The 2- to 4-wk added delay in reproductive maturation induced by the combination of SD and FR could be highly significant to young rats in the wild. However, the combined effect of SD and FR together was considerably weaker than the reproductive inhibition produced by SD alone in many obligately photoresponsive species. The level of food restriction we chose was relatively modest, and it is possible that greater food restriction, which would be likely for some animals in the wild, might produce a more dramatic effect. buy prednisone
While SD inhibits food intake and body weight gain as well as testicular development (similar inhibition of weight gain by SD was reported by Boon et al. for Wistar rats), the effects of photoperiod on reproduction are not due to inhibition of feeding and body weight. In experiment 2, we found that the effects of SD on reproduction were independent of the effects of food intake or of body weight. Food-restricted LD rats had lower body weights (Fig. 5) but much larger testes (Fig. 4) than SD-ad lib controls. Thus, reduction in food intake and lowered body weight are not the cause of reproductive inhibition by SD. Lower body weight in SD may hold adaptive significance unrelated to reproduction. In wild rodents, it may reduce daily energy requirements in winter (reviewed in ), a response to photoperiod that can be independent of changes in testis size.