Embryonic and Gonadal Development of the Chinese Three-keeled Pond Turtle, Mauremys Reevesii

Abstract

Temperature-dependent sex determination (TSD) is a mechanism in which environmental temperature rather than innate zygotic genotype determines the fate of sexual differentiation during embryonic development. The Chinese three-keeled pond turtle, Mauremys reevesii, has TSD and can thus be compared to other TSD species to elucidate the molecular basis underlying this mechanism. Nevertheless, neither embryogenesis nor gonadogenesis has been described in this species. Here, we investigated the chronology of normal embryonic development and gonadal structures in M. reevesii under both female- and male-producing incubation temperatures (FPT or MPT, respectively). External morphology remained indistinct between the two temperature regimes throughout the studied embryonic stages. However, the sexual differentiation of gonadal structures began earlier in the embryos at FPT than at MPT. Moreover, the offset of the thermosensitive period, at which the gonadal structures often remain sexually undifferentiated, did not occur at the same stage at FPT and MPT. In ovo experiments are particularly important for understanding the functional roles of genes involved in TSD, and the present study provides the basis required for designing such developmental studies in M. reevesii.