Mating patterns and pollen dispersal in a natural knobcone pine (Pinus attenuate Lemmon.) stand

Abstract

Mating system and effective pollen dispersal were studied in a natural stand of knobcone pine (Pinus attenuata Lemmon.) using 11 isozyme loci. Analyses were performed by fitting neighbourhood and mixed-mating models to multilocus genotypic arrays of offspring from four mother trees. Neighbourhoods consisted of all potential outcross males within 11 m of each mother tree (44, on average). Average outcrossing rates of the mother trees were estimated to be 0.97 and 0.96 for the respective models, whereas the population-wide outcrossing rate based on the mixed-mating model and a broader sample of mother trees was 0.92. The estimated proportion of offspring sired by males outside the neighbourhood of each mother tree was 0.56. Thus about 41 per cent of matings resulted from outcrossing with nearby males (within neighbourhoods). Distance and direction of individual males from mother trees and the size (tree height) of males played significant roles in determining outcross mating patterns within neighbourhoods. Male mating success increased with both proximity and tree size, although males east of mother trees accounted for more offspring than males in other directions. Despite the role of proximity, directionality and tree size in determining mating success within neighbourhoods, the effective number of males mating with each female seems to be large.