Size-dependent sex allocation within flowers of the annual herb Clarkia unguiculata (Onagraceae): Ontogenetic and among-plant variation

The relative allocation of resources to male and female functions may vary among flowers within and among individual plants for many reasons. Several theoretical models of sex allocation in plants predict a positive correlati on between the resource status of a Bower or individual and the proportion of reproductive resources allocated to female function. These models assume that, independent of resource status, a negative correlation exists betwee n male and female investment. Focusing on the allocation of resources withi n flowers, we tested these theoretical predictions and this assumption usin g the annual Clarkia unguiculata (Onagraceae). We also sought preliminary e vidence for a genetic component to these relationships. From 116 greenhouse -cultivated plants representing 30 Field-collected maternal families, multi ple flowers and fruits per plant were sampled for gamete production, pollen : ovule ratio, seed number, ovule abortion, seed biomass/fruit, mean indivi dual seed mass, and petal area. If sex allocation changes as predicted, the n (1) assuming that flowers produced early have access to more resources th an those produced later, basal flowers should exhibit a higher absolute and proportional investment in female function than distal flowers and (2) pla nts of high resource status (large plants) should produce flowers with a hi gher proportional investment in female function than those of low resource status. Within plants, variation in floral traits conformed to the first pr ediction. Among plants and families, no significant effects of plant size ( dry stem biomass) on intrafloral proportional sex allocation were observed. We detected no evidence for a negative genetic correlation between male an d female investment per flower, even when controlling for plant size.