Habitat disturbance may form subpopulation genetic structure in an invasive rodent species (Myocastor coypus) within a Japanese river system

Alien species management can be improved by understanding the population genetic structure of alien species that affect native ecosystems. In this study, we analyzed the spatial genetic structure of nutria ( Myocastor coypus ), an invasive rodent species in the Yodo River system in Japan, to improve efficiency of management strategies. We performed genetic analyses of mitochondrial DNA (mtDNA) sequences and 13 microsatellite DNA loci from nutria captured at two locations: the Katsura River and Shirokita Cove, in the upper and lower reaches of the Yodo River system, respectively. Three mtDNA haplotypes (N1, N2, and N3) were identified within the Yodo River system, and the same haplotype (N1) was dominant in both the Katsura River and Shirokita Cove populations. Microsatellite variation was low in both populations. The upstream Katsura River population consisted of a single genetic population, whereas the downstream Shirokita Cove population showed a genetic subdivision likely caused by genetic drift. These results suggest that the Yodo River system populations may have originated from the single ancestral populations. Habitat disruptions, such as severe flood events, may have caused the genetic drift observed in these populations and result in the genetic subdivision within a single river system. Additionally, microsatellite DNA analysis showed that in Shirokita Cove, there was significant isolation-by-distance in female nutria and dispersal occurred over relatively short distances. Therefore, when influence of flooding and migration on population dynamics are considered, a combination of localized intensive trapping and extensive monitoring may be necessary to control nutria density.