1. ¹Division Forest, Nature and Landscape Research, Catholic University of Leuven, Celestijnenlaan 200E, Leuven B-3001, Belgium
2. ²Laboratory of Plant Ecology, Catholic University of Leuven, Arenbergpark 31, Heverlee B-3001, Belgium
3. ³Institute of Nature Conservation, Kliniekstraat 25, Brussels B-1070, Belgium
4. ⁴Institute for Forestry and Game Management, Gaverstraat 4, Geraardsbergen B-9500, Belgium

Correspondence: H Jacquemyn, Division Forest, Nature and Landscape Research, Catholic University of Leuven, Celestijnenlaan 200E, Leuven B-3001, Belgium. E-mail: hans.jacquemyn@biw.kuleuven.be

Received 19 December 2005; Accepted 7 March 2006; Published online 12 April 2006.

Abstract

Long-distance seed dispersal is a crucial determinant of within-population genetic variability and among-population genetic differentiation in plant metapopulations undergoing recurrent local extinctions and (re-)colonization. We investigated the spatial and temporal structure of genetic variation in a metapopulation of Sisymbrium austriacum located along a dynamic river system using dominant AFLP markers. Data on riverbank dynamics and colonization history allowed separating populations based on their age (5 vs >5 years old). Bayesian analysis of population genetic structure indicated that populations were significantly differentiated from each other, but Mantel tests revealed that there was no relationship between pairwise geographic and genetic distances, suggesting that long-distance seed dispersal partly determines spatial genetic structure. Recent populations were less differentiated from each other than old populations. Analysis of molecular variance (AMOVA) indicated that both spatial factors and population age significantly determined genetic diversity, the effects of age being more important than spatial location. Clustering analysis revealed five large clusters, which were related primarily to population age and to a minor extent to geographical location. Our results indicate that the recurrent formation and destruction of riverbank habitats following peak flow events have a large impact on genetic diversity of riparian plant species.