A Penny for Your Thoughts: An Evolutionary History of the Australian Psephennidae (Coleoptera)

Abstract

Historical changes to Australia’s climate have been proposed to have caused the decline of its ancient mesic biome. The fragmentation of habitat will affect species in different ways depending on their dispersal ability and their potential to disperse across inhospitable habitats. The diversification of Australia’s terrestrial species has been shown to have arisen due to climate changes that occurred during the Miocene – Pliocene, especially for those that occupy mesic habitats. Almost no comprehensive studies on freshwater insect groups from these habitats exist. In this thesis I investigate the role of past climate change on the evolution of a group that appear to be a specialist of the mesic zone, the Australian Psephenidae. I test two main hypotheses; first, that climate change during the Miocene has led to the diversification of the group, and second, that the limited dispersal capability of the beetle coupled with its habitat specialisation has led to further diversification within the genus. The molecular systematics and historical biogeography of the Australian Psephenidae was investigated using the mitochondrial DNA COI gene and the nuclear DNA H3 gene. Strong evidence for monophyly of the Australian endemic genus Sclerocyphon was found using three different tree building methods. The species tree revealed that the genus underwent a rapid divergence in the late Miocene, presumably as response to the fragmentation of their mesic habitat as Australia became increasingly arid. The timing of speciation within the Sclerocyphon coincides with other Australian freshwater taxa, and implies a vicariant explanation for the current distribution of the genus which is linked to the contraction of the mesic zone. Other vicariant events, such as the flooding of Bass Strait and the birth of Australia’s arid zone have also contributed to the current distribution patterns seen in the Sclerocyphon. More recent Pleistocene climatic events have resulted in further diversification within some of the lineages.