Assessing the diversity of Australian tarantulas (Araneae: Theraphosidae) using DNA barcoding and iterative species delimitation

Tarantulas (Araneae: Theraphosidae) are one of the most diverse and widespread families of mygalomorph spiders, with over 1000 species recognised globally. While tarantulas can be found across most of mainland Australia, from arid regions to tropical forests, the Australian fauna are not yet well characterised. There are currently only 10 nominal species, up to 8 of which are currently recognised as distinct species. Here, we aim to undertake the first continent-wide assessment of species diversity of tarantulas in Australia using an iterative, hypothesis-testing approach. We apply a biological species concept and use DNA sequence data from three independent loci to delimit putative species based on evidence of lack of gene flow. First, we use the mitochondrial DNA marker 16S to identify a set of putative species hypotheses. We then test each hypothesis under the expectations of neotypy, allotypy and allophyly using two independent nuclear loci, EF1γ and 28S rRNA. Genealogically exclusive lineages are inferred using haplotype networks for each nuclear locus, interpreted to represent non-interbreeding entities and hence represent distinct biological species. We find evidence for there being at least 20 distinct biological species of tarantula in Australia, with the highest species richness in northern Australia. Our results are in line with other DNA-based studies of Australian mygalomorphs that have uncovered undescribed species diversity. Given the low number of samples included here, there is likely to be an even greater species diversity of tarantulas in Australia.