ELF, P.K.*; LANG, J.W.; FIVIZZANI, A.J.: Dynamics of Exogenous ³H Estradiol Uptake in Turtle Eggs During Development.

Sex steroids in the egg yolks of reptiles with TSD (temperature-dependent sex determination) likely affect sex determination and differentiation in some lizards, turtles and crocodilians. In order to determine yolk estradiol (E) dynamics during embryonic development, ³H-estradiol (³H-E) was applied to painted turtle, Chrysemys picta, eggs incubated at male (26^o) and female (30^o) producing temperatures. Developing embryos were staged and yolk material collected. ³H-E incorporation into yolks, whole embryos and embryonic organs was determined using liquid scintillation spectrophotometry. Yolk ³H-E levels decrease during development, and show significant differences between male vs. female incubation temperatures. Significant differences in ³H-E incorporation into male and female developing gonads and brains were also apparent. These results parallel patterns documented previously in endogenous E decline during development in this and other TSD reptiles, and provide additional support for the hypothesis that yolk hormones mediate TSD in these species.