LANDRY, CAROL L.* and BEVERLY J. RATHCKE. Dept. of Ecology and Evolutionary Biology, University of Michigan, Ann Arbor MI. - Pollination biology of White Mangrove (Combretaceae: Laguncularia racemosa): Can pollinator foraging behavior determine plant breeding systems?
Botanists have long been intrigued by the myriad of breeding systems
found in the Plant Kingdom, particularly by the ways in which the
different systems evolve and are maintained. We are interested in how
the interactions between flowering plants and their pollinators affect
the evolution and maintenance of plant breeding systems, and are
currently studying androdioecy in White Mangrove (Combretaceae:
Laguncularia racemosa), a self-compatible tree species found in
mangrove forests throughout the Neotropics and in western Africa.
Androdioecy is an extremely rare breeding system defined as having two
kinds of plants, one producing hermaphroditic (perfect) flowers and
the other producing male flowers. We have found several populations of
White Mangrove in Florida that are strictly hermaphroditic, while
androdioecious populations have 2%-67% male plants. Here we discuss
the effect that pollinator foraging behavior and pollinator visitation
rate have on both hermaphroditic and androdioecious populations. We
hypothesize that the foraging behavior of insect pollinators is an
important factor in determining the breeding system of White Mangrove.
Specifically, if most insects forage for long bouts within a tree
before moving on to the next tree, they will promote selfing in that
population and male trees will be lost from the population. However,
if most insects forage for short bouts within a tree and move more
frequently between trees, they will promote outcrossing in that
population and androdioecy will be maintained. In addition, we
hypothesize that an increase in pollinator visitation rate to male
plants relative to hermaphroditic plants will result in greater male
success and therefore, in greater proportions of male plants in
androdioecious populations. Our preliminary data support these
hypotheses, including evidence that honeybees may promote the loss of
males in androdioecious populations of White Mangrove.
Key words: androdioecy, breeding systems, insect pollination, Laguncularia racemosa, plant-pollinator interactions, pollination biology