Short-term exposure to dim light at night affects reproduction and metabolism-linked processes in adult male tree sparrows (Passer montanus)

Anthropogenic factors, particularly urbanization, have immense implications for the natural light-dark cycle of the species. The present study deliberates on the effects of dim light at night on the transcript expression of reproductive, steroidogenic, and metabolic gene markers in adult male tree sparrows (Passer montanus). Adult male birds were procured locally and were divided into two groups (n = 6 birds/group). Both groups were exposed to 12 h of light and 12 h of darkness, but group two (dLAN group) with a constant dim light (10 lx) during the dark hours. The experiment was run for 2 weeks. After that, birds were sampled, and the hypothalamus, liver, and gonads were harvested and used for gene expression analysis. Blood plasma was used for hormonal and biochemical assays. The findings suggest that 2 weeks of exposure did not significantly change the body mass, cholesterol, glucose, and testosterone assay. However, an increase in testicular volume was observed in dLAN-treated birds. Furthermore, elevation in hypothalamic transcripts (Tshβ, Dio2, GnRH, and Eya3) involved in the seasonal reproduction, along with an increase in steroidogenic transcripts (StAr, Scp2, Srd5a1, Hsd11b2, and Er) in the testis was observed; besides, liver metabolic transcript levels (Acaca, Fasn, Hmcg, Idh2, Sdhaf4, Sdhaf2, Sdhc, Fh, Mdh, Foxo1, and Vip) were also elevated in the dLAN-treated group compared to the control group. Overall, the study shows that even a short-term exposure to the lower intensity of dim light at night of 2 weeks of duration can stimulate the hypothalamic gonadal axis and liver metabolism in tree sparrows. These results could play a role in understanding the effect of light at night on the physiology of diurnal avian species.