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Size-dependent sex allocation within flowers of the annual herb Clarkia unguiculata (Onagraceae): ontogenetic and among-plant variation¹

Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, California 93106 USA; and Department of Ecology and Evolutionary Biology, University of California, Irvine, California 92697 USA

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 correlation between the resource status of a flower or individual and the proportion of reproductive resources allocated to female function. These models assume that, independent of resource status, a negative correlation exists between male and female investment. Focusing on the allocation of resources within flowers, we tested these theoretical predictions and this assumption using the annual Clarkia unguiculata (Onagraceae). We also sought preliminary evidence for a genetic component to these relationships. From 116 greenhouse-cultivated plants representing 30 field-collected maternal families, multiple flowers and fruits per plant were sampled for gamete production, pollen : ovule ratio, seed number, ovule abortion, seed biomass/fruit, mean individual seed mass, and petal area. If sex allocation changes as predicted, then (1) assuming that flowers produced early have access to more resources than those produced later, basal flowers should exhibit a higher absolute and proportional investment in female function than distal flowers and (2) plants of high resource status (large plants) should produce flowers with a higher proportional investment in female function than those of low resource status. Within plants, variation in floral traits conformed to the first prediction. 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 and female investment per flower, even when controlling for plant size.

Key Words: Clarkia unguiculata • gender • Onagraceae • pollen : ovule ratio • seed mass • sex allocation • size dependence

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