title: Phylogeographic insights into the invasion history and secondary spread of the signal crayfish in Japan.
abstract: Successful invasion by nonindigenous species is often attributed to high propagule pressure, yet some foreign species become widespread despite showing reduced genetic variation due to founder effects. The signal crayfish (Pacifastacus leniusculus) is one such example, where rapid spread across Japan in recent decades is believed to be the result of only three founding populations. To infer the history and explore the success of this remarkable crayfish invasion, we combined detailed phylogeographical and morphological analyses conducted in both the introduced and native ranges. We sequenced 16S mitochondrial DNA of signal crayfish from across the introduced range in Japan (537 samples, 20 sites) and the native range in western North America (700 samples, 50 sites). Because chela size is often related to aggressive behavior in crayfish, and hence, their invasion success, we also measured chela size of a subset of specimens in both introduced and native ranges. Genetic diversity of introduced signal crayfish populations was as high as that of the dominant phylogeographic group in the native range, suggesting high propagule pressure during invasion. More recently established crayfish populations in Japan that originated through secondary spread from one of the founding populations exhibit reduced genetic diversity relative to older populations, probably as a result of founder effects. However, these newer populations also show larger chela size, consistent with expectations of rapid adaptations or phenotypic responses during the invasion process. Introduced signal crayfish populations in Japan originate from multiple source populations from a wide geographic range in the native range of western North America. A combination of high genetic diversity, especially for older populations in the invasive range, and rapid adaptation to colonization, manifested as larger chela in recent invasions, likely contribute to invasion success of signal crayfish in Japan.
authors.affiliation: Institute of Nature and Environmental Technology Kanazawa University Kanazawa 920-1192 Japan.
authors.forename: Nisikawa
authors.initials: N
authors.lastname: Usio
authors.affiliation: Graduate School of Fisheries Sciences Hokkaido University Hakodate 041-8611 Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Azuma
authors.affiliation: Department of Natural Resources and Environmental Sciences University of Illinois Urbana Illinois 61801; School of Aquatic and Fishery Sciences University of Washington Seattle Washington 98195.
authors.forename: Eric R
authors.initials: ER
authors.lastname: Larson
authors.affiliation: Pacific Biological Station Fisheries and Oceans Canada Nanaimo British Columbia V9T 6N7 Canada.
authors.forename: Cathryn L
authors.initials: CL
authors.lastname: Abbott
authors.affiliation: School of Aquatic and Fishery Sciences University of Washington Seattle Washington 98195.
authors.forename: Julian D
authors.initials: JD
authors.lastname: Olden
authors.affiliation: Center for Toki and Ecological Restoration Niigata University Niigata 950-2181 Japan.
authors.forename: Hiromi
authors.initials: H
authors.lastname: Akanuma
authors.affiliation: Center for Environmental Biology and Ecosystem Studies National Institute for Environmental Studies Tsukuba 305-8506 Japan.
authors.forename: Kenzi
authors.initials: K
authors.lastname: Takamura
authors.affiliation: Center for Environmental Biology and Ecosystem Studies National Institute for Environmental Studies Tsukuba 305-8506 Japan.
authors.forename: Noriko
authors.initials: N
authors.lastname: Takamura
keywords: Biological invasion; Pacifastacus leniusculus; freshwater; mitochondrial DNA; population genetics; propagule pressure