The rise and fall of differentiated sex chromosomes in geckos

Abstract

Amniotes possess variability in sex determination, ranging from environmental sex determination to genotypic sex determination with differentiated sex chromosomes. Differentiated sex chromosomes have emerged independently several times. Their noteworthy convergent characteristic is the evolutionary stability, documented among amniotes in mammals, birds, and some lineages of lizards, snakes and turtles. Combining the analysis of multiple partial transcriptomes with the comparison of copy gene numbers between male and female genomes, we uncovered partial gene content of the highly differentiated ZZ/ZW sex chromosomes in the gecko genus Paroedura. The differentiated ZZ/ZW sex chromosomes of these geckos share genes with the part of the chicken chromosome 4 homologous with the XX/XY sex chromosomes of viviparous mammals and the ZZ/ZW sex chromosomes of lacertid lizards, as well as with the chicken chromosome 15, homologous with the XX/XY sex chromosomes of iguanas and ZZ/ZW sex chromosomes of softshell turtles. Along with other analogous cases, this finding reinforces the observation that particular chromosomes are repeatedly coopted for the function of sex chromosomes in amniotes. Notably, according to the phylogenetic distribution, the subclade of the genus Paroedura represents a rare case of the reversal of the for a considerable evolutionary time highly differentiated ZZ/ZW sex chromosomes back to poorly differentiated state.

Chromosome Painting Does Not Support a Sex Chromosome Turnover in Lacerta agilis Linnaeus, 1758

“…The fact that the LST_L probe painted 5 chromosomes in L. agilis as well as in L. strigata indicates that these 2 species share the same sex chromosome system. If L. agilis had experienced a hypothetical sex chromosome turnover, leading to the formation of neo-sex chromosomes derived from LAG5, and the original lacertid Z chromosome had returned to the autosomal state (as in the sex chromosome turnover in the lineage of the genus Paroedura , Gekkonidae, which includes P. picta and several other species [Koubová et al, 2014;Rovatsos et al, 2019a]), the LST_L probe would have hybridized with 6 chromosomes in L. agilis (3 homologous pairs). The hy- bridization of the LST_L probe with 5 chromosomes was observed in multiple complete metaphases, which confirms the reliability of our results.…”

A mobile sex-determining region, male-specific haplotypes, and rearing environment influence age at maturity in Chinook salmon

“…Translocation of the sex-determining region among chromosomes has important implications for the evolutionary potential of populations. Movement of the sex-determining region can cause once-differentiated sex chromosomes to become similar again (Rovatsos et al 2019). Alternatively, translocation and could enhance adaptation through capture and subsequent sex-linkage of genes (Tennessen et al 2018).…”

How to identify sex chromosomes and their turnover

“…Therefore, elevated SNP density in the heterogametic sex can be used to infer sex‐linked regions when mapped to a reference genome generated from the homogametic sex (Darolti et al, ; Vicoso et al, ; Wright et al, ). In contrast, in regions where the Y has largely degenerated, we expect SNP density to be lower in males when mapped to a female genome as the X is effectively hemizygous in males (Rovatsos, Farkačová, Altmanová, Johnson Pokorná, & Kratochvíl, ; Rovatsos, Rehák, Velenský, & Kratochvíl, ; Rovatsos, Vukić, & Kratochvíl, ). Therefore, an absence of SNPs in females can indicate X‐linked sequences.…”