XVI International Botanical Congess

We have examined patterns of chloroplast (cp) DNA, allozyme, RAPD and quantitative trait variation in Senecio gallicus Vill. (Asteraceae). This is a diploid, annual plant that occurs in both coastal and ruderal inland areas of the Iberian Peninsula and southern France. The species appears to have a strong propensity for long-distance seed dispersal. A major part of the coastal vs. inland divergence as inferred from cpDNA haplotype frequencies was concordant with the geographic subdivision in RAPD and quantitative traits, but strongly contrasted with the geographic uniformity of the species for allozymes. This concordance across cytoplasmic and various nuclear markers (cpDNA vs. RAPDs and quantitative traits) suggests that geographic uniformity for allozymes is more attributable to low rates of evolution and/or small genome sampling rather than high rates of pollen dispersal, slow rates of nuclear lineage sorting, or indirect balancing selection. It is further suggested that isolation of populations in Atlantic-Mediterranean coastal refugia during previous glacial maxima, and the effects of subsequent colonization events in inland areas, have had an important effect on molding the present genetic structure of the species.