Phylogenetic relationships and species delimitation of bunchgrass lizards of the genus Sceloporus from Mexico with the description of a new species

Molecular data continue to serve as an invaluable tool to assess
species limits and patterns of cryptic diversity, particularly in areas
harboring high levels of biodiversity. The Sceloporus scalaris group,
known as bunchgrass lizards, contains 13 described and one undescribed
species distributed throughout high elevation biotas of Mexico. However,
recent studies suggest that diversity in the group may be substantially
underestimated. We collect new sequence data from four independent loci to
determine the evolutionary distinctiveness and phylogenetic relationships
of an isolated population of bunchgrass lizard in the Sierra San Juan
(SSJ) in the Mexican state of Nayarit. Concatenation and coalescent-based
phylogenetic and species delimitation analyses suggest that this
population represents a distinct evolutionary lineage allied to the S.
scalaris group. We describe the new SSJ population as a new species to
better account for its morphological and evolutionary distinctiveness.
Divergence within the species occurred during the Neogene and Quaternary,
most likely due to range shifts associated with mountain uplift and
glacial-interglacial cycles. Our results provide additional evidence that
supports the importance of the Mexican highlands as a biodiversity hotspot
which maintains cryptic lineages awaiting discovery.

分子数据始终是评估物种类群界定与隐存多样性（cryptic diversity）格局的关键工具，在生物多样性高度富集的区域尤为重要。被称为丛草蜥蜴（bunchgrass lizards）的鳞片鬣蜥（Sceloporus scalaris）类群，共计包含13个已描述物种与1个未描述物种，广泛分布于墨西哥全境的高海拔生物群落中。然而，近期研究显示该类群的物种多样性可能被严重低估。本研究采集了4个独立基因座的全新序列数据，旨在明确墨西哥纳亚里特州圣胡安山脉（Sierra San Juan, SSJ）内一处孤立的丛草蜥蜴种群的演化独特性与系统发育（phylogenetic）关系。基于序列拼接法与溯祖理论（coalescent-based）的系统发育分析及物种界定（species delimitation）结果表明，该种群属于与鳞片鬣蜥类群亲缘关系紧密的独立演化支系（evolutionary lineage）。为更好地体现该种群的形态与演化独特性，我们将此圣胡安山脉种群正式描述为新物种。该物种种内分化发生于新近纪（Neogene）与第四纪（Quaternary）时期，其成因大概率与山地隆升及冰期-间冰期旋回（glacial-interglacial cycles）伴随的分布区迁移有关。本研究结果进一步佐证了墨西哥高地作为生物多样性热点区域（biodiversity hotspot）的重要性，该区域仍留存有待发掘的隐存支系。