François Bonhomme

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.

Origins and Phylogenetic Relationships of the Laboratory Mouse

Archaeological and historical records indicate that mice were already bred as pets three millennia ago: it was then logical that these small mammals should be used by early scientists for performing their experiments. Even if this choice may retrospectively appear relatively opportunistic, it nevertheless turned out to be an excellent one in the modern context of biomedical research, especially in genetics, where the mouse has become an emblematic model. Because they are all derived from a relatively small pool of ancestors, laboratory mice exhibit a rather limited amount of genetic polymorphism. For this reason, strains of mice recently derived from different species of the genus Mus have been developed that represent an interesting addition to the arsenal of mouse geneticists, because some of them can be crossed with classical laboratory strains to produce viable and fertile offspring segregating for a large number of polymorphisms of natural origin. These strains are helpful for making genome annotations because they make it possible to establish high-resolution/high-density genetic maps that, in turn, allow establishing refined genotype–phenotype correlations. In this chapter, we describe the origins of laboratory mice and their phylogenetic relationships with other mammalian species. We also discuss the advantage of strains established from wild specimens as an almost unlimited source of polymorphisms.