Evolutionary Insights of the ZW Sex Chromosomesin Snakes: A New Chapter Added by the AmazonianPuffing Snakes of the Genus Spilotes.

Affiliation

Instituto Nacional de Pesquisas da Amazônia, Coordenação de Biodiversidade, Laboratory of Animal Genetics, Av. André Araújo 2936, Petrópolis, Manaus CEP: 69067-375, AM, Brazil. [Email]

Abstract

Amazonian puffing snakes (Spilotes; Colubridae) are snakes widely distributed in the Neotropical region. However, chromosomal data are scarce in this group and, when available, are only limited to karyotype description using conventional staining. In this paper, we focused on the process of karyotype evolution and trends for sex chromosomes in two Amazonian Puffer Snakes (S.pulllatus and S.sulphureus). We performed an extensive karyotype characterization using conventional and molecular cytogenetic approaches. The karyotype of S.sulphureus (presented here for the first time) exhibits a 2n = 36, similar to that previously described in S.pullatus. Both species have highly differentiated ZZ/ZW sex chromosomes, where the W chromosome is highly heterochromatic in S.pullatus but euchromatic in S.sulphureus. Both W chromosomes are homologous between these species as revealed by cross-species comparative genomic hybridization, even with heterogeneous distributions of several repetitive sequences across their genomes, including on the Z and on the W chromosomes. Our study provides evidence that W chromosomes in these two species have shared ancestry.

Keywords

Amazonian snakes,CGH,advanced snakes,heterochromatin,repeat accumulation,sex chromosomes,