Historical and Contemporary Mating Patterns in Remnant Populations of the Forest Tree Fraxinus Excelsior L

Abstract

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 (E = 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 (t(m) = 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.

Native bees mediate long-distance pollen dispersal in a shade coffee landscape mosaic

“…Pollen dispersal curves in both habitats exhibited a fat-tailed distribution, indicating that even isolated trees received pollen from a relatively large number of pollen donors (i.e., 36). Past gene flow studies have focused on partly self-compatible species with unspecialized flowers (23,(37)(38)(39)(40)(41)(42)(43) and have occasionally found that isolated trees in agricultural landscapes receive pollen from a large number of distant sires (23,38). However, Africanized honey bees may have been the primary vectors of gene flow in these studies (23,24).…”

Paternity analysis of pollen-mediated gene flow for Fraxinus excelsior L. in a chronically fragmented landscape

“…Remnant stands are typically separated by hundreds of metres although some can be isolated by more than one kilometre. In this catchment, F. excelsior is present in only five forest remnants, two of them within the Carrifran Burn and three others in its immediate surroundings (Figure 1; see also Bacles et al, 2005).…”

The resilience of forest fragmentation genetics—no longer a paradox—we were just looking in the wrong place

“…The first is through extensive gene flow via pollen and/or seed (in many cases over 10 s of km; e.g. White et al, 2002;Bacles et al, 2005), which can maintain connectivity even in highly fragmented and degraded landscapes where trees persist at very low densities in matrices of varied land use (for example, Breed et al, 2011;Lander et al, 2011). The second is due to the long-lived nature of trees and the existence of overlapping generations on single sites that serves to retard the loss of genetic diversity (for example, Lowe et al, 2005;Petit and Hampe, 2006;Bacles and Jump, 2010;Davies et al, 2010).…”