The effect of size-selective predation on prey communities and their traits is well documented, but the relative roles of genetic adaptation and phenotypic plasticity continue to be debated. We looked for evidence of genetic adaption in a population of the water flea Daphnia pulex that faced a novel, introduced predator, Eurasian perch (Perca fluviatilis), selectively preying upon large zooplankton. Theory predicts adaptive changes towards a faster life history. We compared growth, age and length at maturation, egg size, and fecundity of two groups of clones kept in common-garden conditions, 13 clones isolated at around the time of the perch introduction and 14 isolated 3 years after. All animals were photographed daily and observed every third hour to detect maturation and measure the clutch size. Post-introduction clones matured earlier, but this was an indirect response triggered by genetic change in growth: post-introduction clones had faster growth prior to maturation than pre-introduction ones, reaching earlier the size threshold for maturation, but the threshold itself remained unchanged. Post-introduction clones showed also higher clutch size for 2nd and 3rd clutch, and slower growth from maturation (first appearance of eggs) to the moult after the release of the first clutch. Egg size did not differ between the periods. The experiment shows how life-history responses to predation involve multiple interlinked traits and both direct and indirect genetic responses.

中文翻译：

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野生水蚤种群的快速生活史进化以响应新的大小依赖性捕食

大小选择性捕食对猎物群落及其特征的影响已得到充分证明，但遗传适应和表型可塑性的相对作用仍在争论中。我们在水蚤 Daphnia pulex 种群中寻找遗传适应的证据，该种群面临一种新的引入捕食者，欧亚鲈鱼（Perca fluviatilis），选择性捕食大型浮游动物。理论预测朝着更快的生活史发生适应性变化。我们比较了在普通花园条件下饲养的两组克隆的生长、年龄和成熟长度、卵大小和繁殖力，其中 13 个克隆是在鲈鱼引入时分离的，14 个克隆是在 3 年后分离的。每天对所有动物拍照并每三小时观察一次以检测成熟并测量离合器大小。引入后的克隆成熟得更早，但这是由生长的遗传变化引发的间接反应：引入后的克隆在成熟前的生长速度比引入前的更快，更早达到成熟的大小阈值，但阈值本身保持不变。引入后的克隆在第 2 和第 3 窝中也表现出较大的窝大小，并且在第一个窝释放后从成熟（卵的首次出现）到换羽的生长速度较慢。不同时期的鸡蛋大小没有差异。该实验显示了生活史对捕食的反应如何涉及多个相互关联的特征以及直接和间接的遗传反应。但门槛本身保持不变。引入后的克隆在第 2 和第 3 窝中也表现出较大的窝大小，并且在第一个窝释放后从成熟（卵的首次出现）到换羽的生长速度较慢。不同时期的鸡蛋大小没有差异。该实验显示了生活史对捕食的反应如何涉及多个相互关联的特征以及直接和间接的遗传反应。但门槛本身保持不变。引入后的克隆在第 2 和第 3 窝中也表现出较大的窝大小，并且在第一个窝释放后从成熟（卵的首次出现）到换羽的生长速度较慢。不同时期的鸡蛋大小没有差异。该实验显示了生活史对捕食的反应如何涉及多个相互关联的特征以及直接和间接的遗传反应。