Preparing for hibernation in ground squirrels: Adrenal androgen production in summer linked to environmental severity in winter

Boonstra, Rudy, Bradley, Adrian J. and Delehanty, Brendan (2011) Preparing for hibernation in ground squirrels: Adrenal androgen production in summer linked to environmental severity in winter. Functional Ecology, 25 6: 1348-1359. doi:10.1111/j.1365-2435.2011.01890.x

Author Boonstra, Rudy
Bradley, Adrian J.
Delehanty, Brendan
Title Preparing for hibernation in ground squirrels: Adrenal androgen production in summer linked to environmental severity in winter
Journal name Functional Ecology   Check publisher's open access policy
ISSN 0269-8463
Publication date 2011-12
Sub-type Article (original research)
DOI 10.1111/j.1365-2435.2011.01890.x
Volume 25
Issue 6
Start page 1348
End page 1359
Total pages 12
Place of publication Oxford, U.K.
Publisher Wiley-Blackwell Publishing
Collection year 2012
Language eng
Formatted abstract
1. At high latitudes, evolutionary adaptations focus on those that maximize survival, with hibernation being a major one used by many smaller mammals. Typically, mammalian hibernators overwinter in sites that are ≈0°C. However, in arctic regions, such sites do not exist, necessitating hibernation at sites well below 0°C. Lipid, the normal fuel of most hibernators, may not provide sufficient glucose needed by certain tissues to permit survival, with muscle breakdown being required. Critical to enhancing muscle stores are high concentrations of anabolic androgens prior to hibernation when the gonads are inactive.

2. We compare and contrast androgen levels in arctic ground squirrels (AGS) (Urocitellus parryii Richardson) from the Yukon and Columbian ground squirrel (CGS) (U. columbianus Ord) from southern Alberta.

3. In males, changes in testes mass over the active season were similar between AGS and CGS. In contrast, during the breeding and the nonbreeding, pre-hibernation periods, androgen levels in AGS were 6–10 and 20–25 times, respectively, those of CGS. From the breeding to the pre-hibernation periods, androgen levels declined 41% in AGS, but 86% in CGS. In females, androgen levels in AGS were high throughout the active season and, prior to hibernation, were 24 times those in CGS.

4. In pre-hibernating AGS, we determined the source of these high androgen levels from two studies. First, using a hormonal challenge protocol to probe the hypothalamic-pituitary-adrenal axis, we found that androgen levels in both females and males decreased ≥10% in response to suppression by dexamethasone (an artificial glucocorticoid that inhibits ACTH release) and increased ≥18% in response to direct adrenal stimulation by adrenocorticorticotropic homone (ACTH). Second, by sequential hormonal injections in males of gonadotropin-releasing hormone (GnRH) and of ACTH coupled with gonadectomy (GDX), followed by adrenalectomy (ADX), we found that GnRH had no effect, whereas ACTH stimulated androgen levels by >40%, both before and after GDX. After ADX, levels fell by 80%. Thus, the adrenals, not the gonads, are the source of these androgens.

5. We hypothesize that pre-hibernating AGS have evolved a solution seen in no other known mammal: exploiting the benefits of high adrenal androgen levels prior to hibernation to build muscle that is then catabolized overwinter. The unknown is how AGS have mitigated the costs of these high androgen levels.
Keyword Arctic climate
Adrenal androgens
Anabolic steroids
Muscle anabolism and catabolism
Seasonal reproductive status
Annual cycle
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2012 Collection
School of Biomedical Sciences Publications
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Citation counts: TR Web of Science Citation Count  Cited 14 times in Thomson Reuters Web of Science Article | Citations
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