Serum thyroxine and seasonal fattening of free-living Piute ground squirrels, Spermophilus mollis (Rodentia: Sciuridae).
Serum thyroxine and body composition of free-living Piute ground squirrels were examined during the season of above-ground activity. Serum thyroxine titers were 2-10 times higher than those reported in laboratory studies on other species. Among juveniles, both body size and lipid content were negatively correlated with thyroxine, whereas these variables were not significantly correlated among adults. Significant sex differences in serum thyroxine were observed for both age groups. Results suggest that the seasonal cycle of body weight is driven by an underlying metabolic cycle but that individual fattening schedules are determined by environmental conditions.
D000818:Animals; D001835:Body Weight; D005260:Female; D050356:Lipid Metabolism; D008297:Male; D012589:Sciuridae / Q000097:blood / Q000502:physiology*; D012621:Seasons; D012737:Sex Factors; D013974:Thyroxine / Q000097:blood*
D013974:Thyroxine