Classically, testosterone (T) was considered the principal regulator of aggression. However, recent studies in birds have found aggression and T uncoupled during the non-breeding season. Circulating testosterone comes with costs such as immunosuppression and energy expenditure. Instead, the pro-hormone, dehydroepiandrosterone (DHEA), is circulated and activated within the brain via conversion into oestradiol (E 2 ), avoiding the costs associated with T. At present the site of DHEA synthesis is unknown. My thesis investigated the existence of an analogous pathway in non-breeding red squirrels (Tamiasciurus hudsonicus ) with two studies: (a) a field study investigating the effects of E2 on aggression and (b) a laboratory study that attempted [...]
