Control of oocyte recruitment and selection in podarcis sicula, the italian wall lizard

Reproduction in lizards, as in other vertebrates, is regulated by a complex interplay of ambient and endogenous factors. Changes in temperature and photoperiod in particular modulate the release of gonadotropin and ovarian factors and these, directly or indirectly, control different ovarian activities. In this review, mechanisms regulating oocyte recruitment and selection will be discussed and integrated with original data on the Italian wall lizard Podarcis sicula. In particular, starting from the colonization of the gonadal anlage by the primordial germ cells we will show how oocytes and follicles recruitment proceed throughout the year and how these two processes are influenced by exogenous FSH, oestradiol and progesterone in different periods of the ovarian cycle. In addition, by reporting results of unilateral ovariectomy (ULO), follicle ablation (ULA) and follicle puncture (PU) experiments we will demonstrate that clutch size in this species is probably regulated by two ovarian factors, one inhibiting and the other promoting the recruitment of new primary follicles from the pool of prefollicular oocytes. We hypothesize the former factor being released systemically by the oocyte to stop follicle recruitment by a dose dependent mechanism. The latter factor would be produced by the follicle cells and would have a promoting effect by acting at a strictly local level. This control mechanism cannot be bypassed by administering gonadotropins or steroids, by placing the animals at high temperature or by exposure to cadmium, a known endocrine disrupter that promotes prefollicular oocyte recruitment.