Random amplified polymorphic DNA diversity of marginal and central populations in Pinus contorta subsp. latifolia

Fifteen populations of lodgepole pine (Pinus contorta subsp. latifolia) were surveyed for diversity across 52 random amplified polymorphic DNAs (RAPDs). The objective was to compare single-locus and multilocus structures in four marginal, three intermediate, and eight central populations. Single-locus estimates indicated average observed and expected heterozygosity to be 0.19 and 0.17, respectively. When these estimates were split into population categories, a clear trend of increasing diversity was detected in the direction of marginal to central populations. F-statistics indicated an excess of heterozygotes, with F(IS) ranging from -0.08 for marginal populations to -0.15 for central populations and averaging -0.12 over 15 populations. The estimates of F(ST) decreased towards the margins of the species range, indicating increased population differentiation. Forty-nine of 52 RAPDs tested neutral in the Ewens-Watterson analysis. Multilocus analysis showed significant two-locus and high-order gametic disequilibria in all 15 populations. The most prominent components of the two-locus analysis were the variance of disequilibrium (VD, 46.2%) and the multilocus Wahlund effect (31.9%). This high value for VD indicated that founder effects could explain much of the observed multilocus associations. When analyzed by population categories, the VD showed a decreasing trend indicating that variation due to founder effects was more prominent in marginal populations. The two-locus Wahlund effect (WC) that is characteristic of strong population subdivision was highest in the central populations. This indicated significant levels of gene flow between populations with different allelic combinations.