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

Abstract

Summary1 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.

Genetic lineages of the invasive Aegilops triuncialis differ in competitive response to neighboring grassland species

“…1, 2). This result supports those of previous work demonstrating genetic lineages respond differently to competition (Cahill et al 2005;Latta et al 2004;Muller and Bartelheimer 2013). We add to this body of work by showing that genetic lineages within the invaded range respond differently to competition.…”

“…Furthermore, we demonstrate that genetic identity of the target individual is more important to competitive response than presence of a neighbor. Although intraspecific variation in competition has been recognized as an important factor in competitive response and interactions (Cahill et al 2005;Gustafson et al 2004;Latta et al 2004), invasive traits tend to be thought of as uniform within species (but see Bossdorf et al 2008;Kinter and Mack 2004). Here we show evidence that lineages can differ in their response to competition, and that one lineage may use its resilience to competition as a mechanism of invasion, while the other appears more vulnerable to competition and may depend on disturbance or other factors that limit direct plant-plant interactions for its success.…”

The Adaptive Significance of Drought Escape in Avena Barbata, an Annual Grass

“…Avena barbata is a highly selfing (Ͼ95%; Latta et al 2004) European annual grass that has invaded the Mediterranean climatic region in the southwestern United States (Garcia et al 1989;Cluster and Allard 1995) since its introduction over 200 years ago (Clegg and Allard 1972). The plants used for the initial cross were collected at xeric (Ͻ500 mm annual rainfall) and mesic sites (Ͼ500 mm annual rainfall) in California (Latta et al 2004).…”

“…We focused on A. barbata because of its history of use in the study of drought adaptation. The parental mesic and xeric Avena ecotypes are known to differ at five allozyme loci associated with drought adaptation (Hamrick and Allard 1972) and a suite of quantitative traits including seed size, flowering time, root depth, competitive ability, and fecundity (Hamrick and Allard 1975;Latta et al 2004). We used these RILs because recombination following the initial cross released phenotypic variation (Rieseberg et al 1999;Burke and Arnold 2001), increasing our power to detect selection (Geber and Griffen 2003).…”

Epistasis in natural populations of a predominantly selfing plant

“…There are three possible routes for divergent epistasis to evolve. The structure of genetically divergent neighborhoods can be a result of divergent selection resulting from spatial heterogeneity, for example, soil or microclimatic differences (Allard et al, 1972;Latta et al, 2004;Johansen-Morris and Latta, 2006;Ramakrishnan et al, 2006). Such structure can be also caused by genetic drift under limited seed and pollen dispersal (Williams, 1994;Siol et al, 2008), and strongly resemble the micro-environmental selection effect when seed dispersal and environmental heterogeneity occur at similar scale (Volis et al, 2004a).…”