GENDER VARIATION AND INBREEDING DEPRESSION IN GYNODIOECIOUS-GYNOMONOECIOUS SILENE NUTANS (CARYOPHYLLACEAE)

Gynodioecy involves the stable co-occurrence of females and hermaphrodites. Its maintenance theoretically depends on differences in female and male reproductive success among gender morphs. Although many gynodioecious species also include gynomonoecious individuals that carry a mixture of female and perfect flowers, little is known about the male and female fitness of this third morph. Here, we present the first study of the reproductive system of Silene nutans, including females, gynomonoecious plants, and hermaphrodites. By measuring 10 floral traits in controlled conditions, we showed that females bear smaller and lighter flowers than hermaphrodites, with female and perfect flowers of gynomonoecious plants being intermediates. By measuring pollen quantity and quality, we showed that gynomonoecious plants had a lower potential male fitness than hermaphrodites at the level of both flowers and individuals. In addition, gynomonoecious plants were shown to widely vary their proportion of female flowers (0.03-0.9) and their floral traits, suggesting a quantitative restoration of male fertility. Finally, controlled pollinations showed evidence for inbreeding depression (delta = 0.3) in progeny of hermaphrodites and gynomonoecious individuals, affecting both pre- and postdispersal traits; this could provide a selective advantage for females.