Effects of pinealectomy and melatonin on the photoperiodic gonadal response of the male lizard Anolis carolinensis

The effects of pinealectomy and exogenous melatonin treatment on the photoperiodic testicular response in the lizard Anolis carolinensis were examined at two times of year. In the summer (July–August) neither pinealectomy nor melatonin affected the photoperiodic response. In the fall (September–October) pinealectomy had a progonadal effect in lizards maintained on either LD 8:16 or LD 14:10 photoperiods. Melatonin blocked the gonadal development in response to pinealectomy on LD 8:16 but melatonin did not inhibit the acceleration in testicular development caused by pinealectomy on LD 14:10. However, melatonin did inhibit testicular development in intact (nonpinealectomized) anoles exposed to LD 14:10. These results show that pinealectomy can modify testicular function in Anolis, that the effects of pinealectomy are seasonal, and that melatonin may be a reproductively active factor involved.