Ephemeral resources promote adaptive sociality in wild guppies

Sociality can facilitate the discovery of novel resources, yet it can also entail costs, including increased competition, aggression, sexual harassment and disease transmission. Selection should therefore favour social flexibility as a response to changes in resource conditions, allowing individuals to adjust their social associations optimally. Quantifying these social adjustments and how they allow individuals to benefit in dynamically changing resource environments can provide insight into the adaptive capacity of wild animal populations. We experimentally studied social flexibility in wild guppies (Poecilia reticulata) by examining their fission-fusion dynamics. Using mixed-sex sets of individually marked fish, we manipulated recent foraging experience by presenting them with unpredictable, ephemeral food patches or control patches in the wild. Guppies exposed to ephemeral food patches significantly increased their sociality, doubling the proportion of time spent social compared to controls. This shift was driven by an increase in the probability of starting social contact and a decrease in the probability of ending social contact. Stronger increases in sociality were associated with individuals more often locating ephemeral food patches, mediated by foraging motivation. Importantly, increased sociality was not merely the result of local aggregation, as exposure to ephemeral food patches increased, rather than reduced, spatial activity. And stronger spatial activity did not result in more time spent social. In a second experiment, fish were briefly presented with food patches they could see and smell but not actually consume. Again, fish increased their level of sociality compared to control, indicating that the observed social response was not merely driven by satiation-related changes in activity budgets. Together, our results highlight the adaptive and dynamic nature of fission-fusion social systems and support the view that wild animals adaptively shape their social environment in response to fluctuations in resource variability.