Individual differences and variation in the reproductive strategies of cooperative breeders

Abstract

Ecological differences are instrumental to the evolution of cooperative breeding, because they mean that the costs and benefits of forming a group and sharing reproduction differ between individuals and environments. Current evolutionary models do not fully explain the diversity of cooperative breeders' strategies, which suggests that these models neglect important ecological factors and are insufficiently complex. The goal of this PhD is to understand the factors that influence the evolution of cooperative-breeding strategies. My thesis incorporates some of the overlooked individual variation and uncertainty into models of skew, to get further insights into the reproductive games of cooperative breeders. I combine theoretical and empirical approaches, including a cross-species comparison and a dataset analysis. We first develop a model which reveals that the link between subordinate outside options and their effect on group productivity shapes skew and group formation. Using a meta-analysis I find that relatedness correlates positively with skew within species, suggesting that kin forego reproduction because the indirect benefits of helping are sufficient. We then develop a theoretical model to explore the effect of uncertainty which predicts that dominants should evolve to acquire information about the outside options of subordinates, but not their relatedness to those subordinates. Another key facet of variation is sex differences in life histories, which might select for different response rules for costly cooperative behaviours and reproductive strategies. While parental conflict and reproductive conflict both influence group productivity in theoretical models, my work shows that combining these two games does not change their predictions, which suggests that they can be studied separately. Using data from wild dwarf mongooses (Helogale parvula), I uncovered an interaction between sex and period in contributions to costly sentinel activity, with males contributing more than females in the second fortnight after individuals acquire dominance. Empirical studies testing the predictions of this thesis are needed to determine whether their hold true. Future studies should investigate how variation and uncertainty about other factors influence evolutionary games, to define what influences animals’ strategies.