Population Studies in Predominantly Self-Pollinating Species. X. Variation in Natural Populations of Avena fatua and A. barbata

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Abstract
Quantitative estimates were made of the degree of polymorphism at 3 marker loci and the amount of phenotypic and genetic variability for 3 quantitative characters in several natural populations of the wild oat spp. Avena fatua and A. barbata. The results showed that these species differ markedly in population structure. A. barbata was largely monomorphic whereas A. fatua was highly polymorphic. Evidence was presented for heterozygote advantage as a factor maintaining polymorphism in A. fatua. Estimates of between and within-family variability showed that while both species have a substantial genetic component of total variability, there is a relatively smaller genetic but a relatively larger non-genetic component in A. barbata accounting for its greater overall phenotypic variation in nature. The differences in the modes of variation and population structure between the 2 spp. are briefly discussed in relation to their adaptive strategies. It was postulated that A. barbata relies less on genetic diversity and more on phenotypic plasticity than A. fatua in adapting to heterogeneous environments.