Conserved ZZ/ZW sex chromosomes in Caribbean croaking geckos (Aristelliger: Sphaerodactylidae)

Abstract

Current understanding of sex chromosome evolution is largely dependent on species with highly degenerated, heteromorphic sex chromosomes, but by studying species with recently evolved or morphologically indistinct sex chromosomes we can greatly increase our understanding of sex chromosome origins, degeneration and turnover. Here, we examine sex chromosome evolution and stability in the gecko genus Aristelliger. We used RADseq to identify sex‐specific markers and show that four Aristelliger species, spanning the phylogenetic breadth of the genus, share a conserved ZZ/ZW system syntenic with avian chromosome 2. These conserved sex chromosomes contrast with many other gecko sex chromosome systems by showing a degree of stability among a group known for its dynamic sex‐determining mechanisms. Cytogenetic data from A. expectatus revealed homomorphic sex chromosomes with an accumulation of repetitive elements on the W chromosome. Taken together, the large number of female‐specific A. praesignis RAD markers and the accumulation of repetitive DNA on the A. expectatus W karyotype suggest that the Z and W chromosomes are highly differentiated despite their overall morphological similarity. We discuss this paradoxical situation and suggest that it may, in fact, be common in many animal species.

Independent Evolution of Sex Chromosomes in Eublepharid Geckos, A Lineage with Environmental and Genotypic Sex Determination

“…Several species of the genus Paroedura (family Gekkonidae) demonstrate homologous sex chromosomes for 60-92 MY, with a more recent turnover of an inner clade to a novel GSD system [16]. In addition, conserved sex chromosomes were also recently described in the sphaerodactylid genus Aristelliger [24]. The genus Coleonyx with sex chromosomes conserved for around 34 million years as revealed here further demonstrate that several gekkotan subclades have evolutionary stable sex chromosomes.…”

“…Emerging molecular and molecular cytogenetic evidence supports that geckos evolved sex chromosomes independently multiple times. The male-heterogametic sex chromosomes in the genus Coleonyx are partially homologous to GGA1, GGA6 and GGA11 (this study), the XX/XY sex chromosomes of the pygopodid geckos to GGA4q [22], the ZZ/ZW sex chromosomes of the sphaerodactylid genus Aristelliger to GGA2 [24] and the ZZ/ZW sex chromosomes of several species of the genus Paroedura to GGA4p and GGA15 [16]. The sex chromosomes are homologous to the GGAZ syntenic block, both in the phyllodactylid Phyllodactylus wirshingi [23] and the gekkonid Gekko hokouensis [54], two widely diverged species phylogenetically separated by lineages with other sex determination systems [16][17][18][19][20][21][22][23].…”

“…In any case, geckos are an excellent group for testing general hypotheses on sex determination. Molecular cytogenetics and next generation sequencing methodologies (e.g., DNAseq, RNAseq, RADseq) allow us to gradually start resolving the puzzle of the gecko variability in sex determination [7,16,[22][23][24], but data are still scarce in this old, highly diversified lineage encompassing over 2000 currently recognized species [25]. Up to now, the eyelid geckos (family Eublepharidae), the gecko group with phylogenetically important position among squamates, was largely neglected in the application of modern sequencing approaches for the study of sex determination.…”

Independent Evolution of Sex Chromosomes in Eublepharid Geckos, a Lineage with Environmental and Genotypic Sex Determination

“…Emerging molecular and molecular cytogenetic evidence supports that geckos evolved sex chromosomes independently multiple times. The male-heterogametic sex chromosomes in the genus Coleonyx are partially homologous to GGA1, GGA6 and GGA11 (this study), the XX/XY sex chromosomes of the pygopodid geckos to GGA4q [20], the ZZ/ZW sex chromosomes of the sphaerodactylid genus Aristelliger to GGA2 [22] and the ZZ/ZW sex chromosomes of several species of the genus Paroedura to GGA4p and GGA15 [14]. The sex chromosomes are homologous to the GGAZ syntenic block, both in the phyllodactylid Phyllodactylus wirshingi [21] and the gekkonid Gekko hokouensis [52], two widely diverged species phylogenetically separated by lineages with other sex determination systems [14][15][16][17][18][19][20][21].…”

“…Molecular cytogenetics and next generation sequencing methodologies (e.g. DNAseq, RNAseq, RADseq) allow us to gradually start resolving the puzzle of the gecko variability in sex determination [5,14,[20][21][22], but data are still scarce in this old, highly diversified lineage encompassing over 2000 currently recognized species [23]. Up to now, the eyelid geckos (family Eublepharidae), the gecko group with phylogenetically important position among squamates, was largely neglected in the application of modern sequencing approaches for the study of sex determination.…”