Floral sex ratio strategy in wind-pollinated monoecious species subject to wind-pollination efficiency and competitive sharing among male flowers as a game

To explain the floral sex ratio strategy in wind-pollinated monoccious species, we developed four models with special reference to wind-pollination efficiency (WPE) and competitive sharing among male flowers (CSM). WPE is a function that follows a Poisson distribution and explains the frequency of seeds fertilized by an individual via wind-pollination, whereas CSM is defined by the sharing of female flowers among male flowers within the local breeding population. We argued the applicability of the results to the actual tendencies observed in wind-pollinated monoecious species and found that a game model with WPE and CSM was the most applicable. The model predicted that individuals should change their gender expression in the following order: female phase (female flowers only), male phase (male flowers only), and constant male phase (individuals constantly allocate reproductive resources to male flowers, and remaining resources to female flowers), with increasing reproductive resources. However, the trend is likely to be influenced by the variation in the reproductive investment among individuals and the degree of WPE. Thus, large variation and low pollination efficiency enable three phases to co-occur within a population. Actual trends in real populations correspond to our prediction. (c) 2005 Elsevier Ltd. All rights reserved.