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Hague MTJ, Miller LE, Stokes AN, Feldman CR, Brodie ED, Brodie ED. Conspicuous coloration of toxin-resistant predators implicates additional trophic interactions in a predator-prey arms race. Mol Ecol 2023; 32:4482-4496. [PMID: 36336815 DOI: 10.1111/mec.16772] [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] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/23/2022] [Revised: 10/21/2022] [Accepted: 11/03/2022] [Indexed: 08/08/2023]
Abstract
Antagonistic coevolution between natural enemies can produce highly exaggerated traits, such as prey toxins and predator resistance. This reciprocal process of adaptation and counter-adaptation may also open doors to other evolutionary novelties not directly involved in the phenotypic interface of coevolution. We tested the hypothesis that predator-prey coevolution coincided with the evolution of conspicuous coloration on resistant predators that retain prey toxins. In western North America, common garter snakes (Thamnophis sirtalis) have evolved extreme resistance to tetrodotoxin (TTX) in the coevolutionary arms race with their deadly prey, Pacific newts (Taricha spp.). TTX-resistant snakes can retain large amounts of ingested TTX, which could serve as a deterrent against the snakes' own predators if TTX toxicity and resistance are coupled with a conspicuous warning signal. We evaluated whether arms race escalation covaries with bright red coloration in snake populations across the geographic mosaic of coevolution. Snake colour variation departs from the neutral expectations of population genetic structure and covaries with escalating clines of newt TTX and snake resistance at two coevolutionary hotspots. In the Pacific Northwest, bright red coloration fits an expected pattern of an aposematic warning to avian predators: TTX-resistant snakes that consume highly toxic newts also have relatively large, reddish-orange dorsal blotches. Snake coloration also seems to have evolved with the arms race in California, but overall patterns are less intuitively consistent with aposematism. These results suggest that interactions with additional trophic levels can generate novel traits as a cascading consequence of arms race coevolution across the geographic mosaic.
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Affiliation(s)
- Michael T J Hague
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
| | - Lauren E Miller
- Department of Biology, University of Virginia, Charlottesville, Virginia, USA
| | - Amber N Stokes
- Department of Biology, California State University, Bakersfield, California, USA
| | - Chris R Feldman
- Department of Biology, University of Nevada, Reno, Nevada, USA
| | - Edmund D Brodie
- Department of Biology, Utah State University, Logan, Utah, USA
| | - Edmund D Brodie
- Department of Biology, University of Virginia, Charlottesville, Virginia, USA
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Radousky YA, Hague MTJ, Fowler S, Paneru E, Codina A, Rugamas C, Hartzog G, Cooper BS, Sullivan W. Distinct Wolbachia localization patterns in oocytes of diverse host species reveal multiple strategies of maternal transmission. Genetics 2023; 224:iyad038. [PMID: 36911919 PMCID: PMC10474932 DOI: 10.1093/genetics/iyad038] [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: 11/28/2022] [Revised: 02/21/2023] [Accepted: 02/21/2023] [Indexed: 03/14/2023] Open
Abstract
A broad array of endosymbionts radiate through host populations via vertical transmission, yet much remains unknown concerning the cellular basis, diversity, and routes underlying this transmission strategy. Here, we address these issues, by examining the cellular distributions of Wolbachia strains that diverged up to 50 million years ago in the oocytes of 18 divergent Drosophila species. This analysis revealed 3 Wolbachia distribution patterns: (1) a tight clustering at the posterior pole plasm (the site of germline formation); (2) a concentration at the posterior pole plasm, but with a significant bacteria population distributed throughout the oocyte; and (3) a distribution throughout the oocyte, with none or very few located at the posterior pole plasm. Examination of this latter class indicates Wolbachia accesses the posterior pole plasm during the interval between late oogenesis and the blastoderm formation. We also find that 1 Wolbachia strain in this class concentrates in the posterior somatic follicle cells that encompass the pole plasm of the developing oocyte. In contrast, strains in which Wolbachia concentrate at the posterior pole plasm generally exhibit no or few Wolbachia in the follicle cells associated with the pole plasm. Taken together, these studies suggest that for some Drosophila species, Wolbachia invade the germline from neighboring somatic follicle cells. Phylogenomic analysis indicates that closely related Wolbachia strains tend to exhibit similar patterns of posterior localization, suggesting that specific localization strategies are a function of Wolbachia-associated factors. Previous studies revealed that endosymbionts rely on 1 of 2 distinct routes of vertical transmission: continuous maintenance in the germline (germline-to-germline) or a more circuitous route via the soma (germline-to-soma-to-germline). Here, we provide compelling evidence that Wolbachia strains infecting Drosophila species maintain the diverse arrays of cellular mechanisms necessary for both of these distinct transmission routes. This characteristic may account for its ability to infect and spread globally through a vast range of host insect species.
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Affiliation(s)
- Yonah A Radousky
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Michael T J Hague
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - Sommer Fowler
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Eliza Paneru
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Adan Codina
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Cecilia Rugamas
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Grant Hartzog
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, USA
| | - Brandon S Cooper
- Division of Biological Sciences, University of Montana, Missoula, MT 59812, USA
| | - William Sullivan
- Department of Molecular, Cell, and Developmental Biology, University of California Santa Cruz, Santa Cruz, CA 95064, USA
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Gendreau KL, Hornsby AD, Hague MTJ, McGlothlin JW. Gene Conversion Facilitates the Adaptive Evolution of Self-Resistance in Highly Toxic Newts. Mol Biol Evol 2021; 38:4077-4094. [PMID: 34129031 PMCID: PMC8476164 DOI: 10.1093/molbev/msab182] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Reconstructing the histories of complex adaptations and identifying the evolutionary mechanisms underlying their origins are two of the primary goals of evolutionary biology. Taricha newts, which contain high concentrations of the deadly toxin tetrodotoxin (TTX) as an antipredator defense, have evolved resistance to self-intoxication, which is a complex adaptation requiring changes in six paralogs of the voltage-gated sodium channel (Nav) gene family, the physiological target of TTX. Here, we reconstruct the origins of TTX self-resistance by sequencing the entire Nav gene family in newts and related salamanders. We show that moderate TTX resistance evolved early in the salamander lineage in three of the six Nav paralogs, preceding the proposed appearance of tetrodotoxic newts by ∼100 My. TTX-bearing newts possess additional unique substitutions across the entire Nav gene family that provide physiological TTX resistance. These substitutions coincide with signatures of positive selection and relaxed purifying selection, as well as gene conversion events, that together likely facilitated their evolution. We also identify a novel exon duplication within Nav1.4 encoding an expressed TTX-binding site. Two resistance-conferring changes within newts appear to have spread via nonallelic gene conversion: in one case, one codon was copied between paralogs, and in the second, multiple substitutions were homogenized between the duplicate exons of Nav1.4. Our results demonstrate that gene conversion can accelerate the coordinated evolution of gene families in response to a common selection pressure.
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Affiliation(s)
- Kerry L Gendreau
- Department of Biological Sciences, Virginia Tech, Blacksburg, United States
| | - Angela D Hornsby
- Department of Biological Sciences, Virginia Tech, Blacksburg, United States.,Philip L. Wright Zoological Museum, Division of Biological Sciences, University of Montana, Missoula, United States
| | - Michael T J Hague
- Division of Biological Sciences, University of Montana, Missoula, MT, United States
| | - Joel W McGlothlin
- Department of Biological Sciences, Virginia Tech, Blacksburg, United States
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Abstract
Heritable symbionts have diverse effects on the physiology, reproduction and fitness of their hosts. Maternally transmitted Wolbachia are one of the most common endosymbionts in nature, infecting about half of all insect species. We test the hypothesis that Wolbachia alter host behaviour by assessing the effects of 14 different Wolbachia strains on the locomotor activity of nine Drosophila host species. We find that Wolbachia alter the activity of six different host genotypes, including all hosts in our assay infected with wRi-like Wolbachia strains (wRi, wSuz and wAur), which have rapidly spread among Drosophila species in about the last 14 000 years. While Wolbachia effects on host activity were common, the direction of these effects varied unpredictably and sometimes depended on host sex. We hypothesize that the prominent effects of wRi-like Wolbachia may be explained by patterns of Wolbachia titre and localization within host somatic tissues, particularly in the central nervous system. Our findings support the view that Wolbachia have wide-ranging effects on host behaviour. The fitness consequences of these behavioural modifications are important for understanding the evolution of host-symbiont interactions, including how Wolbachia spread within host populations.
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Affiliation(s)
- Michael T. J. Hague
- Division of Biological Sciences, University of Montana, 32 Campus Dr., Missoula, MT 59812
| | - H. Arthur Woods
- Division of Biological Sciences, University of Montana, 32 Campus Dr., Missoula, MT 59812
| | - Brandon S. Cooper
- Division of Biological Sciences, University of Montana, 32 Campus Dr., Missoula, MT 59812
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Abstract
Heritable symbionts can modify a range of ecologically important host traits, including behavior. About half of all insect species are infected with maternally transmitted Wolbachia, a bacterial endosymbiont known to alter host reproduction, nutrient acquisition, and virus susceptibility. Here, we broadly test the hypothesis that Wolbachia modifies host behavior by assessing the effects of eight different Wolbachia strains on the temperature preference of six Drosophila melanogaster subgroup species. Four of the seven host genotypes infected with A-group Wolbachia strains (wRi in Drosophila simulans, wHa in D. simulans, wSh in Drosophila sechellia, and wTei in Drosophila teissieri) prefer significantly cooler temperatures relative to uninfected genotypes. Contrastingly, when infected with divergent B-group wMau, Drosophila mauritiana prefers a warmer temperature. For most strains, changes to host temperature preference do not alter Wolbachia titer. However, males infected with wSh and wTei tend to experience an increase in titer when shifted to a cooler temperature for 24 h, suggesting that Wolbachia-induced changes to host behavior may promote bacterial replication. Our results indicate that Wolbachia modifications to host temperature preference are likely widespread, which has important implications for insect thermoregulation and physiology. Understanding the fitness consequences of these Wolbachia effects is crucial for predicting evolutionary outcomes of host-symbiont interactions, including how Wolbachia spreads to become common.IMPORTANCE Microbes infect a diversity of species, influencing the performance and fitness of their hosts. Maternally transmitted Wolbachia bacteria infect most insects and other arthropods, making these bacteria some of the most common endosymbionts in nature. Despite their global prevalence, it remains mostly unknown how Wolbachia influence host physiology and behavior to proliferate. We demonstrate pervasive effects of Wolbachia on Drosophila temperature preference. Most hosts infected with A-group Wolbachia prefer cooler temperatures, whereas the one host species infected with divergent B-group Wolbachia prefers warmer temperatures, relative to uninfected genotypes. Changes to host temperature preference generally do not alter Wolbachia abundance in host tissues, but for some A-group strains, adult males have increased Wolbachia titer when shifted to a cooler temperature. This suggests that Wolbachia-induced changes to host behavior may promote bacterial replication. Our results help elucidate the impact of endosymbionts on their hosts amid the global Wolbachia pandemic.
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Affiliation(s)
- Michael T J Hague
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
| | - Chelsey N Caldwell
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
| | - Brandon S Cooper
- Division of Biological Sciences, University of Montana, Missoula, Montana, USA
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Hague MTJ, Mavengere H, Matute DR, Cooper BS. Environmental and Genetic Contributions to Imperfect wMel-Like Wolbachia Transmission and Frequency Variation. Genetics 2020; 215:1117-1132. [PMID: 32546497 PMCID: PMC7404227 DOI: 10.1534/genetics.120.303330] [Citation(s) in RCA: 23] [Impact Index Per Article: 5.8] [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: 05/08/2020] [Accepted: 06/13/2020] [Indexed: 12/11/2022] Open
Abstract
Maternally transmitted Wolbachia bacteria infect about half of all insect species. They usually show imperfect maternal transmission and often produce cytoplasmic incompatibility (CI). Irrespective of CI, Wolbachia frequencies tend to increase when rare only if they benefit host fitness. Several Wolbachia, including wMel that infects Drosophila melanogaster, cause weak or no CI and persist at intermediate frequencies. On the island of São Tomé off West Africa, the frequencies of wMel-like Wolbachia infecting Drosophila yakuba (wYak) and Drosophila santomea (wSan) fluctuate, and the contributions of imperfect maternal transmission, fitness effects, and CI to these fluctuations are unknown. We demonstrate spatial variation in wYak frequency and transmission on São Tomé. Concurrent field estimates of imperfect maternal transmission do not predict spatial variation in wYak frequencies, which are highest at high altitudes where maternal transmission is the most imperfect. Genomic and genetic analyses provide little support for D. yakuba effects on wYak transmission. Instead, rearing at cool temperatures reduces wYak titer and increases imperfect transmission to levels observed on São Tomé. Using mathematical models of Wolbachia frequency dynamics and equilibria, we infer that temporally variable imperfect transmission or spatially variable effects on host fitness and reproduction are required to explain wYak frequencies. In contrast, spatially stable wSan frequencies are plausibly explained by imperfect transmission, modest fitness effects, and weak CI. Our results provide insight into causes of wMel-like frequency variation in divergent hosts. Understanding this variation is crucial to explain Wolbachia spread and to improve wMel biocontrol of human disease in transinfected mosquito systems.
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Affiliation(s)
- Michael T J Hague
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812
| | - Heidi Mavengere
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Daniel R Matute
- Department of Biology, University of North Carolina, Chapel Hill, North Carolina 27599
| | - Brandon S Cooper
- Division of Biological Sciences, University of Montana, Missoula, Montana 59812
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Hague MTJ, Stokes AN, Feldman CR, Brodie ED, Brodie ED. The geographic mosaic of arms race coevolution is closely matched to prey population structure. Evol Lett 2020; 4:317-332. [PMID: 32774881 PMCID: PMC7403720 DOI: 10.1002/evl3.184] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [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: 12/10/2019] [Revised: 05/11/2020] [Accepted: 05/22/2020] [Indexed: 01/09/2023] Open
Abstract
Reciprocal adaptation is the hallmark of arms race coevolution. Local coadaptation between natural enemies should generate a geographic mosaic pattern where both species have roughly matched abilities across their shared range. However, mosaic variation in ecologically relevant traits can also arise from processes unrelated to reciprocal selection, such as population structure or local environmental conditions. We tested whether these alternative processes can account for trait variation in the geographic mosaic of arms race coevolution between resistant garter snakes (Thamnophis sirtalis) and toxic newts (Taricha granulosa). We found that predator resistance and prey toxin levels are functionally matched in co-occurring populations, suggesting that mosaic variation in the armaments of both species results from the local pressures of reciprocal selection. By the same token, phenotypic and genetic variation in snake resistance deviates from neutral expectations of population genetic differentiation, showing a clear signature of adaptation to local toxin levels in newts. Contrastingly, newt toxin levels are best predicted by genetic differentiation among newt populations, and to a lesser extent, by the local environment and snake resistance. Exaggerated armaments suggest that coevolution occurs in certain hotspots, but prey population structure seems to be of particular influence on local phenotypic variation in both species throughout the geographic mosaic. Our results imply that processes other than reciprocal selection, like historical biogeography and environmental pressures, represent an important source of variation in the geographic mosaic of coevolution. Such a pattern supports the role of "trait remixing" in the geographic mosaic theory, the process by which non-adaptive forces dictate spatial variation in the interactions among species.
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Affiliation(s)
- Michael T J Hague
- Division of Biological Sciences University of Montana Missoula Montana 59812.,Department of Biology University of Virginia Charlottesville Virginia 22904
| | - Amber N Stokes
- Department of Biology California State University Bakersfield California 93311
| | - Chris R Feldman
- Department of Biology University of Nevada Reno Nevada 89557
| | - Edmund D Brodie
- Department of Biology Utah State University Logan Utah 84322
| | - Edmund D Brodie
- Department of Biology University of Virginia Charlottesville Virginia 22904
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Hague MTJ, Toledo G, Geffeney SL, Hanifin CT, Brodie ED, Brodie ED. Large-effect mutations generate trade-off between predatory and locomotor ability during arms race coevolution with deadly prey. Evol Lett 2018; 2:406-416. [PMID: 30283691 PMCID: PMC6121790 DOI: 10.1002/evl3.76] [Citation(s) in RCA: 15] [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] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2018] [Revised: 07/10/2018] [Accepted: 07/13/2018] [Indexed: 01/06/2023] Open
Abstract
Adaptive evolution in response to one selective challenge may disrupt other important aspects of performance. Such evolutionary trade‐offs are predicted to arise in the process of local adaptation, but it is unclear if these phenotypic compromises result from the antagonistic effects of simple amino acid substitutions. We tested for trade‐offs associated with beneficial mutations that confer tetrodotoxin (TTX) resistance in the voltage‐gated sodium channel (NaV1.4) in skeletal muscle of the common garter snake (Thamnophis sirtalis). Separate lineages in California and the Pacific Northwest independently evolved TTX‐resistant changes to the pore of NaV1.4 as a result of arms race coevolution with toxic prey, newts of the genus Taricha. Snakes from the California lineage that were homozygous for an allele known to confer large increases in toxin resistance (NaV1.4LVNV) had significantly reduced crawl speed compared to individuals with the ancestral TTX‐sensitive channel. Heterologous expression of native snake NaV1.4 proteins demonstrated that the same NaV1.4LVNV allele confers a dramatic increase in TTX resistance and a correlated decrease in overall channel excitability. Our results suggest the same mutations that accumulate during arms race coevolution and beneficially interfere with toxin‐binding also cause changes in electrophysiological function of the channel that may affect organismal performance. This trade‐off was only evident in the predator lineage where coevolution has led to the most extreme resistance phenotype, determined by four critical amino acid substitutions. If these biophysical changes also translate to a fitness cost—for example, through the inability of T. sirtalis to quickly escape predators—then pleiotropy at this single locus could contribute to observed variation in levels of TTX resistance across the mosaic landscape of coevolution.
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Affiliation(s)
- Michael T J Hague
- Department of Biology University of Virginia Charlottesville Virginia 22903
| | - Gabriela Toledo
- Department of Biology University of Virginia Charlottesville Virginia 22903
| | - Shana L Geffeney
- Department of Biology Utah State University Uintah Basin Vernal Utah 84322
| | - Charles T Hanifin
- Department of Biology Utah State University Uintah Basin Vernal Utah 84322
| | - Edmund D Brodie
- Department of Biology Utah State University Logan Utah 84322
| | - Edmund D Brodie
- Department of Biology University of Virginia Charlottesville Virginia 22903
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Hague MTJ, Avila LA, Hanifin CT, Snedden WA, Stokes AN, Brodie ED, Brodie ED. Toxicity and population structure of the Rough-Skinned Newt (Taricha granulosa) outside the range of an arms race with resistant predators. Ecol Evol 2016; 6:2714-24. [PMID: 27066249 PMCID: PMC4798830 DOI: 10.1002/ece3.2068] [Citation(s) in RCA: 16] [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: 11/05/2015] [Revised: 02/11/2016] [Accepted: 02/22/2016] [Indexed: 01/07/2023] Open
Abstract
Species interactions, and their fitness consequences, vary across the geographic range of a coevolutionary relationship. This spatial heterogeneity in reciprocal selection is predicted to generate a geographic mosaic of local adaptation, wherein coevolutionary traits are phenotypically variable from one location to the next. Under this framework, allopatric populations should lack variation in coevolutionary traits due to the absence of reciprocal selection. We examine phenotypic variation in tetrodotoxin (TTX) toxicity of the Rough-Skinned Newt (Taricha granulosa) in regions of allopatry with its TTX-resistant predator, the Common Garter Snake (Thamnophis sirtalis). In sympatry, geographic patterns of phenotypic exaggeration in toxicity and toxin-resistance are closely correlated in prey and predator, implying that reciprocal selection drives phenotypic variation in coevolutionary traits. Therefore, in allopatry with TTX-resistant predators, we expect to find uniformly low levels of newt toxicity. We characterized TTX toxicity in northwestern North America, including the Alaskan panhandle where Ta. granulosa occur in allopatry with Th. sirtalis. First, we used microsatellite markers to estimate population genetic structure and determine if any phenotypic variation in toxicity might be explained by historical divergence. We found northern populations of Ta. granulosa generally lacked population structure in a pattern consistent with northern range expansion after the Pleistocene. Next, we chose a cluster of sites in Alaska, which uniformly lacked genetic divergence, to test for phenotypic divergence in toxicity. As predicted, overall levels of newt toxicity were low; however, we also detected unexpected among- and within-population variation in toxicity. Most notably, a small number of individuals contained large doses of TTX that rival means of toxic populations in sympatry with Th. sirtalis. Phenotypic variation in toxicity, despite limited neutral genetic divergence, suggests that factors other than reciprocal selection with Th. sirtalis likely contribute to geographic patterns of toxicity in Ta. granulosa.
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Affiliation(s)
- Michael T J Hague
- Department of Biology University of Virginia Charlottesville Virginia
| | - Leleña A Avila
- Museum of Vertebrate Zoology University of California Berkeley California
| | - Charles T Hanifin
- Department of Biology Utah State University, Uintah Basin Campus Vernal Utah
| | | | - Amber N Stokes
- Department of Biology California State University Bakersfield California
| | | | - Edmund D Brodie
- Department of Biology University of Virginia Charlottesville Virginia
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Hague MTJ, Routman EJ. Does population size affect genetic diversity? A test with sympatric lizard species. Heredity (Edinb) 2015; 116:92-8. [PMID: 26306730 DOI: 10.1038/hdy.2015.76] [Citation(s) in RCA: 54] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/25/2014] [Revised: 06/25/2015] [Accepted: 07/16/2015] [Indexed: 01/09/2023] Open
Abstract
Genetic diversity is a fundamental requirement for evolution and adaptation. Nonetheless, the forces that maintain patterns of genetic variation in wild populations are not completely understood. Neutral theory posits that genetic diversity will increase with a larger effective population size and the decreasing effects of drift. However, the lack of compelling evidence for a relationship between genetic diversity and population size in comparative studies has generated some skepticism over the degree that neutral sequence evolution drives overall patterns of diversity. The goal of this study was to measure genetic diversity among sympatric populations of related lizard species that differ in population size and other ecological factors. By sampling related species from a single geographic location, we aimed to reduce nuisance variance in genetic diversity owing to species differences, for example, in mutation rates or historical biogeography. We compared populations of zebra-tailed lizards and western banded geckos, which are abundant and short-lived, to chuckwallas and desert iguanas, which are less common and long-lived. We assessed population genetic diversity at three protein-coding loci for each species. Our results were consistent with the predictions of neutral theory, as the abundant species almost always had higher levels of haplotype diversity than the less common species. Higher population genetic diversity in the abundant species is likely due to a combination of demographic factors, including larger local population sizes (and presumably effective population sizes), faster generation times and high rates of gene flow with other populations.
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Affiliation(s)
- M T J Hague
- Department of Biology, San Francisco State University, San Francisco, CA, USA
| | - E J Routman
- Department of Biology, San Francisco State University, San Francisco, CA, USA
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