Meeting Abstract
Many free-living ground squirrel species are sexually dimorphic in hibernation phenology. The underlying causes of these differences are unknown. Androgens, testosterone (T) in particular, inhibit hibernation. To determine the influence of endogenous androgens on annual timing of hibernation and aggression, we measured circulating levels of T and dehydroepiandrosterone (DHEA), an adrenal androgen implicated in non-mating season aggression in other species, in free-living male arctic ground squirrels (Urocitellus parryii, AGS). We also manipulated endogenous androgen levels by surgical castration, and consequently compared body temperature records from intact (n=24) and castrated (n=9) males to elucidate the influence of endogenous androgens on annual body temperature rhythms. Unsurprisingly, the highest T levels (0.69±0.20 ng/mL) were found among reproductively mature male AGS in spring, whereas, both immature males in spring and all males in late summer had T levels an order of magnitude lower (0.06±0.00 and 0.07±0.01 ng/mL, respectively). DHEA levels were higher in males during the late summer compared to reproductively mature males in spring (124.6±20.8 and 40.6±4.2 pg/mL, respectively). Eliminating gonadal androgens via castration resulted in males remaining heterothermic significantly later in spring (Julian date 112.1 ± 2.9) than reproductive males (87.1±3.9) but did not change the timing of hibernation onset (castrate: 284.8±1.0 vs. intact: 276.2±3.1). We conclude that while androgens play a significant role in spring hibernation phenology of males, their role in fall hibernation onset is unclear.
