Rosa Elena, van Nouhuys Saskya, Saastamoinen Marjo
Department of Biosciences Metapopulation Research Centre University of Helsinki Helsinki Finland.
Department of Entomology Cornell University Ithaca NY USA.
Ecol Evol. 2017 Nov 7;7(24):10710-10720. doi: 10.1002/ece3.3571. eCollection 2017 Dec.
Aggregation can confer advantages in animal foraging, defense, and thermoregulation. There is a tight connection between the evolution of insect sociality and a highly effective immune system, presumably to inhibit rapid disease spread in a crowded environment. This connection is less evident for animals that spend only part of their life cycle in a social environment, such as noneusocial gregarious insects. Our aim was to elucidate the effects of group living by the gregarious larvae of the Glanville fritillary butterfly with respect to individual performance, immunity, and susceptibility to a parasitoid. We were also interested in the role of family relative to common postdiapause environment in shaping life-history traits. Larvae were reared at high or low density and then exposed to the pupal parasitoid wasp , either in presence or absence of a previous immune challenge that was used to measure the encapsulation immune response. Surviving adult butterflies were further tested for immunity. The wasp offspring from successfully parasitized butterfly pupae were counted and their brood sex ratios assessed. Larvae reared at high density grew larger and faster than those at low density. Despite high mortality due to parasitism, survival was greater among individuals with high pupal immunity in both density treatments. Moreover, butterfly pupae reared at high density were able to kill a larger fraction of individuals in the parasitoid broods, although this did not increase survival of the host. Finally, a larger proportion of variation observed in most of the traits was explained by butterfly family than by common postdiapause rearing environment, except for adult survival and immunity, for which this pattern was reversed. This gregarious butterfly clearly benefits from high conspecific density in terms of developmental performance and its ability to fight a parasitoid. These positive effects may be driven by cooperative interactions during feeding.
聚集可以在动物觅食、防御和体温调节方面带来优势。昆虫社会性的进化与高效的免疫系统之间存在紧密联系，大概是为了抑制疾病在拥挤环境中的快速传播。对于那些仅在生命周期的一部分时间处于社会环境中的动物，这种联系就不那么明显了，比如非社会性群居昆虫。我们的目的是阐明群居的格兰维尔豹纹蝶幼虫的群居生活对个体表现、免疫力和对寄生蜂易感性的影响。我们还对家族相对于滞育后共同环境在塑造生活史特征方面的作用感兴趣。将幼虫以高或低密度饲养，然后在有或没有先前用于测量包囊免疫反应的免疫挑战的情况下，使其暴露于蛹寄生蜂。对存活的成年蝴蝶进一步进行免疫测试。统计成功寄生的蝴蝶蛹产生的黄蜂后代数量，并评估其后代的性别比例。高密度饲养的幼虫比低密度饲养的幼虫长得更大、更快。尽管由于寄生导致高死亡率，但在两种密度处理中，蛹免疫力高的个体存活率更高。此外，高密度饲养的蝴蝶蛹能够杀死寄生蜂幼虫中更大比例的个体，尽管这并没有提高宿主的存活率。最后，除了成年蝴蝶的存活率和免疫力外，大多数性状观察到的较大比例的变异是由蝴蝶家族而非滞育后共同饲养环境解释的，而成年蝴蝶的存活率和免疫力的情况则相反。这种群居蝴蝶在发育表现及其对抗寄生蜂的能力方面显然受益于高同种密度。这些积极影响可能是由进食期间的合作互动驱动的。
