Islands under the desert: molecular systematics and evolutionary origins of stygobitic water beetles (Coleoptera : Dytiscidae) from central Western Australia

Abstract

Calcrete aquifers in the Yilgarn Craton of central Western Australia have recently been found to contain a rich invertebrate stygofauna, including the world's most diverse collection of stygobitic dytiscid water beetles. Our aim was to determine the evolutionary relationships between 11 species of stygobitic dytiscids and epigean species of the tribe Bidessini. Phylogenetic analyses of 1431 base pairs of mitochondrial DNA (mtDNA), including segments of cytochrome oxidase 1, 16S rRNA, tRNA _leu and NADH dehydrogenase 1 genes, revealed that 10 of the 11 species form a natural group within the Bidessini and are most closely related to epigean taxa from the genera Allodessus Guignot, Boongurrus Larson, Limbodessus Guignot and Liodessus Guignot. The analyses support the morphological taxonomy of the stygobitic beetles at the species level, but generic level classification is not concordant with mtDNA lineages. Sympatric species of the large Tjirtudessus Watts & Humphreys and smaller Nirridessus Watts & Humphreys are more closely related to each other than either are to their congeners, suggesting a possible case of sympatric speciation. The analyses indicate that there have been multiple independent origins of stygobitic dytiscids and that origins correlate with the onset of aridity during the Miocene and also provide evidence that each calcrete aquifer may represent a 'subterranean island'.