Effects of the group's mix of sizes and personalities on the emergence of alternative mating systems in water striders

摘要

Although much work has analysed how individual behavioural plasticity and adaptations to ecological conditions (e.g. density, sex-ratio, resource distribution) shape mating systems, few studies have assessed the relative importance of multiple factors in explaining why mating systems vary from one sub-population to the next even in the same ecological conditions. Differences among groups in their phenotypic composition, such as their average phenotype, within-group variation in phenotype, or the phenotype of individuals occupying key social roles might shape the mating system emerging at the group level and explain some portion of mating system variability. Here, we take advantage of the mating system flexibility of stream water striders (Aquarius remigis) to investigate how phenotypic composition affects the mating system emerging at the group level. Groups exhibited stable mating systems varying from scramble polygyny with intense sexual conflict, to systems with a clear dominant male guarding a "harem" of females. We found that male size asymmetries and the personality of the largest individuals within groups had important effects on the group's mating system. The group's average male and female personality, size, and social plasticity also explained some of the variation in mating systems. Our study is one of the first to quantify significant relationships between group phenotypic composition and mating system variability.