From Social Experience to Social Behaviour: Hormonal and Behavioural Phenotypes During Adolescence in Male Guinea Pigs

ABSTRACT Adolescence is the transition from juvenility to adulthood and is characterised by prominent endocrine, neural and behavioural alterations. Thus, adolescence represents a sensitive phase during which social experiences can shape endocrine and behavioural phenotypes. Although the influence of the social environment during adolescence has been widely investigated, most studies assessed such effects only before and after a given social experience, providing limited insight into how these phenotypes change within this ontogenetic phase. Our goal was therefore to examine potential effects of different social environments on the endocrine and behavioural phenotype in male guinea pigs by repeatedly assessing them during adolescence. For this approach, 20 domestic adolescent male guinea pigs ( Cavia aperea f. porcellus ) were housed in two distinct social environments: while males of both groups lived in heterosexual pairs, males of one group additionally received regular social stimulation through repeated short encounters with unfamiliar conspecifics, whereas males of the other group did not. This procedure increased the frequency and diversity of social interactions. Hormone concentrations and behavioural parameters were assessed repeatedly throughout the experiment. We hypothesised males from the two social conditions to differ in their hormonal and behavioural phenotype across adolescence. The difference in baseline cortisol concentrations between the social conditions changed over time. In addition, repeatability analyses revealed social‐condition‐specific patterns in different components of cortisol responsiveness, suggesting that adolescent social environments may not only influence endocrine phenotypes themselves but also the stability of inter‐individual differences in these traits. Males with additional social stimulation showed increased sociopositive and courtship behaviour across social contexts, which may reflect social niche conformance to a socially more variable and less predictable environment. Taken together, these findings show that social experiences during adolescence can shape endocrine and behavioural phenotypes in male guinea pigs, but that these adjustments may differ in their temporal dynamics.