High rates of gene flow by pollen and seed in oak populations across Europe

PLoS One. 2014 Jan 13;9(1):e85130. doi: 10.1371/journal.pone.0085130. eCollection 2014.

Abstract

Gene flow is a key factor in the evolution of species, influencing effective population size, hybridisation and local adaptation. We analysed local gene flow in eight stands of white oak (mostly Quercus petraea and Q. robur, but also Q. pubescens and Q. faginea) distributed across Europe. Adult trees within a given area in each stand were exhaustively sampled (range [239, 754], mean 423), mapped, and acorns were collected ([17,147], 51) from several mother trees ([3], [47], 23). Seedlings ([65,387], 178) were harvested and geo-referenced in six of the eight stands. Genetic information was obtained from screening distinct molecular markers spread across the genome, genotyping each tree, acorn or seedling. All samples were thus genotyped at 5-8 nuclear microsatellite loci. Fathers/parents were assigned to acorns and seedlings using likelihood methods. Mating success of male and female parents, pollen and seed dispersal curves, and also hybridisation rates were estimated in each stand and compared on a continental scale. On average, the percentage of the wind-borne pollen from outside the stand was 60%, with large variation among stands (21-88%). Mean seed immigration into the stand was 40%, a high value for oaks that are generally considered to have limited seed dispersal. However, this estimate varied greatly among stands (20-66%). Gene flow was mostly intraspecific, with large variation, as some trees and stands showed particularly high rates of hybridisation. Our results show that mating success was unevenly distributed among trees. The high levels of gene flow suggest that geographically remote oak stands are unlikely to be genetically isolated, questioning the static definition of gene reserves and seed stands.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Europe
  • Gene Flow / genetics*
  • Hybridization, Genetic
  • Pollen / genetics*
  • Quercus / genetics*
  • Reproduction
  • Seedlings / genetics
  • Seeds / genetics*
  • Trees / genetics

Grant support

The work was funded by the European Project "Fairoak" ("Synthetic maps of gene diversity and provenance performance for utilisation and conservation of oak genetic resources in Europe", European Commission Directorate General VI Agriculture, contract FAIR PL95-0297), and the European Union Project "Oakflow" ("Intra- & interspecific gene flow in oaks as mechanisms promoting genetic diversity and adaptive potential", QLK5-2000-00960). The Swiss State Secretariat for Education and Research (SER, 99.0838) financially supported FG and AD. DS received a PhD grant from Copenhagen University. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.