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）长期以来一直是研究的焦点，但其演化机制仍存在诸多争议。诸多两栖动物物种的变态时间会对多种环境因子呈现出相似的可塑性响应，因此可能存在不止一种环境因子对可塑性的演化产生了影响。然而，目前尚不清楚针对不同因子的可塑性响应是否独立演化。本研究以滞育小鲵（Hynobius retardatus）的幼体为研究对象，基于变态完成时间构建原因特异性Cox比例风险模型（cause-specific Cox proportional hazards model），以此分析两个实验因子（水位与食物类型）对应的幼体可塑性响应间的关联。当饲养于低水位条件，或以同种幼体而非摇蚊科（Chironomidae）幼虫为食时，源自临时池塘的幼体变态时间早于源自永久池塘的幼体。该变态加速现象仅与幼体来源池塘的永久性相关，而与池塘内同种幼体密度（同类相食频率的指示指标）无关。两种可塑性响应呈现显著相关性，提示二者可能协同演化。一旦可塑性作为适应生境干涸的演化性状得以演化，便可通过预先存在的发育通路，相对轻易地演变为对其他生态因子（如食物类型）的响应。