Gene flow in Plantago I. Gene flow and neighbourhood size in P. lanceolata

Abstract

The genetic population structure and gene flow in the obligatory outbreeding plant species Plantago lanceolata L. were determined in the Westduinen (Wd) pasture population in the South-West of the Netherlands. Three experiments were performed: the measurement of genetic structure using allozyme variation, pollen flow in a wind-tunnel and the distribution of an allozyme marker in a garden experiment. The position and allozyme genotype of 524 plants from eight subpopulations in the Westduinen population were determined. The population exhibited local differentiation: genotype frequencies within subpopulations were mostly in Hardy-Weinberg equilibrium, and gene frequencies varied significantly between subpopulations. The wind-tunnel experiments showed that wind speed, source height and capture height of pollen influenced the pollen-mediated gene flow and therefore neighbourhood sizes. In the garden experiment a clear picture of actual pollen flow could be shown. Estimates of neighbourhood and gene transport parameters from the data of the three experiments indicated restricted gene flow: neighbourhood size (Ne) was between 14 and 20 plants, mean gene transport per generation (M) between 0·2 and 1·4 metres. We argue that this combination of small effective number and low gene transport leads to the substructuring of the Westduinen population of P. lanceolata.