Influence of light intensity and wavelength on testicular responses in male Brahminy myna

Experiments were performed on photosensitive male Brahminy myna to investigate the light intensity and wavelength dependent effect on photoperiodic induction of testicular growth. In the first experiment, we examined the comparative effect on complete (13L:11D) and skeleton (6L:6D:1L:11D) photoperiod with 700 lux intensity (series first) and inductive effects of 1-h light pulse (intensity=2, 10, 50 and 100 lux) in skeleton photoperiod (second series). In the third series, birds were exposed to 13L:11D at different light intensity (50, 100, 500 and 1000 lux). In the second experiment, birds were subjected to a long photoperiod (13L:11D) with photo-phase being applied at 100 lux intensity, with two wavelengths: green (500 nm), red (640 nm) and a group under white light served as control (first series). In the second series, birds were exposed to 6L:6D:1L:11D with red and green light wave lengths at 50 and 100 lux intensity level. The third experiment analyzed the phase-dependent effect of light wavelength on photoperiodic clock, employing skeleton photoperiods (6L:6D:1L:11D) at 50 lux intensity with 6 and 1-h light pulses given at the same wavelength, 500 nm (green/green), 640 nm (red/red) and a group exposed to both pulses of white light (white/white) served as control (series first). In the second series, the two light pulses were given at a different wavelength combination, 6 h at 500 nm (green) and 1 h at 640 nm (red) in one group and vice-versa in the other. Taking all things into consideration, results demonstrate that intensity and wavelength of light play an important role in photoperiodic induction of seasonal responses in Brahminy myna and suggest that the avian photoperiodic response system is capable of fine discrimination between different light intensities and spectra.