Phenology, pollination ecology and breeding system of Polyalthia coffeoides and P. korinti (Annonaceae)

Abstract

Comparatively little is known of the reproductive biology of palaeotropical Annonaceae. Populations of Polyalthia coffeoides and P. korinti have been studied in dry and intermediate zone forests of Sri Lanka. The petals separate early in development, but subsequently close to form a pollination chamber over the reproductive organs. Formation of the chamber is coincident with elevated internal temperatures and scent production over a twoday period. GC-MS analysis of the odour reveals the presence of volatiles that mimic beetle sex pheromones. The primary effective pollinator of both species is an Endaeus weevil (Coleoptera: Curculionidae), with pollen grains generally observed around the mouthparts and legs. The weevils are abundant and active around the flowers in the late evening and overnight. The flowers are protogynous, and studies of pollen/ovule ratios suggest that both species are facultatively xenogamous; this is corroborated by controlled pollination experiments, which reveal greater fruitset following cross-pollination than self-pollination. Variation in ISSR molecular markers indicates that both species have a mixed mating system.