<p><strong>Multilocus species delimitation in the <em>Crotalus</em> <em>triseriatus</em> species group (Serpentes: Viperidae: Crotalinae), with the description of two new species</strong></p>

Abstract

Members of the Crotalus triseriatus species group of montane rattlesnakes are widely distributed across the highlands of Mexico and southwestern USA. Although five species are currently recognized within the group, species limits remain to be tested. Genetic studies suggest that species may be paraphyletic and that at least one cryptic species may be present. We generate 3,346 base pairs of DNA sequence data from seven nuclear loci to test competing models of species delimitation in the C. triseriatus group using Bayes factor delimitation. We also examine museum specimens from the Trans-Mexican Volcanic Belt for evidence of cryptic species. We find strong support for a nine-species model and genetic and morphological evidence for recognizing two new species within the group, which we formally describe here. Our results suggest that the current taxonomy of the C. triseriatus species group does not reflect evolutionary history. We suggest several conservative taxonomic changes to the group, but future studies are needed to better clarify relationships among species and examine genetic patterns and structure within wide-ranging lineages.

Cryptic diversity in the Mexican highlands: Thousands of UCE loci help illuminate phylogenetic relationships, species limits and divergence times of montane rattlesnakes (Viperidae: Crotalus)

“…We included multiple exemplars of all currently described taxa to assess both species limits and phylogenetic relationships. Taxa in the group include C. aquilus , C. armstrongi , C. campbelli , C. lepidus ( C. l. lepidus , C. l. klauberi and C. l. maculosus ), C. morulus , C. pusillus , C. ravus ( C. r. ravus , C. r. brunneus and C. r. exiguus ), C. tlaloci and C. triseriatus (Bryson et al, ). We included Agkistrodon piscivorus as an outgroup taxon to root tree topologies (Alencar et al, ).…”

“…Part of the discrepancy seems to result from the fact that many molecular studies rely solely on mtDNA (Bryson et al, ; Castoe & Parkinson, ; Murphy et al,; Parkinson, ; Parkinson, Campbell, Chippindale, & Schuett, ), which often conflict with phylogenies from other sources of data (Grummer, Bryson, & Reeder, ; Leaché & McGuire, ). An additional difficulty in resolving the rattlesnake tree is that many groups rapidly diversified during the late Miocene during periods of global climate change (Zachos, Pagani, Sloan, Thomas, & Billups, ) and mountain formation in Mexico (Blair & Sánchez‐Ramírez, ; Bryson et al, ). Rapid radiations increase the likelihood of gene tree species tree conflicts, particularly in species with large effective population sizes (Maddison, ).…”

“…Previous mtDNA work on the group indicates multiple instances of paraphyly and the presence of cryptic species (Bryson et al, ). A subsequent study based on multilocus and morphological data described two new species and elevated one subspecies to species status (Bryson et al, ). Nine species are now recognized in the group, although phylogenetic relationships among species remain uncertain, and it is likely that additional species‐level diversity awaits discovery.…”

A genomic evaluation of taxonomic trends through time in coast horned lizards (genus Phrynosoma)

“…When conducting coalescent‐based species delimitation, failing to partition samples into the correct groups can have a greater negative consequence on the performance of a model than lumping species. Several empirical studies have demonstrated that models containing more species tend to receive higher marginal likelihoods (Bryson et al., ; Nieto‐Montes de Oca et al., ), raising the general concern that coalescent methods may result in oversplitting (Sukumaran & Knowles, ). We found that SDM performance varied considerably depending on the number of species in the model (Table ; Figure b).…”

“…Models with higher marginal likelihood scores were considered to have outperformed those with lower scores. Several empirical studies have demonstrated that models containing more species tend to receive higher marginal likelihoods (Bryson et al., ; Nieto‐Montes de Oca et al., ). Therefore, we tested for a positive relationship between SDM performance and the number of taxa in the model.…”