A Multilocus Study of Natural Populations of Pinus sylvestris

Abstract

Genetic variation of Pinus sylvestris was studied in three natural populations in northern Sweden (latitudes 66°40′N, 65°30′N, and 64°30′N). From seed harvests of each population the macrogametophyte and embryo of 133–134 seeds were studied with respect to 14 variable enzyme loci. The dègree of genetic differentiation between the populations was very low (GST=0.006). The average fixation indices in the populations were 0.135, 0.092, and 0.085, respectively. These positive fixation indices are probably mostly due to selfing. Garnetic disequilibrium between the loci was studied in zygotes and separately in the ovule and pollen pools. Disequilibrium was also divided into between and within individual components. Small, but significant disequilibria were found in the ovule pool of the northernmost population. The between individual component was also significant in this population. As the significantly associated locus pairs were unlinked, we concluded that the disequilibria are due to restricted effective population size. The decrease in the effective size may be due to uneven seed production, partial selfing and different male and female numbers, which are all known to occur in populations of Pinus sylvestris.