title: Heterospecific pollen deposition in Delphinium barbeyi: linking stigmatic pollen loads to reproductive output in the field.
abstract: OBJECTIVE
  Most pollinators are generalists and therefore are likely to transfer heterospecific pollen among co-flowering plants. Most work on the impacts of heterospecific pollen deposition on plant fecundity has utilized hand-pollination experiments in greenhouse settings, and we continue to know very little about the reproductive effects of heterospecific pollen in field settings.
  
  
  METHODS
  We explored how patterns of naturally deposited heterospecific pollen relate to the reproductive output of Delphinium barbeyi, a common subalpine perennial herb in the Rocky Mountains (USA). We assessed a wide range of naturally occurring heterospecific pollen proportions and pollen load sizes, and linked stigmatic pollen deposition directly to seed set in individual carpels in the field.
  
  
  RESULTS
  We found that heterospecific pollen deposition in D. barbeyi is common, but typically found at low levels across stigmas collected in our sites. Neither conspecific nor heterospecific pollen deposition was related to carpel abortion. By contrast, we saw a significant positive relationship between conspecific pollen amount and viable seed production, as well as a significant negative interaction between the effects of conspecific pollen and heterospecific pollen amount, whereby the effect of conspecific pollen on viable seed production became weaker with greater heterospecific deposition on stigmas.
  
  
  CONCLUSIONS
  To our knowledge, this is the first demonstration of a relationship between heterospecific pollen and seed production in a field setting. In addition, it is the first report of an interaction between conspecific and heterospecific pollen quantities on seed production. These findings, taken with the results from other studies, suggest that greenhouse hand-pollination studies and field studies should be more tightly integrated in future work to better understand how heterospecific pollen transfer can be detrimental for plant reproduction.
authors.affiliation: Department of Environmental Studies, University of California, Santa Cruz, CA 95064, USA, Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA and hbriggs@ucsc.edu.
authors.forename: Heather M
authors.initials: HM
authors.lastname: Briggs
authors.affiliation: Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA and Department of Environmental Sciences, Emory University, Atlanta, GA 30322, USA.
authors.forename: Lucy M
authors.initials: LM
authors.lastname: Anderson
authors.affiliation: Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA and Department of Environmental Sciences, Emory University, Atlanta, GA 30322, USA.
authors.forename: Laila M
authors.initials: LM
authors.lastname: Atalla
authors.affiliation: Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA and Department of Environmental Sciences, Emory University, Atlanta, GA 30322, USA.
authors.forename: André M
authors.initials: AM
authors.lastname: Delva
authors.affiliation: Department of Environmental Sciences, Emory University, Atlanta, GA 30322, USA.
authors.forename: Emily K
authors.initials: EK
authors.lastname: Dobbs
authors.affiliation: Rocky Mountain Biological Laboratory, Crested Butte, CO 81224, USA and Department of Environmental Sciences, Emory University, Atlanta, GA 30322, USA.
authors.forename: Berry J
authors.initials: BJ
authors.lastname: Brosi
mesh_terms: D003120:Colorado; D031882:Delphinium / Q000502:physiology*; D035264:Flowers / Q000502:physiology; D011058:Pollen / Q000502:physiology*; D054817:Pollination; D012098:Reproduction / Q000502:physiology; D012639:Seeds / Q000502:physiology
keywords: field studies; hand-pollination studies; interspecific pollen transfer; pollen quality; seed set; stigmas