title: Losing one's touch: Evolution of the touch-sensitive stigma in theMimulus guttatusspecies complex.
abstract: OBJECTIVE
  The stigmas of several species are touch sensitive and respond to pressure by closing. Previous research suggests that stigma closure could prevent self pollination within a flower during a pollinator's visit or enhance male function by increasing pollen export. Both factors could be favored in outcrossers, and neither would be beneficial in selfers.
  
  
  METHODS
  We investigated variation in stigma-closing and the duration of closure in annual and perennial populations of the variable speciesMimulus guttatusand whether four closely related selfing species (M. cupriphilus,M. laciniatus,M. nasutus, andM. pardalis) have lost their touch sensitivity. We grew plants in a controlled environment and performed experiments with and without the addition of pollen to the stigma.
  
  
  RESULTS
  InM. guttatus, the speed of stigma-closing was rapid and unaffected by the deposition of pollen. Populations varied significantly in closing speed, which may reflect their geographic location. For annual populations only, anther-stigma separation significantly affected closing speed. Also, stigmas that closed quickly stayed closed longer, and stigmas that received pollen remained closed longer. Finally, in the selfing species, stigma-closing was more variable; some populations have entirely lost the ability to respond to touch.
  
  
  CONCLUSIONS
  We discuss our results in the context of traits that promote outcrossing and traits that are under selection during the evolution of selfing. This is the first characterization of variation in touch responses across multiple populations within a species and the first to demonstrate the loss of touch sensitivity in selfing lineages.
authors.affiliation: Department of Biology, Syracuse University, 110 College Place, Syracuse, New York 13244 USA friedman@syr.edu.
authors.forename: Jannice
authors.initials: J
authors.lastname: Friedman
authors.affiliation: Department of Biology, Syracuse University, 110 College Place, Syracuse, New York 13244 USA.
authors.forename: Katherine S
authors.initials: KS
authors.lastname: Hart
authors.affiliation: Department of Biology, Syracuse University, 110 College Place, Syracuse, New York 13244 USA.
authors.forename: Meghan C
authors.initials: MC
authors.lastname: den Bakker
mesh_terms: D000818:Animals; D035264:Flowers / Q000502:physiology*; D006801:Humans; D032241:Mimulus / Q000145:classification / Q000502:physiology*; D018521:Plant Physiological Phenomena; D011058:Pollen / Q000502:physiology*; D054817:Pollination / Q000502:physiology*; D012098:Reproduction / Q000502:physiology; D013045:Species Specificity; D013997:Time Factors; D014110:Touch / Q000502:physiology
keywords: Mimulus; Phrymaceae; herkogamy; mating system; outcrossing; pollination; selfing; touch-sensitive stigma