Yolk hormone levels in the eggs of snapping turtles and painted turtles.

Abstract Although yolk steroids appear to play important roles in the development, growth, and behavior of some birds, their effects in oviparous reptiles are largely unknown. These investigations were initiated to determine initial levels of steroid hormones in the yolks of eggs from two turtle species. Clutches of snapping turtle ( Chelydra serpentina ) and of painted turtle ( Chrysemys picta ) eggs were collected and individual egg yolks were analyzed for estradiol-17β (E 2 ) and testosterone (T) using specific RIAs. E 2 and T levels differed significantly between species, the mean E 2 value in snapping turtles was 2.78±0.095 (ng/g) compared to 0.89±0.064 (ng/g) for painted turtles, and the mean value for T in snapping turtle yolks was 2.56±0.098 (ng/g) compared to 0.68±0.045 (ng/g) for painted turtles. In addition, E 2 levels were greater than T levels in both species. Within each species, there were significant differences among clutches from different females. E 2 levels in the snapping turtle yolks varied from a clutch mean of 1.38 to 4.55 ng/g and in painted turtles, the clutch means for E 2 varied from 0.34 to 1.34 ng/g. T levels demonstrated similar phenomena within species, with levels in snapping turtles varying from a clutch mean of 0.68 to 4.71 ng/g. Painted turtle levels of T varied from a clutch mean of 0.22 to 0.72 ng/g. There were also significant differences in the E 2 /T ratio, however, E 2 /T ratios did not differ between species. Painted turtle follicles of different sizes showed significant differences in levels of both E 2 and T, and these differences may reflect differing deposition patterns of these steroids in the egg yolk of this turtle during vitellogenesis. The differences in E 2 and T concentration reported here could have important implications for development, growth, and behavior in oviparous reptilian species.