Phylogenetic evidence from freshwater crayfishes that cave adaptation is not an evolutionary dead-end

Caves are perceived as isolated, extreme habitats with a set of uniquely specialized biota, which long ago led to the idea that caves are ‘evolutionary dead-ends.’ This suggests that cave-adapted taxa may be doomed for extinction before they can diversify or transition to a more stable state. However, this hypothesis has not been explicitly tested in a phylogenetic framework with multiple independent cave-dwelling groups. Here we use the freshwater crayfish, a group with dozens of cave-dwelling species in multiple lineages, as a system to test this hypothesis. We consider historical patterns of lineage diversification and habitat transition as well as current patterns of geographic range size. We find that while cave-dwelling lineages have small relative range sizes and rarely transition back to the surface, they exhibit remarkably similar diversification patterns to those of other habitat types and appear to be able to maintain a diversity of lineages through time. This suggests that cave-adaptation is not a ‘dead-end’ for freshwater crayfish, which has positive implications for our understanding of biodiversity and conservation in cave habitats.

洞穴被视为一类孤立且极端的生境，拥有独特特化的生物区系，这一特性早在很久以前便催生了“洞穴属于进化死端”的观点。该观点认为，适应洞穴生活的类群可能在实现谱系分化或过渡至更稳定的生存状态前，就已难逃灭绝的命运。然而，这一假说尚未在涵盖多个独立穴居类群的系统发育框架（phylogenetic framework）中得到明确检验。本研究以淡水螯虾（freshwater crayfish）为研究系统——该类群的多个进化谱系中存在数十个穴居物种，以此对该假说进行检验。我们分析了谱系分化与生境转换（habitat transition）的历史模式，以及当前的地理分布范围大小（geographic range size）格局。研究发现，尽管穴居谱系的相对分布范围较小，且极少逆转回地表生境，但它们的分化模式与其他生境类型的类群极为相似，且能够在漫长的时间尺度上维持多样的进化谱系。这表明，对于淡水螯虾而言，洞穴适应并非“进化死端”，这一结果对于我们理解洞穴生境中的生物多样性与保护工作具有积极的启示意义。