Snails in the desert: Assessing the mitochondrial and morphological diversity and the influence of aestivation behavior on lineage differentiation in the Australian endemic Granulomelon Iredale, 1933 (Stylommatophora: Camaenidae).

Progressive aridification since the mid-Miocene has had a significant influence on the evolution of the biota in the arid zone of central Australia. Especially moisture sensitive groups, such as snails, are often restricted to topographically complex areas, which have acted as refugia in an otherwise inhospitable environment. This historical fragmentation is deemed to be a potent agent of allopatric lineage diversification. Camaenid land snails are amongst only a few terrestrial gastropods that have managed to survive in the arid zone probably due to their ability to escape desiccation through aestivation. Here, we present the first study of the mitochondrial lineage differentiation in an endemic land snail genus from the Australian 'Red Centre', Granulomelon Iredale, 1933. Exposing significant incongruence between mtDNA phylogeny and morphology-based taxonomy, we completely revise the species and genus level taxonomy of this camaenid group. We demonstrate that this genus contains three species, G. grandituberculatum, G. adcockianum and G. squamulosum, which have so far been assigned to different genera: Granulomelon Iredale, 1933 (junior synonym: Baccalena Iredale, 1937), Basedowena Iredale, 1937 and Pleuroxia Ancey, 1887. Two of these species are widespread comprising multiple divergent mitochondrial lineages. Based on a molecular clock estimate, these lineages diverged approximately during the mid-Pleistocene, a period of particularly severe aridification. The phylogeographic patterns are consistent with an isolation-by-distance model in one species but not the other. We suggest that these differences can be attributed to their distinctive aestivation behavior.