title: Does stronger pollen competition improve offspring fitness when pollen load does not vary?
abstract: OBJECTIVE
  Competition among pollen grains from a single donor is expected to increase the quality of the offspring produced because of the recessive deleterious alleles expressed during pollen-tube growth. However, evidence for such an effect is inconclusive; a large number of studies suffer from confounding variation in pollen competition with variation in pollen load.
  
  
  METHODS
  In this study, we tested the effect of pollen competition on offspring performance independently of pollen-load variation. We compared seed mass and early seedling performance in Dalechampia scandens (Euphorbiaceae) between crosses in which variation in pollen competition was achieved, without variation in pollen load, by manipulating the dispersion of pollen grains on the stigmas.
  
  
  RESULTS
  Despite a large sample size (211 crosses on 20 maternal plants), we failed to find an effect of pollen competition on seed characteristics or early seedling performance. Paternal effects were always limited, and pollen competition never reduced the within-father (residual) variance.
  
  
  CONCLUSIONS
  These results suggest that limited within-donor variation in genetic quality of pollen grains reduces the potential benefits of pollen competition in the study population. The lack of paternal effects on early sporophyte performance further suggests that benefits of pollen competition among pollen from multiple donors should be limited as well, and it raises questions about the significance of pollen competition as a mechanism of sexual selection.
authors.affiliation: Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway christophe.pelabon@ntnu.no.
authors.forename: Christophe
authors.initials: C
authors.lastname: Pélabon
authors.affiliation: Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
authors.forename: Lauriane
authors.initials: L
authors.lastname: Hennet
authors.affiliation: Norwegian Institute for Nature Research, 7485 Trondheim, Norway.
authors.forename: Geir H
authors.initials: GH
authors.lastname: Bolstad
authors.affiliation: Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
authors.forename: Elena
authors.initials: E
authors.lastname: Albertsen
authors.affiliation: Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
authors.forename: Øystein H
authors.initials: ØH
authors.lastname: Opedal
authors.affiliation: Centre for Biodiversity Dynamics, Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway.
authors.forename: Runa K
authors.initials: RK
authors.lastname: Ekrem
authors.affiliation: Department of Biology, Norwegian University of Science and Technology, 7491 Trondheim, Norway School of Biological Sciences, King Henry Building, King Henry I Street, University of Portsmouth, Portsmouth PO1 2DY, UK Institute of Arctic Biology, University of Alaska, Fairbanks, Alaska 99775 USA.
authors.forename: W Scott
authors.initials: WS
authors.lastname: Armbruster
mesh_terms: D005075:Biological Evolution; D018548:Cotyledon / Q000502:physiology; D019665:Euphorbiaceae / Q000502:physiology*; D018525:Germination; D008954:Models, Biological; D009929:Organ Size; D011058:Pollen / Q000502:physiology*; D012639:Seeds / Q000502:physiology; D013997:Time Factors
keywords: Dalechampia scandens; Euphorbiaceae; evolvability; germination; paternal effect; pollen tube growth; prezygotic selection; sexual selection