Résumé
Native to China and Mongolia, the brown rat (Rattus norvegicus) now enjoys
a worldwide distribution. While black rats and the house mouse tracked the
regional development of human agricultural settlements, brown rats did not
appear in Europe until the 1500s, suggesting their range expansion was a
response to relatively recent increases in global trade. We inferred the
global phylogeography of brown rats using 32 k SNPs, and detected 13
evolutionary clusters within five expansion routes. One cluster arose
following a southward expansion into Southeast Asia. Three additional
clusters arose from two independent eastward expansions: one expansion
from Russia to the Aleutian Archipelago, and a second to western North
America. Westward expansion resulted in the colonization of Europe from
which subsequent rapid colonization of Africa, the Americas and
Australasia occurred, and multiple evolutionary clusters were detected. An
astonishing degree of fine-grained clustering between and within sampling
sites underscored the extent to which urban heterogeneity shaped genetic
structure of commensal rodents. Surprisingly, few individuals were recent
migrants, suggesting that recruitment into established populations is
limited. Understanding the global population structure of R. norvegicus
offers novel perspectives on the forces driving the spread of zoonotic
disease, and aids in development of rat eradication programmes.