Avian predation pressure as a potential driver of periodical cicada cycle length

The extraordinarily long life cycles, synchronous emergences at 13- or 17-year intervals, and complex geographic distribution of periodical cicadas (Magicicada spp.) in eastern North America are an evolutionary enigma. Although a variety of factors, including satiation of above-ground predators and avoidance of interbrood hybridization, have been hypothesized to shape the evolution of this system, no empirical support for these mechanisms has previously been reported beyond the observation that bird predation can extirpate small, experimentally mistimed emergences. Here we show that periodical cicada emergences appear to set populations of potential avian predators on numerical trajectories that result in significantly lower potential predation pressure during the subsequent emergence. This result provides new support for the importance of predators in shaping periodical cicada life history, offers an ecological rationale for why emergences are synchronized at the observed multi-year intervals, and may explain some of the developmental plasticity observed in these unique insects.

北美东部地区的周期蝉（Magicicada spp.）拥有超长的生命周期、以13或17年为间隔的同步羽化现象，以及复杂的地理分布格局，这一直是演化生物学领域的一大未解之谜。尽管学界已提出多种假说，认为包括地面捕食者捕食饱和、避免群间杂交在内的多种因素塑造了该类群的演化，但此前除了『鸟类捕食可导致实验性羽化时机错位的小型种群灭绝』这一观测结果外，尚无这些机制的实证支撑。本研究发现，周期蝉的羽化事件会使得潜在鸟类捕食者的种群数量沿特定动态轨迹变化，从而在后续的羽化期显著降低潜在捕食压力。这一结果为捕食者在塑造周期蝉生活史特征中的重要作用提供了新的实证支持，为羽化事件以观测到的多年间隔同步发生提供了生态学解释，同时或可阐释这类独特昆虫所展现出的部分发育可塑性机制。