Subspecies distributions of Mus musculus in China. Sampling locations are indicated. CAS1 and CAS2 are two main subclades of M. m. castaneus from Figure 2. Mus and Dom are used as abbreviations for M. m. musculus and M. m. domestics, respectively. The five main districts are southwest China (SWC), north China (NC), central China (CC), east China (EC) and southeast China (SEC).