Meeting Abstract
Appropriate levels of aggression can ensure acquisition of territory and mates during the breeding season and acquisition of limited sources during non-breeding conditions. Unlike some seasonal breeders, male and female Siberian hamsters (Phodopus sungorus) display increased aggression when reproductively inactive (short days; SD), a time when gonads are regressed and gonadal steroids are low. It has been hypothesized that SD aggression is mediated by adrenal rather than gonadal steroids. This study tested this idea by examining adrenal responsiveness in reproductively active (long day; LD) and SD female Siberian hamsters in response to an ACTH challenge, and quantifying area of the adrenocortical layers and adrenal medulla across the seasons. SD females displayed significantly more aggression and a more robust adrenal response to ACTH, when compared to LD females. Specifically, DHEA levels in response to an ACTH challenge were significantly elevated in SD but not in LD females. Cortisol levels, in contrast, were significantly elevated in all females regardless of condition. The zona reticularis (adrenal source of DHEA), but not the other layers of the adrenal cortex, was larger in LD females, showing that there are dynamic steroid-specific morphological changes in adrenals across seasons. These findings support the idea that adrenal DHEA plays a key role in regulating SD aggression in female Siberian hamsters, and that there is a seasonal switch from a gonadal to an adrenal source of sex steroids across the seasons. More broadly, this work contributes to our understanding of environmental and neuroendocrine regulation of aggression in hamsters and likely other mammalian species.
