Ecological contributions to body shape evolution in salamanders of the genus Eurycea (Plethodontidae)

BackgroundBody shape can be both a consequence and cause of a species’ evolution and ecology. There are many examples of phenotypes associated with specific ecological niches, likely as a result of specific selective regimes. A classic example of this is the phenotypic change associated with colonization of caves, including body and limb elongation. However, studies explicitly testing for differences in body shape between cave-dwelling and non-cave-dwelling lineages have been limited and so the role of the cave environment in determining morphological characteristics is still not completely understood. Here we examine variation in body shape among 405 individuals representing 20 species in the salamander genus Eurycea (Plethodontidae) and select outgroups exhibiting great diversity in morphology, ecological niche, and life history.ResultsAfter analyzing morphometric data in a phylogenetic context using phylogenetic MANOVA and examination of the phylomorphospace, we found significant differences in body shape among cave-dwelling and non-cave-dwelling species and between aquatic and terrestrial species. Notably, limb elongation and reduced body and tail size characterized cave-dwelling species. Terrestrial species also exhibited elongation of the limbs and digits. We also observed differences in shape variance among paedomorphic and biphasic species. Our results suggest that the functional limitations imposed by habitat and life history played a key role in the evolution of body shape in this group in the context of their phylogenetic history.研究背景 体型既是物种演化与生态的产物，亦是驱动物种演化与生态进程的重要因素。诸多与特定生态位相关的表型特征已被报道，这类关联大概率源于特异性选择压力的作用。其中，物种定居洞穴后产生的表型改变便是典型案例之一，这类改变包括躯体与附肢的延长。然而，专门检验穴居与非穴居支系间体型差异的研究仍较为匮乏，因此洞穴环境在塑造类群形态特征中的作用尚未完全明晰。本研究以隶属于无肺螈科（Plethodontidae）的蝾螈属（Eurycea）20个物种的405个个体，以及在形态、生态位与生活史维度上具有丰富多样性的选定外类群（outgroups）为研究对象，展开体型变异分析。 研究结果 通过系统发育多元方差分析（phylogenetic MANOVA）结合系统发育形态空间（phylomorphospace）分析形态测量数据后，本研究发现：穴居与非穴居物种间、水生与陆生物种间的体型均存在显著差异。值得注意的是，附肢延长、躯体与尾部尺寸减小是穴居物种的典型形态特征。陆生物种同样表现出附肢与趾骨的延长。此外，本研究还观察到幼态持续型（paedomorphic）与双相型（biphasic）物种间的形态方差存在显著差异。本研究结果表明，在类群的系统发育背景下，生境与生活史所施加的功能限制，在该类群的体型演化过程中发挥了关键作用。