Emergence time dataset from Temporal isolation between sympatric host plants cascades across multiple trophic levels of host-associated insects

Phenological differences between host plants can promote temporal isolation among host-associated populations of insects with life cycles tightly coupled to plant phenology. Divergence in the timing of spring budbreak between two sympatric sister oak species has been shown to promote temporal isolation between host plants and their host-associated populations of a cynipid gall wasp. Here, we examined the generality of this mechanism by testing the hypothesis of cascading temporal isolation for five additional gall-formers and three natural enemy species associated with these same oak species. The timing of adult emergence from galls differed significantly between host-associated populations for all nine species and parallels the direction of the phenological differences between host plants. Differences in emergence timing can reduce gene flow between host-associated populations by diminishing mating opportunities and/or reducing the fitness of immigrants due to differences in the availability of ephemeral resources. Our study suggests that cascading temporal isolation could be a powerful ‘biodiversity generator’ across multiple trophic levels in tightly coupled plant–insect systems.

寄主植物（host plants）的物候差异（phenological differences）可促进生活周期与植物物候紧密耦合的昆虫寄主关联种群（host-associated populations）间的时间隔离（temporal isolation）。已有研究表明，两个同域姊妹栎类物种（sympatric sister oak species）间的春季芽萌动（spring budbreak）时序分化，可推动寄主植物及其对应的瘿蜂科瘿蜂（cynipid gall wasp）的寄主关联种群间形成时间隔离。本研究针对与上述栎类物种共生的另外5种造瘿昆虫（gall-formers）与3种天敌（natural enemy）物种，通过检验级联时间隔离（cascading temporal isolation）假说，探究该机制的普遍性。所有9个物种的成虫从虫瘿（gall）中羽化的时序，在不同寄主关联种群间均存在显著差异，且与寄主植物的物候差异方向一致。羽化时序的差异可通过减少交配机会，或因瞬变资源（ephemeral resources）的可用性差异降低迁入个体的适合度（fitness），从而降低寄主关联种群间的基因流（gene flow）。本研究表明，级联时间隔离可成为紧密耦合的植物-昆虫系统中，跨多个营养级（trophic levels）的强大“生物多样性生成器（biodiversity generator）”。