SGER: Plasma and Yolk Hormones in a Viviparous TSD Lizard

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Sex determination in crocodilians, most turtles and some lizard species is regulated by egg incubation temperature, a phenomenon termed temperature-dependent sex determination (TSD).The discovery that TSD occurs in some species of viviparous skinks was perhaps the most surprising and intriguing development in the field of TSD in recent years and merited an article in Nature (Robert and Thompson, 2001). Though the underlying mechanisms of TSD remain elusive and the process responsible for converting an environmental temperature cue to a molecular signal is unknown, estradiol (E2) has been implicated in the sex determination process. This research will examine the hormone characteristics of the viviparous TSD skink, Eulamprys tympanum. In this study, hormone levels for five steroid hormones will be measured in serum or yolk samples from male adults, female adults and developing embryos that have been exposed to different environmental temperatures. Because E. tympanum embryos develop in utero, they are exposed to both their individual yolk hormones, plus those of maternal circulation, this study will document plasma hormone levels in gravid females as well. Because skinks are the only viviparous TSD species known to date, this project will provide valuable insights into the evolution of temperature-dependent sex determination and its mechanisms. Undergraduate students at the University of Minnesota Crookston campus will be involved in this work receiving training in hormone isolation and characterization and also interacting with an international collaborator on the project.