ZZ/ZW Sex Chromosomes in the Endemic Puerto Rican Leaf-Toed Gecko (<b><i>Phyllodactylus wirshingi</i></b>)

Abstract

Investigating the evolutionary processes influencing the origin, evolution, and turnover of vertebrate sex chromosomes requires the classification of sex chromosome systems in a great diversity of species. Among amniotes, squamates (lizards and snakes) - and gecko lizards in particular - are worthy of additional study. Geckos possess all major vertebrate sex-determining systems, as well as multiple transitions among them, yet we still lack data on the sex-determining systems for the vast majority of species. We here utilize restriction-site associated DNA sequencing (RADseq) to identify the sex chromosome system of the Puerto Rican endemic leaf-toed gecko (Phyllodactylidae: Phyllodactylus wirshingi), in order to confirm a ZZ/ZW sex chromosome system within the genus, as well as to better categorize the diversity within this poorly characterized family. RADseq has proven an effective alternative to cytogenetic methods for determining whether a species has an XX/XY or ZZ/ZW sex chromosome system - particularly in taxa with non-differentiated sex chromosomes - but can also be used to identify which chromosomes in the genome are the sex chromosomes. We here identify a ZZ/ZW sex chromosome system in P. wirshingi. Furthermore, we show that 4 of the female-specific markers contain fragments of genes found on the avian Z and discuss homology with P. wirshingi sex chromosomes.

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

“…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]. Therefore, it seems that the ancestors of these two species independently co-opted the same region for the role of sex chromosomes rather than that sex chromosomes were in these two lineages inherited from their common ancestor.…”

“…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.…”

The rise and fall of differentiated sex chromosomes in geckos

“…According to the hypothesis on ancestral ESD in amniotes, sex chromosomes evolved potentially more than 40 times in this group (Johnson Pokorná & Kratochvíl, ; Rovatsos, Vukić, & Kratochvíl, ). As far as we know, genes linked to sex chromosomes are known only in 17 amniote lineages representing 15 putative independent origins of sex chromosomes (the situation is more complex in snakes; Gamble et al, ), and this limited information points to several independent cooptions of the same syntenic blocks (Figure ): the homologs of the ancestral XY of viviparous mammals homologous to the short arm of the chicken chromosome 4 play the role of a part of ZW sex chromosomes in the Paroedura species with differentiated sex chromosomes (this study), as well as in lacertid lizards (Rovatsos, Vukić, Altmanová, et al, ; Rovatsos, Vukić, & Kratochvíl, ); the chicken chromosome 15 shares genes with the XY sex chromosomes of iguanas (Alföldi et al, ; Altmanová et al, ; Rovatsos, Pokorná, et al, ), ZW sex chromosomes of softshell turtles (Kawagoshi, Uno, Matsubara, Matsuda, & Nishida, ; Rovatsos et al, ) and a part of differentiated ZW sex chromosomes of the Paroedura geckos (this study); the homologs of avian ZW sex chromosomes were independently coopted as XY sex chromosomes in Staurotypus turtles (Kawagoshi, Uno, Nishida, & Matsuda, ), ZW sex chromosomes in Gekko hokouensis (Kawai et al, ) and ZW sex chromosomes in Phyllodactylus wirshingi (Nielsen, Daza, Pinto, & Gamble, ); the turtles Glyptemys insculpta and Siebenrockiella crassicollis share genes on their probably independently evolved X chromosomes homologous to chicken chromosome 5 (Kawagoshi, Nishida, & Matsuda, ; Montiel et al, ); and finally, a block syntenic with chicken chromosome 28 was coopted for the role of sex chromosomes in anguimorphan lizards (varanids, beaded lizards and at least some anguids; Rovatsos et al, ) and the same block represents the oldest evolutionary stratum of multiple sex chromosomes of monotremes (Cortez et al, ). On the other hand, based on the current knowledge regarding partial gene content, sex chromosomes seem to have only evolved from other parts of the ancestral amniote genomes in just two amniote lineages: snakes (Gamble et al, ; Rovatsos et al, ; Vicoso et al, ), and bearded dragon Pogona vitticeps and its close relatives (Ezaz et al, , ).…”

Do male and female heterogamety really differ in expression regulation? Lack of global dosage balance in pygopodid geckos

“…The pygopodid sex chromosomes are homologous to chromosome 4q of the chicken and the human chromosome 4. It seems that sex chromosomes in the pygopodid ancestor evolved independently from sex chromosomes of other amniotes, as no amniote group studied to date with known partial gene content of sex chromosomes share sex-linked gene content with pygopodids 27 , including three other gekkotan lineages: Phyllodactylus wirshingi (its ZZ/ZW chromosomes are syntenic with chicken Z; GGAZ), Gekko hokouensis (GGAZ as well, but likely independently derived), and the geckos of the genus Paroedura (GGA4p and GGA15) 27,51,52 . It should be noted that previously reported synteny of amniote sex chromosomes with chromosome GGA4 in lacertid lizards, geckos of the genus Paroedura , and therian mammals involved the small arm (GGA4p) not the larger arm (GGA4q) of the fourth chicken chromosome.…”