Annual changes in serum sex steroids in male and female black (Ursus americanus) and polar (Ursus maritimus) bears.

摘要: The adaptation of black and polar bears to their environments is proportional the severity climate food restriction. Both mate during spring, despite differences in recent metabolic state. Reproductive activity follows 4 mo torpor, whereas reproduction occurs prior torpor. goals this study were measure annual changes serum sex steroids male female bears, determine if levels these associated with condition or photoperiod. Serum testosterone (T) concentrations elevated spring bears. Moreover, increase T was correlated age testis size. progesterone (P4) increased pregnant fall coincident time expected implantation. No increases P4 observed nonpregnant estradiol (E2) 2 We found that measured change independent Therefore, our results suggest photoperiod may be a more important regulator steroid than condition.