Potential rapid evolution of foot morphology in Italian plethodontid salamanders (Hydromantes strinatii) following the colonization of an artificial cave

How organisms respond to environmental change is a long-standing question in evolutionary biology. Species invading novel habitats provide an opportunity to examine contemporary evolution in action, and decipher the pace of evolutionary change over short time scales. Here we characterized phenotypic evolution in the Italian plethodontid salamander, Hydromantes strinatii following the recent colonization of an artificial cave by a forest floor population. When compared with a nearby and genetically related population in the natural forest floor and a nearby cave population, the artificial cave population displayed significant differences in overall foot shape, with more inter-digital webbing relative to the other populations. Further, this population evolved significantly larger feet, which corresponded more closely to those found in other cave populations than to forest floor populations to which the cave population is closely related. Finally, we quantified the rate of evolution for both foot shape and foot area, and found that both traits displayed large and significant evolutionary rates, at levels corresponding to other classic cases of rapid evolution in vertebrates. Together these findings reveal that the response to novel environmental pressures can be large and rapid, and that the anatomical shifts observed in the artificial cave population of H. strinatii may represent a case of rapid evolution in response to novel environmental pressures.

生物如何响应环境变化，是进化生物学（evolutionary biology）领域长期存在的核心科学问题。入侵新生境的物种为研究当代进化（contemporary evolution）过程、解析短时间尺度下的进化速率提供了绝佳契机。本研究针对意大利无肺螈科（Plethodontidae）蝾螈物种斯特氏山螈（Hydromantes strinatii）的表型进化（phenotypic evolution）特征展开系统表征，该种群源自林地表种群，近期定殖于一处人工洞穴。通过与邻近且遗传亲缘关系相近的林地表自然种群、邻近洞穴种群进行对照，我们发现该人工洞穴种群的整体足形存在显著差异：其趾间蹼（inter-digital webbing）相较于其他两组更为发达。此外，该种群的足面积显著增大，其足部形态与其他洞穴种群更为接近，而非与其亲缘关系更近的源林地表种群。最后，我们对足形及足面积的进化速率（evolutionary rate）进行了量化分析，发现两项性状均表现出显著且极高的进化速率，其水平与脊椎动物（vertebrate）中其他经典的快速进化案例相当。综上，本研究结果表明，生物对新生境环境压力的响应可兼具大幅性与快速性；斯特氏山螈人工洞穴种群所观察到的解剖学特征转变，或代表了一类响应新生境环境压力的快速进化案例。