VOLIS, S.*, S. MENDLINGER, and D. WARD. Mitrani Department for Desert Ecology, The Blaunstein Institute for Desert Research, Ben Gurion University, Beer Sheva, 84100, ISRAEL. - Tests for adaptive RAPD and allozyme variation in population genetic structure of wild barley, Hordeum spontaneum Koch.
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