Individual differences in behavior: a multi-trait study comparing different ant species

Animal personality, characterized by consistent individual variation in behavioral expression, and behavioral syndromes, underlying correlations between behaviors, have been studied in numerous vertebrate and invertebrate species, including ants. Yet, research on the evolutionary origins of this (co)variation has progressed more slowly than studies showing its occurrence, partly due to varying methodologies preventing comparisons among species. In this study, we applied a comparative framework to investigate patterns of average behaviors and behavioral variation in four ant species belonging to two different subfamilies: Formica fusca and Camponotus aethiops (Formicinae), Aphaenogaster senilis and Messor barbarus (Myrmicinae). We analyzed four behaviors reflecting the responses of ants in foraging or social contexts: exploratory activity, reaction-to-prey, reaction-to-brood, and sociability. All traits except sociability showed moderate to high repeatability in each species. When comparing species for each personality trait, in terms of both average behavioral expression and among-individual variance, we found evidence that phylogeny influences these parameters in the reaction-to-prey test, with closely related species showing more similar behavioral profiles. Other differences among species appear to stem from ecological differences. Evidence of behavioral syndromes was found only in A. senilis, with clear correlation between reaction-to-brood and reaction-to-prey, as well as between reaction-to-brood and exploratory activity. Taken together, our findings suggest that our protocol is robust for assessing personality traits across different ant species and that phylogeny may influence the expression of inter-individual differences in certain behavioral traits. These results call for further studies exploring the evolutionary basis of animal personality within a comparative framework.