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. K E Y W O R D S :Body size shifts, character displacement, cryptic diversity, morphological evolution, phylogenomics, sympatry.

BackgroundCongruent 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.ResultsUsing 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.ConclusionsIn 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.Electronic supplementary materialThe online version of this article (10.1186/s12862-019-1408-1) contains supplementary material, which is available to authorized users.

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.