Data from: Convergent evolution of alternative developmental trajectories associated with diapause in African and South American killifish

Annual killifish adapted to life in seasonally ephemeral water-bodies exhibit desiccation resistant eggs that can undergo diapause, a period of developmental arrest, enabling them to traverse the otherwise inhospitable dry season. Environmental cues that potentially indicate the season can govern whether eggs enter a stage of diapause mid-way through development or skip this diapause and instead undergo direct development. We report, based on construction of a supermatrix phylogenetic tree of the order Cyprinodontiformes and a battery of comparative analyses, that the ability to produce diapause eggs evolved independently at least six times within African and South American killifish. We then show in species representative of these lineages that embryos entering diapause display significant reduction in development of the cranial region and circulatory system relative to direct-developing embryos. This divergence along alternative developmental pathways begins mid-way through development, well before diapause is entered, during a period of purported maximum developmental constraint (the phylotypic period). Finally, we show that entering diapause is accompanied by a dramatic reduction in metabolic rate and concomitant increase in long-term embryo survival. Morphological divergence during the phylotypic period thus allows embryos undergoing diapause to conserve energy by shunting resources away from energetically costly organs thereby increasing survival chances in an environment that necessitates remaining dormant, buried in the soil and surrounded by an eggshell for much of the year. Our results indicate that adaptation to seasonal aquatic environments in annual killifish imposes strong selection during the embryo stage leading to marked diversification during this otherwise conserved period of vertebrate development.年生鳉鱼（Annual killifish）适应于季节性临时水体生存，其卵具备抗干燥特性，可进入滞育（diapause）——一段发育停滞的时期——从而得以渡过原本严酷的旱季。能够潜在指示季节变化的环境线索，可调控胚胎在发育中途进入滞育阶段，或是跳过该滞育过程转而进行直接发育。本研究基于鳉形目（Cyprinodontiformes）的超级矩阵系统发育树构建与一系列比较分析，证实产生滞育卵的能力在非洲与南美洲的鳉鱼中至少独立演化了六次。随后，针对这些演化支系的代表物种的研究显示，相较于直接发育的胚胎，进入滞育的胚胎的颅区与循环系统发育显著减弱。这种沿不同发育路径的分化始于发育中途，远早于滞育的启动，且发生在被认为是发育约束最强的时期——胚型期（phylotypic period）。最后，本研究证实，进入滞育会伴随代谢速率的急剧下降，同时提升胚胎的长期存活率。因此，在胚型期发生的形态分化，可使进入滞育的胚胎将资源从高能耗器官转移，从而节省能量，提升其在一年中大部分时间都处于土壤掩埋、被卵壳包裹的休眠环境中的存活概率。本研究结果表明，年生鳉鱼对季节性水生环境的适应，在胚胎阶段施加了强烈的选择压力，使得原本保守的脊椎动物发育时期出现了显著的分化。