title: Geographic variation in floral allometry suggests repeated transitions between selfing and outcrossing in a mixed mating plant.
abstract: OBJECTIVE
  Isometric and allometric scaling of a conserved floral plan could provide a parsimonious mechanism for rapid and reversible transitions between breeding systems. This scaling may occur during transitions between predominant autogamy and xenogamy, contributing to the maintenance of a stable mixed mating system.
  
  
  METHODS
  We compared nine disjunct populations of the polytypic, mixed mating species Oenothera flava (Onagraceae) to two parapatric relatives, the obligately xenogamous species O. acutissima and the mixed mating species O. triloba. We compared floral morphology of all taxa using principal component analysis (PCA) and developmental trajectories of floral organs using ANCOVA homogeneity of slopes.
  
  
  RESULTS
  The PCA revealed both isometric and allometric scaling of a conserved floral plan. Three principal components (PCs) explained 92.5% of the variation in the three species. PC1 predominantly loaded on measures of floral size and accounts for 36% of the variation. PC2 accounted for 35% of the variation, predominantly in traits that influence pollinator handling. PC3 accounted for 22% of the variation, primarily in anther-stigma distance (herkogamy). During O. flava subsp. taraxacoides development, style elongation was accelerated relative to anthers, resulting in positive herkogamy. During O. flava subsp. flava development, style elongation was decelerated, resulting in zero or negative herkogamy. Of the two populations with intermediate morphology, style elongation was accelerated in one population and decelerated in the other.
  
  
  CONCLUSIONS
  Isometric and allometric scaling of floral organs in North American Oenothera section Lavauxia drive variation in breeding system. Multiple developmental paths to intermediate phenotypes support the likelihood of multiple mating system transitions.
authors.affiliation: Altenbergrain 21 University of Bern, Institute of Plant Sciences, 3013 Bern, Switzerland.
authors.forename: Holly E
authors.initials: HE
authors.lastname: Summers
authors.affiliation: W357 Seeley G. Mudd Hall, Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853.
authors.forename: Sally M
authors.initials: SM
authors.lastname: Hartwick
authors.affiliation: W355 Seeley G. Mudd Hall, Department of Neurobiology and Behavior, Cornell University, Ithaca, NY 14853.
authors.forename: Robert A
authors.initials: RA
authors.lastname: Raguso
mesh_terms: D005075:Biological Evolution; D035264:Flowers / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology; D005843:Geography; D008800:Mexico; D031664:Oenothera / Q000033:anatomy & histology* / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D012098:Reproduction; D014481:United States
keywords: Onagraceae; breeding system; floral traits; geographic variation; isometry; mating system; outcrossing; pollination; reproductive strategies