ALLOZYME DIVERSITY AND GENETIC-STRUCTURE IN SOUTH-WESTERN POPULATIONSOF HEATHER, CALLUNA-VULGARIS

Genetic diversity, population genetic structure and gene flow in Callu na vulgaris (L.) Hull were assessed by means of seven allozyme loci sc ored in 18 populations from the South-Western area of the species' ran ge. Genetic diversity was lower (H-T = 0.20) than reported for long-li ved widespread species but was characterized by a high number of allel es per locus (5.60 at the species level) of which more than 70% were r are. More than 95% of genetic variation was found at the intrapopulati on level (G(ST) = 0.047). High levels of past gene flow were inferred, based on the allozyme data (N-m = 5.2 from G(ST), N-m = 10.2 from the 'private allele' method). Calluna vulgaris exhibited several geograph ic patterns of genetic variation. Both cluster analysis, constructed w ith various genetic distances and principal components analysis showed that Spanish and Pyrenean populations were clearly different from tho se collected in the Massif Central and Belgium. Also, a trend for decr easing genetic diversity towards Northern populations was detected. Th ese patterns might be related to the post-glacial history of Calluna. In addition, it is shown that isolation by distance has played a role in the geographic shaping of genetic variation in this species.