Island syndrome in rodents; a comparative study on island forms of the bank vole, Myodes glareolus
Islands are extremely variable habitats, differing in shape, size, degree of isolation, geography and climate. They are often described as ‘natural laboratories’ and have proven beneficial for testing theories on evolution and adaptation. Rodents on islands are often characterised by differences in demography, morphology and behaviour compared to adjacent mainland populations. One of the most notable and extensively reported differences is in body size. Several adaptive theories have been suggested to explain these phenomena, which have been termed ‘island syndrome’, yet few have been empirically tested. The bank vole (Myodes glareolus) is a good model for studying the evolution of island syndrome, being present throughout the British mainland as well as on 13 small offshore islands. Voles on four of these islands exhibit the gigantism characteristic of island syndrome. The aim of this study was to compare insular and mainland populations of voles to determine whether island syndrome is truly an adaptive response to life in insular habitats, or whether it is driven by more random processes such as founder effects and genetic drift. In this thesis, I present data on body size, demography and skull morphology along with phylogenetic analyses based on mitochondrial DNA sequences from island and mainland populations of bank voles around the UK. Whilst I was able to demonstrate insular changes in body size, I was unable to demonstrate any demographic differences consistent with the predictions of island syndrome. Phylogenetic analyses revealed that body size differentiation on islands was not related to phylogeographic history. There was little evidence for a single unifying theory explaining the existence of island syndrome, thus I conclude that this biological pattern is probably caused by multiple environmental and genetic factors.
AuthorsHare, Emma J.
- Theses