Rathcke, Beverly .
Pollen limitation and sex allocation in an andromonoecious shrub, Calliandra haematomma (Fabaceae), on San Salvador Island, Bahamas.
POLLEN limitation of seed set has been found to be relatively common in plant populations, contradicting Bateman’s prediction that female fitness should be limited by resources rather than mating. However, andromonecious species, i.e. species with male flowers and hermaphroditic flowers on the same plant, would seem unlikely to be pollen limited given their male-biased sex ratios (hermaphroditic flowers have both male and female function). Self-compatible plants are also less likely to be pollen limited. The shrub, Calliandra haematomma var correllii (Fabaceae), on San Salvador Island in the Bahamas is andromonoecious and plants are self-compatible. The red “shaving brush” inflorescences have an average of 11 florets. In the study population, 77% of the inflorescences had only male florets, 93% of the total florets were male, and the pollen:ovule ratio was 1176. Smaller plants were more male-biased, and some were male-only as predicted by size-dependent sex allocation theory. Despite the strong male bias and self-compatibility, fruit set of larger shrubs was highly pollen-limited. Fruit set of inflorescences augmented with either cross-pollen or self-pollen was over twice that from natural pollination. Although Bahama Woodstars (an endemic hummingbird) were frequent flower visitors, they appear to be ineffective pollinators. Visits by Bananaquits were infrequent, and the few insect visitors appeared to be nectar thieves, rather than pollinators. The strong male bias in this plant population may reflect selection from ineffective pollinators as well as shrub size.
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pollen limitation and andromonoecy
1 - University of Michigan, Department of Ecology & Evolutionary Biology, 830 North University Avenue, Ann Arbor, Michigan, 48109-1048, USA
Presentation Type: Oral Paper:Papers for Topics
Date: Monday, July 31st, 2006
Time: 2:15 PM