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Zancolli G, Calvete JJ, Cardwell MD, Greene HW, Hayes WK, Hegarty MJ, Herrmann HW, Holycross AT, Lannutti DI, Mulley JF, Sanz L, Travis ZD, Whorley JR, Wüster CE, Wüster W. When one phenotype is not enough: divergent evolutionary trajectories govern venom variation in a widespread rattlesnake species. Proc Biol Sci 2020; 286:20182735. [PMID: 30862287 DOI: 10.1098/rspb.2018.2735] [Citation(s) in RCA: 47] [Impact Index Per Article: 11.8] [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: 11/12/2022] Open
Abstract
Understanding the origin and maintenance of phenotypic variation, particularly across a continuous spatial distribution, represents a key challenge in evolutionary biology. For this, animal venoms represent ideal study systems: they are complex, variable, yet easily quantifiable molecular phenotypes with a clear function. Rattlesnakes display tremendous variation in their venom composition, mostly through strongly dichotomous venom strategies, which may even coexist within a single species. Here, through dense, widespread population-level sampling of the Mojave rattlesnake, Crotalus scutulatus, we show that genomic structural variation at multiple loci underlies extreme geographical variation in venom composition, which is maintained despite extensive gene flow. Unexpectedly, neither diet composition nor neutral population structure explain venom variation. Instead, venom divergence is strongly correlated with environmental conditions. Individual toxin genes correlate with distinct environmental factors, suggesting that different selective pressures can act on individual loci independently of their co-expression patterns or genomic proximity. Our results challenge common assumptions about diet composition as the key selective driver of snake venom evolution and emphasize how the interplay between genomic architecture and local-scale spatial heterogeneity in selective pressures may facilitate the retention of adaptive functional polymorphisms across a continuous space.
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Affiliation(s)
- Giulia Zancolli
- 1 Molecular Ecology and Fisheries Genetics Laboratory, School of Natural Sciences, Bangor University , Bangor LL57 2UW , UK
| | - Juan J Calvete
- 2 Evolutionary and Translational Venomics Laboratory, CSIC , Jaume Roig 11, Valencia 46010 , Spain
| | - Michael D Cardwell
- 3 Department of Biology, San Diego State University , San Diego, CA 92182 , USA
| | - Harry W Greene
- 4 Department of Ecology and Evolutionary Biology, Cornell University , Corson Hall, Ithaca, NY 14853 , USA
| | - William K Hayes
- 5 Department of Earth and Biological Sciences, School of Medicine, Loma Linda University , Loma Linda, CA 92350 , USA
| | - Matthew J Hegarty
- 6 Institute of Biological, Environmental and Rural Sciences, Aberystwyth University , Aberystwyth SY23 3EE , UK
| | - Hans-Werner Herrmann
- 7 Wildlife Conservation and Management, School of Natural Resources and the Environment, University of Arizona , 1064 East Lowell Street (ENR2), Tucson, AZ 85721 , USA
| | - Andrew T Holycross
- 8 Natural History Collections, Arizona State University , 734 W. Alameda Drive, Tempe, AZ 85282 , USA
| | - Dominic I Lannutti
- 9 Department of Biological Sciences, University of Texas at El Paso , 500 W. University, El Paso, TX 79968 , USA
| | - John F Mulley
- 1 Molecular Ecology and Fisheries Genetics Laboratory, School of Natural Sciences, Bangor University , Bangor LL57 2UW , UK
| | - Libia Sanz
- 2 Evolutionary and Translational Venomics Laboratory, CSIC , Jaume Roig 11, Valencia 46010 , Spain
| | - Zachary D Travis
- 5 Department of Earth and Biological Sciences, School of Medicine, Loma Linda University , Loma Linda, CA 92350 , USA
| | - Joshua R Whorley
- 10 Seattle Central College, Science, Technology, Engineering & Mathematics Division , 1701 Broadway Ave. E., Seattle, WA 98122 , USA
| | - Catharine E Wüster
- 1 Molecular Ecology and Fisheries Genetics Laboratory, School of Natural Sciences, Bangor University , Bangor LL57 2UW , UK
| | - Wolfgang Wüster
- 1 Molecular Ecology and Fisheries Genetics Laboratory, School of Natural Sciences, Bangor University , Bangor LL57 2UW , UK
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Zancolli G, Baker TG, Barlow A, Bradley RK, Calvete JJ, Carter KC, de Jager K, Owens JB, Price JF, Sanz L, Scholes-Higham A, Shier L, Wood L, Wüster CE, Wüster W. Is Hybridization a Source of Adaptive Venom Variation in Rattlesnakes? A Test, Using a Crotalus scutulatus × viridis Hybrid Zone in Southwestern New Mexico. Toxins (Basel) 2016; 8:toxins8060188. [PMID: 27322321 PMCID: PMC4926154 DOI: 10.3390/toxins8060188] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2016] [Revised: 06/02/2016] [Accepted: 06/09/2016] [Indexed: 11/16/2022] Open
Abstract
Venomous snakes often display extensive variation in venom composition both between and within species. However, the mechanisms underlying the distribution of different toxins and venom types among populations and taxa remain insufficiently known. Rattlesnakes (Crotalus, Sistrurus) display extreme inter- and intraspecific variation in venom composition, centered particularly on the presence or absence of presynaptically neurotoxic phospholipases A₂ such as Mojave toxin (MTX). Interspecific hybridization has been invoked as a mechanism to explain the distribution of these toxins across rattlesnakes, with the implicit assumption that they are adaptively advantageous. Here, we test the potential of adaptive hybridization as a mechanism for venom evolution by assessing the distribution of genes encoding the acidic and basic subunits of Mojave toxin across a hybrid zone between MTX-positive Crotalus scutulatus and MTX-negative C. viridis in southwestern New Mexico, USA. Analyses of morphology, mitochondrial and single copy-nuclear genes document extensive admixture within a narrow hybrid zone. The genes encoding the two MTX subunits are strictly linked, and found in most hybrids and backcrossed individuals, but not in C. viridis away from the hybrid zone. Presence of the genes is invariably associated with presence of the corresponding toxin in the venom. We conclude that introgression of highly lethal neurotoxins through hybridization is not necessarily favored by natural selection in rattlesnakes, and that even extensive hybridization may not lead to introgression of these genes into another species.
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Affiliation(s)
- Giulia Zancolli
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Timothy G Baker
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Axel Barlow
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
- Evolutionary and Adaptive Genomics Group, Institute for Biochemistry and Biology, University of Potsdam, Karl-Liebknecht-Str. 24-25, Haus 29, 14476 Potsdam (Golm), Germany.
| | - Rebecca K Bradley
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Juan J Calvete
- Venomics and Structural Proteomics Laboratory, Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Científicas (CSIC), Jaume Roig 11, 46010 Valencia, Spain.
| | - Kimberley C Carter
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Kaylah de Jager
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - John Benjamin Owens
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Jenny Forrester Price
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Libia Sanz
- Venomics and Structural Proteomics Laboratory, Instituto de Biomedicina de Valencia, Consejo Superior de Investigaciones Científicas (CSIC), Jaume Roig 11, 46010 Valencia, Spain.
| | - Amy Scholes-Higham
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Liam Shier
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Liam Wood
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Catharine E Wüster
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
| | - Wolfgang Wüster
- Molecular Ecology and Fisheries Genetics Lab, School of Biological Sciences, Bangor University, Bangor LL57 2UW, UK.
- Chiricahua Desert Museum, P.O. Box 376, Rodeo, NM 88056, USA.
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Barlow A, Baker K, Hendry CR, Peppin L, Phelps T, Tolley KA, Wüster CE, Wüster W. Phylogeography of the widespread African puff adder (Bitis arietans) reveals multiple Pleistocene refugia in southern Africa. Mol Ecol 2013; 22:1134-57. [PMID: 23286376 DOI: 10.1111/mec.12157] [Citation(s) in RCA: 61] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/07/2012] [Revised: 10/19/2012] [Accepted: 10/29/2012] [Indexed: 11/30/2022]
Abstract
Evidence from numerous Pan-African savannah mammals indicates that open-habitat refugia existed in Africa during the Pleistocene, isolated by expanding tropical forests during warm and humid interglacial periods. However, comparative data from other taxonomic groups are currently lacking. We present a phylogeographic investigation of the African puff adder (Bitis arietans), a snake that occurs in open-habitat formations throughout sub-Saharan Africa. Multiple parapatric mitochondrial clades occur across the current distribution of B. arietans, including a widespread southern African clade that is subdivided into four separate clades. We investigated the historical processes responsible for generating these phylogeographic patterns in southern Africa using species distribution modelling and genetic approaches. Our results show that interior regions of South Africa became largely inhospitable for B. arietans during glacial maxima, whereas coastal and more northerly areas remained habitable. This corresponds well with the locations of refugia inferred from mitochondrial data using a continuous phylogeographic diffusion model. Analysis of data from five anonymous nuclear loci revealed broadly similar patterns to mtDNA. Secondary admixture was detected between previously isolated refugial populations. In some cases, this is limited to individuals occurring near mitochondrial clade contact zones, but in other cases, more extensive admixture is evident. Overall, our study reveals a complex history of refugial isolation and secondary expansion for puff adders and a mosaic of isolated refugia in southern Africa. We also identify key differences between the processes that drove isolation in B. arietans and those hypothesized for sympatric savannah mammals.
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Affiliation(s)
- Axel Barlow
- School of Biological Sciences, Environment Centre Wales, Bangor University, Bangor LL57 2UW, UK.
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