Evolution of Multilocus Genetic Structure in Avena hirtula and Avena barbata

• Published in: Genetics (Austin) Vol. 135; no. 4; pp. 1125 - 1139
• Main Authors: Allard, R. W, Garcia, P, Saenz-de-Miera, L. E, de-la-Vega, M. P
• Format: Journal Article
• Language: English
• Published: Bethesda, MD Genetics Soc America 01.12.1993; Genetics Society of America
• Subjects: Alleles; Avena barbata; Biological and medical sciences; Biological Evolution; California; Chromosome Mapping; Classical genetics, quantitative genetics, hybrids; Enzymes - genetics; Evolution; Fundamental and applied biological sciences. Psychology; Gene Frequency; Genes, Plant; Genetics; Genetics of eukaryotes. Biological and molecular evolution; Grasses; Investigations; Poaceae - genetics; Pteridophyta, spermatophyta; Selection, Genetic; Spain; Species Specificity; Vegetals; Europe; Spain; California; Monocotyledones; Avena barbata; Genetic variability; Gramineae; Enzyme; Angiospermae; Population structure; Spermatophyta; Population genetics; Polymorphism
• ISSN: 0016-6731; 1943-2631; 1943-2631
• DOI: 10.1093/genetics/135.4.1125

Avena barbata, an autotetraploid grass, is much more widely adapted than Avena hirtula, its diploid ancestor. We have determined the 14-locus genotype of 754 diploid and 4751 tetraploid plants from 10 and 50 Spanish sites, respectively. Allelic diversity is much greater in the tetraploid (52 alleles) than in the diploid (38 alleles): the extra alleles of the tetraploid were present in nonsegregating heteroallelic quadriplexes. Seven loci were monomorphic for the same allele (genotypically 11) in all populations of the diploid: five of these loci were also monomorphic for the same allele (genotypically 1111) in all populations of the tetraploid whereas two loci each formed a heteroallelic quadriplex (1122) that was monomorphic or predominant in the tetraploid. Seven of the 14 loci formed one or more highly successful homoallelic and/or heteroallelic quadriplexes in the tetraploid. We attribute much of the greater heterosis and wider adaptedness of the tetraploid to favorable within-locus interactions and interlocus (epistatic) interactions among alleles of the loci that form heteroallelic quadriplexes. It is difficult to account for the observed patterns in which genotypes are distributed ecogeographically except in terms of natural selection favoring particular alleles and genotypes in specific habitats. We conclude that natural selection was the predominant integrating force in shaping the specific genetic structure of different local populations as well as the adaptive landscape of both the diploid and tetraploid.