Female-biased sexual allocation in cosexual plants: Result of sink-limited growth of fruits

To explain female-biased sexual allocation in cosexual plants, I developed a game theoretic model incorporating a source-sink relationship of flower and fruit growth. In this model, flower/fruit growth rate is either limited by its sink strength (the product of its potential relative growth rate and absolute size) or by the source strength (supply rate of reproductive resources) of the plant. I show that female-biased sexual allocation is evolutionarily stable if fruit growth is sink-limited at least in the early stage of its growth. The degree of female-bias is strong if the supply rate of reproductive resources is large relative to the potential relative growth rate. The degree of female-bias is also strong if the relative cost of producing one seed compared with that of producing one ovule is large, in contrast to previous sexual allocation models, in which the sexual allocation ratio was independent of the costs of producing one ovule and one seed. Thus, sink-limitation of fruit growth can be a general factor that selects for female-biased sexual allocation observed in cosexual plants irrespective of their mating systems.