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Figure 5 
Mismatch distributions for (A) clade A, (B) clade B1, and (C) clade B2 of the polkadot 
skate (Dipturus chinensis) and Bayesian skyline plots for (D) clade A, (E) clade B1, and 
(F) clade B2, based on the mitochondrial cytochrome 6 gene sequences (931 base pairs) 
of 214 individuals that were obtained from 7 locations around Japan between 2010 and 
2017 or were obtained through the International Nucleotide Sequence Database Col- 
laboration for populations in Taiwan or off the Korean Peninsula. In panels A-C, solid 
and dashed lines represent the observed and simulated distributions under the sudden 
expansion model, respectively. In panels D—F, dashed lines indicate the female effective 
population size (NV) multiplied by the generation interval, and the shaded area indicates 
the 95% highest posterior density interval. 
Hirase and Ikeda, 2014). Genetic divergence between the 
Sea of Japan and the East China Sea has not been indi- 
cated for the polkadot skate, but Misawa et al. (2019b) sug- 
gested that populations of ocellate spot skate diverge at the 
boundary of those seas. They suggested that the Tsushima 
Strait and the Tsushima Current act as geographic barri- 
ers for dispersal that can limit distribution of ocellate spot 
skate and that the Kuroshio Current may have prevented 
dispersal of that species because of the absence of a major 
population of ocellate spot skate from the Pacific coast of 
central Japan. Different from their influence on ocellate 
OOS O10 G15 O20 
Time (million years ago) 
spot skate, the Tsushima and Kuroshio Currents may have 
an effect on the dispersal of polkadot skate (see the “Evolu- 
tionary history” section). 
The population of polkadot skate on the Pacific coast of 
northern Honshu (Aomori Prefecture) can be regarded as 
the Oyashio lineage. In contrast, for some shallow-water 
organisms, the Tsushima lineage is the lineage distributed 
on the Pacific coast of northern Honshu (Kojima et al., 
2004; Akihito et al., 2008; Katafuchi et al., 2011; Kokita 
and Nohara, 2011; Hirase et al., 2012; Hirase and Ikeda, 
2014). The Tsugaru Warm Current, one of the branches 
