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Geitonogamous Pollination and Its Consequences in Gernium caespitosum

Mark B. Hessing
American Journal of Botany
Vol. 75, No. 9 (Sep., 1988), pp. 1324-1333
Stable URL: http://www.jstor.org/stable/2444455
Page Count: 10
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Geitonogamous Pollination and Its Consequences in Gernium caespitosum
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Abstract

In many plants, the frequency of geitonogamous (within-plant) pollination is likely to increase as a function of the number of simultaneously blooming flowers. This increase in self-pollination often produces inbreeding depression. Thus, a dilemma may exist in that individuals cannot increase seed production without lowering the average fitness of each seed. Conditions necessary for the existence of the dilemma were confirmed in large individuals of the herbaceous perennial Geranium caespitosum. Manually geitonogamously pollinated flowers initiated as many fruits as manually outcrossed flowers, but showed a subsequently greater number of embryo abortions, matured fewer seeds, and had a lower average seed weight. Observations of pollinators and dye transfer showed that geitonogamous bee pollinations increased as the number of flowers per plant increased. A simple model predicted that detrimental effects from geitonogamy become likely when 55 flowers are simultaneously blooming. Plants with 55 or more flowers produced 30% of the flowers in populations. The effect, and possible circumvention, of the dilemma on Geranium, and angiosperm breeding systems in general, is discussed.

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