Divergence and variation of quantitative traits between allozyme genotypes ofAvena barbatafrom contrasting habitats

Abstract

Summary 1 Avena barbata occurs as two multilocus allozyme genotypes associated with moist (mesic) and dry (xeric) habitats in California. We examined the divergence of quantitative traits between these genotypes, and heritable trait variation in the progeny of a cross. 2 A replacement series showed that the mesic genotype was competitively superior to the xeric. Early germination could alter this competitive outcome, but there was very little difference between the genotypes in germination time. 3 The mesic genotype exhibited larger seeds, and seedlings, as well as greater fecundity. However, there was no difference in relative growth rate between the genotypes. Thus the early size advantage of the mesic genotype seems to be due primarily to larger seed size. 4 Seedlings of the xeric genotype expressed a greater root mass ratio (RMR), and allocated a higher fraction of their root mass deeper in the soil when grown in artificial soil columns than did the mesic genotype. 5 We crossed the two genotypes and allowed the F1 to propagate by self-fertilization to yield F3 families. There was significant among-family (i.e. genetic) variation in RMR, root mass allocation by depth, and seed size. F3 families did not vary significantly in rooting depth per unit shoot mass. 6 In a competition experiment similar to that above, there was significant variation among F3 families in fecundity, but not dry mass, and family by competitor interactions were not significant. 7 There was little correlation among traits across F3 family means, indicating no common genetic basis to the traits. This suggests that novel combinations of characters can be created through crossing between genetically diverged populations. In addition, there was a significant family by block (environment) interaction for RMR, indicating that the degree of plasticity in this character has heritable variation that can respond to natural selection.