title: Low flower-size variation in bilaterally symmetrical flowers: Support for the pollination precision hypothesis.
abstract: OBJECTIVE
  The evolutionary shift from radial to bilateral symmetry in flowers is generally associated with the evolution of low flower-size variation. This phenomenon supports the hypothesis that the lower size variation in bilateral flowers can be attributed to low pollinator diversity. In this study, we propose two other hypotheses to explain low flower-size variation in bilateral symmetrical flowers. To test the three hypotheses, we examined the relative importance of pollinator diversity, composition, and bilateral symmetry itself as selective forces on low flower-size variation.
  
  
  METHODS
  We examined pollinator diversity and composition and flower-size variation for 36 species in a seminatural ecosystem with high bee richness and frequent lepidopteran visitation.
  
  
  RESULTS
  Bilateral flowers were more frequently visited than radial flowers by larger bees, but functional-group diversity of the pollinators did not differ between symmetry types. Although bilateral flowers had significantly lower flower-size variation than radial flowers, flower-size variation did not vary with pollinator diversity and composition but was instead related to bilateral symmetry.
  
  
  CONCLUSIONS
  Our results suggest that the lower size variation in bilateral flowers might have evolved under selection favoring the control of pollinator behavior on flowers to enhance the accurate placement of pollen on the body of the pollinator, independent of pollinator type. Because of the limited research on this issue, future work should be conducted in various types of plant-pollinator communities worldwide to further clarify the issue.
authors.affiliation: Graduate school of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan nikke.home.pc@gmail.com.
authors.forename: Aoi
authors.initials: A
authors.lastname: Nikkeshi
authors.affiliation: Faculty of Human Development, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan.
authors.forename: Daiki
authors.initials: D
authors.lastname: Kurimoto
authors.affiliation: Graduate school of Human Development and Environment, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan Faculty of Human Development, Kobe University, 3-11 Tsurukabuto, Nada, Kobe 657-8501, Japan.
authors.forename: Atushi
authors.initials: A
authors.lastname: Ushimaru
mesh_terms: D000818:Animals; D005075:Biological Evolution; D004175:Diptera / Q000502:physiology; D035264:Flowers / Q000033:anatomy & histology / Q000502:physiology; D065948:Grassland; D006927:Hymenoptera / Q000502:physiology; D007564:Japan; D007915:Lepidoptera / Q000502:physiology; D019684:Magnoliopsida / Q000033:anatomy & histology* / Q000502:physiology*; D054817:Pollination
keywords: actinomorphy; flower-size variation; pollinator composition; pollinator diversity; stabilizing selection; zygomorphy