Concentrations of steroid hormones in layers and biopsies of chelonian egg yolks.

The actions of circulating hormones, although relatively well understood for adults, are largely unknown for their developing embryos. Transfer of maternal hormones to the egg is known to occur in oviparous species, and recently the presence of hormonally heterogeneous yolk layers has been described in two avian species. To investigate the possibility of a similar phenomenon occurring in chelonian species, egg yolk layers were analyzed in the painted turtle (Chrysemys picta marginata) and the red-eared slider turtle (Trachemys scripta elegans), two species that exhibit temperature-dependent sex determination. There was a similar pattern of hormonally heterogeneous yolk layers in both species: concentrations of progesterone and testosterone were significantly higher in the external yolk layer while concentrations of 17beta-estradiol were significantly higher in the intermediate and internal layers. This pattern of hormone deposition concurs with previously published studies of plasma hormone profiles from females of temperate-zone turtle species. Yolks of freshly laid eggs were also sampled using a biopsy technique to examine the concordance of early yolk hormone concentrations and offspring sex. No relationship was found between yolk hormone concentrations and individual offspring sex. Previous work showing that maternally derived yolk estradiol concentrations are correlated with female-biased sex ratios was, however, replicated. These findings suggest that offspring sex is influenced, in part, by the maternal hormone environment.