title: Pollinator visitation patterns strongly influence among-flower variation in selfing rate.
abstract: OBJECTIVE
  Adjacent flowers on Mimulus ringens floral displays often vary markedly in selfing rate. We hypothesized that this fine-scale variation in mating system reflects the tendency of bumble-bee pollinators to probe several flowers consecutively on multiflower displays. When a pollinator approaches a display, the first flower probed is likely to receive substantial outcross pollen. However, since pollen carryover in this species is limited, receipt of self pollen should increase rapidly for later flowers. Here the first direct experimental test of this hypothesis is described.
  
  
  METHODS
  In order to link floral visitation sequences with selfing rates of individual flowers, replicate linear arrays were established, each composed of plants with unique genetic markers. This facilitated unambiguous assignment of paternity to all sampled progeny. A single wild bumble-bee was permitted to forage on each linear array, recording the order of floral visits on each display. Once fruits had matured, 120 fruits were harvested (four flowers from each of five floral displays in each of six arrays). Twenty-five seedlings from each fruit were genotyped and paternity was unambiguously assigned to all 3000 genotyped progeny.
  
  
  RESULTS
  The order of pollinator probes on Mimulus floral displays strongly and significantly influenced selfing rates of individual fruits. Mean selfing rates increased from 21 % for initial probes to 78 % for the fourth flower probed on each display.
  
  
  CONCLUSIONS
  Striking among-flower differences in selfing rate result from increased deposition of geitonogamous (among-flower, within-display) self pollen as bumble-bees probe consecutive flowers on each floral display. The resulting heterogeneity in the genetic composition of sibships may influence seedling competition and the expression of inbreeding depression.
authors.affiliation: Department of Biological Sciences, University of Wisconsin-Milwaukee, 53201, USA. karron@uwm.edu
authors.forename: Jeffrey D
authors.initials: JD
authors.lastname: Karron
authors.forename: Karsten G
authors.initials: KG
authors.lastname: Holmquist
authors.forename: Rebecca J
authors.initials: RJ
authors.lastname: Flanagan
authors.forename: Randall J
authors.initials: RJ
authors.lastname: Mitchell
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001516:Bees / Q000502:physiology*; D035264:Flowers / Q000502:physiology*; D054817:Pollination / Q000502:physiology*; D012098:Reproduction