Development of sexual traits during embryogenesis in an alpine skink with temperature-induced sex reversal

Temperature-induced sex reversal is a poorly understood trait in reptiles, described for only a small number of species. In the Eastern three-lined skink (Bassiana duperreyi), genotypic females exposed to cold temperatures reverse sex and develop as phenotypic males. We characterized embryonic development in B. duperreyi for the first time using eggs from wild communal nests. We observed variation in developmental stage at lay, suggesting females coordinate nesting despite becoming gravid at different times, potentially representing an early evolutionary shift towards viviparity. The development of sexual traits was like that of the other species with temperature-induced sex reversal (Pogona vitticeps). Ovotestes were observed in a small number of individuals regardless of genotypic sex and across all three incubation temperatures (18, 20 and 23°C). Notably, ovotestes were observed later in development in B. duperreyi, potentially representing differences in the influence of temperature on sexual development between the two species. Genotypic females also displayed temporary pseudohermaphroditism, which is characterized by the simultaneous presence of ovaries and bilobed hemipenes. These data represent foundational information for B. duperreyi required to support future research on the molecular underpinnings of sex reversal.