HISTORICAL AND CONTEMPORARY MATING PATTERNS IN REMNANT POPULATIONS OF THE FOREST TREE FRAXINUS EXCELSIOR L

• Published in: Evolution 2005-05, Vol.59 (5), p.979-990
• Main Authors: Bacles, Cecile F. E, Burczyk, Jaroslaw, Lowe, Andrew J, Ennos, Richard A
• Format: Article
• Language: English
• Subjects: Alleles; Biological Evolution; Demography; Effective pollen dispersal; F-statistics; Forests; fragmented landscape; Fraxinus - genetics; Fraxinus - physiology; Fraxinus excelsior; Fraxinus excelsior L; Gene flow; Gene Frequency; Genetic diversity; Genetic loci; Genetic Variation; Genetics, Population; Microsatellite Repeats - genetics; Microsatellites; Models, Biological; neighborhood model; Plant reproduction; Pollen; Pollen - physiology; Population Dynamics; Population genetics; Quantitative genetics; REGULAR ARTICLES; Reproduction - physiology; Scotland; Seeds - genetics; Street trees; Trees; Watersheds
• ISSN: 0014-3820; 1558-5646
• DOI: 10.1554/04-653

Genetic variation at microsatellite markers was used to quantify genetic structure and mating behavior in a severely fragmented population of the wind-pollinated, wind-dispersed temperate tree Fraxinus excelsior in a deforested catchment in Scotland. Remnants maintain high levels of genetic diversity, comparable with those reported for continuous populations in southeastern Europe, and show low interpopulation differentiation (Θ = 0.080), indicating that historical gene exchange has not been limited (Nm = 3.48). We estimated from seeds collected from all trees producing fruits in three of five remnants that F. excelsior is predominantly outcrossing (tm = 0.971 ± 0.028). Use of a neighborhood model approach to describe the relative contribution of local and long-distance pollen dispersal indicates that pollen gene flow into each of the three remnants is extensive (46–95%) and pollen dispersal has two components. The first is very localized and restricted to tens of meters around the mother trees. The second is a long-distance component with dispersal occurring over several kilometers. Effective dispersal distances, accounting for the distance and directionality to mother trees of sampled pollen donors, average 328 m and are greater than values reported for a continuous population. These results suggest that the opening of the landscape facilitates airborne pollen movement and may alleviate the expected detrimental genetic effects of fragmentation.