ELF, P.K.*; ROBERT, K.; THOMPSON, M.; FIVIZZANI, A.; University of Minnesota Crookston; University of Sydney; University of Sydney; University of North Dakota: Temperature-dependent sex determination in a viviparous lizard: what role do hormones play?
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 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 implicated in the process of sex determination in some TSD species, but little is known about the involvement of sex steroids in E. tympanum. In preliminary studies we found that circulating maternal plasma hormones appeared to be more sensitive to temperature than those in the yolk, and in fact male circulating plasma hormones demonstrated a similar phenomenon. To further investigate these findings three experiments were designed to determine the dynamics of the hormonal environment of developing embryos and temperature effects on plasma hormones. In the first experiment yolk and plasma samples were collected from pregnant skink females maintained at the predominantly male (30oC) and female (20oC)producing temperatures and these were assayed for androstenedione, DHT, corticosterone, estradiol and testosterone. In the second experiment, male skinks were incubated at either the male or female producing temperature for a week then half from each group were switched to the alternate temperature and plasma was sampled from all animals and hormones measured at 24 and 48 hours after the switch. In the third experiment pregnant females incubated at the male producing temperature were treated with estradiol during the thermosensitive period to accomplish sex reversal of the embryos. Here we present outcomes of these experiments.
