Sex steroids in green anoles (Anolis carolinensis): uncoupled maternal plasma and yolking follicle concentrations, potential embryonic steroidogenesis, and evolutionary implications.

The sex steroids testosterone (T) and estradiol-17beta (E2) play important roles in vertebrate reproduction and development. However, little is known about the relationship between plasma steroid levels (which can influence reproductive function) and yolk steroid levels (which can influence embryonic development) in oviparous species. Therefore, we examined the extent to which T and E2 are coupled in plasma and yolking follicles in adult females and explored the dynamics of yolk and embryo steroid content during egg incubation in green anoles (Anolis carolinensis). T and E2 levels were determined for the plasma and yolking follicles of breeding females and for whole embryos and yolks at several developmental stages by radioimmunoassay. Plasma and yolk concentrations of T and E2 were not correlated. On average, plasma T was only 30% that of plasma E2, but yolking follicle T was over 600% that of yolking follicle E2. Total yolk T and E2 content generally declined over the course of incubation. However, yolk T was an order of magnitude higher than yolk E2, and it showed a secondary peak in magnitude after approximately 75% of incubation was completed. Similarly, total embryonic T content rose by over 400% in the latter half of incubation whereas E2 did not change. These results demonstrate that plasma and yolking follicle steroid levels produced by breeding females can be uncoupled. Furthermore, embryos themselves may begin producing T, but likely not E2, during the latter stages of incubation. Thus, steroid exposure may be independently shaped by selection to serve both reproductive and developmental functions.