Cytonuclear dynamics in selfing populations under selection.

We develop a mathematical model to delimit the role of natural selection in maintaining nuclear and cytoplasmic polymorphisms in selfing populations. We provide explicit time-dependent solutions for joint cytonuclear frequencies under any combination of constant fertility, viability, and gametic selection and exact analytical conditions for the maintenance of polymorphisms under joint cytonuclear selection. The equilibrium structure is determined by the relative magnitude of echo fitnesses, defined as the rate at which individuals survive and produce offspring with their own genotype. Both nuclear and cytoplasmic polymorphisms can be maintained under biologically meaningful conditions, although the majority of the parameter combinations will lead to fixation. The theoretical framework developed here should be very useful in formally dissecting the form and strength of selection on cytonuclear genotypes in populations with negligible levels of outcrossing.