title: The influence of androgens on hibernation phenology of free-living male arctic ground squirrels.
abstract: Free-living ground squirrel species are sexually dimorphic in hibernation phenology. The underlying causes of these differences are not yet known. Androgens, testosterone (T) in particular, inhibit hibernation. To determine the influence of endogenous androgens on annual timing of hibernation we first 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 cycles. The highest T levels (0.53±0.10ng/mL) were in 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 (0.07±0.01 and 0.06±0.00ng/mL, respectively). DHEA levels were higher in males during the late summer compared to reproductively mature males in spring (120.6±18.9 and 35.9±2.3pg/mL, respectively). Eliminating gonadal androgens via castration resulted in males delaying euthermy by extending heterothermy significantly in spring (Apr 22 ±2.9) than reproductive males (Mar 28 ±3.9) but did not change the timing of hibernation onset (castrate: Oct 12 ±1.0 vs. intact: Oct 3 ±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.
authors.affiliation: Western Kentucky University, 1906 College Heights Blvd, Bowling Green, KY 42101, USA. Electronic address: melanie.richter@wku.edu.
authors.forename: M M
authors.initials: MM
authors.lastname: Richter
authors.affiliation: Institute of Arctic Biology, University of Alaska Fairbanks, Alaska 99775, United States. Electronic address: bmbarnes@alaska.edu.
authors.forename: B M
authors.initials: BM
authors.lastname: Barnes
authors.affiliation: Department of Biology, University of Portland, Oregon 97203, United States. Electronic address: oreilly@up.edu.
authors.forename: K M
authors.initials: KM
authors.lastname: O'Reilly
authors.affiliation: Center for Systems Biology, Massachusetts General Hospital, Harvard Medical School, Boston, MA 02114-2506, United States. Electronic address: afenn@mgh.harvard.edu.
authors.forename: A M
authors.initials: AM
authors.lastname: Fenn
authors.affiliation: Department of Biological Sciences and Center for Bioengineering Innovation, Northern Arizona University, Flagstaff, 86001 Arizona. Electronic address: loren.buck@nau.edu.
authors.forename: C L
authors.initials: CL
authors.lastname: Buck
mesh_terms: D000374:Aggression / Q000502:physiology; D000728:Androgens / Q000502:physiology*; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D002369:Castration; D003687:Dehydroepiandrosterone / Q000502:physiology; D006605:Hibernation / Q000502:physiology*; D008297:Male; D012098:Reproduction / Q000502:physiology; D012589:Sciuridae / Q000502:physiology*; D012621:Seasons; D013739:Testosterone / Q000502:physiology
chemical_list: D000728:Androgens; D013739:Testosterone; D003687:Dehydroepiandrosterone
keywords: Androgen; Arctic ground squirrel; Hibernation phenology