title: Disruption of the distylous syndrome in Primula veris.
abstract: OBJECTIVE
  Distyly is a floral polymorphism characterized by the presence of two discrete morphs with reciprocal positioning of anthers and stigmas in flowers on different plants within the same population. Although reciprocal herkogamy and associated floral traits are generally thought to be discrete and strict polymorphisms, little is known about variation in floral traits related to the distylous syndrome within and among populations of a single species. In this study, variation in floral morphology and reciprocal positioning of the sexual organs in the distylous Primula veris (cowslip) is quantified.
  
  
  METHODS
  Data were collected in ten populations occurring in two contrasting habitat types (grasslands and forests), and for each population the average level of reciprocity was assessed, the strength of the self-incompatibility system was determined, and seed production under natural conditions was quantified.
  
  
  RESULTS
  In grassland populations, flowers showed clear distyly with low and symmetric reciprocity indices at both the lower and upper level. In forests, P. veris produced larger flowers that showed strong deviations in stigma-anther separation, especially in the L-morph. This deviation was mainly driven by variation in stigma height, resulting in high and asymmetric reciprocity indices and the occurrence of several short-styled homostylous plants. Self-incompatibility was, however, strict in both habitats, and morph ratios did not differ significantly from isoplethy. The observed shift in reciprocity in forest populations was associated with a significant reduction in seed production in the L-morph.
  
  
  CONCLUSIONS
  The results indicate that populations of P. veris show habitat-specific variation in flower morphology. Deviations from perfect reciprocal positioning of stigmas and anthers also translate into reduced seed production, suggesting that small changes in sexual organ reciprocity can have far-reaching ecological and evolutionary implications.
authors.affiliation: Division of Plant Ecology and Systematics, Biology Department, University of Leuven, Belgium and Research Institute for Nature and Forest, Kliniekstraat 25, BE-1070 Brussels, Belgium Division of Plant Ecology and Systematics, Biology Department, University of Leuven, Belgium and Research Institute for Nature and Forest, Kliniekstraat 25, BE-1070 Brussels, Belgium rein.brys@inbo.be.
authors.forename: Rein
authors.initials: R
authors.lastname: Brys
authors.affiliation: Division of Plant Ecology and Systematics, Biology Department, University of Leuven, Belgium and Research Institute for Nature and Forest, Kliniekstraat 25, BE-1070 Brussels, Belgium.
authors.forename: Hans
authors.initials: H
authors.lastname: Jacquemyn
mesh_terms: D017753:Ecosystem; D035264:Flowers / Q000033:anatomy & histology / Q000254:growth & development / Q000502:physiology*; D065928:Forests; D065948:Grassland; D011110:Polymorphism, Genetic; D031825:Primula / Q000033:anatomy & histology / Q000235:genetics / Q000254:growth & development / Q000502:physiology*; D012098:Reproduction; D060436:Self-Incompatibility in Flowering Plants
keywords: Cowslip; Primula veris; disassortative mating; distyly; herkogamy; heterostyly; legitimate pollination; plant mating system; primrose; self-incompatibility; sexual organ reciprocity