Fig. 4: Assessment of genetic variation of the MUS-1 sublineage.

a Divergence time estimates were determined using BEAST software. A strict clock of 1.1×10⁻⁷ substitutions/site/year was applied to the whole mitochondrial sequence (16,038 bp). The node ages and 95% highest posterior density intervals (blue vertical bars) of node ages within 1000 years are shown for nodes with particularly ancient divergence times. Nodes with >50% bootstrap values (Fig. 3a) are marked with black circles. The colours of the vertical bars associated with the sample codes indicate the countries where the samples were collected. The eastward movement of MUS-1 can be characterised by five steps (I–V): (1) broad spatial expansion into eastern Europe and western part of western China, (2) dispersal to the eastern part of western China, (3) dispersal to northern China, (4) dispersal to the Korean Peninsula and (5) colonisation and expansion in the Japanese Archipelago. The first two steps (I and II) may be correlated with the end of the last Ice Age (ca. 15,000 years ago) and the end of the Younger Dryas (11,600 years ago), respectively. b Geographic distribution of the seven earliest emerging haplogroups (M1a1–M1a7), as defined by the ML phylogenetic tree (Fig. 3). M1a7, the haplogroup located on the eastern edge of western China, experienced further range extension into northern China, Korea (M1a7-3) and Japan (M1a7-3J), sequentially. The times of the emergence of haplogroups were estimated in the BEAST analysis, except for M1a7-3J, which was obtained based on the mismatch distribution analysis (Table 2).