Host-Pathogen Dynamics in the Evolution of Ageing and Immunity

Abstract

Pathogens are ubiquitous in nature and have evolved a plethora of different strategies for infecting their various hosts. This has in turn had substantial impacts on the evolution of hosts, which have evolved a wide variety of different mechanisms for resisting and tolerating infection. The evolution of hosts in response to their pathogens, and the coevolution of hosts and pathogens in response to each other, have therefore been extremely important processes for generating the diversity of life we see today, and will also determine the future threats of pathogens to humans, animals and ecosystems in general. Theoretical models have been used to generate theories explaining how many biological phenomena have come to evolve and thus are an important part of the study of evolution in host-pathogen systems.

One particularly important feature of host responses to disease is age-related heterogeneity. Almost all organisms experience a change in their responses to disease as they age, but the nature and timing of these changes varies both between and within species. However, very little is known about why hosts have evolved these different patterns of age-related immunity and what implications this has had on the evolution of pathogens.

In this thesis, I review existing models of host-pathogen coevolution before developing a new method for investigating coevolution in systems where one species evolves much faster than the other. I then go on to explore two different mechanisms for the evolution of age-specific host resistance to infection: the case where the levels of resistance in two different life-stages can evolve independently and the case where the timing of a fixed change in the level of resistance can evolve. Finally, I consider the implications of adding age-structure into previously non-age-structured models of host-pathogen coevolution by considering a specific case of coevolution between pathogen virulence and host tolerance.

Date of Award	24 Apr 2024
Original language	English
Awarding Institution	University of Bath
Supervisor	Ben Ashby (Supervisor) & Nicholas Priest (Supervisor)