Author contributions
Study conception and design: JKP. Data collection: YL, JS, TK, SC, BC, RG, YJW, YK, SCK, and TN. Data analysis and interpretation: YL, GN, YK, and JKP. Manuscript preparation: YL, GN, EK, YK, and JKP.
Figure legends
Figure 1. Sample locations of M. virgata and distribution of the two mtDNA cox1 lineages. The map shows sea surface temperature in the northwestern Pacific in spring (2003 – 2011). CCC, China Coastal Current; TWC, Taiwan Warm Current; CRDW, Changjian River Diluted Water; SCC, Subei Coastal Current; YSWC, Yellow Sea Warm Current; EKWC, East Korea Warm Current; TSWC, Tsushima Warm Current; OC, Oyashio Current; LC, Liman Current. The dash/dotted line separates two biogeographic regions: the North Pacific Temperate Biotic Region; above the line) and Indo-West Pacific Warm-water Biotic Region; below the line). Populations are labelled with numbers (the southern and northern lineages are indicated in red and blue colored circles, respectively) that correspond with those shown in Table 1.
Figure 2. Phylogenetic tree and haplotype network constructed from mtDNA cox1 . In the phylogenetic tree (A), numbers on branches are statistical support values for ML (bootstrap values)/BI (posterior probabilities). In the haplotype network (B), colors represent sampling locations of M. virgata . The size of each circle is proportional to the frequency of that haplotype. The crossbars on the lines indicate the number of nucleotide substitutions. Open circles represent hypothetical haplotypes.
Figure 3. Phylogenetic tree and haplotype network constructed from nrDNA ITS1. In the phylogenetic tree (A), numbers at nodes are statistical support values for ML (bootstrap values)/BI (posterior probabilities). In the haplotype network (B), each circle represents one allele and color indicates lineage population. Circle size is proportional to the frequency of that haplotype. The crossbars on each branch indicate the number of nucleotide substitution.
Figure 4. Plot of principal component analysis of northern and southern lineages using 15 shell morphological characters. PC1 explains 72.14% of the variation; PC2 6.67% of the variation.
Figure 5. Estimates of divergence times using BEAST. A, 0.7%/Mya; B, 2.4%/Mya. Numbers above nodes are the mean divergence times. Horizontal bars represent 95% highest posterior densities of the divergence time estimates.
Figure 6. Mismatch distributions for the northern and southern lineages using mtDNA cox1 sequence data. The red dotted lines represent the observed frequency of pairwise differences, and the blue solid lines indicate the expected values of the sudden population expansion model.
Figure 7. Hypothesized NW Pacific coastline (dotted line) during early Pleistocene showing that three NWP marginal seas (the East Sea [ES]/the Sea of Japan [SJ], East China Sea [ECS] and South China Sea [SCS]) were isolated due to sea level decline (modified from Ota, 1998). The current land mass topography is indicated in dark grey.