title: Why is gynodioecy a rare but widely distributed sexual system? Lessons from the Lamiaceae.
abstract: Gynodioecy, a sexual system where females and hermaphrodites co-occur, is found in << 1% of angiosperm species. To understand why gynodioecy is rare, we need to understand why females are maintained in some lineages, but not in others. We modelled the evolution of gynodioecy in the Lamiaceae, and investigated whether transition rates between gynodioecious and nongynodioecious states varied across the family. We also investigated whether the evolution of gynodioecy was correlated with the evolution of a herbaceous growth form and temperate distribution. Transition rates differed between Lamiaceae subfamilies. In the Nepetoideae, there were many transitions towards gynodioecy (n = 11), but also many reversions to nongynodioecy (n = 29). In addition, a herbaceous growth form, but not a temperate distribution, affected the rate of transitions both towards and away from gynodioecy; transitions towards gynodioecy occurred ˜16 times more frequently and transitions away from gynodioecy occurred ˜11 times more frequently in herbaceous lineages than in woody lineages. Within the Lamiaceae, lineages in which gynodioecy has frequently evolved also have a high rate of reversions to the nongynodioecious state. Consequently, to understand why gynodioecy is rare, we need to understand why sexual systems are more evolutionarily labile in some lineages than in others.
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.|Department of Ecology and Evolutionary Biology, University of Toronto, Toronto, ON, M5S 3B2, Canada.
authors.forename: L Ruth
authors.initials: LR
authors.lastname: Rivkin
authors.affiliation: Department of Biological Sciences, Kent State University, Kent, OH, 44242-0001, USA.
authors.forename: Andrea L
authors.initials: AL
authors.lastname: Case
authors.affiliation: Department of Integrative Biology, University of Guelph, Guelph, ON, N1G 2W1, Canada.
authors.forename: Christina M
authors.initials: CM
authors.lastname: Caruso
mesh_terms: D005843:Geography; D019686:Lamiaceae / Q000502:physiology*; D008954:Models, Biological; D010802:Phylogeny; D012098:Reproduction; D013045:Species Specificity; D013997:Time Factors
keywords: angiosperm; herbaceous; phylogeny; temperate zone; transition rate