Season of birth affects social behaviours and stress physiology differently in males and females of the wild cavy (Cavia aperea)

Behavioural, physiological, and life-history traits are often shaped by the environment. The pace-of-life syndrome (POLS) hypothesis suggests that environmental differences affect individuals consistently, i.e. shaping personality traits. Recently, the original POLS concept has been refined to incorporate predictable differences between sexes. Here, we test POLS predictions regarding aggressiveness, affiliative interactions and their relationship with fearlessness, boldness and blood cortisol concentrations in a precocial rodent. We induced differences in pace-of-life by dynamically changing photoperiod (simulating spring or autumn). We measured boldness, fearlessness, social behaviours and baseline cortisol concentrations in both sexes. In addition, females were tested in a group integration situation. We show that affiliative and aggressive interactions in a social encounter test represent consistent (i.e. personality) traits. In accordance with POLS predictions, social behaviours differed between animals born in different seasons, facing predictably different life histories under natural conditions, albeit in a sex-specific way. Autumn-born males were less aggressive while autumn-born females were more aggressive. While there was no seasonal difference in baseline or stress-induced cortisol concentrations during integration into groups of unfamiliar females, spring-born females lost more body mass, indicating higher levels of stress. The non-social personality traits predicted aggressive behaviour in social situations, again, in a sex-specific way. While bold males showed more interactions in general and more aggressive interactions, boldness did not affect reactions of females. Fearless males and females initiated more aggressive interactions. Taken together, these results indicate that social personality traits interact with non-social personality traits in a complex, sex-specific way, leading to sex-specific syndromes.