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 q uantitative traits were used to examine geographic differentiation among 65 British Columbia provenances of red alder (Alnus rubra Bong.). Principal c omponents analysis showed that variation in quantitative traits can be redu ced 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, a llozyme frequencies, and geographic variables revealed complex associations of quantitative traits with the latitude, distance to the coast, and eleva tion of the seed source. There were no significant correlations among alloz yme frequencies and quantitative traits, but the frequency of the most comm on allele at most loci decreased with latitude. Further, cluster analysis b ased on Nei's genetic distance revealed a strong differentiation among isla nd and mainland provenances at one allozyme locus. This differentiation can be interpreted as a result of migration from two different refugia since t he 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.