Meeting Abstract
Experimental studies with turtles known to have temperature-dependent sex determination (TSD), a form of environmental sex determination, suggest that moisture conditions during incubation may influence development and sex determination. Wetter substrates produce more males, whereas drier substrates produce more females. These results are consistent with findings in the field that sex ratios obtained from Loggerhead turtle (Caretta caretta) nesting beaches show a poor relationship with temperatures recorded in situ and more males were found in wetter years. When the relative moisture levels are considered with nest temperatures, sex ratio trends become more predictable. In this study, we used the freshwater turtle Trachemys scripta to test the effect of moisture on (i) embryonic growth (ii) sex ratio and (iii) gene expression and methylation patterns of two important sex determining genes, Sox9 and aromatase. We found an effect of incubation moisture on the embryonic development reflected in growth rate and sex ratio. Gene expression analysis showed a dimorphic expression pattern between males and females of aromatase and Sox9, where the first was expressed only in females and the latter only in male gonads. Furthermore, we found a sex-specific methylation pattern in the aromatase promoter that is consistent with the expression patterns. To our knowledge, this is the first study to address the effect of moisture at genetic and epigenetic levels in systems active during TSD.
