). These results suggest that SNPs and structural variants contribute to the evolution of novel traits and highlight the utility of the San Salvador Island pupfish system as an evolutionary model for craniofacial development.
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Affiliation(s)
- Joseph A McGirr
- Environmental Toxicology Department, University of California, Davis, CA
| | - Christopher H Martin
- Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, CA
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Martin CH, Gould KJ. Surprising spatiotemporal stability of a multi-peak fitness landscape revealed by independent field experiments measuring hybrid fitness. Evol Lett 2020; 4:530-544. [PMID: 33312688 PMCID: PMC7719547 DOI: 10.1002/evl3.195] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2019] [Revised: 07/23/2020] [Accepted: 09/14/2020] [Indexed: 12/14/2022] Open
Abstract
The effect of the environment on fitness in natural populations is a fundamental question in evolutionary biology. However, experimental manipulations of both environment and phenotype at the same time are rare. Thus, the relative importance of the competitive environment versus intrinsic organismal performance in shaping the location, height, and fluidity of fitness peaks and valleys remains largely unknown. Here, we experimentally tested the effect of competitor frequency on the complex fitness landscape driving adaptive radiation of a generalist and two trophic specialist pupfishes, a scale-eater and molluscivore, endemic to hypersaline lakes on San Salvador Island (SSI), Bahamas. We manipulated phenotypes, by generating 3407 F4/F5 lab-reared hybrids, and competitive environment, by altering the frequency of rare transgressive hybrids between field enclosures in two independent lake populations. We then tracked hybrid survival and growth rates across these four field enclosures for 3-11 months. In contrast to competitive speciation theory, we found no evidence that the frequency of hybrid phenotypes affected their survival. Instead, we observed a strikingly similar fitness landscape to a previous independent field experiment, each supporting multiple fitness peaks for generalist and molluscivore phenotypes and a large fitness valley isolating the divergent scale-eater phenotype. These features of the fitness landscape were stable across manipulated competitive environments, multivariate trait axes, and spatiotemporal heterogeneity. We suggest that absolute performance constraints and divergent gene regulatory networks shape macroevolutionary (interspecific) fitness landscapes in addition to microevolutionary (intraspecific) competitive dynamics. This interplay between organism and environment underlies static and dynamic features of the adaptive landscape.
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Affiliation(s)
- Christopher H. Martin
- Department of Integrative BiologyUniversity of California, BerkeleyBerkeleyCalifornia94720
- Museum of Vertebrate ZoologyUniversity of California, BerkeleyBerkeleyCalifornia94720
| | - Katelyn J. Gould
- Department of BiologyUniversity of North Carolina at Chapel HillChapel HillNorth Carolina27515
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McGirr JA, Martin CH. Ecological divergence in sympatry causes gene misexpression in hybrids. Mol Ecol 2020; 29:2707-2721. [PMID: 32557903 DOI: 10.1111/mec.15512] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [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: 03/11/2020] [Revised: 05/21/2020] [Accepted: 06/01/2020] [Indexed: 12/17/2022]
Abstract
Ecological speciation occurs when reproductive isolation evolves as a byproduct of adaptive divergence between populations. Selection favouring gene regulatory divergence between species could result in transgressive levels of gene expression in F1 hybrids that may lower hybrid fitness. We combined 58 resequenced genomes with 124 transcriptomes to identify patterns of hybrid gene misexpression that may be driven by adaptive regulatory divergence within a young radiation of Cyprinodon pupfishes, which consists of a dietary generalist and two trophic specialists-a molluscivore and a scale-eater. We found more differential gene expression between closely related sympatric specialists than between allopatric generalist populations separated by 1,000 km. Intriguingly, 9.6% of genes that were differentially expressed between sympatric species were also misexpressed in F1 hybrids. A subset of these genes were in highly differentiated genomic regions and enriched for functions important for trophic specialization, including head, muscle and brain development. These regions also included genes that showed evidence of hard selective sweeps and were significantly associated with oral jaw length-the most rapidly diversifying skeletal trait in this radiation. Our results indicate that divergent ecological selection in sympatry can contribute to hybrid gene misexpression which may act as a reproductive barrier between nascent species.
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Affiliation(s)
- Joseph A McGirr
- Department of Biology, University of North Carolina, Chapel Hill, NC
| | - Christopher H Martin
- Department of Biology, University of North Carolina, Chapel Hill, NC.,Department of Integrative Biology and Museum of Vertebrate Zoology, University of California, Berkeley, CA
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