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Title: The drivers of variation in susceptibility to the amphibian-killing fungus, Batrachochytrium dendrobatidis
Author: Smith, Donal
Awarding Body: University of Salford
Current Institution: University of Salford
Date of Award: 2019
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The fungal pathogen Batrachochytrium dendrobatidis (Bd) is regarded as a primary driver of the dramatic global declines experienced by amphibian populations in recent decades. The threat posed by Bd extends into pristine regions, decimating populations naïve to the pathogen. The patterns of genetic variation in amphibians in natural habitats, and the degree to which this influences traits such as response to novel pathogens, is therefore of particular relevance to conservation biology. To examine the interplay between geographic context and population genetics, and the role that individual-level traits play in shaping critical components of host viability in the face of exposure to Bd, I focused on a set of mainland and isolated island common toad (Bufo bufo) populations situated on the edge of their range in northwest Scotland. Microsatellites were used to characterise patterns of genetic variability across eleven populations. It was found that seawater serves to isolate demes, producing high levels of population differentiation, and that loss of genetic diversity parallels degree of isolation. Standardised laboratory experiments showed that Bd-induced mortality in amphibians with no prior history of exposure to the pathogen was predicted by population of origin and individual mass, but not by population-level allelic diversity or heterozygosity at microsatellite loci. Restriction site-associated DNA sequencing (RADseq) was then used to genotype individuals exposed to Bd at over 10,000 single nucleotide polymorphism (SNP) loci. This revealed clear genetic structure not discernible through microsatellite analysis. Outlier loci putatively related to local adaptation were identified, but it was not possible to characterise their function. No loci with a clear association to disease response were identified. These findings underscore the importance of habitat in forming discrete populations, and how this can shape variation in fundamental phenotypic traits, including disease response. These responses are, however, rather idiosyncratic, and not predicted by factors such as level of population isolation or neutral genetic diversity. SNP datasets generated through RADseq hold great potential in further unravelling the dynamics of the amphibian-Bd system, but these are likely to remain complex and context-dependent.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available