XVI International Botanical Congess

Recent models of gynodioecious plants have shown how metapopulation dynamics can have an important impact on sex ratio evolution if the fitness of one or both sexes is frequency-dependent, and if the sex ratio varies among local populations. Recent studies of Silene vulgaris, a gynodioecious weed, show that several components of fitness are frequency-dependent owing to pollen limitation. Fruit set in females, the number of seeds/fruit produced by females, and the viability of seeds produced by hermaphrodites, all increase as the local frequency of hermaphrodites increases. The net effect of this is to favor hermaphrodites relative to females when fitness is averaged across demes. These experimental results will be discussed in the context of current theories of sex ratio evolution in metapopulations.