Molecular phylogenetics, evolution and systematics of isopoda

Abstract

Isopods are a remarkably diverse group of crustaceans that can be found in virtually all environments. Although the monophyly of this group is well supported, there remains uncertainty about the phylogenetic relationships within the group. The use of molecular data to infer the phylogeny of isopods offers a promising complement to the evidence provided by morphological data. This study uses a range of techniques to shed light on various aspects of isopod evolution. I inferred the phylogenetic relationships among isopod lineages and evaluated support for several major suborders. I estimated the timeframe for the isopods colonisation of the deep sea, freshwater and terrestrial habitats. Using mitochondrial genomes, I investigated patterns of evolutionary rate variation in isopods and other crustaceans. Lastly, I described two new species of asellotan isopods from the Australian deep sea, and extended the occurrence of one species to New South Wales, and one genus to Australia, improving our knowledge of Australian fauna. My thesis shows that the isopods colonised different environments many millions of years ago. In the case of the deep-sea clades, this study contradicts the hypothesis that the deep-sea fauna went extinct during anoxic events. The colonisation of continental environments coincided with the formation of the supercontinent Pangaea and with the diversification of vascular plants. Some suborders were found to be paraphyletic, conflicting with classical morphological views. My analyses of isopods and other crustaceans’ mitogenomes did not reveal any impact of lineage-by-gene interactions. This indicates that standard molecular-clock analysis can be used for analysing the mitogenomes of isopods and other crustaceans. Together with the other analyses presented in this thesis, my work contributes to the discussion of isopod systematics, to the understanding of the evolution of isopods, and to the provision of data for comparisons with other crustaceans.