title: Stable Cretaceous sex chromosomes enable molecular sexing in softshell turtles (Testudines: Trionychidae).
abstract: Turtles demonstrate variability in sex determination ranging from environmental sex determination (ESD) to highly differentiated sex chromosomes. However, the evolutionary dynamics of sex determining systems in this group is not well known. Differentiated ZZ/ZW sex chromosomes were identified in two species of the softshell turtles (Trionychidae) from the subfamily Trionychinae and Z-specific genes were identified in a single species. We tested Z-specificity of a subset of these genes by quantitative PCR comparing copy gene numbers in male and female genomes in 10 species covering the phylogenetic diversity of trionychids. We demonstrated that differentiated ZZ/ZW sex chromosomes are conserved across the whole family and that they were already present in the common ancestor of the extant trionychids. As the sister lineage, Carettochelys insculpta, possess ESD, we can date the origin of the sex chromosomes in trionychids between 200 Mya (split of Trionychidae and Carettochelyidae) and 120 Mya (basal splitting of the recent trionychids). The results support the evolutionary stability of differentiated sex chromosomes in some lineages of ectothermic vertebrates. Moreover, our approach determining sex-linkage of protein coding genes can be used as a reliable technique of molecular sexing across trionychids useful for effective breeding strategy in conservation projects of endangered species.
authors.affiliation: Faculty of Science, Charles University, Department of Ecology, Viničná 7, 12844 Praha 2, Czech Republic.
authors.forename: Michail
authors.initials: M
authors.lastname: Rovatsos
authors.affiliation: Turtle Island, Turtle Conservation Center, Am Katzelbach 98, 8054 Graz, Austria.
authors.forename: Peter
authors.initials: P
authors.lastname: Praschag
authors.affiliation: Museum of Zoology, Senckenberg Dresden, A. B. Meyer Building, 01109 Dresden, Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Fritz
authors.affiliation: Faculty of Science, Charles University, Department of Ecology, Viničná 7, 12844 Praha 2, Czech Republic.
authors.forename: Lukáš
authors.initials: L
authors.lastname: Kratochvšl
mesh_terms: D060105:Animal Shells / Q000033:anatomy & histology; D000818:Animals; D005075:Biological Evolution; D002874:Chromosome Mapping; D005260:Female; D059647:Gene-Environment Interaction; D049690:History, Ancient; D008297:Male; D010802:Phylogeny; D012335:RNA, Ribosomal / Q000235:genetics* / Q000266:history; D012730:Sex Chromosomes / Q000737:chemistry*; D019849:Sex Determination Processes; D014426:Turtles / Q000033:anatomy & histology / Q000145:classification / Q000235:genetics*
chemical_list: D012335:RNA, Ribosomal