Molecular basis of photoperiodic control of reproductive cycle in a subtropical songbird, the Indian weaver bird (Ploceus philippinus)

• First study on genetic regulation of reproductive cycle in a subtropical bird.
• Gene expression levels varied with the photoperiod-induced testicular phases.
• Rapid switching between DIO2 and DIO3 genes induced photoperiodic response.
• GnRH and DIO2 gene expressions were positively correlated with testis size.
• GnRH and GnIH mRNA expressions were almost in antiphase under long days.

Less is known about genetic basis of photoperiodic regulation of reproductive cycle in subtropical birds. This study measured the expression levels of DIO2, DIO3, GnRH, and GnIH genes in Indian weaver birds subjected to short days (8 h light:16 h darkness, 8L:16D) and long days (16L:8D) for 48 weeks. Whereas small, reproductively inactive testes were maintained under short days, weaver birds underwent testis recrudescence – regression cycle under long days. Relative expression levels of DIO2, DIO3, GnRH and GnIH genes were quantified by the real-time PCR (qPCR) in hypothalamus of birds (n = 4) sampled at the beginning of the experiments, and after 10 and 48 weeks of short and long day exposures. These sample times represented photosensitive unstimulated (day 0), and under long days the recrudescence (photostimulated, after 10 weeks) and regression (photorefractory, after 48 weeks) testicular phases. Birds under short days served as controls. The expression pattern of these genes corresponded with testicular phases. High and low GnRH and DIO2 levels were found in birds with large and small testes, respectively. By-and-large the converse was true for GnIH and DIO3 expression levels. Thus, after 10 weeks of exposure, there was a significant difference in the mRNA levels between short and long day birds, with small and large testes, respectively. The results also suggest for a possible rapid switching between DIO2 and DIO3 and GnRH and GnIH expressions during testis maturation – regression cycle in Indian weaver birds.