We tested the adaptive importance of allozyme and RAPD variation in population genetic structure of wild barley, Hordeum spontaneum. The test involved: 1) a nested sampling design with four population groups representing a definite environment each; and 2) a comparison of observed variation in molecular markers with that expected as a result of natural selection. An analysis of selection done previously on fitness-related traits by reciprocal introductions served as guidelines for expected pattern of RAPD and allozyme variation. We found no concordance between the observed pattern of population genetic structure and that expected under the null hypothesis of environment-specific natural selection. Limited gene flow and genetic drift could explain the pattern of variation over all loci as well as in each locus studied. Our results oppose repeatedly suggested adaptive importance of molecular marker variation in wild barley. The fact that environmentally-induced adaptation, detected by fitness-related traits, was not reflected in inter-population genetic structure assessed by RAPD and allozyme markers: 1) strongly enhances the neutralists' point of view in a neutralist-selectionist debate; and 2) doubts the methodology that regards significant correlation between some environmental parameter and allozyme frequencies in one or more loci as evidence of selection on the latter.

Key words: adaptation, Hordeum spontaneum, molecular markers, population differentiation