Meeting Abstract
Temperature-dependent sex determination (TSD) is a mechanism by which temperature determines the sex of the embryo. Experimental studies with turtles presenting TSD suggest moisture conditions during egg incubation may influence sex determination, showing that wetter substrates produce males, whereas drier substrates produce females. This relationship is consistent with findings from field studies where sex ratios obtained from Loggerhead turtle (Caretta caretta) nesting beaches show a poor relationship with temperature recorded in situ. However, when the effect of moisture (particularly rainfall) is added to nest temperatures, sex ratio trends become more predictable. Still, the mechanisms by which environmental factors (temperature or moisture) affect sex determination remain unknown. It has been suggested that embryonic sex differences are initially determined by different patterns of nuclear DNA methylation. Evidence supporting this hypothesis was found in the American alligator (Alligator mississippiensis), where males showed elevated aromatase promoter methylation compared to females, while the opposite occurred in the Sox9 promoter, displaying an inverse relationship between methylation and expression levels. These results led us to hypothesize that moisture can influence sex ratios in turtles via an epigenetic mechanism regulating the expression of sex determination/differentiation genes. Here we tested the effects of moisture on sex determination by exploring DNA methylation in the gonadal aromatase and Sox9 promoter of the freshwater turtle Trachemys scripta. Such a mechanism would affect gene expression, and hence sex ratios, in species with environmental sex determination.
