ARMSTRONG, JOSEPH E. Behavior, Ecology, Evolution, and Systematics Section, Campus Box 4120 - Biological Sciences, Illinois State University, Normal, IL 61790-4120. - Competition among floral brooding insects and reproductive success in Anaxagorea crassipetala (Annonaceae).
Anaxagorea crassipetala is a small understory tree of Central American
lowland rainforests. As the specific epithet suggests, petals of the
outer whorl are thick and fleshy having the general appearance and
texture of little bananas. Floral brooding is commonly associated with
obligate mutualism and with beetle pollination, but while a brood
substrate is a large reward, competition for this reward may affect
the reproductive success of all parties. In this case beetle
mutualists compete for this limited and ephemeral brood substrate with
non-pollinating fruit flies and beetles. While beetle pollinators only
visit during anthesis, non-pollinating insects who oviposit prior to
anthesis win the competition both with the mutualists and
non-pollinating, floral-brooding insects who visit during anthesis. By
experimentally denying access to pre-anthesis flowers, the
reproductive success, as measured by fruit set, of the tree was
significantly increased over open access controls. No mutualist beetle
reproduction was recorded. This may be the result of a high rate of
competition from fruit flies, whose feeding larvae may reduce the
attractiveness of the petals as a brood substrate. Even among the
fruit flies, oviposition prior to anthesis resulted in significantly
higher reproductive success than ovipositions on the day of anthesis.
Flowers were visited at a rate significantly higher than pre-anthesis
buds suggesting that while ovipositing in buds increased fruit fly
reproductive success, non-attractive buds were difficult to find in
comparison to scent-producing flowers.
Key words: Anaxagorea crassipetala, Annonaceae, beetle pollination, competition, floral brooding, tropical