Summary: A model for polyandry in oaks via female choice:
a rigged lottery
Kathleen J. Craft, Joel S. Brown, Antonio J. Golubski
and Mary V. Ashley
Department of Biological Sciences, University of Illinois at Chicago, Chicago, Illinois, USA
Questions: Why do oaks produce surplus ovules and abort fertilized embryos? How do
remote stands of oaks have such genetically diverse offspring?
Mathematical methods: Two-phase weighted lottery held in each female flower. Pollen clouds
are modelled using one of two different functions to relate each father's representation among
the pollen pool at a maternal tree to its distance from the maternal tree.
Key assumptions: Flowers act independently of each other. All ovules of each flower are
fertilized. One embryo matures to become an acorn and all other embryos are aborted. Lottery
#1 is based solely on each `father's' geographic distance from each maternal tree. Closer fathers
have a higher chance of fertilizing an ovule and winning the first lottery. Lottery #2 is based on
maternal choice. Female flowers selectively abort embryos fertilized by `common' fathers.
`Common' fathers are those that are over-represented among each flower's embryos.
Predictions: Offspring diversity is maximized at an intermediate number of ovules. The
number and distribution of fathers in the pollen cloud affect how many ovules are necessary to