Comparative phylogeography of Cyclops vicinus Uljanin, 1875 and Cyclops kikuchii Smirnov, 1932 with implications for differences in their ecological characteristics

Cyclops kikuchii and Cyclops vicinus are lentic freshwater cyclopoid copepods commonly found in Eurasia, including the Japanese archipelago, where a recent study revealed they were morphologically and molecularly distinguishable. However, their distribution patterns and ecological characteristics are not yet understood. We sought to establish their spatial distributions in Japan and determine whether they have similar phylogeographic patterns using mitochondrial cytochrome c oxidase subunit I. We found that C. vicinus appeared frequently in the south of Japan as opposed to the north, where C. kikuchii dominated. The Japanese C. kikuchii consists of two phylogroups with a large genetic differentiation (ca. 0.1 as the Kimura 2 Parameter distance), suggesting a case of secondary contact. Neither species showed clear signs of demographic expansion after bottleneck events in Japan. Unlike C. kikuchii, which had many private haplotypes across Japan, C. vicinus possessed several geographically widespread haplotypes, suggesting that its realized range of dispersal and frequency of effective dispersal are larger than those of C. kikuchii's. We thus argue that the dispersal ability is stronger in C. vicinus than in C. kikuchii. Judging from the data of our present and previous studies, this argument may hold for their entire geographic range.