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Abstract Detail

The Evolution of Pollen Performance

Mazer, Susan J [1], Hove, Alisa A [2].

Winning in style:  do longer styles intensify male gametophytic selection in wild populations of Clarkia (Onagraceae)?

One proposed function of relatively long styles is to prevent poor-quality pollen from reaching the stylar base. If this is the case, then long styles should exhibit higher rates of pollen failure (attrition) than short styles, particularly under conditions where pollen competes for access to ovules (i.e., seed production per fruit is not pollen-limited). We tested this prediction by collecting senescing styles from 730 flowers in multiple populations of two insect-pollinated Clarkia species over 2 years (2009 and 2010). Style length consistently had a positive effect on pollen deposition; longer styles received more pollen than shorter styles. Given that the amount of pollen deposited might affect the rate of pollen failure independently of style length, we conducted multivariate analyses to detect the independent effects of pollen deposition, style length, and time of style harvest on pollen attrition rates. We examined three measures of pollen attrition: a) the proportion of pollen grains deposited that failed to produce tubes that reached the base of the stigma (the stigma-style junction, or SSJ); b) the proportion of pollen tubes detected at the SSJ that failed to reach the base of the style; and c) the proportion of pollen grains deposited that failed to reach the base of the style. In both taxa, the amount of pollen deposited on the stigma was positively correlated with pollen attrition rates from the stigma to the SSJ and from the stigma to the style base.  In Clarkia unguiculata, however, the amount of pollen deposited had a negative effect on the pollen attrition rate from the SSJ to the base of the style; stigmas with higher pollen deposition had lower rates of attrition from the SSJ to the style base.  By contrast, in C. xantiana ssp. xantiana, pollen deposition was independent of the attrition rate from the SSJ to the style base. For both taxa, the patterns were qualitatively unchanged when stigmas receiving < 100 pollen grains — and therefore free of intense pollen competition — were excluded from analysis. We conclude that attrition rates in these taxa were mediated by style length, but that the effect of style length was primarily to increase pollen deposition, which indirectly affects pollen attrition either through stigma clogging or negative pollen-pollen interactions.

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Related Links:
Mazer lab website

1 - University of California, Santa Barbara, Ecology, Evolution & Marine Biology, 4119 Life Sciences Bldg, Santa Barbara, CA, 93106, USA
2 - Warren Wilson College, Biology Department, Cpo 6217 , P.O. Box 9000, Asheville, NC, 28815, USA

Pollen competition
natural selection
style length

Presentation Type: Symposium or Colloquium Presentation
Session: SY03
Location: Snake/Boise Centre
Date: Monday, July 28th, 2014
Time: 4:30 PM
Number: SY03007
Abstract ID:177
Candidate for Awards:None

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