Genetic diversity and differentiation in a southern beech subjected to introgressive hybridisation

MARCHELLI, P; GALLO, L

HEREDITY

Año: 2001 vol. 87 p. 284 - 293

0018-067X

Diversity and di€erentiation among 11 Argentine populations of the South American southern beech,Nothofagus nervosa (Phil.) Dimitri & Milano, were studied using eight isozyme gene markers. Geneticdiversity, observed heterozygosity, mean number of alleles per locus, Gregorius' genetic distance,amount of genetic di€erentiation and mean level of di€erentiation among populations were estimated.Introgression of N. obliqua into the gene pool of N. nervosa was analysed using two species-speci®cisozyme gene markers (Adh-A and Pgi-B). As in most forest tree species, the main genetic variationwas found within populations. Mean observed heterozygosity for the species was 17.3%, whilst meanlevel of genetic di€erentiation (dge) was 4.6%. The most di€erentiated locus was Mdh-B withdi€erences in 10% of the e€ective number of genes. From the analysis of the species distributionpattern it is suggested that genetic variation is geographically structured through the di€erent lakewatersheds along which the species is distributed. The occurrence of natural interspeci®c hybridiza-tion in some of the watersheds, together with the unidirectional gene ¯ow along these watershedssharpens this latitudinal structure. Di€erent evolutionary stages in the introgressive hybridizationprocess are apparently taking place in di€erent lake watersheds.