The cytonuclear effects of facultative apomixis - I. Disequilibrium dynamics in diploid populations

We comprehensively analyze the cytonuclear effects of generalized mixed mat ing, including all combinations of selfing, outcrossing, and apomixis, the asexual production of seeds. After first deriving the time-dependent soluti ons for nonrandom associations (disequilibria) between a diallelic cytoplas mic marker and the alleles and genotypes at a diploid nuclear locus, we del imit all possible dynamical behaviors and the conditions under which each o ccurs. As in standard mixed mating systems, all disequilibria ultimately de cay to zero except when outcrossing is absent, in which case permanent dise quilibria result if the allelic association is initially nonzero. When at l east some outcrossing is present, any initial allelic association decays at a constant geometric rate, whereas genotypic disequilibria may first incre ase in magnitude or change sign. Although selfing and apomixis tend to reta rd the decay of disequilibria (or approach to equilibrium) and often to the same extent, apomixis can have a stronger effect under some conditions. We also determine the dynamics of cytonuclear disequilibria in specific examp les that may be of particular interest for empirical studies of hybrid zone s. The results suggest several practical guidelines for experimental design and data analysis and show how the cytonuclear disequilibrium dynamics und er mating system alone furnish a quantitative baseline for null hypotheses against which to test for the presence of other evolutionary forces, (C) 20 00 Academic Press.