Regional subdivision in wild barley allozyme variation: adaptive or neutral?

Abstract

We examined the adaptive importance of allozyme variation in wild barley (Hordeum spontaneum). The test involved a nested sampling design with four population groups, each representing a different environment, and a comparison of observed allozyme variation with that expected under the assumption that allozymes are not neutral. Measurements of plant fitness in indigenous and alien environments in reciprocal introductions of seeds and seedlings in the four environments provided a guideline for the expected pattern of allozyme variation. The results showed considerable variation in both the degree of regional and population subdivision and the pattern of the subdivision among loci. The observed pattern of variation was ambiguous. Although two alleles exhibited a pattern of distribution that cannot be explained by genetic drift as a function of geographic distance, we failed to detect either a significant relationship between genetic distance and environmental similarity or any favored epistatic allele combinations across the four environments. Our results suggest that interpretation of allozyme variation in wild barley as adaptive and directly related to local environment still needs justification. Although we could not reject the null hypothesis, a proposed methodology seeking a concordance between observed and "adaptive" (i.e., expected under hypothesis that allozymes are not neutral) allozyme variation may prove to be effective in resolving the neutralist-selectionist debate when applied to other species.