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

Abstract

Previous 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.

Seasonal reproductive cycle and variability in plasma testosterone levels in the domestic duck (Anas platyrhynchos)

“…A similar hormonal pattern has been reported for the subtropical bird Ploceus philippinus (TSUTSUI et al, 1994) and also for the canary Serinus canarius (NOTTEBOHM et al, 1987).…”

“…Seasonal variations in gonadal activity have been observed for different wild bird species inhabiting temperate regions as a consequence of interaction between environmental and hormonal factors (TSUTSUI et al, 1994). In these species, LH and sex steroid concentrations increase in spring, remain relatively high during the reproductive phase, and decline to basal levels at the end of reproduction (BALL, WINGFIELD, 1987).…”

Involvement of Threshold Photoperiod in Control of Reproductive Rhythmicity in Migratory Blackheaded Bunting,Emberiza Melanocephala

“…Long-day exposure leads to an increase in gonadal growth and a rise in testosterone and luteinizing hormone levels in European quails (Boswell et al 1993;Boswell et al 1995;Bernard and Ball 11-12h 11-12h From Miller 1959;Lofts 1962;Kumar and Tewary 1983;Dixit 1983, 1986;Tewary and Ravikumar 1989;Boswell et al 1993;andTsutsui et al 1994. 1997); a rise in luteinizing hormone, testosterone, and testicular and body growth in male blackheaded buntings Jain and Kumar 1995); an elevated testosterone level and increased testicular weight in Indian weaver bird (Tsutsui et al 1994); an increased body weight in zebra finches (Meijer et al 1996); testicular and body growth in red cross bill (Hahn 1995); ovarian growth in white crowned sparrows (Schwabl et al 1988); and a higher concentration of estradiol in Japanese quail (Brain et al 1988). The circulating plasma estradiol was not detectable (< 10 pg/mL) at the beginning of the experiment in all birds.…”