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Pollen Competition among Two Species of Senecio (Asteraceae) That Form a Hybrid Zone on Mt. Etna, Sicily

Mark A. Chapman, David G. Forbes and Richard J. Abbott
American Journal of Botany
Vol. 92, No. 4 (Apr., 2005), pp. 730-735
Stable URL: http://www.jstor.org/stable/4126205
Page Count: 6
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
Pollen Competition among Two Species of Senecio (Asteraceae) That Form a Hybrid Zone on Mt. Etna, Sicily
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Abstract

Hybridization between interfertile, sympatric or parapatric, plant species can be reduced significantly by conspecific pollen advantage (CPA), whereby conspecific pollen has an advantage over heterospecific pollen in terms of ovule fertilization. We examined CPA in two interfertile species of Senecio, S. aethnensis, and S. chrysanthemifolius (Asteraceae), which form a hybrid zone on Mt. Etna, Sicily. Individuals of both species were pollinated with pollen mixtures containing 0, 25, 50, 75, or 100% heterospecific pollen, and offspring were genotyped to determine if they were products of conspecific or heterospecific pollen fertilizing the ovules. The mean proportion of hybrid offspring produced on S. aethnensis plants was not significantly different to that expected based on the proportion of heterospecific pollen applied to the flower head. However, S. chrysanthemifolius mother plants showed moderate CPA, with the proportion of hybrid offspring significantly less than expected. Seed set or seed germination was not reduced, hence the CPA found for S. chrysanthemifolius acts before ovule fertilization. The consequences of asymmetry in CPA on the reproductive isolation of S. aethnensis are briefly discussed, along with other mechanisms that may play a role in the maintenance of the hybrid zone on Mt. Etna.

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