Interactive Seasonal Changes in the Testis and Thymus of the Lizard Calotes versicolor Daudin

The development and secretory activity of testis of lizards is modulated by environmental factors, especially temperature, and it follows a seasonal pattern. Testosterone, secreted by the testis, modulates the functioning of the thymus which governs the immunity of animals. Thymosin is synthesized and secreted by the thymus and governs the development of immunity. At the time when the thymus is hypoactive the other lymphoid tissues take care of the maintenance of immunity. In the present study, the testis and thymus of Calotes versicolor were studied during the different months of the breeding as well as non-breeding phases, and the specific variations were observed. The recrudescence of testis begins in the month of March and attains the peak in June, which coincides with the beginning of breeding phase. During this period, significant increase in the weight of testis was found. The fully developed testis is maintained during July to September. During the breeding phase the thymus was regressed and had shrunken thymocytes indicating poor secretion of thymosin. From October onwards, the weight of the testis decreased, indicating regression. During the non-breeding phase, from November to February, the testis was fully regressed, when testis was devoid of spermatozoa. During this phase the thymus was well-developed, and the thymocytes were enlarged indicating substantial activity.