Sex Chromosome Turnover in Bent-Toed Geckos (Cyrtodactylus)

Abstract

Lizards and snakes (squamates) are known for their varied sex determining systems, and gecko lizards are especially diverse, having evolved sex chromosomes independently multiple times. While sex chromosomes frequently turnover among gecko genera, intrageneric turnovers are known only from Gekko and Hemidactylus. Here, we used RADseq to identify sex-specific markers in two species of Burmese bent-toed geckos. We uncovered XX/XY sex chromosomes in Cyrtodactylus chaunghanakwaensis and ZZ/ZW sex chromosomes in Cyrtodactylus pharbaungensis. This is the third instance of intrageneric turnover of sex chromosomes in geckos. Additionally, Cyrtodactylus are closely related to another genus with intrageneric turnover, Hemidactylus. Together, these data suggest that sex chromosome turnover may be common in this clade, setting them apart as exceptionally diverse in a group already known for diverse sex determination systems.

Lizards as Model Organisms of Sex Chromosome Evolution: What We Really Know from a Systematic Distribution of Available Data?

“…The evolutionary variability of sex determination systems in lizards goes beyond transitions between TSD and GSD and may involve changes of the sex chromosome pair. Sex-determining loci may shift among different chromosomes or a new master sex-determining gene may emerge in a new pair and an extensive sex chromosome turnover has been documented in Gekkonidae and Pleurodonta [ 15 , 131 , 132 ]. For example, the family Gekkonidae is supposed to have an ancestral TSD which is retained in some lineages and shows multiple switches to both male and female heterogamety [ 76 , 78 ].…”

“…For example, the family Gekkonidae is supposed to have an ancestral TSD which is retained in some lineages and shows multiple switches to both male and female heterogamety [ 76 , 78 ]. In the genera Cyrtodactylus , Hemidactylus and Gekko male and female heterogamety may also co-occur, suggesting that sex chromosome turnover may also contribute to interspecific diversification [ 15 , 76 , 110 , 133 ].…”

“…For example, the conserved ZW pair in birds shows no homology with the XY of mammals or the snake ZW pair [ 135 , 136 ]. Non-homology of sex chromosomes has been demonstrated also between most main lizard evolutionary lineages, as well as within families showing sex chromosome turnover and multiple shifts between GSD and TSD (e.g., References [ 14 , 15 , 78 , 132 ]). Nevertheless, recent studies highlighted the occurrence of partial homologies between the Z chromosome of Gekko hokouensis , the avian Z chromosome, the X chromosome of giant musk turtles of the genus Staurotypus .…”

“…The growing interest in lizard sex determination and sex chromosome systems produced in recent years a sensible increase of the available data on different taxonomic groups (e.g., References [ 12 , 13 , 14 , 15 , 16 , 17 ]), which might be useful to provide novel insights on the phylogenetic distribution of different systems.…”

Remnant of Unrelated Amniote Sex Chromosomal Linkage Sharing on the Same Chromosome in House Gecko Lizards, Providing a Better Understanding of the Ancestral Super-Sex Chromosome

“…Gecko lizards appear to exhibit an unusually high frequency of turnovers in SDSs during their evolutionary process, creating variability in sex determination under the ‘evolutionary trap hypothesis’ [ 36 , 46 ]. Repeated turnovers of SDS in the gecko lizards provide opportunities to better understand the evolutionary forces and processes driving sex chromosome transitions [ 47 ]. Accordingly, gecko lizard sex determination is labile, and Hemidactylus exhibits intrageneric transitions.…”