Leapfrogging the Mexican highlands: influence of biogeographical and ecological factors on the diversification of highland species

In order to understand the processes that generate and maintain diversity, it is important to disentangle the roles of ecology and geography in speciation. We investigated the biogeographical and ecological factors that influenced the diversification of tree frogs (genus Sarcohyla) in the Mexican highlands, a region with high levels of endemism. Using single nucleotide polymorphism data for 58 samples, we found support for seven distinct genetic clusters within the Sarcohyla bistincta species complex, corresponding to Sarcohyla calthula, Sarcohyla pentheter and five populations within S. bistincta. A species tree analysis using the multispecies coalescent model did not support the monophyly of the five S. bistincta populations. We used niche modelling to calculate the ecological overlap among lineages; we found a degree of overlapping for most of the lineages, suggesting that ecological differentiation did not play a key role in their genetic divergence. Speciation and population structure in the complex have been shaped primarily by geological events, landscape modifications and climate changes during the Pleistocene. We discuss the relevance of genetic diversity for inferring the degree of species threats and recovery for conservation assessments.

为阐明驱动物种多样性产生与维持的生物学过程，厘清物种形成过程中生态与地理因素的相对作用至关重要。我们针对墨西哥高地——一个特有性水平极高的区域——内树蛙属（Sarcohyla）的物种分化展开研究，解析影响其分化的生物地理与生态因子。本研究基于58个样本的单核苷酸多态性（single nucleotide polymorphism, SNP）数据，在双带树蛙复合种（Sarcohyla bistincta species complex）内鉴定出7个独立的遗传聚类群，分别对应卡氏树蛙（Sarcohyla calthula）、佩氏树蛙（Sarcohyla pentheter）以及双带树蛙（S. bistincta）内的5个种群。我们采用多物种溯祖模型（multispecies coalescent model）开展物种树分析，结果显示该双带树蛙的5个种群并不构成单系群。我们通过生态位建模（niche modelling）计算各演化支间的生态重叠度，发现多数演化支间存在一定程度的生态重叠，表明生态分化并未在其遗传分化过程中发挥关键作用。该复合群的物种形成与种群结构主要受更新世（Pleistocene）时期的地质事件、景观改造与气候变化塑造。我们还探讨了遗传多样性在物种保护评估中，对推断物种受威胁程度与种群恢复潜力的参考价值。