BOWDEN, R.M.*; EWERT, M.A.; LIPAR, J.L.; NELSON, C.E.: Hormones in Yolk Layers and Offspring Sex Ratios Vary Seasonally in Turtles
The presence of hormones in yolks of freshly laid eggs has recently been described in reptiles. These hormones are probably of maternal origin. Their potential to influence offspring sex may be enhanced by temperature-dependent sex determination. Profiles of circulating hormones have been described for several temperate turtles. There appears to be a general pattern to the seasonal oscillations in testosterone (T), progesterone (P), and estradiol (E2). To determine whether this pattern is represented in egg yolks, we measured T, P, and E2 concentrations via radioimmunoassay in three layers of yolk from eggs of early and late nesting female painted turtles (Chrysemys picta). Also, we extracted small yolk biopsies to measure T and E2. We compared the hormone concentrations from the biopsied eggs to the sex ratio of their clutchmates to determine whether maternally-derived yolk hormones influence offspringsex. T and P concentrations were highest in the exterior layer of yolks and E2 concentrations were lowest. The same layered pattern of hormones occurred in red-eared sliders (Trachemys scripta elegans). Yolk E2 concentrations varied seasonally in painted turtles, with low levels in all yolk layers early in the nesting season and higher levels in all layers later on. Neither T nor P exhibited significant seasonal variation. In the yolk biopsies, there also was seasonal variation in E2, but not in T. We found a significant correlation with sex ratio for E2, but not for T.
