The Company We Keep: Effects of Different Social Environments on Male Guinea Pig Behaviour and Hormones Over the Course of the Ontogeny

ABSTRACT Social environments change over the course of an individual's life, and individuals must adjust to these different environments throughout their ontogeny. Therefore the aim of this study was to examine whether two different social environments cause differences in behaviour and endocrine profiles over the course of the ontogeny in male domestic guinea pigs, from juvenile phase to early adulthood. For this purpose, 20 males lived in two different social environments. The different social environments consisted of heterosexual pair housing, with one group receiving additional social stimulation by unfamiliar guinea pigs (3× per week, up to 10 min), and the other group not receiving it. The results show that the stimulated males displayed more sociopositive and sexual/courtship home enclosure behaviour in adolescence and adulthood, as well as social interest behaviour in social behavioural tests, but there were no differences in testosterone or hypothalamic–pituitary‐adrenocortical‐axis (re‐)activity, for which basal and reaction values of cortisol were used as an indicator. The results also show that testosterone values were not stable across or within ontogenetic phases in either treatment group, whereas cortisol reaction values were stable within and across ontogenetic phases in both treatment groups, except for the first reaction value in the juvenile phase. The differences in behaviour may be adjustments to the social environment by the stimulated males, which might show more sociopositive behaviour because they live in an environment where the advantages of more sociopositive behaviour might outweigh other behavioural strategies. The lack of hormonal differences between the two groups could point towards different factors mediating the behavioural differences. A possible mediating factor could be social learning, though the involvement of testosterone as another mediating factor cannot be ruled out. Overall the results show that behavioural adjustments to the different social environments have taken place, which can be considered evidence of behavioural plasticity in a changing social environment and potentially of social niche conformance.