Initiation of speciation across multiple dimensions in a rock-restricted, tropical lizard.

Population isolation and concomitant genetic divergence, resulting in strong phylogeographical structure, is a core aspect of speciation initiation. If and how speciation then proceeds and ultimately completes depends on multiple factors that mediate reproductive isolation, including divergence in genomes, ecology and mating traits. Here we explored these multiple dimensions in two young (Plio-Pleistocene) species complexes of gekkonid lizards (Heteronotia) from the Kimberley-Victoria River regions of tropical Australia. Using mitochondrial DNA screening and exon capture phylogenomics, we show that the rock-restricted Heteronotia planiceps exhibits exceptional fine-scale phylogeographical structure compared to the codistributed habitat generalist Heteronotia binoei. This indicates pervasive population isolation and persistence in the rock-specialist, and thus a high rate of speciation initiation across this geographically complex region, with levels of genomic divergence spanning the "grey zone" of speciation. Proximal lineages of H. planiceps were often separated by different rock substrates, suggesting a potential role for ecological isolation; however, phylogenetic incongruence and historical introgression were inferred between one such pair. Ecomorphological divergence among lineages within both H. planiceps and H. binoei was limited, except that limestone-restricted lineages of H. planiceps tended to be larger than rock-generalists. By contrast, among-lineage divergence in the chemical composition of epidermal pore secretions (putative mating trait) exceeded ecomorphology in both complexes, but with less trait overlap among lineages in H. planiceps. This system-particularly the rock-specialist H. planiceps-highlights the role of multidimensional divergence during incipient speciation, with divergence in genomes, ecomorphology and chemical signals all at play at very fine spatial scales.

Predictors of phylogeographic structure among codistributed taxa across the complex Australian monsoonal tropics.

Differences in the geographic scale and depth of phylogeographic structure across codistributed taxa can reveal how microevolutionary processes such as population isolation and persistence drive diversification. In turn, environmental heterogeneity, species' traits, and historical biogeographic barriers may influence the potential for isolation and persistence. Using extensive SNP data and a combination of population genetic summary statistics and landscape genomic analyses, we explored predictors of the scale and depth of phylogeographic structure in codistributed lizard taxa from the topographically and climatically complex monsoonal tropics (AMT) of Australia. We first resolved intraspecific lineages and then tested whether genetic divergence across space within lineages is related to isolation by distance, resistance and/or environment and whether these factors differ across genera or between rock-related versus habitat generalist taxa. We then tested whether microevolutionary processes within lineages explain differences in the geographic scale and depth of intraspecific phylogeographic lineages. The results indicated that landscape predictors of phylogeographic structure differ between taxa. Within lineages, there was prevalent isolation by distance, but the strength of isolation by distance is independent of the taxonomic family, habitat specialization, and climate. Isolation by environment is the strongest predictor of landscape-scale genetic divergence for all taxa, with both temperature and precipitation acting as limiting factors. The strength of isolation by distance does not predict the geographic scale of the phylogeographic structure. However, more localized lineages had higher mean individual heterozygosity and less negative Tajima's D. This result implies that finer-scale phylogeographic structuring within species is associated with larger and more stable populations and, hence, persistence.

A new velvet gecko (Oedura: Diplodactylidae) from Groote Eylandt, Northern Territory.

Over the last decade, the combination of biological surveys, genetic diversity assessments and systematic research has revealed a growing number of previously unrecognised vertebrate species endemic to the Australian Monsoonal Tropics. Here we describe a new species of saxicoline velvet gecko in the Oedura marmorata complex from Groote Eylandt, a large island off the eastern edge of the Top End region of the Northern Territory. Oedura nesos sp. nov. differs from all congeners in combination of moderate size, and aspects of tail morphology and colouration. It has not been reported from the nearby mainland regions (eastern Arnhem Land) suggesting it may be an insular endemic, although further survey work is required to confirm this. While Groote Eylandt is recognised as a contemporary ecological refuge for declining mammal species of northern Australia, newly detected endemic species suggest it may also be of significance as an evolutionary refuge for many taxa, especially those associated with sandstone escarpments.

Crypsis and convergence: integrative taxonomic revision of the Gehyra australis group (Squamata: Gekkonidae) from northern Australia.

For over two decades, assessments of geographic variation in mtDNA and small numbers of nuclear loci have revealed morphologically similar, but genetically divergent, intraspecific lineages in lizards from around the world. Subsequent morphological analyses often find subtle corresponding diagnostic characters to support the distinctiveness of lineages, but occasionally do not. In recent years it has become increasingly possible to survey geographic variation by sequencing thousands of loci, enabling more rigorous assessment of species boundaries across morphologically similar lineages. Here we take this approach, adding new, geographically extensive SNP data to existing mtDNA and exon capture datasets for the Gehyra australis and G. koira species complexes of gecko from northern Australia. The combination of exon-based phylogenetics with dense spatial sampling of mitochondrial DNA sequencing, SNP-based tests for introgression at lineage boundaries and newly-collected morphological evidence supports the recognition of nine species, six of which are newly described here. Detection of discrete genetic clusters using new SNP data was especially convincing where candidate taxa were continuously sampled across their distributions up to and across geographic boundaries with analyses revealing no admixture. Some species defined herein appear to be truly cryptic, showing little, if any, diagnostic morphological variation. As these SNP-based approaches are progressively applied, and with all due conservatism, we can expect to see a substantial improvement in our ability to delineate and name cryptic species, especially in taxa for which previous approaches have struggled to resolve taxonomic boundaries.

On and off the rocks: persistence and ecological diversification in a tropical Australian lizard radiation.

BACKGROUND: Congruent patterns in the distribution of biodiversity between regions or habitats suggest that key factors such as climatic and topographic variation may predictably shape evolutionary processes. In a number of tropical and arid biomes, genetic analyses are revealing deeper and more localised lineage diversity in rocky ranges than surrounding habitats. Two potential drivers of localised endemism in rocky areas are refugial persistence through climatic change, or ecological diversification and specialisation. Here we examine how patterns of lineage and phenotypic diversity differ across two broad habitat types (rocky ranges and open woodlands) in a small radiation of gecko lizards in the genus Gehyra (the australis group) from the Australian Monsoonal Tropics biome. RESULTS: Using a suite of approaches for delineating evolutionarily independent lineages, we find between 26 and 41 putative evolutionary units in the australis group (versus eight species currently recognised). Rocky ranges are home to a greater number of lineages that are also relatively more restricted in distribution, while lineages in open woodland habitats are fewer, more widely distributed, and, in one case, show evidence of range expansion. We infer at least two shifts out of rocky ranges and into surrounding woodlands. Phenotypic divergence between rocky ranges specialist and more generalist taxa is detected, but no convergent evolutionary regimes linked to ecology are inferred. CONCLUSIONS: In climatically unstable biomes such as savannahs, rocky ranges have functioned as zones of persistence, generators of diversity and a source of colonists for surrounding areas. Phenotypic divergence can also be linked to the use of differing habitat types, however, the extent to which ecological specialisation is a primary driver or secondary outcome of localised diversification remains uncertain.

Species delimitation in the Gehyra nana (Squamata: Gekkonidae) complex: cryptic and divergent morphological evolution in the Australian Monsoonal Tropics, with the description of four new species.

Recent advances in molecular genetic techniques and increased fine scale sampling in the Australian Monsoonal Tropics (AMT) have provided new impetus to reassess species boundaries in the Gehyra nana species complex, a clade of small-bodied, saxicolous geckos which are widely distributed across northern Australia. A recent phylogenomic analysis revealed eight deeply divergent lineages that occur as a series of overlapping distributions across the AMT and which, as a whole, are paraphyletic with four previously described species. Several of these lineages currently included in G. nana are phenotypically distinct, while others are highly conservative morphologically. Here we use an integrated approach to explore species delimitation in this complex. We redefine G. nana as a widespread taxon with complex genetic structure across the Kimberley of Western Australia and Top End of the Northern Territory, including a lineage with mtDNA introgressed from the larger-bodied G. multiporosa. We describe four new species with more restricted distributions within the G. nana complex. The new species are phylogenetically divergent and morphologically diagnosable, and include the relatively cryptic G. paranana sp. nov. from the western Northern Territory, the large-bodied G. pseudopunctata sp. nov. from the southern Kimberley ranges, G. granulum sp. nov., a small-bodied form with granules on the proximal lamellae from the north-west and southern Kimberley ranges and the small-bodied G. pluraporosa sp. nov. restricted to the northern Kimberley. Our revision largely stabilises the taxonomy of the G. nana complex, although further analyses of species limits among the remaining mostly parapatric lineages of G. nana sensu stricto are warranted.

Cryptic lineage diversity, body size divergence, and sympatry in a species complex of Australian lizards (Gehyra).

Understanding the joint evolutionary and ecological underpinnings of sympatry among close relatives remains a key challenge in biology. This problem can be addressed through joint phylogenomic and phenotypic analysis of complexes of closely related lineages within, and across, species and hence representing the speciation continuum. For a complex of tropical geckos from northern Australia-Gehyra nana and close relatives-we combine mtDNA phylogeography, exon-capture sequencing, and morphological data to resolve independently evolving lineages and infer their divergence history and patterns of morphological evolution. Gehyra nana is found to include nine divergent lineages and is paraphyletic with four other species from the Kimberley region of north-west Australia. Across these 13 taxa, 12 of which are restricted to rocky habitats, several lineages overlap geographically, including on the diverse Kimberley islands. Morphological evolution is dominated by body size shifts, and both body size and shape have evolved gradually across the group. However, larger body size shifts are observed among overlapping taxa than among closely related parapatric lineages of G. nana, and sympatric lineages are more divergent than expected at random. Whether elevated body size differences among sympatric lineages are due to ecological sorting or character displacement remains to be determined.