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

The individualised social niche results from interactions of an individual with its social environment. The social environment can change during lifetime. Thus, individuals need to be able to conform to different individualised social niches over lifetime. Our goal was therefore to elucidate when and how social niche conformance in guinea pigs occurs. 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, which is a crucial factor for constituting individualised social niches. 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 juvenile male guinea pigs the social environment induced hormonal adjustments and behavioural changes, thereby laying the grounds for social niche conformance.