OOCYTE AND FOLLICULAR DEVELOPMENT IN IMMATURE EASTERN FENCE LIZARDS

The early stages of oogenesis and follicular organization occur in utero in mammals. In contrast, the early stages of oogenesis and follicular organization in reptiles occur during postnatal development. The increased accessibility to individuals undergoing these processes and the relatively large, yolk-laden oocytes make reptiles, such as lizards, an especially useful model for studying reproductive development. Seasonal cycles of oocyte and follicular maturation have been described in adults of numerous species of lizards; however, few studies have examined these processes in immature lizards. In this study, immature female Eastern Fence Lizards (Sceloporus undulatus) were collected monthly over a 2-year-period. The gonads and reproductive tracts were photographed in situ at 1–5x magnification for examination at the gross anatomical level. Left ovaries were removed, embedded in paraffin wax, sectioned on a rotary microtome, and stained using Masson’s trichrome. Ovarian and follicular stages were assigned to each lizard based on previously established histological criteria. Relationships between body size, capture date, and ovarian and follicular developmental stage were evaluated. Ovarian stage was assigned based on the most advanced follicle. Most ovaries were comprised of follicles of varying stages. As expected, there was a positive relationship between body size and ovarian stage; however, the relationship between time of year and ovarian stage is more complex when considering immature lizards of different sizes. Larger, yet still immature, lizards have a greater proportion of follicles at an advanced stage, in comparison to smaller individuals. Previous studies and our unpublished observations suggest that female Sceloporus undulatus obtain reproductive maturity within 1-2 years, depending on the timing of hatching and growth rates. Our data suggests that lizards that do not attain sexual maturity in their first year exhibit a prolonged period of pubescence, as indicated by advanced stages of previtellogenic follicles