Prolonged stigma and flower lifespan in females of the gynodioecious plant Geranium sylvaticum

Abstract

In gynodioecious plants females need a reproductive advantage over hermaphrodites to be maintained in the same population. Generally, three main proximate causes for a female advantage are considered: inbreeding avoidance, different resource allocation patterns, and differences in ecological interactions. A mechanism potentially causing a female advantage that is rarely discussed is a difference in floral longevity between the genders. Females may have a longer stigma lifespan than hermaphrodites, which can affect pollination. Stigma and flower lifespan are rarely documented in gynodioecious species, although it is a common observation in dioecious species that female plants flower longer than males. Here we focus on the stigma and flower lifespan of gynodioecious Geranium sylvaticum, which could potentially contribute to the female advantage observed in this and other closely related species. We measured the stigma and flower lifespan in unpollinated flowers of female, hermaphrodite and plants with an intermediate gender expression. Our results show that stigma lifespan is almost twice as long in females as in hermaphrodites and intermediate plants. Also flower lifespan is longest in females. We discuss the potential mechanisms through which an increased floral lifespan can lead to a female advantage despite the generally lower pollinator visitation rates observed in females by reviewing available studies. Our study shows that increased floral persistence in females can be an important aspect in the maintenance of females in gynodioecious plants and should be taken into account as a potential proximate cause for a female advantage.