Not only is the house mouse a close cultural successor to humans, its genetic diversity is also far superior to ours, as shown by global genome research. In it, scientists reconstructed the development of three subspecies of domestic mice and found a surprisingly high degree of interbreeding. Genetic bottlenecks also reveal where and when domestic mice can benefit from human breeding – and where not.
The house mouse (Mus musculus) has a long history of success. Due to their ability to adapt to humans, their ancestors were able to spread all over the world from their area of origin in North India. Only Europe remained free from house mice for a long time. It was not until the Bronze Age that the eastern subspecies Mus musculus musculus first appeared, then in ancient times the Romans introduced the subspecies Mus musculus domesticus, which is dominant here to this day. However, a third subspecies of mice, Mus musculus castaneus, remained in South Asia.
However, it was not clear when and where these three subspecies arose, how they are genetically related, and to what extent they intertwine. Therefore, Kazumichi Fujiwara of the University of Hokkaido and his colleagues have now studied the genetic diversity of domestic mice around the world in more detail. To this end, they analyzed and compared the genomes of 141 domestic mice from all regions of the world. ‘This is the first genome study in wild domestic mice to cover all three subspecies,’ explains the team.
More genetic diversity than humans
Analyzes have shown: House mice are not only more numerous than humans, their genetic diversity is also much greater, as confirmed by DNA analyzes. One reason is likely that these three subspecies are geographically and genetically less isolated than previously thought. “Our results significantly change the simple idea of a subspecies triangle,” say Fujiwara and his colleagues.
The dominant European subspecies M. musculus domesticus can reproduce with its southern neighbor M. musculus musculus only to a limited extent. As a result, wild domestic mice in our country belong almost exclusively to the subspecies domesticus. However, in Asia, the two subspecies of domestic mice there mix so intensely that there are hardly any mice with a “clean” genome of just one subspecies. “The pattern of the genes indicates that castaneus and musculus have been mixed in Asia for 10,000 years,” the researchers say.
Population development reflects our history
Gene comparison also showed a split of three subspecies of domestic mice. Accordingly, families of domesticus and musculus mice diverged approximately 245,000 years ago. Much later, around 188,000 years ago, the two subspecies musculus and castaneus split. The latter, according to the team, could explain why the two types of house mice often mix up to this day.
Interesting: The history of the pet mouse population also reflects human history. The ancestors of pet mice, which are widespread in Germany today, experienced a marked decline in population that then spread between 50,000 and 5,000 years ago. The development of the M. musculus musculus subspecies was similar. “This sequence of genetic bottlenecks and then proliferation is probably closely related to the spread of agriculture,” explain Fujiwara and his colleagues.
Also important for research in laboratory mice
Under the research teams, elucidating the history and genetics of pet mice is important not only for basic research and evolutionary biology, but also for research involving laboratory mice. Because even inbred strains – mostly descendants of wild domestic mice of Mus musculus domesticus – are relatively different from each other and also contain a small fraction of other subspecies.
‘Understanding the background and evolutionary history of this species also significantly contributes to understanding such mouse models in research,’ write the researchers. (Genome Biology and Evolution, 2022; doi: 10.1093 / gbe / evac068)
Source: Hokkaido University