FSTFST 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 FstFst for a neutral allele by bringing together cytonuclear genomes with contrasting modes of inheritance. The relationships between cytonuclear disequilibrium and increment in FstFst are explored and confirmed through Monte Carlo simulations. Results show that the transient increment in FstFst 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 FstFst for a neutral paternal or maternal organelle allele. Selection on selective organelle sites facilitates the transient increment in FstFst for a neutral nuclear allele. Partial selfing can significantly reinforce the transient increment in FstFst. These theoretical insights highlight the roles of transient cytonuclear disequilibrium as a biological factor in evolving population differentiation and refine our practical interpretations of FstFst with cytonuclear markers.