Japanese Wild Populations Research Articles

Genetic Variation of Wild and Hatchery Populations of the Pacific Oyster Crassostrea gigas Assessed by Microsatellite Markers

Microsatellite DNA technique was used to detect the genetic variation between five hatchery populations of the Pacific oyster from China and two wild populations from Japan. Seven microsatellite loci screened in this study showed high polymorphism in both hatchery and wild populations, as observed in an average number of allele per locus (19.1–29.9) and average expected heterozygosity (0.916–0.958). No significant difference in average allelic richness or expected heterozygosity was observed between Chinese hatchery populations and Japanese wild populations. Pairwise FST values and heterogeneity tests of allele frequencies showed significant genetic differentiation between all populations. According to the neighbor-joining tree constructed on the basis of the DC distance, the seven populations fell into three groups showing a clear division between hatchery and wild populations, and between the northern and southern hatchery populations. Assignment tests correctly assigned high percentages (97%–100%) of individuals to their original populations and demonstrated the feasibility of microsatellite analysis for discrimination between populations. The information obtained in this study is useful for designing suitable management guidelines and selective breeding programs for the Pacific oyster in China.

Cultivar selection prior to introduction may increase invasiveness: evidence from Ardisia crenata

Ardisia crenata (Myrsinaceae), an evergreen shrub with attractive red fruits introduced from Japan to the USA for ornamental purpose, invades the understory of mesic hardwood forests, forming dense patches (up to 300 stems per m2), and competitively displaces native understory plants by creating dense local shade. Comparison of the wild genotype that grows in mature evergreen broadleaf forests in central Kyushu, Japan, with the ecotype invading north central Florida revealed how selection for desirable cultivars might have inadvertently selected for traits that enhance the invasive potential of the species. In Japanese wild populations in deeply shaded evergreen forests, natural selection apparently maintained efficient architecture with a low degree of self-shading and large seed mass to enhance seedling shade tolerance. Cultivar selection for showy appearance can explain the greater fecundity but smaller seed size observed in the Florida populations compared to the Japanese population. Artificial selection for densely foliated appearance can also explain the greater degree of self-shading and less-efficient light use in the Florida genotype compared to the Japanese wild type grown under a common environment. Furthermore, the Florida ecotype allocated more biomass to root carbohydrate storage. These trait modifications resulted in slower growth rates, but greater competitive ability to cast shade upon neighbors and higher resprouting potential in the Florida populations. How traits are modified through the processes of artificial selection and cultivation must be taken into consideration in the evolutionary ecology of many other invasive plants introduced as ornamental plants.

Geographic Variation and Diversity in the Mitochondrial DNA of the Medaka, Oryzias latipes, as Determined by Restriction Endonuclease Analysis

Analysis of mitochondrial DNA (mtDNA) restriction fragment length polymorphism in Japanese wild populations of the medaka, Oryzias latipes revealed a large number of mtDNA haplotypes that form three distinct clusters (clusters A, B and C). The average nucleotide diversities among these three clusters are 8.9% (A versus B), 8.4% (A versus C), and 7.3% (B versus C). Cluster A consists of seven haplotypes and was subdivided into two subclusters. The nucleotide diversity in cluster A is low, ranging from 0.3% to 1.4% (mean 0.8%). Cluster B has 55 haplotypes and was subdivided into 11 subclusters. The nucleotide diversity in cluster B is high, ranging from 0.1 to 4.8% (mean 1.5%). Cluster C consists of only one haplotype, found in two sites of the Kanto district. The geographic distributions of mtDNA haplotypes in clusters A and B appear fully concordant with the previously described ranges of the Northern Population and the Southern Population defined by allozymes. Moreover, the distributions of mtDNA haplotypes in the subclusters show strong geographical associations. The distribution patterns of mtDNA haplotypes suggest some migration events of the medaka.

Intraspecific variation of isoenzymes in Taenia taeniaeformis

The technique of isoenzyme electrophoresis was applied to Japanese wild populations of Taenia taeniaeformis (isolated from Norway rats) and three laboratory reared isolates (KRN isolated from a Malaysian Norway rat, BMM from a Belgian house mouse and ACR from a Japanese gray red-backed vole). The average heterozygosities of Japanese wild populations were fairly small and total genetic variability was 0.0499. The genetic make-up of T.taeniaeformis in Norway rats was rather uniform in the whole of Japan. In KRN isolate, each of all 10 loci examined possessed the allele which was predominant in Japanese wild populations. Similarly, each of 9 loci in BMM isolate possessed the same alleles, but one of 2 alleles at HK locus was different from that in the others. T. taeniaeformis parasitizing house mice and rats were considered to be genetically closely related to each other. In ACR isolate, 7 out of 10 loci possessed different alleles from those in the other populations. It was considered that ACR isolate was genetically distant and its phylogenetic origin in Japan should be different from worms parasitizing Norway rats.

Detection of isozyme polymorphism and estimation of geographic variation in the brown planthopper,Nilaparvata lugens(Homoptera: Delphacidae)

AbstractIsozyme polymorphism in the brown planthopper,Nilaparvata lugens(Stål) was investigated using isoelectric focusing. Four of the 18 enzyme systems assayed were polymorphic. Allelic designations could be made for two enzyme systems (PGM and AK), but not for GPI and IDH, and GPI seemed to be sex-linked. Using the two highly polymorphic enzyme systems, GPI and PGM, geographic variation was estimated among several Asian (except Japanese) laboratory populations and several Japanese wild populations. Significant variation was observed among the Asian (except Japanese) populations, but the genetic structures of Japanese populations were very similar to each other. These results are suggestive of substantial differentiation among Asian populations and large panmictic structure of the migrant population.

Genetic divergence in wild populations of Medaka, Oryzias latipes (Pisces: Oryziatidae) from Japan and China

Allozyme studies of the cyprinodont fish Oryzias latipes have revealed that the wild populations of this species have differentiated regionally, and that Japanese wild populations are composed of two distinct groups, the Northern Population and the Southern Population. In order to elucidate the genetic relationship and the origin of the two major populations, allozymic characters of the specimens from 21 localities in Japan and China were compared. Although Chinese populations could be distinguished from Japanese ones, they were more closely related to the Southern Population, and showed few allozymic traits of the Northern Population. It is likely that the latter is a relic population which has survived the glacial period along the western coast of north-eastern Japan.

Allozymic Variation and Regional Differentiation in Wild Populations of the Fish Oryzias latipes

Allozymic variation was studied at 21 loci in Japanese wild populations of the freshwater fish Oryzias latipes, collected at 53 localities. By means of the unique alleles at the Adh, Pgm, Idh and Sod loci, the Japanese populations could be divided into two major groups, the 'Northern Population' and the 'Southern Population.' No clinal distribution was observed at these loci, but the boundary of two regions was very distinct. The Southern Population was further divided into five subpopulations by the unique alleles at Acp, Amy, Aat, Me and Pgd. In this case also, the boundary was clear. The Northern Population was very homogeneous. On the other hand, the Southern Population was variable. These results show that Japanese wild populations of medaka are remarkably differentiated regionally. As little clinal distribution is observed, it is supposed that the differentiation is primarily due to geographical isolation.