Interindividual differences in ants: exploratory activity and aggression are consistent over time and not correlated in Formica fusca

Abstract Many animals show interindividual differences in behavioural expression that are consistent across time and/or contexts (referred to as animal personality). Exploratory activity, aggression, and boldness are among the most studied personality traits. A behavioural syndrome refers to a consistent correlation between two or more behavioural traits across individuals, meaning that an individual displaying a certain level of one trait (e.g. high aggressiveness) is also likely to exhibit a predictable level of another trait (e.g. high exploratory tendency or boldness). Although several studies have investigated personality in ants, particularly at the colony level, interindividual variability at the individual level and its relationship with behavioural syndromes remain poorly documented. We repeatedly tested individual foragers of the widespread ant species Formica fusca using three behavioural assays: an open-field test to assess exploratory activity, a boldness assay to measure risk-taking tendencies, and nestmate/alien encounters to evaluate aggression. Our results show that exploration and aggression towards non-nestmates are consistent over time, indicating that they characterise individual behavioural types in F. fusca workers. Moreover, aggression towards nestmate and alien ants are repeatable at colony level (i.e. group personality). However, boldness and response to nestmates are not significantly repeatable at individual level. Despite the widespread documentation on behavioural syndromes across animal taxa, including ants, we found no significant correlation between exploration and aggression in F. fusca . Given that these behavioural traits are often positively correlated in other species, their independence in F. fusca is intriguing and calls for further investigations to broaden our knowledge and understanding of consistent interindividual differences in social insects.