Population genetics of the northern Pacific seastar Asterias amurensis (Echinodermata: Asteriidae): allozyme differentiation among Japanese,Russian, and recently introduced Tasmanian populations

The northern Pacific seastar Asterias amurensis Lütken was recently introduced to Tasmanian waters, possibly through ballast water discharged from ocean-going vessels. Three Tasmanian populations and seven native populations from Japan and eastern Russia were examined in 1994 for variation at 22 allozyme loci. There was significant spatial heterogeneity in gene frequencies among the native populations, especially for the ocus APK ^*, where G _ST was a very high 0.47. The Tasmanian populations could not be separated genetically from one another, suggesting they have a common origin from a single introduction. The average heterozygosity per locus of the Tasmanian populations (0.116 to 0.127, mean 0.123) was 30 to 40% less than that of the native populations (0.177 to 0.216, mean 0.192), suggesting that colonisation of Tasmanian waters was accompanied by a population-size bottle-neck. The Tasmanian seastars were genetically more closely related to the two populations from central Japan (Suruga and Tokyo Bays) than to populations from Vladivostok, northern Japan (Yoichi, Nemuro and Mutsu Bays) or southern Japan (Ariake Sea). However, there were significant differences between the populations from Tasmania and central Japan, which may be attributable to founder effects or may mean that the true source of the Tasmanian introduction has yet to be identified.