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Title: The evolution of multiple defences
Author: Wang, Lingzi
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2019
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This thesis aims to explore the evolution of multiple defences. Single defences have received considerable attention due to their specific effects in protecting organisms, but the research about multiple defences is relatively limited. Specifically, this thesis focuses on how the connection between defences is related to evolution (not the specific effect of protection in each defence). Chapters 2 and 3 focus on the connection between earlier and later defences using mathematical models. Chapters 4 and 5 focus on the connection between two synergistically acting defences, and their relationship with diversification rates using phylogenetics. In Chapter 2, I explore the evolutionary reason for multiple defences and the trade-off between earlier and later defences. I find the conditions for multiple defences versus single defences and also found that, typically, the investment is more in earlier than later defences. In Chapter 3, I explore the defence phenotype variances in earlier and later defences in mutation-selection balance. I find that, typically, the earlier defence variance evolves to be less than the later defence variances, and I also find some factors that can influence the equilibrium variances. Both Chapter 2 and 3 show the relative importance of earlier defence to the later defences, due to their chances to use the defences. In Chapter 4, I study the coevolution between two synergistically acting defences, aposematism and group-living, and find that the root ancestor state is possibly group-living, which is slightly against intuition, as most previous research thinks otherwise. I also find the possible evolutionary dynamics of the four binary states from the ancestor till now and into the future, and the probability equilibrium values of the four states. In Chapter 5, I have extended the study of defences into a macroevolution point of view and study the association between defences and diversification rates. Here I have obtained further evidence to "escape and radiate" hypothesis regarding the association between aposematism and faster diversification rates. I also find that group-living is positively associated with diversification rates, which is new in this area to my knowledge. The previous research about chemical defences in this topic is not consistent, which might be because chemical defences are usually deployed later, therefore, are less important for protection and can be more variable, as I have proposed in Chapter 2 and 3. In all, the findings here imply that the connection between defences plays an important role in the evolution of multiple defences. This can help us to further understand the evolutionary reasons and patterns of multiple defences and their application in certain practical areas.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral