Concentrations of steroid hormones in layers and biopsies of chelonian eggyolks

The actions of circulating hormones, although relatively well understood fo r adults, are largely unknown for their developing embryos. Transfer of mat ernal hormones to the egg is known to occur in oviparous species, and recen tly the presence of hormonally heterogeneous yolk layers has been described in two avian species. To investigate the possibility of a similar phenomen on occurring in chelonian species, egg yolk layers were analyzed in the pai nted turtle (Chrysemys picta marginata) and the red-eared slider turtle (Tr achemys scripta elegans), two species that exhibit temperature-dependent se x determination. There was a similar pattern of hormonally heterogeneous yo lk layers in both species: concentrations of progesterone and testosterone were significantly higher in the external yolk layer while concentrations o f 17 beta -estradiol were significantly higher in the intermediate and inte rnal layers. This pattern of hormone deposition concurs with previously pub lished studies of plasma hormone profiles from females of temperate-zone tu rtle species. Yolks of freshly laid eggs were also sampled using a biopsy t echnique to examine the concordance of early yolk hormone concentrations an d offspring sex. No relationship was found between yolk hormone concentrati ons and individual offspring sex. Previous work showing that maternally der ived yolk estradiol concentrations are correlated with female-biased sex ra tios was, however, replicated. These findings suggest that off-spring sex i s influenced, in part, by the maternal hormone environment. (C) 2001 Academ ic Press.