Pollination ecology and breeding system of Xylopia championii (Annonaceae): curculionid beetle pollination, promoted by floral scents and elevated floral temperatures

Abstract

Data on the reproductive biology of the Annonaceae are rather fragmentary, particularly for paleotropical species. The pollination ecology and breeding system of the Sri Lankan endemic Xylopia championii (Annonaceae) are described in detail. The pollination ecology was investigated using a diverse range of approaches, including (1) observations of flower-level and population-level phenology, (2) assessments of floral visitors and effective pollinators, (3) monitoring of floral temperature in situ using a digital data logger, and (4) analysis of scent chemistry using solid-phase microextraction sampling and gas chromatography-mass spectrometry identification of volatiles. The breeding system was evaluated using pollen/ovule ratios and field-based controlled-pollination experiments. Intrafloral dichogamy (protogyny) occurs over a 2-d period, with a reproductively inactive phase between the pistillate and staminate phases, although there is no evidence of interfloral dichogamy. The inner petals close to form a pollination chamber during the reproductively active phases. The flowers are pollinated by a species of Endaeus weevil (Coleoptera: Curculionidae). Floral chamber temperatures are elevated to 8°C above ambient levels. The floral scent contains a combination of volatiles that have previously been observed in fruits and other flowers and that possibly mimic insect pheromones. Xylopia championii has an essentially xenogamous breeding system, promoted by protogyny. Although X. championii possesses numerous clear adaptations for cantharophily, there is no evidence for a species-specific interaction. The beetles are attracted to the flowers by strong scents; rewards offered to the beetles include heat energy and protection from predators. Low levels of fruit set in natural conditions suggest that pollinator availability may be a limiting factor. © 2007 by The University of Chicago. All rights reserved.