Isolation-by-distance within naturally established populations of European beech (Fagus sylvatica)

Abstract

In plants, the magnitude of seed and pollen dispersal plays a pivotal role in shaping genetic structure of populations. Restricted dispersal of genes can stimulate the increase of inbreeding as well as spatial clustering of relatives. These phenomena are explained by the theory of isolation-by-distance. Because of its biology, European beech ( Fagus sylvatica L.) seems to be susceptible to isolation-by-distance. However, to date fine-scale effects, including biparental inbreeding and a spatial genetic structure are not fully recognized for this species. In this study, two populations of European beech were investigated, both representing a dense beech forest, typical for Central Europe. Using nine microsatellite markers and a recently developed method, we found a significant level of biparental inbreeding in both populations. Spatial autocorrelation analysis revealed that both populations exhibit clustering of related individuals up to 40 m. The observed spatial genetic structure fit well to the log-linear regression model. Thus, results confirmed our hypothesis of the presence of the isolation-by-distance effect. Furthermore, based on these results we inferred a dispersal mode, both for seeds and pollen; in particular, seed dispersal was 10–100 times more restricted than pollen flow, although a significant portion of short-distance pollinations responsible for biparental inbreeding cannot be excluded.