F(ST) in the cytonuclear system.

Selection on nuclear (or organelle) sites inevitably affects the spatial distribution of a neutral organelle (or nuclear) allele via transient cytonuclear disequilibrium. Here I examine this effect in terms of F(st) for a neutral allele by bringing together cytonuclear genomes with contrasting modes of inheritance. The relationships between cytonuclear disequilibrium and increment in F(st) are explored and confirmed through Monte Carlo simulations. Results show that the transient increment in F(st) for a neutral allele is not only related to the vectors of seed and pollen dispersal but also to the mode of its inheritance. Such increments can be substantial under certain conditions. Seed dispersal is more effective than pollen dispersal in changing the transient increment. The cumulative effects from multiple selective nuclear sites can amplify the transient increment in F(st) for a neutral paternal or maternal organelle allele. Selection on selective organelle sites facilitates the transient increment in F(st) for a neutral nuclear allele. Partial selfing can significantly reinforce the transient increment in F(st). These theoretical insights highlight the roles of transient cytonuclear disequilibrium as a biological factor in evolving population differentiation and refine our practical interpretations of F(st) with cytonuclear markers.