Thermal and Hormonal Effects on Gene Expression and Development in the Red-Eared Slider Turtle

Abstract

Sex determination refers to the process by which cues from genes (genotypic sex determination) or environmental conditions (environmental sex determination) trigger bipotential gonads to develop into either ovaries or testes. Temperature-dependent sex determination (TSD) is a well-studied form of environmental sex determination in reptiles. The red-eared slider turtle (Trachemys scripta elegans) exhibits a form of TSD where cool incubation temperatures produce males and warm incubation temperatures produce females. In species with TSD, gonadal differentiation is regulated by network of genes and hormones that induce male or female development. TSD is most frequently studied in the laboratory using constant male and female incubation temperatures, which fail to capture the variability that organisms experience in the wild. We use ecologically relevant laboratory incubations to better understand the underlying mechanisms organizing the sex-determining process in T. scripta. Fluctuating incubations and exogenous hormones are used to produce ecologically relevant expression profiles for sex-determining genes and to decouple the effects of temperature and hormone environment on gonadal differentiation. This research represents the first time that fluctuating temperatures and hormones have been used in concert to characterize the molecular mechanisms underlying TSD and highlights the value of using laboratory conditions that more closely mimic environmental conditions.