Multilocus structure in thePinus contorta – Pinus banksianacomplex

Abstract

Natural hybridization between lodgepole pine ( Pinus contorta Dougl. ex Loud.) and jack pine ( Pinus banksiana Lamb.) in western Canada provides a distinct opportunity to infer evolutionary and demographic determinants of nonrandom associations of the alleles at different loci occurring in this Pinus contorta – Pinus banksiana complex (PCBC). Here, we investigated multilocus associations among and within 40 PCBC populations sampled from central and northwestern Alberta, using 39 random amplified polymorphic DNA (RAPD) markers. For each of the 40 PCBC populations, we examined distributions of 741 pairs of linkage (gametic) disequilibria (LD) between the 39 RAPDs and measured the “average” multilocus associations using the summary statistics that allow for packaging of individual LD in each population. We then partitioned the variance of LD in the total population to assess the causes of multilocus population structure. The results showed that (i) LD were more prominent in hybrid populations than in parental populations; (ii) multilocus Wahlund effect was a much more important determinant of population structure than its single-locus counterpart, particularly in hybrid populations; and (iii) considerable mutlilocus associations across the populations within each taxa group was due to the presence of different multilocus haplotypes in different populations. Such results are best explained by the fact that PCBC populations are geographically and ecologically marginal and are produced at the balance between mixing of two distinct gene pools creating new recombinants and selection in favor of parental gametes, but against the recombinants.