Inferring the invasion mechanisms of the red swamp crayfish in China using mitochondrial DNA sequences

The red swamp crayfish, Procambarus clarkii, is a native species in north-eastern Mexico and south-central USA. P. clarkii was introduced to China in 1929 and has been used as an aquaculture species in China since 1983. It currently exists in most of the provinces of China, but threatens local fish, crustaceans, aquatic plants and local freshwater ecosystems. We examined the genetic variation in partial mitochondrial ND2 gene of 831 individuals collected from 25 P. clarkii populations in 13 provinces of China to infer the expansion pathways and mechanisms. Six haplotypes were detected. All six haplotypes appeared in four populations in Nanjing and a population located near Nanjing whereas only 1–5 of the six haplotypes were present in other populations. These data suggest that the populations in Nanjing are probably the source of all other populations in China. There were no significant relationships between geographic distances and genetic distances in 25 populations, whereas significant relationship was found in four populations in Qinhuai River covering 50 km in Nanjing. These data suggest that the expansion mainly be human-mediated in large scale, and active disposal or non-anthropogenic passive dispersal might have played an important role in expansion at a smaller scale. In some places far away from Nanjing, several haplotypes existed, suggested multiple introduction events may have happened. Although aquaculture of this species could bring huge economic benefit, its potential to negatively affect native biota and entire ecosystems should not be ignored.