Seasonal breeders rely on light as a key environmental cue to trigger reproductive activities. While studies have been focused on male white-rumped munia (Lonchura striata), the effects on females are largely unknown. This study examined how light compositions affect female reproductive physiology. In the first experiment, female birds were exposed to short day (SD; 8 L:16D) and long day (LD; 15 L:9D) for a single day to study various transcripts involved in seasonal reproduction. The second experiment included SD and LD along with an added photoperiod of 12 L:12D, and the treatment extended for 30 d. In the third experiment, female birds were exposed to the above three photoperiod conditions, including natural day length (NDL), to assess morphological changes across 18 months. The fourth experiment evaluated seasonal variations in reproductive parameters across four months: March, June, September, and December. The fifth focused on illuminance levels (10, 50, and 100 lux) under a photoperiod of 12 L:12D, and the sixth assessed responses to red (650 nm) and blue light (450 nm) at a constant irradiance of 0.5 W/m2. In all six experiments, an assessment of body mass and follicular diameter was done, while Experiment 3 specifically examined full-body moult and primary flight feather moult as well. Hypothalamic tissue was analysed for reproductive and epigenetic markers. The first experiment revealed enhanced expression of Tshβ and Eya3 in the long-day group, while no significant changes in other reproductive (Dio2, GnRh, Dio3 and GnIh) and epigenetic (Tet1, Hat1, Hdac2, Dnmt1 and Dnmt3b) transcripts were observed. The second experiment observed increased expression of Tshβ exclusively under 15 L:9D, while Tet1, Hat1 and Dnmt1 transcripts were increased under 12 L:12D. Experiment 3 demonstrated distinct morphological responses to different photoperiods, with significant increases in follicular diameter under 15 L:9D and NDL conditions at the 7th month, but this effect was delayed until the 10th month under 12 L:12D. In contrast, no change was observed under 8 L:16D. Seasonal variations in transcripts were noted, with the highest expression of Tshβ, Dio2, GnRh, Eya3, Hat1, Tet1 and Dnmt3b in September compared to other months. The fifth experiment showed that exposure to 100 lux increased key reproductive markers (Tshβ, Dio2, and GnRh) and epigenetic regulators (Hat1 and Tet1), while the sixth experiment found no significant differences between red and blue light treatment. Overall, the findings highlight the importance of light duration and illuminance in reproductive responses. While no robust change in epigenetic transcript was observed under laboratory conditions in female birds, the epigenetic changes observed in the seasonal experiment suggest that seasonal reproductive cycles are under regulation of epigenetic mechanisms at the molecular level.
Lalpekhlui et al. (Tue,) studied this question.