Maternal Plasma and Egg Yolk Testosterone Concentrations during Embryonic Development in Green Anoles (Anolis carolinensis)

Abstract

Sex steroids of presumably maternal origin have been found in avian, crocodilian, and chelonian egg yolks, and they can affect offspring morphology and behavior. The present study reports testosterone (T) levels to which embryos are potentially exposed in the green anole (Anolis carolinensis), a lizard with genotypic sex determination. We documented plasma and yolk T concentrations in adult females, in their developing follicles and eggs, and in freshly oviposited and incubating eggs. Plasma T was higher in reproductively active than in reproductively inactive females. Within reproductively active females, those with a single, large yolking follicle had higher plasma T than those that had one or more shelling, oviductal eggs. Individual females contributed different amounts of T to their yolks, but within females, more mature follicles or eggs consistently had higher yolk T concentrations than did less mature follicles or eggs. Similar to previous research, yolk T concentrations at oviposition were higher in male eggs than in female eggs. However, T levels during incubation did not differ by embryo sex, but rather increased in both male and female eggs. These results suggest that T plays a role in the reproductive physiology of females and potentially in the phenotypic development of their offspring. Furthermore, whereas the yolk T increase observed during follicular maturation is clearly a maternal influence, it remains unclear whether that observed during egg development (i.e., postfertilization) results from a lack of T uptake by the embryo as yolk is absorbed, from embryonic production of T that diffuses into the yolk, or from some combination of these processes. Because lizard embryos are comparatively well developed at oviposition, the assumption that yolk steroids are strictly of maternal origin may require modification, and the possibility that embryos are modulating their own steroid environment needs to be explored.