Abstract

We estimated allele frequencies for 10 polymorphic allozyme loci in samples from 18 natural populations of Nothofagus nervosa (Fagaceae), analyzed the genetic structure and inferred the recent evolutionary history of this southern Beech. Genetic variation in N. nervosa is organized as in most widely distributed, allogamous, anemochoric, anemophilic trees: high levels of within population polymorphism (A = 3.04, He = 0.28), considerable deficiency of heterozygotes (mean FIS = 0.186) and moderate differentiation among populations (FST = 0.051). The UPGMA dendrogram revealed five groups of populations, two of which may have been isolated since before the last glacial period. Correlations among alleles at multiallelic loci do not follow the pattern expected for random differentiation of populations from a single source. The presence of a number of alleles with low frequencies, moderate genetic diferentiation among populations and high levels of genetic variation within populations, all argue that N. nervosa populations survived the last glaciation in large refuges, and probably colonized in waves. Our results suggest at least 4 refuges from which the current populations of raulf have derived; the current genetic structure of the species is best explained by post-glacial expansion.