Nadezhda I. Zaslavskaya

Development of Microsatellite Markers for Japanese Scallop (Mizuhopecten yessoensis) and Their Application to a Population Genetic Study

A bstractThe Japanese scallop (Mizuhopectenyessoensis) is one of the main fishery products in Japan, but with the expansion of culture operations of the Japanese scallop, various problems have been encountered including high mortality, poor growth, poor seed production, and so on. Moreover, there is concern that many years of cultivation may have affected the genetic structure of the scallop population. To approach these problems and concerns, we developed microsatellite markers as a molecular tool for population genetic studies. By using 4 microsatellite markers as well as a mitochondrial marker, we investigated the genetic structure of samples from the islands of Hokkaido (14 populations) and Honshu (Tohoku, 3 populations) in Japan, and south Primorye (4 populations) in Russia. All the populations sampled had high genetic diversity (average expected heterozygosity, 0.7011 to 0.7622; haplotype diversity, 0.6090 to 0.8848), and almost all showed a tendency of homozygote excess, which was significant in 2 populations. Hierarchical analysis of molecular variance tests based on the microsatellite and mitochondrial markers indicated that the 3 geographic regions were genetically divergent from one another, with little evidence of divergence within regions. Homogeneity in allele frequency distributions between natural and cultured scallops and allele frequency stability over a period of 2 decades indicated that the culturing operations have probably not had a substantial effect on the genetic structure of the populations.

The species composition of the nemertean genus Oerstedia (Nemertea: Hoplonemertea) in the Far Eastern seas of Russia

According to the literature, six species of nemerteans of the Oerstedia genus occur in the Far Eastern seas of Russia. The results of genetic (28S) and allozyme (11 loci) analysis revealed that O. oculata (Kulikova, 1987), O. zebra (Chernyshev, 1993) and O. valentinae (Chernyshev, 1993) are junior synonyms of O. polyorbis Iwata, 1954, while O. phoresiae (Kulikova, 1987) is a valid species. The species validity of O. dorsalis sensu Iwata, 1954 was also corroborated. New data on the variability and distribution of certain nemerteans are furnished.

Allozyme comparison of the species and colour morphs of the nemertean genus Quasitetrastemma Chernyshev, 2004 (Hoplonemertea: Tetrastemmatidae) from the Sea of Japan

Biochemical genetics was applied to clarify the taxonomic status of the colour morphs of Quasitetrastemma nigrifrons and the sibling species Quasitetrastemma stimpsoni. Five colour morphs and two species were compared using 17 and 24 allozyme loci, respectively. The high average genetic identity value obtained for most of the colour morphs of Q. nigrifrons (I = 0.981) suggests that they belong to the same species. Both Q. stimpsoni and Q. nigrifrons have a lower average I-value (I = 0.718 ± 0.089) and are therefore considered to be separate species. According to the allozyme data, Q. nigrifrons var. pallidum is a heterogeneous group; most specimens are more similar to Q. nigrifrons, although some are closer to Q. stimpsoni.

Phylogeography of Littorina sitkana in the northwestern Pacific Ocean: evidence of eastward trans-Pacific colonization after the Last Glacial Maximum

We investigated genetic diversity and population structure of the Sitka periwinkle Littorina sitkana along the coastlines of the northwestern Pacific (NWP) to evaluate the possibility of trans-Pacific colonization of this species from the NWP to the northeastern Pacific (NEP) after the Last Glacial Maximum. We sampled L. sitkana from 32 populations in the NWP, and sequenced a region of the mitochondrial cytochrome b oxidase gene for population genetic analyses. The results were compared with those of previous reports from the NEP. The genetic diversity of L. sitkana was much higher in the NWP than in the NEP. Genetic connectivity between the NWP and NEP populations was indicated by an extremely abundant haplotype in the NEP that was also present in eastern Hokkaido and the Kuril Islands. To confirm these results, we compared sequences of the longest intron of the aminopeptidase N gene (APN54) in the nuclear genome in four populations of L. sitkana in the NWP with previous results from the NEP. Again, much higher genetic diversity was found in the NWP than in the NEP and genetic connectivity was supported between the Kuril Islands and the NEP. These results imply postglacial colonization of this species from the NWP to the NEP, probably along the Kuril and Aleutian Island chains. This study is the first report of possible trans-Pacific postglacial colonization of a direct-developing gastropod, inferred from genetic data.

The population-genetic structure of Corbicula japonica prime, 1864 (Bivalvia: Cyrenidae) in estuarine water bodies of the Primorsky Region

The population-genetic structure of the bivalve Corbicula japonica from ten estuarine localities in the Primorsky Region was investigated using nine allozyme loci as gene markers. This study revealed spatial genetic heterogeneity between the investigated populations (Gst = 0.05); its degree was dependent on the distance between populations. No linkage disequilibrium was found for any pair of loci. The index of genetic similarity between pairs of populations varied from 0.916 to 0.994. The genetic heterogeneity of the C. japonica populations is probably a result of genetic drift balanced by an irregular gene flow. Such an equilibrium may indicate a relatively recent expansion of C. japonica, which may have occurred during the Holocene climatic optimum (about 7500 years ago).