The Unique Australian Subterranean Dytiscidae: Diversity, Biology, and Evolution

The western half of the Australian arid zone harbours the richest diversity of obligate subterranean dytiscids in the world, which are found in isolated calcrete (carbonate) aquifers. Each calcrete usually supports from one to three beetle species that are locally endemic to a specific calcrete, and display the full array of adaptations to living in a permanently dark, aquatic environment. The origin of this dytiscid diversity likely dates back to the late Miocene to Pliocene when central and western Australia was dominated by a more benign, mesic environment. Subsequent aridification led to relictualisation of the fauna to the calcrete aquifers which, because of their physical isolation from each other, have been described as ‘islands under the desert’. Here we provide an overview of this remarkable fauna of dytiscids, and outline what is currently known about their diversity, life history, respiratory physiology, modes of speciation, population biology, and outline their conservation issues and areas for future research.