'Inconstant males' and the maintenance of labile sex expression in subdioecious plants
Résumé
• Here, we evaluate the role of pollen limitation and selfing in the maintenance oflabile sex expression in subdioecious plant species.• We used a literature survey to explore which factors correlated with a significantoccurrence of hermaphrodites in dioecious species. We developed models to explorethe selective maintenance of labile sex expression. The models had similar ecologicalassumptions but differed in the genetic basis of sex lability.• We found that a significant frequency of hermaphrodites was associated withanimal pollination, and that hermaphrodites were ‘inconstant’ males with perfectflowers, suggesting evolution through the gynodioecious pathway. Models showedthat a modifier converting pure males into inconstant males could be maintainedunder a wide range of reduction in both male and female fitness. Pollen limitationand self-fertilization facilitated invasion of the modifier. Depending on the geneticsof sex determination, we found pure dioecy, stable subdioecy (trioecy), and situationswhere inconstant males coexisted with either pure females or pure males.Under selfing and pollen limitation, certain conditions selected for inconstant maleswhich will drive populations to extinction.• We discuss our results in relation to the evolution towards, and the breakdown of,dioecy, and the ecological and evolutionary implications of labile sex expression