GENETIC-VARIATION AT ALLOZYME AND RAPD LOCI IN SESSILE OAK QUERCUS-PETRAEA (MATT) LIEBL - THE ROLE OF HISTORY AND GEOGRAPHY

The nuclear genetic variation within and among 21 populations of sessi le oak was estimated at 31 RAPD loci in conjunction with previous esti mates of variation at eight allozyme loci. The aim of the study was to assess the relative role of isolation-by-distance and postglacial his tory on patterns of nuclear variation. Because of its small effective population size and maternal transmission, the chloroplast genome is a good marker of population history. Both kinds of nuclear variation (R APD and allozyme) were therefore compared, first, to the geographical distances among populations and, secondly, to chloroplast DNA restrict ion polymorphism in the same populations. Multiple Mantel tests were u sed for this purpose. Although RAPDs revealed less genetic diversity t han allozymes, levels of genetic differentiation (G(ST)) were identica l. The standard genetic distance calculated at all RAPD loci was corre lated with geographical distances but not with the genetic distance ca lculated from chloroplast DNA data. Conversely, allozyme variation was correlated with chloroplast DNA variation, but not with geography. Po ssibly, divergent selection at two allozyme loci during the glacial pe riod could explain this pattern. Because of its greater number of loci assayed, RAPDs probably provided a less biased picture of the relativ e role of geography and history.