Effects of season and photoperiod on the plasma and intratesticular testosterone levels in Indian weaver birds inhabiting the subtropical zone

Abstract

AbstractPrevious studies showed marked changes in the plasma gonadotropin concentration in response to fluctuations in natural and artificial environmental conditions in Indian weaver birds. Therefore, we studied the effects of season and photoperiod on the plasma and intratesticular testosterone levels in this subtropical bird. Although the plasma testosterone concentration changed markedly during the annual breeding cycle, the level did not show a parallel change with testicular weight. The testicular weight was maximal in the breeding phase (June) and minimal in the nonbreeding phase (December), while the plasma testosterone concentration showed two large peaks, one in the breeding and the other in nonbreeding phases. No significant difference in the plasma testosterone level was detected between these two phases. A similar change in plasma testosterone levels was evident in female birds. The intratesticular testosterone content per unit weight was unexpectedly higher in the nonbreeding phase than in the breeding phase. Therefore, calculated total testosterone content per testis showed no statistically significant difference between the two phases despite the small testicular mass in the nonbreeding phase. On the other hand, exposure to short‐day (SD) photoperiods for 10 weeks during the breeding phase, which caused a marked decrease in the testicular weight, tended to decrease the plasma testosterone concentration. Similarly, exposure to long‐day (LD) photoperiods for 10 weeks during the nonbreeding phase tended to induce an increase in the circulating testosterone level in addition to a marked increase in the testicular weight. However, such an effect of artificial photoperiod on testosterone levels was statistically not significant due to a large variance. These results suggest that in Indian weaver birds testosterone actively circulates not only in the breeding phase but also in the nonbreeding phase. Not only photoperiod but also other environmental factors may be involved in the regulation of circulating testosterone in male birds. © Wiley‐Liss, Inc.