ELF, P.K.*; ROBERT, K.A.; THOMPSON, M.B.; FIVIZZANI, A.J.; University of Minnesota Crookston; University of Sydney; University of Sydney; University of North Dakota: Steroid hormone levels in maternal plasma and yolk during embryonic development in a viviparous TSD reptile
The Australian skink, Eulamprus tympanum, is a viviparous reptile that exhibits temperature-dependent sex determination (TSD). In this system, the pregnant female actively thermoregulates to select the sex of her offspring. The TSD pattern displayed is female-male, with exclusively males produced at 32oC, approximately 75% males at 30oC, and 55% males at 25oC. Sex steroid hormones in the yolks of reptile eggs have been quantified and are implicated in the process of sex determination in some TSD species, and play roles in post-hatch growth and behaviors in some avian species, but nothing is known about the levels of hormones present in the yolk of E. tympanum. In a preliminary study designed to determine the hormonal environment of developing embryos, we collected yolk from pregnant skink females maintained at the predominantly male producing temperature, an intermediate temperature and 20oC. Since circulating plasma hormones would also contribute to the embryonic environment, blood samples were taken from females at the time of yolk collection. The embryos were staged and the yolk and plasma frozen until assay. Measurement of androstenedione, dihydrotestosterone, estradiol and testosterone in both yolk and plasma samples was accomplished by extraction, followed by column separation, and individual hormone fractions were quantified via RIA to determine any temperature effects and correlations between yolk and circulating maternal plasma levels. pelf@mail.crk.umn.edu
