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 ¼ 0.043), also indicating long-distance gene flow in C. japonicum. Longdistance 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. Heredity (2006) 96, 79-84.

Small but not isolated: a population genetic survey of the tropical tree Cariniana estrellensis (Lecythidaceae) in a highly fragmented habitat

“…Indeed, even in a highly fragmented landscape, we observed a moderate to high frequency (23.5-53%) of gene immigration, indicating that pollen movement beyond the boundaries of the small fragment can reach distances 41 km (i.e., the distance between the small studied population and the nearest pollen source). Gene flow by pollen dispersal beyond the edges of seemingly isolated forest fragments has been reported for several plant species, including species that are animal-pollinated (Nason and Hamrick, 1997;Dow and Ashley, 1998;Dick et al, 2003;Sato et al, 2006;Nazareno and Carvalho, 2009;Buschbom et al, 2011;Ottewell et al, 2012;Côrtes et al, 2013;Tambarussi, 2013;Saro et al, 2014).…”

Reproductive ecology of the Sitka willow (Salix sitchensis ).

“…Sato et al (2006) found low levels of genetic structure and attributed this to high levels of pollen and seed dispersal. Weak genetic structure may be the result of pollen and seed dispersal as well as post-recruitment mortality (Hardesty et al 2005).…”

“…Windpollinated species are expected to have a higher genetic diversity and lower population differentiation than insect-pollinated species, as wind-dispersed pollen can travel great distances (Dow and Ashley 1998;Sato et al 2006). Salix sitchensis appears to be wind and insect-pollinated, with a higher proportion of wind pollination (Chapter 2).…”

“…Pollen transport between plants can occur by wind or animal (often insect) vectors. Wind-pollinated species will in theory have a higher genetic diversity and lower population differentiation than insectpollinated species, as wind-dispersed pollen can travel great distances (Dow and Ashley 1998;Sato et al 2006). Insect-pollinated species are expected to have a lower genetic diversity and higher population differentiation as insects will spread pollen over shorter distances (Govindaraju 1988).…”

“…Weak or absent genetic structure between populations has been correlated to high levels of seed and pollen dispersal between plots (Hardesty et al 2005;Sato et al 2006). Widespread seed dispersal may eliminate population genetic structure even if pollen dispersal is limited (reviewed in Hardesty et al 2005).…”