Sanders, KateRasmussen, Arne R.Nankivell, James Henry2023-07-242023-07-242023https://hdl.handle.net/2440/138946The front-fanged elapids (Elapidae: Hydrophiinae) are the dominant radiation of terrestrial snakes on the Australian continent, and within the last 10 million years have invaded tropical marine habitats to become the most species rich clade of marine reptiles alive today. My thesis had two broad aims in relation to the Hydrophiinae radiation: 1) Investigating the hidden diversity within the subfamily and 2) Why do some groups diversify rapidly and others do not? Numerous species of the sea snake genus Aipysurus have suffered declines in their former stronghold – the offshore reefs of the Timor Sea. However, the discovery of previously overlooked populations on the Western Australian Coast has highlighted critical gaps in our knowledge of these species. I used thousands of nuclear SNPs to show that, in four of five codistributed Aipysurus species, deep genetic divergences separate coastal Western Australian from offshore Timor Sea populations. I used morphological and colour pattern traits to characterise differences in these lineages and found convergent changes towards larger and longer bodies and paler body colouration in the Western Australian Coast compared to the Timor Sea lineages. I suggested that these remarkably parallel transitions reflect adaptations relating to locomotion and crypsis in the deep soft sediment habitats of the Western Australian Coast versus the complex and shallow coral reefs of the Timor Sea. I recommended recognition of these historically isolated lineages as Evolutionary Significant Units (ESUs) for management purposes. These results also provide a valuable framework for investigating the roles of biogeography and adaptation in lineage diversification. I also investigated lineage formation in the sister group to Aipysurus, Emydocephalus, using nuclear SNPs combined with morphological and ecological data. Emydocephalus is a small fish-egg eating specialist with a patchy geographic distribution in the Indo-West Pacific. Within this species, I found very similar morphological and biogeographic patterns to those that I uncovered in Aipysurus, but divergence was much greater and I described the coastal Western Australian population as a new species, Emydocephalus orarius. I also reconstructed a phylogeny of Demansia, the most species rich terrestrial elapid genus in Australia. I found that current species boundaries in the widespread D. psammophis group inadequately represented the lineage diversity in this clade, and described a morphologically distinct new species, Demansia cyanochasma, from the deserts of Southern Australia. Finally, I investigated the evolution of the rapidly radiating Hydrophis group in a macroevolutionary context. I reconstructed a phylogeny using thousands of nuclear SNPs, which provided substantially higher resolution of relationships than previous studies have produced using mitochondrial and low-variation nuclear sequences. For most species, I then used three ecologically relevant morphological characters combined with diet data to define five broad ecomorphs. Ancestral state reconstruction using these data showed that burrowing prey specialisations are the likely ancestral state for Hydrophis. I also uncovered a strong pattern of rapid ecomorphological diversification within major ocean basins, highlighting the clade as an important system for testing hypotheses of adaptive radiation. This thesis provides a basis for understanding the process of lineage diversification, ranging from incipient speciation in Aipysurus through to the ~50 species radiation in Hydrophis. I integrated a combination of new molecular techniques with traditional museum-based data collection and worked with industry partners to improve sampling of molecular and ecological data. This integrative approach has provided a novel perspective on the evolution of the Australian elapid fauna.ensnake; evolution; macroevolution; sea snake; phylogenetics; systematicsThesis