Gender Differences in Reproductive and Physiological Traits in a Gynodioecious Species, Geranium Maculatum (geraniaceae)

Plant species with separate genders often exhibit gender differences in traits related to reproductive allocation. In gynodioecious species, females often produce more seeds than do hermaphrodites, leading to a higher reproductive cost. The mechanisms that allow females to meet the high costs of reproduction are currently under debate. In this study, we test the hypothesis that there are genetically based gender differences in physiological traits that enable females to finance these costs through higher photosynthetic carbon gain in the gynodioecious perennial Geranium maculatum. Females and hermaphrodites were compared in a greenhouse study that minimized environmental and selfing rate differences between the genders. We found that females produced smaller flowers but more of them and more fruits than did hermaphrodites. However, genders did not differ in their seed number, seed mass, fruit set, and reproductive allocation. In addition, genders did not differ in photosynthetic rate (A), leaf N, and water use efficiency inferred from leaf carbon isotope ratio (dC). Overall, G. maculatum shows no genetically based gender differences for most of the reproductive traits or any of the physiological traits measured. Our results suggest that for G. maculatum, the gender fitness differences previously identified in natural populations may be caused by gender differences in microhabitat and/or selfing rate.