The social modulation of behavioural profile and stress responsiveness during adolescence: an adaptive mechanisms?

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Adolescence is the gradual transition from childhood to adulthood. In the bio-medical and bio-psychological sciences, this time is regarded as an important, dangerous, and potentially stressful life stage. From an evolutionary perspective, however, adolescence may also be an opportunity for adaptation. Our previous work in guinea pigs showed a conspicuous environment-dependent canalization of behavioural profiles and stress responsiveness during this phase of life. If males live in large mixed-sex colonies (COL) throughout adolescence, they are characterized by low aggressiveness and low (cortisol) stress responsiveness. In contrast, males housed in pairs (PAIR; one male / one female) from early adolescence on are very aggressive and show high stress responses. During the 1st funding period we focused on underlying mechanisms and dis-covered a heretofore undescribed neuroendocrine pathway including a central role for the interaction of testosterone and stress hormones. The overall aim of this funding period is to elucidate whether the behavioural alterations that occur during adolescence represent adaptations to the social environment in which the individuals live. More specifically, we argue that the low-aggressive profile may be part of a “queuing strategy” that enables COL to live peacefully with unfamiliar conspecifics and to wait for the opportunity to monopolize females. The highly aggressive profile is supposed to be part of a “resource defence strategy” that helps PAIR to defend their female partners aggressively. To test this hypothesis, as a proof of principle, two match-mismatch experiments will be conducted. In experiment 1, triadic situations will be created (one COL, one PAIR, and a female). These situations reflect a low-density situation, in which reproductive success is deter-mined primarily by the outcome of male-male competition. We hypothesize that PAIR (programmed to follow a resource defence strategy) will be dominant over COL and will sire a higher number of offspring. In the corresponding experiment 2, PAIR and COL are introduced into large mixed-sex colonies. This situation reflects a high-density situation where male reproductive success is mostly determined by a “queuing strategy”. We hypothesize that COL (programmed to follow a queuing strategy) cope distinctly better with this situation than PAIR and will hence sire a higher number of offspring. In summary, this project is among the first to study the social modulation of behavioural profiles and stress responsiveness during adolescence within an evolutionary framework. The combined insights from both funding periods will provide a significant new contribution to the understanding of how and why the social environment and hormones interact during this phase of life to shape behavioural profiles.