Data from: Correlated evolution of phenotypic plasticity in metamorphic timing

Phenotypic plasticity has long been a focus of research, but the mechanisms of its evolution remain controversial. Many amphibian species exhibit a similar plastic response in metamorphic timing in response to multiple environmental factors; therefore, more than one environmental factor has likely influenced the evolution of plasticity. However, it is unclear whether the plastic responses to different factors have evolved independently. In this study, we examined the relationship between the plastic responses to two experimental factors (water level and food type) in larvae of the salamander Hynobius retardatus, using a cause-specific Cox proportional hazards model on the time to completion of metamorphosis. Larvae from ephemeral ponds metamorphosed earlier than those from permanent ponds when kept at a low water level or fed conspecific larvae instead of larval Chironomidae. This acceleration of metamorphosis depended only on the permanency of the larvae’s pond of origin, but not on the conspecific larval density (an indicator of the frequency of cannibalism) in the ponds. The two plastic responses were significantly correlated, indicating that they may evolve correlatively. Once plasticity evolved as an adaptation to habitat desiccation, it might have relatively easily become a response to other ecological factors, such as food type via the pre-existing developmental pathway.

表型可塑性（Phenotypic plasticity）长期以来都是生命科学研究的热点领域，但其演化机制始终存在学术争议。诸多两栖动物物种会在变态发育时间上呈现出相似的可塑性响应，以应对多种环境因子，由此推测，不止一种环境因子可能参与了可塑性的演化过程。然而，针对不同环境因子的可塑性响应是否独立演化，目前尚无明确结论。本研究以缓行小鲵（Hynobius retardatus）的幼体为实验对象，以变态完成时长为观测指标，采用病因特异性Cox比例风险模型（cause-specific Cox proportional hazards model），分析了其对两种实验因子——水位与食物类型——的可塑性响应之间的关联。实验结果显示：当幼体处于低水位环境，或以同种幼体而非摇蚊科（Chironomidae）幼虫为食时，来自临时池塘的幼体变态时间早于来自永久池塘的幼体。该变态加速现象仅与幼体原栖息地池塘的永久性相关，而与池塘内同种幼体密度——即同类相食频率的指示指标——无关。两种可塑性响应之间存在显著相关性，表明二者可能协同演化。一旦可塑性作为应对栖息地干旱的适应性特征演化形成，便可能通过已存在的发育通路，相对轻易地拓展为对其他生态因子（如食物类型）的响应机制。