Genetic insights into climate-driven range expansion of a coastal foundation species

Kennedy, John Paul (2021) Genetic insights into climate-driven range expansion of a coastal foundation species. Doctoral thesis (PhD), Manchester Metropolitan University.

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Abstract

In this thesis, I address gaps in our understanding of how climate-driven range expansion can shape genetic variation within a coastal foundation species and how the resulting genetic changes may have broader ecological consequences. To do this, I study the neotropical black mangrove (Avicennia germinans) across its distribution in the United States, and then I focus on its expanding Atlantic Florida range margin. First, in Chapter 2, I find that genetic variation within A. germinans declines towards three range margins in the United States, but that this reduction may not constrain adaptation within this species as range-margin A. germinans exhibit shifts in functional traits consistent with greater cold tolerance. Leveraging these insights and genetic data, I then document patterns in mating system and dispersal, factors that can shape intraspecific genetic variation and influence expansion success, towards the Atlantic Florida range margin. In Chapter 3, I find evidence for plastic shifts towards greater self-fertilisation at this sparsely-populated range margin, a mechanism that can facilitate colonisation of new areas. In Chapter 4, I show how extreme storm events may facilitate poleward expansion of A. germinans and how this form of episodic dispersal can shape genetic variation within newly-colonised populations. Finally, I evaluate potential ecological consequences of the unique genetic variation found within these Atlantic Florida A. germinans. In Chapter 5, at the scale of a range-margin population, I find that genetically-similar A. germinans harboured similar fungal communities, a relationship that may have implications for the fitness of these mangrove hosts. In Chapter 6, using a greenhouse common garden, I demonstrate a genetic basis to adaptative trait shifts within these range-margin A. germinans that may facilitate future range expansion of this species. These novel insights should improve our ability to predict how mangrove range margins may respond to climate change and help inform future mangrove restoration initiatives.