GENETIC DISCONTINUITY AND POPULATION DIFFERENTIATION IN EASTERN NORTH AMERICAN ABIES REVEALED BY CHLOROPLAST MICROSATELLITES

Forest Biotechnology Group, Department of Forestry, 6113 Jordan Hall, North Carolina State University, Raleigh, NC 27695-8008 USA

Uniparentally inherited chloroplast DNA at microsatellite loci provided evidence of genetic discontinuity and population differentiation in three sibling species of eastern North American Abies (Mill.). Fraser (Abies fraseri (Pursh) Poir.), balsam (A. balsamea (L.) Mill.) and intermediate fir (A. balsamea var. phanerolepis Fern.) are closely related, intergrading taxa with minimal reproductive isolation. Taxonomic boundaries are obscured by overlapping morphological, chemical and genetic characteristics. Two highly variable microsatellite loci were assessed to provide insight into evolutionary history and genetic divergence of these taxa. Microsatellite sequences from genomic DNA were PCR-amplified from 78 individuals (26 from each taxon) representing the geographic ranges of Fraser, balsam and intermediate fir, and from regional population samples of Fraser (n=37) and intermediate (n=42) fir. Gene diversity levels at two loci averaged 0.76 and 0.77 in the range wide and regional populations, respectively. Allele frequencies in range wide and regional samples show significant departure from homogeneity in chi - square analysis (p<0.05) in all comparisons between the three taxa. The range wide sample demonstrates a high level of population subdivision as shown by an R_ST value of 0.359. The high level of partitioning of variation between populations was confirmed by a hierarchical analysis of molecular variance (AMOVA). Non-random association of alleles at the two loci was seen in both intermediate (p=0.0) and balsam fir (p=0.055). A parsimonious network analysis based on allele size distribution reveals two distinct clusters of haplotypes related to geographic distribution in range wide samples of Fraser, balsam and intermediate fir.