title: Winning in style: Longer styles receive more pollen, but style length does not affect pollen attrition in wild Clarkia populations.
abstract: OBJECTIVE
  One proposed function of long styles is to intensify selection among male gametophytes relative to short styles. If so, given sufficient competition, longer styles will have higher rates of pollen tube attrition (failure to reach the style base) within the style than shorter ones. Alternatively, style length may influence pollen receipt, which itself may affect attrition rates.
  
  
  METHODS
  We tested these predictions by collecting senescing styles from wild populations of two insect-pollinated Clarkia species. We examined the number of pollen grains adhering to the stigma, length of styles, and rates of attrition from the stigma surface to the stigma-style junction (SSJ), from the SSJ to the style base, and from the stigma surface to the style base. Multivariate analyses estimated the independent effects of pollen grains per stigma, the number of pollen tubes at the SSJ, and style length on attrition.
  
  
  RESULTS
  Style length was generally positively correlated with pollen receipt, and the number of pollen grains per stigma was positively correlated with all three attrition rates. In neither species was any attrition rate affected by style length independent of the number of pollen grains per stigma.
  
  
  CONCLUSIONS
  Pollen attrition was mediated by style length, but the function of style length was primarily to increase the number of germinating pollen grains, which affected attrition rates either through stigma clogging or pollen-pollen interactions. Style length may have a direct effect on pollen receipt due to the stigma's position relative to pollinator body parts, but traits correlated with style length may also directly affect pollen receipt.
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93105 USA mazer@lifesci.ucsb.edu.
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Mazer
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93105 USA.
authors.forename: Arrash
authors.initials: A
authors.lastname: Moghaddasi
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93105 USA.
authors.forename: Alexandra K
authors.initials: AK
authors.lastname: Bello
authors.affiliation: Department of Ecology, Evolution and Marine Biology, University of California, Santa Barbara, Santa Barbara, California 93105 USA.
authors.forename: Alisa A
authors.initials: AA
authors.lastname: Hove
mesh_terms: D031663:Clarkia / Q000033:anatomy & histology* / Q000502:physiology*; D035264:Flowers / Q000033:anatomy & histology* / Q000502:physiology*; D018525:Germination; D016014:Linear Models; D015999:Multivariate Analysis; D010641:Phenotype; D011058:Pollen / Q000502:physiology*; D053205:Pollen Tube / Q000502:physiology; D018401:Sample Size
keywords: Clarkia unguiculata; Clarkia xantiana subsp. xantiana; Onagraceae; gametophytic competition; pollen attrition; pollen competition; pollen deposition; sexual selection; style length