New Country for Old Mice: The Recent Colonization History of Mus musculus domesticus in the Americas

Humans have profoundly influenced the distribution of organisms globally, particularly those that live in close association with human societies. The western house mouse, Mus musculus domesticus, expanded from the Fertile Crescent into Europe several thousand years ago alongside early agricultural societies and was subsequently introduced worldwide through European maritime expansion. Given their close ecological association, human commensals, such as the house mouse, are expected to reflect historic patterns of human movement. Using a dataset of 276 exome sequences of mice sampled from Western Europe, North America, and South America, we reconstruct the demographic history of house mice in the Americas and draw genetic connections to contemporary European population from which they were historically sourced. Admixture graphs reveal that house mice from the Atlantic coast of the Iberian Peninsula are the sister group to all American populations, and a secondary contribution from southern UK populations is evident in North America. Analyses of population structure further support shared ancestry between the Atlantic coast of the Iberian Peninsula and both American continents, between the United Kingdom and North America, between Portugal and Brazil, and between Spain and Argentina. Demographic modeling reveals that American mouse populations diverged roughly within the last 500 years, consistent with the post-15th century arrival of Western European people to the Americas. Together, these results identify Western European mouse populations that share close ancestry with American mouse populations and illustrate how the demographic history of a widespread human commensal species can mirror fine-scale patterns of human migration.