Abstract
Islands are a center of interest in evolutionary biology since the emergence of evolutionary theory itself. They are studied to understand the molecular mechanisms of evolution, adaptation and speciation. Invasive species are of particular interest since they may garner clues and evidence about the processes that took place during the onset of colonization and for understanding mechanisms of adaptation. The aim of this project is to study the evolutionary processes that altogether with isolation shaped the phenotypically known house mouse Mus musculus helgolandicus inhabiting the island of Heligoland. Heligoland is a small island located in the South-East corner of the North Sea and was first colonized by humans in the dawn of the fifteenth century. M. m. helgolandicus were first described by Zimmermann in 1953. Since then they have been thought to form a separate subspecies, which is morphologically different from its continental counterpart M. m. domesticus inhabiting the Western European region. Here, four nuclear diagnostic markers (Abpa, D11 cenB2, Btk and Zfy2 ) and the discriminatory relative tail length (TBLR) were used to differentiate these mice from the other two subspecies M. m. musculus and M. m. domesticus. In addition, the possible routes of colonization and population structure for the invasive mice were investigated using mitochondrial (mt)D-loop DNA sequence and (21) microsatellite loci respectively. Furthermore, whole mtDNA genome was sequenced for 11 individual mice to estimate the onset of colonization on the island from the calculation of mutation frequency in comparison to that of house mouse from Kerguelen archipelago, which has a documented colonization history. Moreover, the whole genome sequence of three individuals was generated and analyzed for single nucleotide polymorphisms (SNPs) which were then used along with data for two po- tential source populations from the two subspecies inhabiting Europe to assign the possible patterns of introgression of haplotypes in M. m. helgolandicus. This study also revisits the morphology of M. m. helgolandicus, in particular, the mandible to assign morphological differences among Heligoland mice on one side and among Heligoland and mainland populations on the other side. Based on the results from diagnostic markers, relative tail length, microsatellites and mtDNA analyses, M. m. helgolandicus are predominantly of M. m. domesticus origin. M. m. helgolandicus population on Heligoland exhibited low genetic diversity compared with other populations from the mainland. The mtDNA data shows that there is a major mtDNA haplotype specic to Heligoland and a minor haplotype represented by a single individual presumably introgressed. Hence, there was a single primary colonization into the island a few hundred years ago and more interestingly, the isolated island shows a case of recent migration from the mainland revealing a signal of refractory to immigration. M. m. helgolandicus displays an elongated mandible which is distinctive for Heligoland. Most likely it was acquired by adaptive forces due to diet changes from a novel environment, with particular a shift to carnivory. The genome is highly intermixed with M. m. musculus haplotypes, pointing to a possible hybrid speciation scenario during the colonization phase.
