Phylogeny, historical biogeography and body size evolution in Pacific Island Crocodile skinks Tribolonotus (Squamata; Scincidae)

Comparative analysis of osteoderms across the lizard body

Osteoderms (ODs) are mineralized tissue embedded within the skin and are particularly common in reptiles. They are generally thought to form a protective layer between the soft tissues of the animal and potential external threats, although other functions have been proposed. The aim of this study was to characterize OD variation across the lizard body. Adults of three lizard species were chosen for this study. After whole body CT scanning of each lizard, single ODs were extracted from 10 different anatomical regions, CT scanned, and characterized using sectioning and nanoindentation. Morphological analysis and material characterization revealed considerable diversity in OD structure across the species investigated. The scincid Tiliqua gigas was the only studied species in which ODs had a similar external morphology across the head and body. Greater osteoderm diversity was found in the gerrhosaurid Broadleysaurus major and the scincid Tribolonotus novaeguineae. Dense capping tissue, like that reported for Heloderma, was found in only one of the three species examined, B. major. Osteoderm structure can be surprisingly complex and variable, both among related taxa, and across the body of individual animals. This raises many questions about OD function but also about the genetic and developmental factors controlling OD shape.

Nomenclature of supra-generic units within the Family Scincidae (Squamata)

The modern classification of skinks is based on a nomenclature that dates to the 1970s. However, there are a number of earlier names in the family group that have been overlooked by recent workers. These names are identified and their validity with respect to the International Code of Zoological Nomenclature investigated, along with their type genera. In most cases, use of these names to supplant junior synonyms in modern day use is avoidable by use of the Reversal of Precedence articles of the Code, but the names remain available in case of future divisions at the tribe and subtribe level. Other names are unavailable due to homonymy, either of their type genera or the stems from similar but non-homonymous type genera. However, the name Egerniini is replaced by Tiliquini, due to a limited timespan of use of Egerniini. A new classification of the Family Scincidae is proposed, providing a more extensive use of Code-regulated levels of classification, including tribes and subtribes, and a detailed synonymy provided for each taxonomic unit.

A molecular phylogeny for the Pacific monitor lizards (Varanus subgenus Euprepiosaurus) reveals a recent and rapid radiation with high levels of cryptic diversity

We provide a geographically well-sampled, time-calibrated molecular phylogeny for the Pacific monitor lizards (Varanus: subgenus Euprepiosaurus) based on ND4 and 16S rRNA mitochondrial DNA sequences. Three well-supported clades, or species groups, are retrieved: the Varanus doreanus Group, the V. jobiensis Group and the V. indicus Group. The subgenus is estimated to have originated in the Mid-Miocene, but extant lineage diversification dates from the Late Miocene and Pliocene. A rapid and widespread radiation of the V. indicus Group into the South-West Pacific islands has occurred in the Pleistocene, but colonization onto these islands did not occur in a linear, stepping-stone fashion. Genetically distinct populations – by tradition classified as V. indicus, but seemingly representing distinct species – occur scattered on Tanimbar, several of the Solomon Islands, the Admiralty Islands, the Louisiade Archipelago, Palau and Guam. Our analyses indicate that Varanus jobiensis is a species complex with several divergent lineages that started to separate in the Pliocene and continued in the Pleistocene, the former coinciding with the uplift of the Central Dividing Range on New Guinea. We find that sympatry among species of Euprepiosaurus has not occurred until divergence times of 4.7–5.8 Myr have accrued.

Combined next-generation sequencing and morphology reveal fine-scale speciation in Crocodile Skinks (Squamata: Scincidae: Tribolonotus)

Next-generation sequencing has vast potential to revolutionize the fields of phylogenetics and population genetics through its ability to collect genomic scale data sets of thousands of orthologous loci. Despite this potential, other types of data (e.g. morphology, ecology) remain important, particularly for studies endeavouring to delimit species. Here, we integrate next-generation sequencing with morphology to examine divergence between populations of Tribolonotus pseudoponceleti on the islands of Buka and Bougainville in the Solomon Archipelago. We used the Ion Torrent PGM to collect over 648 Mbp of sequence data for 12 samples, representing 1526 loci recovered from all samples, and 3342 were recovered from at least six samples. Genetic structure analyses strongly support the distinctiveness of these two populations, and Bayes factor delimitations decisively select speciation between Buka and Bougainville. Principal components and discriminant function analyses reveal concordant morphological divergence. Finally, demographic analyses via diffusion approximation and approximate Bayesian computation prefer a complex model of mid-Pleistocene divergence with migration, and a later decrease or cessation of migration and population size shift, suggesting a scenario in which migration was enabled by Pleistocene merging of these two islands, and limited when isolated by higher sea levels. Further analysis of four Sanger sequenced loci in IMa2 had limited power to distinguish among models including and excluding migration, but resulted in similar population size and divergence time estimates, although with much broader confidence intervals. This study represents a framework for how next-generation sequencing and morphological data can be combined and leveraged towards validating putative species and testing demographic scenarios for speciation.

Phylogeography of the prehensile-tailed skink Corucia zebrata on the Solomon Archipelago

The biogeography of islands is often strongly influenced by prior geological events. Corucia zebrata (Squamata: Scincidae) is endemic to the geologically complex Solomon Archipelago in Northern Melanesia. We examined the level of divergence for different island populations of C. zebrata and discussed these patterns in light of Pleistocene land bridges, island isolation, and island age. Corucia zebrata was sampled from 14 locations across the Solomon Archipelago and sequenced at two mitochondrial genes (ND2 and ND4; 1697 bp in total) and four nuclear loci (rhodopsin, an unknown intron, AKAP9, and PTPN12). Measures of genetic divergence, analyses of genetic variation, and Bayesian phylogenetic inference were used and the data assessed in light of geological information. Populations of C. zebrata on separate islands were found to be genetically different from each other, with reciprocal monophyly on mitochondrial DNA. Populations on islands previously connected by Pleistocene land bridges were marginally less divergent from each other than from populations on other nearby but isolated islands. There are indications that C. zebrata has radiated across the eastern islands of the archipelago within the last 1–4 million years. Nuclear loci were not sufficiently informative to yield further information about the phylogeography of C. zebrata on the Solomon Archipelago. Analyses of the mitochondrial data suggest that dispersal between islands has been very limited and that there are barriers to gene flow within the major islands. Islands that have been isolated during the Pleistocene glacial cycles are somewhat divergent in their mitochondrial genotypes, however, isolation by distance (IBD) and recent colonization of isolated but geologically younger islands appear to have had stronger effects on the phylogeography of C. zebrata than the Pleistocene glacial cycles. This contrasts with patterns reported for avian taxa, and highlights the fact that biogeographic regions for island species cannot be directly extrapolated among taxa of differing dispersal ability.

Ecological guild evolution and the discovery of the world's smallest vertebrate

Living vertebrates vary drastically in body size, yet few taxa reach the extremely minute size of some frogs and teleost fish. Here we describe two new species of diminutive terrestrial frogs from the megadiverse hotspot island of New Guinea, one of which represents the smallest known vertebrate species, attaining an average body size of only 7.7 mm. Both new species are members of the recently described genus Paedophryne, the four species of which are all among the ten smallest known frog species, making Paedophryne the most diminutive genus of anurans. This discovery highlights intriguing ecological similarities among the numerous independent origins of diminutive anurans, suggesting that minute frogs are not mere oddities, but represent a previously unrecognized ecological guild.