Abstract
Almost all lizard families in the pleurodont clade share the same XY system. This system was meticulously studied in Anolis carolinensis, where it shows a highly degenerated Y chromosome and a male-specific X chromosome dosage compensation mechanism. Corytophanids (casque-headed lizards) have been proposed as the only family in the pleurodont clade to lack the XY system. In this study, we worked with extensive genomic and transcriptomic data from Basiliscus vittatus, a member of the Corytophanidae family that inhabits the tropical rainforests of Mexico. We confirmed that B. vittatus underwent a sex chromosome system turnover, which consisted in the loss of the pleurodont XY system and the gain of a new pair of XY chromosomes that are orthologous to chicken chromosome 17. We estimated the origin of the sex chromosome system to have occurred ∼63 Ma in the ancestor of corytophanids. Moreover, we identified 12 XY gametologues with particular attributes, such as functions related to the membrane and intracellular trafficking, very low expression levels, blood specificity, and incomplete dosage compensation in males.
Highlights
Reptile species have undergone numerous sex determination systems turnovers, with lineages shifting more frequently from environmental-dependent sex determination (ESD) to genotypic sex determination (GSD) (Pennell et al 2018)
We observed the same genomic read coverage in both sexes for the orthologous sequences to the X chromosome in A. carolinensis, this chromosome is present in two copies in the male and female genomes of B. vittatus and it is indistinguishable from any other autosome
Autosomes and the pleurodont X chromosome in B. vittatus were assembled on the basis of Anolis carolinensis reference genome
Summary
Reptile species have undergone numerous sex determination systems turnovers, with lineages shifting more frequently from environmental-dependent sex determination (ESD) to genotypic sex determination (GSD) (Pennell et al 2018). Reptiles are an ideal taxon to test predictions on the mechanisms of sex determination because ESD and various types of GSD are present in closely related species of the same lineage and sex determination systems can be both of recent origin (100Myr old) (Bachtrog et al 2014).
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