Molecular and morphological assessment of the widely distributed legless gecko Delma tincta Kluge (Squamata: Pygopodidae), including a taxonomic revision

WA Museum Records and Supplements | Updated 2 weeks ago

ABSTRACT – The pygopodid lizard Delma tincta is widely distributed across Australia, including the arid zone, eastern seaboard and monsoon tropics. Delma is morphologically extremely conservative, and the highly cryptic D. tincta species complex presents a particular taxonomic challenge. Here, we use a large SNP molecular dataset and a detailed morphological dataset to evaluate variation in Delma tincta across its range. Our SNP data strongly support eight monophyletic populations, which we allocate to four species, based on a combination of morphological and genetic distinctiveness. Two of these species, including type D. tincta, have largely overlapping distributions over a vast area in central and northern Australia. The type specimen of D. tincta from Normanton in Queensland was collected 140 years ago and is in very poor condition. In the absence of other information, we elected to assign the name tincta to one of the two clades for which a tissue-sampled specimen was nearest to the type location. A specimen for which we had a sequence was collected 50 km from this locality, and we allocate the name D. tincta to this lineage. The other lineage we name D. hades sp. nov., with a sequenced specimen occurring as close as 200 km to the type location of D. tincta. These sympatric lineages, which are not each other’s closest relatives, are morphologically cryptic and cannot be distinguished from one another without nuclear molecular data. Such cryptic species are a challenge for field ecologists and collection managers, and we provide recommendations for how to treat such taxa. We redescribe the lineage that occurs in eastern Queensland as Delma reticulata Garman. Delma reticulata is also challenging to distinguish from the two sympatric central species, but differs morphologically where they are geographically close to each other in southern Queensland. The most morphologically distinctive lineage is Delma branchia sp. nov., which occurs in the Pilbara and Gascoyne regions of Western Australia and is readily identified by a series of ventrolateral transverse bars that continue down the neck. The four species can be diagnosed from all congeners by unique fixed differences in nuclear SNPs and by aspects of colouration in some instances. Deep genetic structure and significant numbers of fixed and private allelic differences suggest additional species-level diversity may be present within three of the four taxa in the D. tincta species-group, requiring more detailed sampling in future. We comment on ecological and evolutionary patterns in Delma, including problematic patterns of introgression as observed here and in other groups. These new taxa bring the number of Delma species to 25, accounting for nearly half the species diversity of enigmatic pygopods.