The adaptive nature of phenotypic plasticity is widely documented. However, little is known about the evolutionary forces that shape genetic variation of plasticity within populations. Whether genetic variation in plasticity is driven by stabilizing or diversifying selection and whether the strength of such forces remains constant through time, remain open questions. Here, we address this issue by assessing the evolutionary forces that shape genetic variation in antipredator developmental plasticity of Daphnia pulex. Antipredator plasticity in D. pulex is characterized by the growth of a pedestal and spikes in the dorsal head region upon exposure to predator cue. We characterized genetic variation in plasticity using a method that describes the entire dorsal shape amongst >100 D. pulex strains recently derived from the wild. We observed the strongest reduction in genetic variation in dorsal areas where plastic responses were greatest, consistent with stabilizing selection. We compared mutational variation (V_m) to standing variation (V_g) and found that V_g/V_m is lowest in areas of greatest plasticity, again consistent with stabilizing selection. Our results suggest that stabilizing selection operates directly on phenotypic plasticity in Daphnia and provide a rare glimpse into the evolution of fitness-related traits in natural populations.

表型可塑性的适应性已被广泛记录。然而，人们对塑造种群内可塑性遗传变异的进化力量知之甚少。可塑性的遗传变异是否是由稳定选择或多样化选择驱动的，以及这种力量的强度是否随着时间的推移保持不变，仍然是一个悬而未决的问题。在这里，我们通过评估影响水蚤反捕食者发育可塑性遗传变异的进化力量来解决这个问题。 D. pulex的反捕食者可塑性的特点是暴露于捕食者线索后，背侧头部区域会生长出基座和尖峰。我们使用一种描述最近源自野生的超过 100 个D. pulex品系的整​​个背部形状的方法来表征可塑性的遗传变异。我们观察到可塑性反应最大的背部区域遗传变异减少幅度最大，这与稳定选择一致。我们将突变变异 ( V _m ) 与固定变异 ( V _g ) 进行比较，发现V _g / V _m在可塑性最大的区域最低，这再次与稳定选择一致。我们的结果表明，稳定选择直接影响水蚤的表型可塑性，并为自然种群中适应性相关性状的进化提供了难得的一瞥。