Follicular dynamics and germinal bed activity during the annual ovarian cycle of the lizard, Calotes versicolor

Abstract

Changes in size frequency distribution of extrastromal follicles, atretric follicles (AF), and the number of oogonia, oocytes, and primordial follicles in the ovaries are studied in Calotes versicolor during its annual reproductive cycle. Extrastromal follicles were graded into stages I to VI based on their diemeter. Stage I (0.5-0.75 mm) follicles are found throughout the year. The recruitment of stage II (0.76-1 mm) and stage III (1.10-2 mm) follicles occurs during December and March, respectively. Follicles of stage I-III are found in greater number in May. Stage IV vitellogenic follicles (2.10-3 mm) are recruited in April. Advanced vitellogenic follicles (stage VI) are formed between May and August. From April to August, the ovaries of lizards contain vitellogenic follicles of stages IV or V or VI suggesting that once a set of follicles enters vitellogenic phase there is no recruitment of another set of vitellogenic follicles from previtellogenic follicles until the former ovulates. The presence of vitellogenic follicles and at least two sets of CL in July-August suggest that C. versicolor may oviposit at least three clutches of eggs per season. The clutch size in this lizard varies from a maximum 24 eggs in May to a minimum of 13 eggs in September. The previtellogenic AF are found throughout the year. Atresia is more prevalent in stage III suggesting that these follicles are more prone to become atretic. Interestingly, atresia of vitellogenic follicles occurs rarely. Each ovary in C. versicolor has two germinal beds. The germinal beds contain a greater number of oogonia (536-696), primary oocytes (40-71), and primordial follicles (32-55) during prebreeding and early breeding phases of the ovarian cycle.