UMR-CNRS 6553 Ecobio, Université de Rennes 1, Rennes, France.
Université Bretagne Loire, Cité Internationale, Rennes, France.
Insect Sci. 2018 Dec;25(6):1080-1088. doi: 10.1111/1744-7917.12491. Epub 2017 Aug 8.
Organisms often live in unpredictable environments and have to adopt life history strategies that optimize their fitness under these conditions. According to bet-hedging theory, individuals can reduce variation in fitness outcomes by investing in different strategies at the same time. For arthropods, facultative summer diapause enables survival during dry and hot periods of the year, and can be triggered by a decrease in resource abundance. However, the effect of resource depletion on diapause induction has never been disentangled from the effect of the perception of the presence of competitors. Using two solitary parasitoid species of cereal aphids as a model system, Aphidius avenae (Haliday) and Aphidius rhopalosiphi (De Stefani-Perez) (Hymenoptera: Braconidae), we tested whether (i) low absolute host density and/or (ii) high levels of parasitoid females' competition lead to maternal-induced summer diapause in parasitoid offspring. Under summer-like climatic conditions, emerging parasitoid females were (i) reared alone and exposed to different host densities (from 5 to 130 aphids), or (ii) reared together with competing females (from 2 to 20 females) and then exposed individually to 50 aphids. For both parasitoid species, low aphid densities did not induce summer diapause. However, the incidence of summer diapause increased up to a maximum of 11% with increasing levels of competition experienced by female parasitoids. More than 60% of the females produced both diapausing and nondiapausing offspring after being kept at the two highest competition densities. Such a "spreading-the-risk" strategy has likely evolved to optimize parasitoid fitness by preventing the following generation from exposure to low populations of suitable hosts and high mortality from superparasitism. These results provide the first experimental evidence of direct maternal competition-induced diapause in insects, and may change the way we apprehend the evolution of arthropod seasonal ecology, by considering intraspecific competition.
生物通常生活在不可预测的环境中，必须采取能够优化其在这些条件下适应能力的生活史策略。根据避险理论，个体可以通过同时投资于不同的策略来降低适应能力结果的变化。对于节肢动物来说，夏季兼性休眠可以使其在一年中干旱和炎热的时期存活下来，并且可以通过资源丰度的减少来触发。然而，资源枯竭对休眠诱导的影响从未与对存在竞争的感知的影响分开。我们使用两种作为模式系统的独立寄生蜂来测试这一点：麦长管蚜寄生蜂（Aphidius avenae (Haliday)）和桃蚜茧蜂（Aphidius rhopalosiphi (De Stefani-Perez)）（膜翅目：Braconidae），（i）绝对宿主密度低和/或（ii）寄生蜂雌性竞争水平高是否会导致寄生蜂后代发生夏季休眠。在夏季气候条件下，刚羽化的寄生蜂雌性被（i）单独饲养并暴露于不同的宿主密度（从 5 到 130 只蚜虫），或（ii）与竞争雌性一起饲养（从 2 到 20 只雌性），然后单独暴露于 50 只蚜虫。对于这两种寄生蜂，低蚜虫密度不会诱导夏季休眠。然而，随着雌性寄生蜂经历的竞争水平的增加，夏季休眠的发生率增加到最高 11%。在保持在两个最高竞争密度的情况下，超过 60%的雌性产生了休眠和非休眠后代。这种“分散风险”的策略可能是通过防止下一代暴露于适宜宿主数量低和高的超寄生死亡率而进化出来的，以优化寄生蜂的适应能力。这些结果为昆虫中直接由母体竞争诱导的休眠提供了第一个实验证据，并可能通过考虑种内竞争来改变我们对节肢动物季节性生态学进化的理解方式。
