title: Recurrent modification of floral morphology in heterantherous Solanum reveals a parallel shift in reproductive strategy.
abstract: Floral morphology determines the pattern of pollen transfer within and between individuals. In hermaphroditic species, the spatial arrangement of sexual organs influences the rate of self-pollination as well as the placement of pollen in different areas of the pollinator's body. Studying the evolutionary modification of floral morphology in closely related species offers an opportunity to investigate the causes and consequences of floral variation. Here, we investigate the recurrent modification of flower morphology in three closely related pairs of taxa in Solanum section Androceras (Solanaceae), a group characterized by the presence of two morphologically distinct types of anthers in the same flower (heteranthery). We use morphometric analyses of plants grown in a common garden to characterize and compare the changes in floral morphology observed in parallel evolutionary transitions from relatively larger to smaller flowers. Our results indicate that the transition to smaller flowers is associated with a reduction in the spatial separation of anthers and stigma, changes in the allometric relationships among floral traits, shifts in pollen allocation to the two anther morphs and reduced pollen : ovule ratios. We suggest that floral modification in this group reflects parallel evolution towards increased self-fertilization and discuss potential selective scenarios that may favour this recurrent shift in floral morphology and function.
authors.affiliation: School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK mario.vallejo@stir.ac.uk.
authors.forename: Mario
authors.initials: M
authors.lastname: Vallejo-Marín
authors.affiliation: School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK.
authors.forename: Catriona
authors.initials: C
authors.lastname: Walker
authors.affiliation: School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK.
authors.forename: Philip
authors.initials: P
authors.lastname: Friston-Reilly
authors.affiliation: School of Biological and Environmental Sciences, University of Stirling, Stirling FK9 4LA, UK.
authors.forename: Lislie
authors.initials: L
authors.lastname: Solís-Montero
authors.affiliation: Department of Biological Sciences, University of Illinois, Chicago, IL 60607, USA.
authors.forename: Boris
authors.initials: B
authors.lastname: Igic
mesh_terms: D005075:Biological Evolution; D016002:Discriminant Analysis; D035264:Flowers / Q000033:anatomy & histology*; D010802:Phylogeny; D054817:Pollination / Q000502:physiology*; D025341:Principal Component Analysis; D012641:Selection, Genetic; D057945:Self-Fertilization / Q000502:physiology; D032322:Solanum / Q000033:anatomy & histology* / Q000254:growth & development; D013045:Species Specificity
keywords: Solanum (Solanaceae); division of labour; floral evolution; heteranthery; mating system; pollen : ovule ratio