A Bayesian Approach to Social Structure Uncovers Cryptic Regulation of Group Dynamics in Drosophila melanogaster.

Understanding the mechanisms that give rise to social structure is central to predicting the evolutionary and ecological outcomes of social interactions. Modeling this process is challenging, because all individuals simultaneously behave in ways that shape their social environments--a process called social niche construction (SNC). In earlier work, we demonstrated that aggression acts as an SNC trait in fruit flies (Drosophila melanogaster), but the mechanisms of that process remained cryptic. Here, we analyze how individual social group preferences generate overall social structure. We use a combination of agent-based simulation and approximate Bayesian computation to fit models to empirical data. We confirm that genetic variation in aggressive behavior influences social group structure. Furthermore, we find that female decamping due to male behavior may play an underappreciated role in structuring social groups. Male-male aggression may sometimes destabilize groups, but it may also be an SNC behavior for shaping desirable groups for females. Density intensifies female social preferences; thus, the role of female behavior in shaping group structure may become more important at high densities. Our ability to model the ontogeny of group structure demonstrates the utility of the Bayesian model-based approach in social behavioral studies.