A COMPARISON OF POPULATION DIFFERENTIATION ACROSS 4 CLASSES OF GENE MARKER IN LIMBER PINE (PINUS-FLEXILIS JAMES)

We examined genetic differentiation among seven populations of limber pine using four classes of gene marker. Among-population differentiati on was much higher for maternally inherited mitochondrial DNA polymorp hisms than for paternally inherited chloroplast DNA, indicating that w ind-dispersed pollen is the main agent of gene flow. Chloroplast DNA d ifferentiation is consistent with gene flow estimated in a prior pater nity analysis. Using the estimates of seed and pollen flow derived fro m mtDNA and cpDNA differentiation, we predicted the value of F-st expe cted at nuclear loci. Allelic frequency differentiation at seven alloz yme loci was relatively homogeneous across loci and consistent with th e level of differentiation predicted from the organellar haplotypes. B y contrast four of the nine randomly applied polymorphic DNA (RAPD) ma rkers we examined were more strongly differentiated than this predicti on, suggesting the action of diversifying selection. However, the diff erentiated RAPDs and mtDNA were concordant in dividing the populations into two groups, suggesting some historical division. Simulations sho w that such historical division can increase the interlocus variance i n F-st, but neither a historical nor an equilibrium model could accoun t for the joint distribution of F-st estimates across both allozyme an d RAPD loci. Thus at least one group of loci appears to be experiencin g natural selection.