Mitochondrial DNA variation in house mice, Mus domesticus (Rutty)

Molecular and phenotypic distinction of the very recently evolved insular subspecies Mus musculus helgolandicus ZIMMERMANN, 1953

Background

Populations and subspecies of the house mouse Mus musculus were able to invade new regions worldwide in the wake of human expansion. Here we investigate the origin and colonization history of the house mouse inhabiting the small island of Heligoland on the German Bight - Mus musculus helgolandicus. It was first described by Zimmermann in 1953, based on morphological descriptions which were considered to be a mosaic between the subspecies M. m. domesticus and M. m. musculus. Since mice on islands are excellent evolutionary model systems, we have focused here on a molecular characterization and an extended phenotype analysis.

Results

The molecular data show that the mice from Heligoland are derived from M. m. domesticus based on mitochondrial D-loop sequences as well as on four nuclear diagnostic markers, including one each from the sex-chromosomes. STRUCTURE analysis based on 21 microsatellite markers assigns Heligoland mice to a distinct population and D-loop network analysis suggests that they are derived from a single colonization event. In spite of mice from the mainland arriving by ships, they are apparently genetically refractory against further immigration. Mutation frequencies in complete mitochondrial genome sequences date the colonization age to approximately 400 years ago. Complete genome sequences from three animals revealed a genomic admixture with M. m. musculus genomic regions with at least 6.5 % of the genome affected. Geometric morphometric analysis of mandible shapes including skull samples from two time points during the last century suggest specific adaptations to a more carnivorous diet.

Conclusions

The molecular and morphological analyses confirm that M. m. helgolandicus consists of a distinct evolutionary lineage with specific adaptations. It shows a remarkable resilience against genetic mixture with mainland populations of M. m. domesticus despite major disturbances in the past century and a high ship traffic. The genomic admixture with M. m. musculus genetic material may have contributed to the genomic distinction of the Heligoland mice. In spite of its young age, M. m. helgolandicus may thus be considered as a true subspecies of Mus, whose evolution was triggered through fast divergence on a small island.

Electronic supplementary material

The online version of this article (doi:10.1186/s12862-015-0439-5) contains supplementary material, which is available to authorized users.

Genetic differentiation of the house mouse around the Mediterranean basin: matrilineal footprints of early and late colonization

The molecular signatures of the recent expansion of the western house mouse, Mus musculus domesticus, around the Mediterranean basin are investigated through the study of mitochondrial D-loop polymorphism on a 1313 individual dataset. When reducing the complexity of the matrilineal network to a series of haplogroups (HGs), our main results indicate that: (i) several HGs are recognized which seem to have almost simultaneously diverged from each other, confirming a recent expansion for the whole subspecies; (ii) some HGs are geographically delimited while others are widespread, indicative of multiple introductions or secondary exchanges; (iii) mice from the western and the eastern coasts of Africa harbour largely different sets of HGs; and (iv) HGs from the two shores of the Mediterranean are more similar in the west than in the east. This pattern is in keeping with the two-step westward expansion proposed by zooarchaeological data, an early one coincident with the Neolithic progression and limited to the eastern Mediterranean and a later one, particularly evident in the western Mediterranean, related to the generalization of maritime trade during the first millennium BC and onwards. The dispersal of mice along with humans, which continues until today, has for instance left complex footprints on the long ago colonized Cyprus or more simple ones on the much more recently populated Canary Islands.

Of mice and (Viking?) men: phylogeography of British and Irish house mice

The west European subspecies of house mouse (Mus musculus domesticus) has gained much of its current widespread distribution through commensalism with humans. This means that the phylogeography of M. m. domesticus should reflect patterns of human movements. We studied restriction fragment length polymorphism (RFLP) and DNA sequence variations in mouse mitochondrial (mt) DNA throughout the British Isles (328 mice from 105 localities, including previously published data). There is a major mtDNA lineage revealed by both RFLP and sequence analyses, which is restricted to the northern and western peripheries of the British Isles, and also occurs in Norway. This distribution of the 'Orkney' lineage fits well with the sphere of influence of the Norwegian Vikings and was probably generated through inadvertent transport by them. To form viable populations, house mice would have required large human settlements such as the Norwegian Vikings founded. The other parts of the British Isles (essentially most of mainland Britain) are characterized by house mice with different mtDNA sequences, some of which are also found in Germany, and which probably reflect both Iron Age movements of people and mice and earlier development of large human settlements. MtDNA studies on house mice have the potential to reveal novel aspects of human history.

Polymorphism, localization and geographical transfer of mitochondrial DNA in Mus musculus domesticus (Irish house mice)

The analysis of mtDNA restriction fragments from Irish house mice revealed much polymorphism, both within and between populations. Many phenotypes showed geographical localization and there was a strong correlation between geographical distance and genetic divergence. Populations, which are discontinuous and limited to buildings or their vicinity, are apparently the result of short-range migration. Transport by man, with whom the species is closely associated, appears to have negligible impact. There is some evidence of the influence of topographical features on migration and consequent genetic interchange.

Life history and bioeconomy of the house mouse

1. More is known about the western European house mouse, Mus (musculus) domesticus than any other non-human mammal. If laboratory and field information is combined, an extremely valuable understanding of the species' bioeconomy could be obtained. 2. The seven stages of mouse life-history are surveyed (up to birth, nest life, sex life, social structure, population statics and stability, senescence, and death), and the interactions between the changing phenotype and the environment are described. 3. These interactions can be used to build up a model of the opportunities and compromises which result in the fitness of individual mice. It is not yet possible to quantify such a model, but this should in principle be achievable.