The evolution of genetic load in the threatened species

Birley, Thomas (2024) The evolution of genetic load in the threatened species. Doctoral thesis, University of East Anglia.

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Abstract

The detrimental environmental impacts of human activity are driving a profound biodiversity crisis, potentially leading to a sixth mass extinction. Even if these negative impacts are successfully mitigated, the contraction of populations is expected to reduce their fitness. This reduction occurs as population declines increase the frequency of rare deleterious alleles, which could have long-term adverse effects persisting even after populations recover to a viable size. The survival of numerous species may hinge on their ability to tolerate or purge this increased genetic load, which depends on the nature of selection—whether hard or soft.

Hard selection is absolute, independent of population density and frequency, whereas soft selection is relative and influenced by density and frequency. Essentially, soft selection favours the survival of the fittest, while hard selection favours the survival of the sufficiently fit. This thesis explores these two modes of selection, revealing that they produce qualitatively different outcomes for key life-history traits such as fecundity and variables like effective population size, which are partially influenced by the environment. These divergent outcomes present a significant challenge, implying very different prospects for the survival of threatened species. To address this challenge, I develop a novel modelling approach that integrates elements of both hard and soft selection, termed compound selection. Furthermore, the final chapters of this thesis present simulations demonstrating how functional genomics and computational models can be used to design effective captive breeding programs and optimise genetic rescue efforts.

Item Type:	Thesis (Doctoral)
Faculty \ School:	Faculty of Science > School of Environmental Sciences
Depositing User:	Chris White
Date Deposited:	24 Aug 2026 11:22
Last Modified:	24 Aug 2026 11:22
URI:	https://ueaeprints.uea.ac.uk/id/eprint/104304
DOI:

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