Rapid expansion of the distributional range and the population genetic structure of the freshwater amphipod <Emphasis Type="Italic">Crangonyx floridanus</Emphasis> in Japan |
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Authors: | Asako Nagakubo Kazuki Sekiné Yoshiki Tanaka Ryoichi B Kuranishi Shoji Kanada " target="_blank">Koji Tojo |
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Institution: | (1) Department of Biology, Faculty of Science, Shinshu University, 3-1-1 Asahi, Matsumoto Nagano, 390-8621, Japan;(2) Department of Mountain and Environmental Science, Interdisciplinary Graduate School of Science and Technology, Shinshu University, 3-1-1 Asahi, Matsumoto Nagano, 390-8621, Japan;(3) Department of Environmental System Science, Graduate School of Science and Technology, Shinshu University, 3-1-1 Asahi, Matsumoto Nagano, 390-8621, Japan;(4) Natural History Museum and Institute, 955-2 Aoba, Chuou-ku, Chiba 260-8682, Japan;(5) Nippon Engineering College, 5-23-22 Nishikamata, Ota-ku, Tokyo 144-8655, Japan;(6) Institute of Mountain Science, Shinshu University, 3-1-1 Asahi, Matsumoto Nagano, 390-8621, Japan; |
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Abstract: | The freshwater amphipod Crangonyx floridanus (Amphipoda: Crangonyctidae) is considered to have been recently introduced from North America to Japan, and the recorded
sites at which it has been collected now cover nearly all of Japan except for the northern part. In this study, we surveyed
further areas outside of its known distribution range, and examined the population genetic structure and the phylogenetic
relationships between Japanese and North American populations of this species based on nuclear (18S rRNA) and mitochondrial
(COI) DNA sequences. We found that this amphipod has already reached Hokkaido, northernmost Japan, which suggests that it
has undergone rapid expansion in a pattern of concentric circles from the central part of Japan. Genetic analysis showed that
the Japanese population is genetically homogeneous, in contrast to the genetic diversification of this species seen in North
American Crangonyx populations. The process of introducing, establishing, and expanding this amphipod in Japan may be explained as follows.
A limited number of individuals from a North American native population were probably inadvertently introduced and established
somewhere within the Kanto region. The local population size then increased and its distribution range expanded rapidly across
Japan. |
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