Multivariate analysis of allozymic and quantitative trait variation in Alnus rubra:: geographic patterns and evolutionary implications

Frequency data from six polymorphic allozyme loci and measurements of six quantitative traits were used to examine geographic differentiation among 65 British Columbia provenances of red alder (Alnus rubra Bong.). Principal components analysis showed that variation in quantitative traits can be reduced to two underlying dimensions, one representing general vigor including the termination of the growing period and the other being the start of the growing period. Canonical correlation analysis among quantitative traits, allozyme frequencies, and geographic variables revealed complex associations of quantitative traits with the latitude, distance to the coast, and elevation of the seed source. There were no significant correlations among allozyme frequencies and quantitative traits, but the frequency of the most common allele at most loci decreased with latitude. Further, cluster analysis based on Nei's genetic distance revealed a strong differentiation among island and mainland provenances at one allozyme locus. This differentiation can be interpreted as a result of migration from two different refugia since the last glaciation. The island populations presumably originate solely from isolated coastal refugia west of the Cordilleran ice sheet, while mainland populations were also recruited from areas south of the ice.