A dated molecular phylogeny of mite harvestmen (Arachnida: Opiliones: Cyphophthalmi) elucidates ancient diversification dynamics in the Australian Wet Tropics

Austropurcellia, a genus of dispersal-limited arachnids endemic to isolated patches of coastal rainforest in Queensland, Australia, has a remarkable biogeographic history. The genus is a member of the family Pettalidae, which has a classical temperate Gondwanan distribution; previous work has suggested that Austropurcellia is an ancient lineage, with an origin that predates Gondwanan rifting. Subsequently, this lineage has persisted through major climatic fluctuations, such as major aridification during the Miocene and contraction and fragmentation of forest habitats during the Last Glacial Maximum (LGM). In order to understand Austropurcellia's evolutionary and biogeographic history, we generated DNA sequences from both mitochondrial and nuclear loci and combined this information with previously published datasets for the globally-distributed suborder Cyphophthalmi (i.e., all mite harvestmen). We generated phylogenetic trees using maximum likelihood and Bayesian approaches to date divergences using a relaxed molecular clock. According to our estimates, the family Pettalidae diversified in the late Jurassic, in accordance with Gondwanan vicariance. Within Pettalidae, Austropurcellia split from its sister group in the early Cretaceous and began to diversify some 15 Ma later. Therefore, its presence in Australia predates continental rifting-making it one of very few hypothesized examples of Gondwanan vicariance that have withstood rigorous testing. We found a steady rate of diversification within the genus, with no evidence for a shift in rate associated with Miocene aridification. Ages of splits between species predate the Pleistocene, consistent with a "museum" model in which forest refugia acted to preserve existing lineages rather than drive speciation within the group.