Abstract: 14

INVESTIGATION INTO THE USE OF SILASTIC IMPLANTS TO MANIPULATE YOLK STEROID CONCENTRATIONS.

Matthew E. Wilson^{1 *}, Fredric J. Janzen II¹ , Stephen P. Ford.^{1 *}
Iowa State University, Ames, IA ¹

It is believed that steroids play a key role in temperature dependent sex determination, mediating the effect of temperature on gonadal development. Trachemys scripta elegans females deposit significant amounts of testosterone (T₄) into the yolk of their eggs. This opens the possibility that compounds like phytoestrogens and steroid-like pollutants injested or absorbed by females could end up in the yolk, impacting embryonic development. It is not surprising that turtles would deposit T₄, as it can serve as a substrate for aromatization to estradiol-17 (E₂) or reduction to dihydrotestosterone (DHT). To further investigate the role of yolk steroids on turtle development we wanted to establish a method for modulating yolk steroid concentration, by elevating systemic levels in the female. This was accomplished by subcutaneous placement of implants containing no steroid, or 2.5 mg of T₄, E₂ or DHT into T. s. elegans females (8/group) at the start of September and again 4 weeks later. We sampled blood from the brachial sinus immediately prior to implantation and every 2 weeks until hibernation, which began in November. Females were then maintained at 6°C, brought out of hibernation in April and again blood sampled. Prior to hibernation circulating levels of steroids increased markedly (P<.05) for each group (100 fold for T₄, 4 fold for DHT and 8 fold for E₂) when compared to preimplantation values. By Spring, values had returned to baseline for all 3 steroid treated groups. A subset of control (n=5) and T₄ (n=4) turtles were sacrificed in May to collect mature follicles. T₄ concentrations were greater (P<.05) in yolk from T₄-treated females compared to those from controls (215±28 vs 37±8 pg/mg). These data demonstrate the potential of using subcutaneous implants impregnated with steroids as a method for manipulating yolk steroid concentrations.

    This abstract is being presented on Sunday, August 1 at 8:00 AM to 10:15 AM at CUB 2nd Floor Ballroom.