Distribution and genetic characteristics of E phoron shigae ( E phemeroptera: P olymitarcyidae) in K orea

E phoron shigae is distributed in F ar E ast R ussia, K orea and J apan, where it inhabits rivers, streams and lakes. Although this mayfly is a geographically parthenogenetic species, unisex populations have been observed only in J apan. We aimed to answer the following three questions: (i) whether there is a unisex population of E . shigae in K orea; (ii) whether migration and gene flow exists between E . shigae populations in K orea and J apan; and (3) whether E . shigae populations are fragmented in K orea because of mountains running to the north and south. We observed 20 populations across K orea and investigated the sex ratio in 12 populations. Our results showed that all the populations were bisex, and we believe that there is no unisex population of E . shigae in K orea. In addition, we examined the genetic structure of E . shigae in K orea by using the COI gene. The results showed that the K orean populations were clearly divergent from the J apanese populations; the level of genetic distance between the K orean and J apanese populations was interspecific rather than intraspecific. Therefore, parthenogenetic populations of E . shigae probably belong to unisex populations that originated in J apan, while the individuals would have not migrated to K orea. The K orean populations did not show clear fragmentation by geographic barrier, although this mayfly with extremely short adult stage (up to 2 h) could be a comparatively strong disperser across K orea.