Light-induced reproductive responses in white-rumped munia (Lonchura striata)

Abstract

Photoperiod is a primary cue for most birds to initiate reproductive activities. How light influences the reproduction-linked processes in white-rumped munia is largely unknown. A series of experiments were performed on male birds. In experiment one, birds were exposed to either short (SD; 8 L: 16D) or long day length (LD; 15 L:9D) for one day and sampled at 19 h after light onset. In experiment two, birds were exposed to either SD (8 L: 16D), or equinox photoperiod (12 L:12D), or to LD (15 L:9D). In experiment 3, birds were exposed to an equinox photoperiod of 10 lx, 50 lx, or 100 lx. In experiment four, birds were exposed to an equinox photoperiod (0.5 W/m² of light irradiance) of red (RL; 650 nm) or blue light (BL; 450 nm). Experiment 2 to 4 ran for 30 days. For experiment five, birds were procured at four different times of the year, i.e., March, June, September, and December. Body mass and testicular volume size were observed in all experiments. In experiment 2 to 5 sampling was done during the middle of the light phase. Hypothalamic tissue was used for transcription studies of reproductive and epigenetic markers. In experiment 1, higher expressions of Tshβ, Dio2, Eya3, Tet2, and Hat1 while lower expression of Dnmt1 was observed in LD group. In experiment 2, higher expression of Tshβ, Dio2, GnRh, Eya3, and Tet2 while lower expression of of Dio3, GnIh, Hdac2, Dnmt1, and Dnmt3b was observed in both 12 L:12D and 15 L:9D LD groups. In experiment 3, higher expression of Tshβ, Dio2, GnRh, Tet2, and Hat1 while lower expression of Dio3, GnIh, Hdac2, and Dnmt3b was revealed in 50 and 100 lx groups. Experiment 4 resulted in higher expression of Tshβ, Dio2, GnRh, and Tet2 while lower expression of Dio3, GnIh, Hdac2, Dnmt1 and Dnmt3b in blue light group. Seasonal fluctuations were observed in all hypothalamic transcripts studied. Higher expression of Tshβ, Dio2, GnRh, Eya3, Tet2, and Hat1 was revealed in September while Dio3, GnIh, Hdac2, Dnmt1 and Dnmt3b were higher at other time of the year. The results from experiment 1 to 4 suggest that all three components of light i.e., duration, illuminance and spectral composition of light affects reproductive responses. While in nature season controls reproductive responses. Change in epigenetic transcripts suggest that and these responses are mediated by epigenetic mechanisms.