Genetic diversity in longleaf pine (Pinus palustris): influence of historical and prehistorical events

Abstract

Genetic diversity of allozymes at 24 loci was studied in 23 populations of longleaf pine (Pinus palustris Mill.), including three seed orchard populations and an old-growth stand. Overall, the mean number of alleles per polymorphic locus was 2.9, the percentage of polymorphic loci was 92%, and the mean expected heterozygosity was 0.105. These values are comparable with diversity measures found in a similar loblolly pine (Pinus taedaL.) study. Diversity measures of the seed orchard sources and the old-growth stand were similar to those in the other natural seed sources. F statistics indicate very little inbreeding overall (FIS = -0.002) and low differentiation among populations (FST = 0.041). All measures of genetic diversity were significantly related to longitude; western sources tended to have more allozyme diversity. Since growth or survival are not related to longitude, and no important climatic variables are related to longitude within the natural range of longleaf, it is proposed that the east-west variation in longleaf pine is a result of migration from a single refugium in the west (south Texas or northeastern Mexico) after the Pleistocene.