title: Effect of gene flow on spatial genetic structure in the riparian canopy tree Cercidiphyllum japonicum revealed by microsatellite analysis.
abstract: Few studies have analyzed pollen and seed movements at local scale, and genetic differentiation among populations covering the geographic distribution range of a species. We carried out such a study on Cercidiphyllum japonicum; a dioecious broad-leaved tree of cool-temperate riparian forest in Japan. We made direct measurement of pollen and seed movements in a site, genetic structure at the local scale, and genetic differentiation between populations covering the Japanese Archipelago. Parentage analysis of seedlings within a 20-ha study site indicated that at least 28.8% of seedlings were fertilized by pollen from trees outside the study site. The average pollination distance within the study site was 129 m, with a maximum of 666 m. The genotypes of 30% of seedlings were incompatible with those of the nearest female tree, and the maximum seed dispersal distance within the study site was over 300 m. Thus, long-distance gene dispersal is common in this species. The correlation between genetic relatedness and spatial distance among adult trees within the population was not significant, indicating an absence of fine-scale genetic structure perhaps caused by high levels of pollen flow and overlapping seed shadows. Six populations sampled throughout the distribution of C. japonicum in Japan showed significant isolation-by-distance but low levels of genetic differentiation (F(ST) = 0.043), also indicating long-distance gene flow in C. japonicum. Long-distance gene flow had a strong influence on the genetic structure at different spatial scales, and contributes to the maintenance of genetic diversity in C. japonicum.
authors.affiliation: Graduate School for International Development and Cooperation, Hiroshima University, Kagamiyama 1-5-1, Higashi-Hiroshima 739-8529, Japan satou.t-od@nhk.or.jp
authors.forename: T
authors.initials: T
authors.lastname: Sato
authors.forename: Y
authors.initials: Y
authors.lastname: Isagi
authors.forename: H
authors.initials: H
authors.lastname: Sakio
authors.forename: K
authors.initials: K
authors.lastname: Osumi
authors.forename: S
authors.initials: S
authors.lastname: Goto
mesh_terms: D051456:Gene Flow; D014644:Genetic Variation; D019684:Magnoliopsida / Q000235:genetics*; D018895:Microsatellite Repeats; D011058:Pollen; D012098:Reproduction; D012639:Seeds; D014197:Trees