The adaptiveness of a queuing strategy shaped by social experiences during adolescence.

Social experiences during adolescence profoundly influence behavioural and endocrine phenotypes. A key question is whether these environmentally induced changes can adjust the individual to prevailing environmental conditions. Previous work shows that male guinea pigs living in pairs from early adolescence are more aggressive and exhibit distinctly higher cortisol responses than males living in large mixed-sex colonies. In environments with limited numbers of competitors, the high-aggressive phenotype of pair-housed males (PMs) leads to more dominant positions and higher reproductive success compared with colony-housed males (CMs) and thus represents an adaptation to this situation. Here we tested whether CMs, conversely, are better adapted to the complex social life in large groups. For that purpose, pairs of one PM and one CM were placed into large mixed-sex colonies during late adolescence. During the initial days, PMs displayed significantly more aggressive behaviour than CMs. Nevertheless, PMs and CMs achieved only low dominance ranks and did not reproduce at that time. Simultaneously, PMs showed marked increases in testosterone and cortisol as well as substantial reductions in body weight, whereas CMs coped with the situation in a non-stressful way. A few days later, however, PMs changed their high-aggressive strategy to a low-aggressive queuing strategy and could no longer be distinguished from CMs. As a consequence, PMs and CMs did not differ in numbers of sired offspring. In summary, these results demonstrate that adolescence is a sensitive phase not only for adapting to current environmental conditions but also for readjusting phenotypic development when the actual environment deviates from earlier predictions.