The effect of pollen versus seed flow on the maintenance of nuclear-cytoplasmic gynodioecy.

Gynodioecy, where females co-occur with hermaphrodites, is a relatively common sexual system in plants that is often the result of a genetic conflict between maternally inherited male sterility genes in the mitochondrial genome and the biparentally inherited male fertility restorer genes in the nucleus. Previous models have shown that nuclear-cytoplasmic gynodioecy can be maintained under certain conditions by negative frequency-dependent selection, but the effect of other evolutionary processes such as genetic drift and population subdivision is only partially understood. Here, we investigate the joint effects of frequency-dependent selection, drift, and migration through either pollen or seeds on the maintenance of nuclear-cytoplasmic gynodioecy in a subdivided population. We find that the combination of drift and selection causes the loss of gynodioecy under scenarios that would maintain it under the influence of selection alone, and that both seed and, more surprisingly, pollen flow can maintain the polymorphism. In particular, although pollen flow could not avoid the loss of cytoplasmic polymorphism within demes, it allowed the maintenance of nuclear-cytoplasmic polymorphism at the metapopulation level.