Pathogens and the maintenance of genetic variation in an island population of the Seychelles warbler (Acrocephalus sechellensis)

Davies, Charlotte (2021) Pathogens and the maintenance of genetic variation in an island population of the Seychelles warbler (Acrocephalus sechellensis). Doctoral thesis, University of East Anglia.

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The objective of this thesis was to investigate how evolutionary forces shape immunogenetic variation in small populations. To achieve this, I investigated functional variation at key genes in both the innate and adaptive immune systems in the Seychelles warbler (Acrocephalus sechellensis), and how this differed spatio-temporally and in relation to individual traits and fitness components. First, I tracked evolution at one nonsynonymous TLR3 SNP over 25-years. Results showed a significant and consistent temporal decline in the minor TLR3C allele frequency within the original Seychelles warbler population and in all four derived populations. Further investigations showed that positive selection – acting on both survival and reproduction, was driving these temporal changes in the Cousin population. I then investigated whether pre- or post-copulatory sexual selection was acting in relation to the TLR3 locus. I found evidence of both pre-copulatory assortative social pairing, and a post-copulatory bias against paternal inheritance of the TLR3C haplotype. Thus, multiple mechanisms of selection appear be causing contemporary TLR3 evolution in the Seychelles warbler. Lastly, I investigated whether host-microbiome coevolution may interact with functional immunogenetic variation in this species. Using next generation sequencing techniques, I characterised the MHC (both class I and class II), and gut microbiome (GM) variation existing in a subset of individuals. I found that presence of specific MHC alleles, but not MHC diversity, was associated with differences in GM diversity and composition. These results confirm variation in the host’s immune system may play a role in shaping an individual’s GM in a population of wild animals. Collectively, my results provide insight into how different mechanisms can interact to shape functional genetic variation in a natural population. They also raise some important, as yet unanswered, questions about the identity of the selective agents (pathogens) affecting the immunogenetic variation in this species.

Item Type: Thesis (Doctoral)
Faculty \ School: Faculty of Science > School of Biological Sciences
Depositing User: Chris White
Date Deposited: 14 Dec 2021 15:33
Last Modified: 14 Dec 2021 15:33


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