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 Lutken was recently in troduced to Tasmanian waters, possibly through ballast water discharge d from ocean-going vessels. Three Tasmanian populations and seven nati ve populations from Japan and eastern Russia were examined in 1994 for variation at 22 allozyme loci. There was significant spatial heteroge neity in gene frequencies among the native populations, especially for the locus APK, where Gs, was a very high 0.47. The Tasmanian populat ions could not be separated genetically from one another, suggesting t hey have a common origin from a single introduction. The average heter ozygosity per locus of the Tasmanian populations (0.116 to 0.127, mean 0.123) was similar to 30 to 40% less than that of the native populati ons (0.177 to 0.216, mean 0.192), suggesting that colonisation of Tasm anian waters was accompanied by a population-size bottleneck. The Tasm anian seastars were genetically more closely related to the two popula tions from central Japan (Suruga and Tokyo Bays) than to populations f rom Vladivostok, northern Japan (Yoichi, Nemuro and Mutsu Bays) or sou thern 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 th e Tasmanian introduction has yet to be identified.