Genetic relationships in Abies (fir) of eastern United States: an electrophoretic study

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Abstract
Abies (fir) is widely considered to consist of two species in the eastern United States, A. balsamea (L.) Mill, and A. fraseri (Pursh.) Poir., distinguished by relative cone bract to subtending cone scale lengths and number of leaf hypodermal cells. Intermediate individuals have been recognized as A. balsamea var. phanerolepis Fern. An understanding of the relationship between the two putative species hinges on the interpretation of the intermediate. Two alternative hypotheses view the intermediate as either an interspecific hybrid or as an intraspecific variant. Twenty gene loci were electrophorctically analyzed in samples from 12 populations representing all three taxa. All populations shared similar complements of alleles at comparable frequencies for 13 polymorphic loci. Genetic distances among populations ranged from 0.10 to 0.0. Cluster analysis joined populations of A. fraseri with those representing A. balsamea var. phanerolepis at a distance of 0.03 and linked populations of A. balsamea with the other two taxa at 0.06. A hierarchical analysis of the three taxa, delimited by cluster analysis and bract exsertion, places A. balsamea var. phanerolepis intermediate between the two species. These data support a conspecifie status for all of eastern U.S. Abies with gene exchange between populations relatively unrestricted at last contact (≈ 10 000 years BP). Further, A. balsamea var. phenerolepis, while electrophoretically intermediate, is likely not of hybrid origin. Our results are consistent with those of recent studies which conclude that A. fraseri and A. balsamea are very closely related taxa of Pleistocene origin.