Hybridization between Picea rubens and Picea mariana: Differences observed between montane and coastal island populations

Foliage was collected from natural stands of montane and island red spruce (Picea rubens Sarg.) and black spruce (Picea mariana (Mill.) BSP) to examine within- and among-population genetic variation. Samples were scored for frequencies of nuclear ribosomal DNA (rDNA) alleles, and mitochondrial and chloroplast haplotypes. Samples were classified as red spruce, black spruce, or hybrid using two molecular methods: a three character discriminant function based on molecular markers or a three-character molecular index. These results were found to be highly congruent with classification based upon a discriminant function using morphological traits. Among montane populations, hybridization and introgression between red and black spruce did not appear to be a major factor in the observed patterns of variation on elevational transects on Mount Washington and Mount Lafayette, N.H. However, extensive hybridization and introgression were detected among populations on Isle au Haut, Maine. The Mount Lafayette population displayed low variation in rDNA alleles compared with populations on Mount Washington and a range-wide provenance test in Stewartstown, N.H.