The bathyal serpulid Laminatubus alvini ten Hove & Zibrowius, 1986 was described from the periphery of hydrothermal vents of the Galapagos Rift and has been recorded from other vent communities of the East Pacific Rise (EPR). Here we assessed the biodiversity of serpulids collected from eastern Pacific hydrothermal vents and methane seeps using DNA sequences and morphology. Laminatubus alvini showed little genetic variation over a wide geographic range from the Alarcon Rise vents in southern Gulf of California (~23°N), to at least a point at 38°S on the EPR. Specimens from several methane seeps off Costa Rica and the Gulf of California (Mexico) differed markedly from those of Laminatubus alvini on DNA sequence data and in having seven thoracic chaetigers and lacking Spirobranchus-type special collar chaetae, thus fitting the diagnosis of Neovermilia. However, phylogenetic analysis of molecular data showed that L. alvini and the seep specimens form a well-supported clade. Moreover, among the seep specimens there was minimally a ~7% distance in mitochondrial cytochrome b sequences between a shallow-water (1000 m) seep clade restricted to Costa Rica and a deep-water clade (1800 m) from Costa Rica to Gulf of California. We describe the seep taxa here as morphologically indistinguishable L. paulbrooksi n. sp. and L. joycebrooksae n. sp.
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Geographic variation in morphology in the Mohave Rattlesnake (Crotalus scutulatus Kennicott 1861) (Serpentes: Viperidae): implications for species boundaries
The Mohave Rattlesnake (Crotalus scutulatus) is a highly venomous pitviper inhabiting the arid interior deserts, grasslands, and savannas of western North America. Currently two subspecies are recognized: the Northern Mohave Rattlesnake (C. s. scutulatus) ranging from southern California to the southern Central Mexican Plateau, and the Huamantla Rattlesnake (C. s. salvini) from the region of Tlaxcala, Veracruz, and Puebla in south-central Mexico. Although recent studies have demonstrated extensive geographic variation in venom composition and cryptic genetic diversity in this species, no modern studies have focused on geographic variation in morphology. Here we analyzed a series of qualitative, meristic, and morphometric traits from 347 specimens of C. scutulatus and show that this species is phenotypically cohesive without discrete subgroups, and that morphology follows a continuous cline in primarily color pattern and meristic traits across the major axis of its expansive distribution. Interpreted in the context of previously published molecular evidence, our morphological analyses suggest that multiple episodes of isolation and secondary contact among metapopulations during the Pleistocene were sufficient to produce distinctive genetic populations, which have since experienced gene flow to produce clinal variation in phenotypes without discrete or diagnosable distinctions among these original populations. For taxonomic purposes, we recommend that C. scutulatus be retained as a single species, although it is possible that C. s. salvini, which is morphologically the most distinctive population, could represent a peripheral isolate in the initial stages of speciation.
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- Award ID(s):
- 1655571
- NSF-PAR ID:
- 10144114
- Date Published:
- Journal Name:
- Zootaxa
- Volume:
- 4683
- Issue:
- 1
- ISSN:
- 1175-5326
- Page Range / eLocation ID:
- 129 to 143
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Background Snake venoms are trophic adaptations that represent an ideal model to examine the evolutionary factors that shape polymorphic traits under strong natural selection. Venom compositional variation is substantial within and among venomous snake species. However, the forces shaping this phenotypic complexity, as well as the potential integrated roles of biotic and abiotic factors, have received little attention. Here, we investigate geographic variation in venom composition in a wide-ranging rattlesnake (
Crotalus viridis viridis ) and contextualize this variation by investigating dietary, phylogenetic, and environmental variables that covary with venom.Results Using shotgun proteomics, venom biochemical profiling, and lethality assays, we identify 2 distinct divergent phenotypes that characterize major axes of venom variation in this species: a myotoxin-rich phenotype and a snake venom metalloprotease (SVMP)-rich phenotype. We find that dietary availability and temperature-related abiotic factors are correlated with geographic trends in venom composition.
Conclusions Our findings highlight the potential for snake venoms to vary extensively within species, for this variation to be driven by biotic and abiotic factors, and for the importance of integrating biotic and abiotic variation for understanding complex trait evolution. Links between venom variation and variation in biotic and abiotic factors indicate that venom variation likely results from substantial geographic variation in selection regimes that determine the efficacy of venom phenotypes across populations and snake species. Our results highlight the cascading influence of abiotic factors on biotic factors that ultimately shape venom phenotype, providing evidence for a central role of local selection as a key driver of venom variation.
- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.11646/zootaxa.4683.1.7
