Effect of T-photocycle and wavelength on photoperiodic induction in Indian weaver bird (Ploceus philippinus)

Abstract

ABSTRACT Photoperiodic responses of a photosensitive species depend on the species-specific critical day length (CD), determined by the entrainment of the endogenous circadian rhythm of photoinducibility. We examined the entrainment pathway of the circadian photoperiodic system of photosensitive weaver birds. Birds were subjected to T = 22,24 and 26 h photocycles, with 11- and 12-h photophase to study the photoperiodic induction and synchronization of bird’s circadian system with reference of different light wavelengths. Two experiments were performed on adult male weaver birds. In experiment 1, birds were exposed to T = 22 and 26 h LD-cycles, having 11-h photophase with red and blue light wavelength, while in experiment 2, birds were exposed to T = 22, 24 and 26 h LD-cycles, having 12-h photophase with red and blue light wavelength. Observations on change in body mass and testis size were recorded at monthly intervals. There was a significant effect of red light wavelength on photoperiodic induction of testicular growth in the birds exposed to T = 22 h (11L:11D and 12L:10D) and T = 26 h (11L:15D and 12L:14D; both wavelength), but not when exposed to T = 24 h (12L:12D) photophase. Further, body mass regression was faster in birds of T = 26 h photophase (12L:14D) under blue wavelength. Thus, the above results are indicative of the influence of light wavelength on the endogenous programming that times seasonal responses in body fattening and testicular growth-regression of Indian weaver bird.