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Hoplodactylus delcourtiis a presumably extinct species of diplodactylid gecko known only from a single specimen of unknown provenance. It is by far the largest known gekkotan, approximately 50% longer than the next largest-known species. It has been considered a member of the New Zealand endemic genusHoplodactylusbased on external morphological features including shared toe pad structure. We obtained DNA from a bone sample of the only known specimen to generate high-throughput sequence data suitable for phylogenetic analysis of its evolutionary history. Complementary sequence data were obtained from a broad sample of diplodactylid geckos. Our results indicate that the species is not most closely related to extantHoplodactylusor any other New Zealand gecko. Instead, it is a member of a clade whose living species are endemic to New Caledonia. Phylogenetic comparative analyses indicate that the New Caledonian diplodactylid clade has evolved significantly more disparate body sizes than either the Australian or New Zealand clades. Toe pad structure has changed repeatedly across diplodactylids, including multiple times in the New Caledonia clade, partially explaining the convergence in form betweenH. delcourtiand New ZealandHoplodactylus. Based on the phylogenetic results, we placeH. delcourtiin a new genus.

 

Sex determination is a critical element of successful vertebrate development, suggesting that sex chromosome systems might be evolutionarily stable across lineages. For example, mammals and birds have maintained conserved sex chromosome systems over long evolutionary time periods. Other vertebrates, in contrast, have undergone frequent sex chromosome transitions, which is even more amazing considering we still know comparatively little across large swaths of their respective phylogenies. One reptile group in particular, the gecko lizards (infraorder Gekkota), shows an exceptional lability with regard to sex chromosome transitions and may possess the majority of transitions within squamates (lizards and snakes). However, detailed genomic and cytogenetic information about sex chromosomes is lacking for most gecko species, leaving large gaps in our understanding of the evolutionary processes at play. To address this, we assembled a chromosome-level genome for a gecko (Sphaerodactylidae: Sphaerodactylus) and used this assembly to search for sex chromosomes among six closely related species using a variety of genomic data, including whole-genome re-sequencing, RADseq, and RNAseq. Previous work has identified XY systems in two species of Sphaerodactylus geckos. We expand upon that work to identify between two and four sex chromosome cis-transitions (XY to a new XY) within the genus. Interestingly, we confirmed two different linkage groups as XY sex chromosome systems that were previously unknown to act as sex chromosomes in tetrapods (syntenic with Gallus chromosome 3 and Gallus chromosomes 18/30/33), further highlighting a unique and fascinating trend that most linkage groups have the potential to act as sex chromosomes in squamates.

 

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. 

One goal of evolutionary developmental biology is to understand the role of development in the origin of phenotypic novelty and convergent evolution. Geckos are an ideal system to study this topic, as they are species‐rich and exhibit a suite of diverse morphologies—many of which have independently evolved multiple times within geckos.

We characterized and discretized the embryonic development ofLepidodactylus lugubris—an all‐female, parthenogenetic gecko species. We also used soft‐tissue μCT to characterize the development of the brain and central nervous system, which is difficult to visualize using traditional microscopy techniques. Additionally, we sequenced and assembled a de novo transcriptome for a late‐stage embryo as a resource for generating future developmental tools. Herein, we describe the derived and conserved patterns ofL. lugubrisdevelopment in the context of squamate evolution and development.

This embryonic staging series, μCT data, and transcriptome together serve as critical enabling resources to study morphological evolution and development, the evolution and development of parthenogenesis, and other questions concerning vertebrate evolution and development in an emerging gecko model.