[Show abstract][Hide abstract] ABSTRACT:
Testosterone (T) concentrations in many species are sensitive to seasonal changes and to changes in social conditions. However, the effect of the natural or endogenous T increase in the juvenile on their social behaviour is not well understood. In this study, T and behaviour were measured from the pro-social juvenile to the adult stage in semi-feral domestic fowl. During the pro-social phase T levels and the distance chicks maintained between each other, i.e. inter-individual distance (IID) were low. Then, as T increased, a corresponding increase in IID occurred and continued in males until dispersal to individual adult male territories. In the new and initially stable adult social structure, T declined and IID remained high, indicating a new behavioural mechanism was in place. Males first mated as T levels were declining. They were then challenged; then T increased, and then IID increased again. Adult male T levels fluctuate, being low or declining in a socially stable environment and increasing following a challenge, suggesting a regulatory or modulating role for T. The results are consistent with T having an endogenous role: in the juvenile, driving behavioural change towards adulthood, and in adulthood, a modulating role regulating social organisation.