Shaped from an early age: behavioural and hormonal phenotypes in juvenile male guinea pigs living in distinct social environments

Melanie Gleske, Carolin Mundinger, S. Helene Richter, Sylvia Kaiser

Behavioural plasticity enables individuals to vary their behaviour in response to different environmental conditions. As the social environment can change at any time, individuals need to be able to adjust throughout their lives. Our goal was therefore to elucidate when and how behavioural and hormonal adjustments in guinea pigs occur. We focused on juvenility, an important developmental phase characterized by prominent changes of the social environment, since the focus on social interactions shifts from parents to peers. For this approach, juvenile male guinea pigs (Cavia aperea f. porcellus) lived in two distinct social environments: while males of both groups lived in heterosexual pairs, males of one group were socially stimulated (e.g., an unfamiliar individual is introduced into the focus males home enclosure for 10 minutes) regularly whereas males of the other group were not. This procedure increased the number of social interactions. Socially stimulated males showed different adjustments to their social environment in comparison to non-socially stimulated males. They displayed an initially increased stress response, enabling them to adequately react to the unpredictable social encounters. Over time, males then adjusted to this challenging environment and displayed a decrease in stress response again. Moreover, only socially stimulated males showed a significant increase of courtship and sexual behaviour with age. Taken together, these findings demonstrate that already in juvenility the social environment induced hormonal adjustments and behavioural changes in male guinea pigs, thereby highlighting how early-life social experiences can shape individuals’ phenotypes.