Molecular systematics and biogeographic history of oniscidean isopod troglofauna in groundwater calcretes of Central Western Australia.

Abstract

Groundwater calcretes of central Western Australia have revealed an extraordinary diversity of short-range endemic invertebrate subterranean fauna. Although considerable attention has been given to the aquatic dwellers of the calcretes (stygofauna), the subterranean terrestrial fauna of the calcretes (troglofauna), particularly the oniscidean isopods, have been poorly studied. This thesis, including four data chapters, presents the results of multiple-gene and morphological analyses to establish a phylogenetic framework for elucidation of species diversity, systematics, and the biogeographic history of oniscidean isopod troglofauna in arid central Western Australia. The first data chapter focuses on higher level systematic relationships of the isopod fauna. In order to examine the monophyly of the family Platyarthridae, representatives of the main oniscidean families and genera from Australia, South America, Africa and Europe were analysed using molecular and morphological approaches, including data from a Scanning Electron Microscopy study. The phylogenetic analyses of mitochondrial and nuclear genes (COI, 18S, and 28S) showed that Platyarthridae is polyphyletic, and also revealed a very distinct Australian lineage with a unique water conducting system on antenna 2. Based on both morphological and molecular data, a new southern hemisphere oniscidean family, Paraplatyarthridae, occurring from subtropical/temperate to arid regions of Australia and South America, is proposed and described. The second data chapter focuses on the molecular systematics, species diversification and distributional patterns of the oniscidean troglofauna in calcrete aquifers of central Western Australia. The results, based on morphological and multiple-gene molecular approaches, reveal a significant diversity of oniscidean DNA lineages. The application of different species delineation methods, suggests the existence of 28 putative species belonging to four oniscidean families, which most likely represent distinct undescribed species. The phylogenetic analyses show (with some exceptions) that the majority of oniscidean DNA lineages were restricted in their distribution to individual calcrete bodies, lending support to the hypothesis that individual calcretes are equivalent to “Subterranean Islands”. In addition, the occurrence of subtropical, littoral and benthic oniscidean groups in the calcretes suggests complex historical events, including the marine inundation of the Eucla basin during the late Eocene, have shaped the taxonomic representation of the current oniscidean troglofauna. The third data chapter investigates the biogeographic history of the widespread genus Paraplatyarthrus, which showed noticeable morphological diversity, from troglophilic to troglobitic forms. The phylogenetic and molecular clock dating analyses provided evidence that evolutionary transitions from surface to subterranean habitats took place from the late Miocene, and further indicated that troglophile ancestral species independently colonised the calcrete aquifers. These findings support both the climatic relict and adaptive shift hypotheses to explain the evolution of the oniscidean isopod troglofanua with aridity being a significant driver of diversification underground. The final data chapter comprises the morphological description of five new species of the genus Paraplatyarthrus (Paraplatyarthridae fam. nov.) and provides a key to their identification.