title: A first test of elemental allelopathy via heterospecific pollen receipt.
abstract: OBJECTIVE
  Coflowering plants often share pollinators and may receive mixed species pollen loads. Although detrimental effects of heterospecific pollen receipt have been documented, trait-based modifiers of interactions on the stigma remain largely unknown. Chemicals that mediate interactions between sporophytes could also influence pollen-pollen or pollen-style interactions. We test for the first time whether nickel (Ni) accumulation in pollen can lead to "elemental allelopathy" and intensify the fitness consequences of heterospecific pollen receipt.
  
  
  METHODS
  We grew Ni-hyperaccumulator Streptanthus polygaloides in soils augmented with three concentrations of Ni, measured pollen Ni concentration, and hand-pollinated non-Ni hyperaccumulator Mimulus guttatus. We assayed pollen germination, tube growth and seeds of M. guttatus after pure and mixed species pollinations.
  
  
  RESULTS
  Streptanthus polygaloides pollen accumulated Ni in proportion to soil availability and at levels significantly greater than M. guttatus pollen. Although receipt of S. polygaloides pollen increased M. guttatus pollen germination, it decreased the proportion of pollen tubes reaching the ovary and seed number. Increased Ni in pollen, however, did not significantly intensify the effect of S. polygaloides pollen receipt on M. guttatus seed production.
  
  
  CONCLUSIONS
  Different levels of Ni in the pollen of S. polygaloides achieved in the greenhouse did not significantly reduce the fitness of M. guttatus. Stigma tolerance to Ni may also have contributed to the lack of response to increased Ni in heterospecific pollen. This study paves the way for additional tests in other metal hyperaccumulators and recipients, and to identify mechanisms of interactions on the stigma.
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA tia1@pitt.edu.
authors.forename: Heidi M-L
authors.initials: HM
authors.lastname: Wipf
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA.
authors.forename: George A
authors.initials: GA
authors.lastname: Meindl
authors.affiliation: Department of Biological Sciences, University of Pittsburgh, Pittsburgh, Pennsylvania 15260 USA tia1@pitt.edu.
authors.forename: Tia-Lynn
authors.initials: TL
authors.lastname: Ashman
mesh_terms: D064089:Allelopathy; D000704:Analysis of Variance; D019607:Brassicaceae / Q000502:physiology*; D016018:Least-Squares Analysis; D032241:Mimulus / Q000502:physiology*; D011058:Pollen / Q000502:physiology*
keywords: Brassicaeae; Mimulus guttatus; Phrymaceae; Streptanthus polygaloides; elemental allelopathy; heterospecific pollen receipt; metal hyperaccumulation; nickel; pollen–pollen interactions