Zusammenfassung
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 analysed 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.
