Data from: Managing anabolic steroids in pre-hibernating Arctic ground squirrels: obtaining their benefits and avoiding their costs

Androgens have benefits, such as promoting muscle growth, but also
significant costs, including suppression of immune function. In many
species, these trade-offs in androgen action are reflected in regulated
androgen production, which is typically highest only in reproductive
males. However, all non-reproductive Arctic ground squirrels, irrespective
of age and sex, have high levels of androgens prior to hibernating at
sub-zero temperatures. Androgens appear to be required to make muscle in
summer, which, together with lipid, is then catabolized during overwinter.
By contrast, most hibernating mammals catabolize only lipid. We tested the
hypothesis that androgen action is selectively enhanced in Arctic ground
squirrel muscle because of an upregulation of androgen receptors (ARs).
Using Western blot analysis, we found that Arctic ground squirrels have AR
in skeletal muscle more than four times that of Columbian ground
squirrels, a related southern species that overwinters at approximately
0°C and has low pre-hibernation androgen levels. By contrast, AR in lymph
nodes was equivalent in both species. Brain AR was also modestly but
significantly increased in Arctic ground squirrel relative to Columbian
ground squirrel. These results are consistent with the hypothesis that
tissue-specific AR regulation prior to hibernation provides a mechanism
whereby Arctic ground squirrels obtain the life-history benefits and
mitigate the costs associated with high androgen production.