Unrecognised Ant Megadiversity in Monsoonal Australia: The Tetramorium spininode Bolton Group in the Northern Territory

We document unrecognised diversity within the Tetramorium spininode Bolton group of the Australian monsoonal tropics, which has a single described species. At the time of its description, T. spininode was known from just two collections, but there have since been hundreds of collections from throughout monsoonal Australia. We document morphological and genetic (CO1) variation within the group's fauna of the Northern Territory (NT), in the centre of its range, where collection intensity has been highest. We recognise 20 species among 124 CO1-sequenced specimens, and 32 species in total from the NT. A key to these species is provided. The most intensively sampled regions within the NT are the mesic (>1000 mm mean annual rainfall) Top End in the far north (with 14 species) and the semi-arid (500-900 mm) Sturt Plateau region to its south (13 species). Only one species is known from both regions. Given such high regional turnover and highly patchy sampling, we estimate that at least 40 species of the T. spininode group occur in the NT. Similar diversity appears to occur in Western Australia, especially in the Kimberley region, but less in Queensland. Our findings suggest that the total number of species in the T. spininode group is likely to be around 100. Our study provides further evidence that monsoonal Australia is an unrecognised global centre of ant diversity.