Offspring Sex Is Not Determined by Gestation Temperature in a Viviparous Lizard(Eremias multiocellata) from the Desert Steppe of Inner Mongolia

Sex-determining systems show a striking diversity not only among species, but also among popula tions. In reptiles, sex-determina tion is a continuum, from tempera ture-dependent sex determination(TSD) to genetic sex determination(GSD).The multi-ocellated racerunner(Eremias multiocellata)is reported to be a cryptic ZZ/ZW chromosomal TSD species, with male-biased sex ratios at high temperatures in two Gansu populations. However, the generality of the sex-determining pattern in different populations of this species remains unclear. To investigate the mode of sex determina tion in a popula tion of E.multiocellata from the desert steppe of Inner Mongolia,we first identified sex chromosomes via comparative genomic hybridization(CGH). We then conducted a thermal manipulation experiment to determine the effect of gestation temperature on offspring sex ratios.From the CGH studies we found that lizards from the Inner Mongolia population possessed ZZ/ZW sex chromosomes. However, our thermal manipulation experiment showed that gestation temperature did not affect the sex ratio of neonates in this population. In combination, these results rule out TSD in the Inner Mongolia population of E. multiocellata, and suggest that there is widespread geographic variation in the sexdetermining system of this species.