title: Evolutionary stability of sex chromosomes in snakes.
abstract: Amniote vertebrates possess various mechanisms of sex determination, but their variability is not equally distributed. The large evolutionary stability of sex chromosomes in viviparous mammals and birds was believed to be connected with their endothermy. However, some ectotherm lineages seem to be comparably conserved in sex determination, but previously there was a lack of molecular evidence to confirm this. Here, we document a stability of sex chromosomes in advanced snakes based on the testing of Z-specificity of genes using quantitative PCR (qPCR) across 37 snake species (our qPCR technique is suitable for molecular sexing in potentially all advanced snakes). We discovered that at least part of sex chromosomes is homologous across all families of caenophidian snakes (Acrochordidae, Xenodermatidae, Pareatidae, Viperidae, Homalopsidae, Colubridae, Elapidae and Lamprophiidae). The emergence of differentiated sex chromosomes can be dated back to about 60 Ma and preceded the extensive diversification of advanced snakes, the group with more than 3000 species. The Z-specific genes of caenophidian snakes are (pseudo)autosomal in the members of the snake families Pythonidae, Xenopeltidae, Boidae, Erycidae and Sanziniidae, as well as in outgroups with differentiated sex chromosomes such as monitor lizards, iguanas and chameleons. Along with iguanas, advanced snakes are therefore another example of ectothermic amniotes with a long-term stability of sex chromosomes comparable with endotherms.
authors.affiliation: Faculty of Science, Department of Ecology, Charles University in Prague, Viničná 7, 12844 Praha 2, Czech Republic.
authors.forename: Michail
authors.initials: M
authors.lastname: Rovatsos
authors.affiliation: Faculty of Science, Department of Ecology, Charles University in Prague, Viničná 7, 12844 Praha 2, Czech Republic.
authors.forename: Jasna
authors.initials: J
authors.lastname: Vukić
authors.affiliation: Natural History Museum of Crete, University of Crete, Knossou Avenue, 71409 Irakleio, Crete, Greece.
authors.forename: Petros
authors.initials: P
authors.lastname: Lymberakis
authors.affiliation: Faculty of Science, Department of Ecology, Charles University in Prague, Viničná 7, 12844 Praha 2, Czech Republic lukas.kratochvil@natur.cuni.cz.
authors.forename: Lukáš
authors.initials: L
authors.lastname: Kratochvíl
mesh_terms: D000818:Animals; D005075:Biological Evolution; D005260:Female; D008116:Lizards / Q000235:genetics; D008297:Male; D010802:Phylogeny; D012730:Sex Chromosomes; D019849:Sex Determination Processes / Q000235:genetics; D012911:Snakes / Q000235:genetics*
keywords: evolution; reptiles; sex chromosomes; sex determination; snakes