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

Abstract

Quantitative estimates were made of the degree of polymorphism at three marker loci and the amount of phenotypic and genetic variability for three quantitative characters in several natural populations of two wild oat species, Avena fatua and A. barbata. The results showed that, for all the simply inherited characters studied, A. barbata was largely monomorphic whereas A. fatua was highly polymorphic for at least five different marker loci. Evidence was presented for heterozygote advantage as a factor maintaining polymorphism in certain populations of A. fatua. Estimates of between and within-family variability suggested that while both species have a substantial genetic component of total variability, there is a relatively larger nongenetic 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 two species 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.