Seasonal variations in the physiological processes help animal to adapt to the environmental condition, however, informations on this subject in reptiles are scarce. In the present study, garden lizards (Calotes versicolor) were used to study the annual variation in blood immune responses and changes in the lymphoid organs. The lizards were weighed, anaesthetized under mild anesthesia and blood was collected in heparinized syringe. Blood was then processed for determining total leucocyte count, differential leucocyte count and nitroblue tetrazolium reduction test (Slide assay) for assessment of reactive oxygen production by leucocytes. For histomorphological studies, spleen, thymus and testes were excised rapidly, cleaned and weighed and their weight was transformed to thymosomatic, splenosomatic and gonadosomatic indices respectively. Total leucocyte count did not change significantly, however, differential leucocyte count varied during different seasons. Thymosomatic index was lesser in summer and rainy months. Splenosomatic index started increasing from May and remained high up to August (the hot and humid months of the year and reproductively active months). Gonadosomatic index was low from September to March. It started increasing from April and remained at highest level from May to August. Environmental factors play an important role in body physiology, oxidation, and intermediary metabolism and gonadal activity of all the vertebrates, including reptiles. The annual variation in physiology is pivotal to help animals cope with seasonal stressors.
Key words: Seasonal variation, Reptiles, leucocytes, Annual rhythm, lymphoid organs