First record of Daphnia retrocurva Forbes, 1882 (Crustacea, Cladocera, Daphniidae) outside its native North America (Shin Toyone Reservoir, Japan)

Daphnia retrocurva Forbes, 1882 (Crustacea, Cladocera, Daphniidae), a North American freshwater zooplankton species, was found in an artificial reservoir in central Japan. This represents the first record of D. retrocurva not only in Japanese and Asian freshwaters but also from outside North America. Our phylogenetic analysis based on mitochondrial DNA sequences revealed little differentiation between Japanese and North American populations. By combining geographical isolation and the lack of genetic differentiation, we consider Japanese D. retrocurva to be non-indigenous and relatively recently introduced.