Data from: Adaptation in a variable environment: phenotypic plasticity and bet-hedging during egg diapause and hatching in an annual killifish

Two ways in which organisms adapt to variable environments are phenotypic plasticity and bet-hedging. Theory suggests that bet-hedging is expected to evolve in unpredictable environments for which reliable cues indicative of future conditions (or season length) are lacking. Alternatively, if reliable cues exist indicating future conditions, organisms will be under selection to produce the most appropriate phenotype – that is, adaptive phenotypic plasticity. Here we experimentally test which of these modes of adaptation are at play in killifish that have evolved an annual life cycle. These fish persist in ephemeral pools that completely dry each season through the production of eggs that can remain in developmental arrest, or diapause, buried in the soil, until the following rainy season. Consistent with diversified bet-hedging (a risk spreading strategy), we demonstrate that the eggs of the annual killifish Nothobranchius furzeri exhibit variation at multiple levels - whether or not different stages of diapause are entered, for how long diapause is entered, and the timing of hatching - and this variation persists after controlling for both genetic and environmental sources of variation. However, we show that phenotypic plasticity is also present in that the proportion of eggs that enter diapause is influenced by environmental factors (temperature and light level) that vary seasonally. In nature there is typically a large parameter zone where environmental cues are somewhat correlated with seasonality, but not perfectly so, such that it may be advantageous to have a combination of both bet-hedging and plasticity.生物体应对可变环境的两种适应策略为表型可塑性（phenotypic plasticity）与风险分摊策略（bet-hedging）。理论研究表明，在无法获取指示未来环境条件（或季节时长）的可靠线索的不可预测环境中，风险分摊策略（bet-hedging）更易发生演化。反之，若存在可指示未来环境条件的可靠线索，生物体将受到自然选择的作用，演化出最适配的表型——即适应性表型可塑性（adaptive phenotypic plasticity）。本研究针对演化出年生活周期的鳉鱼（killifish）开展实验，以探究这两种适应模式何者在其中发挥作用。这类鱼类依托可滞育于土壤中的卵，在每年完全干涸的临时水塘中存续：这些卵会进入发育停滞状态，即滞育（diapause），埋藏于土壤中，直至下一个雨季来临。与多样化风险分摊策略（diversified bet-hedging，一种风险扩散策略）的理论预期相符，本研究证实：一年生鳉鱼——诺氏假鳃鳉（Nothobranchius furzeri）的卵存在多维度变异：是否进入滞育的不同阶段、滞育持续时长以及孵化时间，且在控制遗传与环境来源的变异后，此类变异依然持续存在。然而，本研究同时发现表型可塑性同样存在：进入滞育的卵的比例会受到季节性变化的环境因子（温度与光照水平）的影响。在自然环境中，通常存在大量参数区间，其中环境线索与季节周期存在一定相关性，但并非完全相关，此时同时采用风险分摊策略与表型可塑性或许具备演化优势。