| Summary: | The aims of this DPhil were the characterisation of major histocompatibility complex class II β loci in the amphibian species Bufo calamita, determination of fitness of four Bufo calamita populations and measurement of genetic diversity at both microsatellite loci and MHC class II β loci. The genetic diversity at microsatellite loci is considered to be neutral to selection and the genetic diversity seen at MHC loci is adaptive. Fitness in the four populations was measured using the known larval fitness traits age at metamorphosis, growth rates and survival. A 114 base pair section of MHC class II loci was characterised in this study. It was shown here that the diversity at neutral microsatellite markers was negatively correlated with adaptive MHC class II variation. No correlation was found between microsatellite HE and the larval fitness traits growth rate, survival and age at metamorphosis. However, MHC class II diversity was found to be associated with survival, and individuals that were heterozygous at both MHC loci had a significantly higher chance of survival than individuals homozygous at one or both of the two loci. A separate part of this DPhil project was the population genetics of six Irish Bufo calamita populations. The genetic structure was investigated using nine polymorphic microsatellite markers. It was found that all populations had similar and moderate levels of genetic diversity, comparable with those on the coast of north-west England. Toad populations were substantially differentiated, implying little migration between sites within historical times. Phylogenetics and estimates of divergence times supported the hypothesis that populations on the north coast of Dingle separated from those around Castlemaine Harbour many thousands of years ago, and are not recent introductions.
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