The roles of hybridisation, contemporary climate change, and recent range shifts on the redistribution of marine biodiversity

Abstract

Global change as a result of human activities has caused unprecedented alterations to biodiversity. One consequence of such alteration is the redistribution of species. Understanding the mechanisms that determine and maintain species’ ranges is at the forefront of ecological and evolutionary research. Current drivers of the redistribution of biodiversity include natural range expansions, anthropogenic transport of species, and contemporary climate change. These can alter both species ranges and evolutionary trajectories in multiple ways. A notorious example is when changes in species distributions bring divergent genotypes into secondary contact, facilitating hybridisation. Despite each of these topics being well studied individually, there remains a dearth of research studying these factors in combination to understand how they reshape biodiversity patterns in the marine environment. It is predicted that an integrative approach studying these factors in combination would enable further understanding how they interact to affect the redistribution of biodiversity.

This thesis used a multidisciplinary approach that combined population genomic data, controlled experimental crosses of divergent genotypes, and environmental datasets to investigate the role of different factors on past, current, and future changes in species distributions. My research has shown that whilst hybridisation can be beneficial for range expansions, this is not always the case. I found evidence that some species that have spread as a result of human mediated transport have undergone secondary contacts, facilitating the colonisation of distant habitats. Conversely, other species with transoceanic distributions may be expected to undergo secondary contact due to anthropogenic transport and the presence of two native lineages, though I found no evidence that range expansion had been preceded by hybridisation. Finally, species that are able to currently hybridise may not perform as well as parental crosses under thermal stress, suggesting that under CCC, hybridisation may not be such a dominant driver of species redistribution.

Taken together, this thesis demonstrates the utility in using a multidisciplinary approach to study factors that can combine to determine species ranges. I have shown that different mechanisms can have dissimilar consequences on species ranges that can be difficult to predict, and that by studying multiple factors can one successfully disentangle the role each one plays in the redistribution of marine biodiversity.

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