Identification Of Sex Chromosome In A Viviparous Lizard Eremias Multiocellata By Means Of Comparative Genomic Hybridization

Reptiles employ most diversified sex determination systems including genotypic sex determination (GSD) and environmental sex determination (ESD) which is mostly regarded as temperature-dependent sex determination (TSD). Eremias multiocellata is a viviparous lizard and was confirmed to exhibit temperature-dependent sex determination (TSD) in previous experiments. Conventional Giemsa staining under light microscopic examination showed the karyotype of this species is2n=36I+2m without heteromorphic sex chromosomes detected. However, a highly differentiated female sex specific chromosome W which is homomorphic with Z chromosome was found in the present study by comparative genomic hybridization (CGH), which was considered as a high resolution cytogenetic method. These results suggested that Eremias multiocellata is the first viviparous reptile reported to have both TSD and ZW heterogametic sex chromosomes. Elevation of Tianzhu is1500m higher than Minqin,and incubation experiments showed sex ratio of offsprings of this population biased differentially from Minqin population, however genomic comparison by chromosome painting approach between two populations (Minqin and Tianzhu) of Eremias multiocellata exhibited no significant difference. We reckon Eremias multiocellata to be a transition species between TSD and GSD, and hypothesize these traits evolved orderly from TSD to GSD and viviparity during its life history.