FINER, MATTHEW S* AND MARTIN T MORGAN. School of Biological Sciences, , Washington State University, , Pullman, WA, 99163. - Geitonogamy and the evolution of inflorescence design in Asclepias speciosa.
Geitonogamy has the unique distinction of having the ecological
properties of outcrossing, but the genetic consequences of selfing.
We investigate the potential of geitonogamy as a selective force in
the evolution of inflorescence design in Asclepias speciosa. We
conducted 1,092 hand outcross pollinations (6 per individual) on two
treatments, one covered in pollinator-excluding bridal veil before and
after pollinations and the other left open to experience the
consequences of natural rates of self-pollinations. The bagged
treatment had significantly higher female fitness than the open
treatment, providing strong evidence that natural rates of
self-pollination significantly reduce fruit set in A. speciosa.
Results were consistent in both undisturbed and fragmented
populations, suggesting geitonogamy may be independent of population
size. Fruit set data provides evidence that geitonogamy, and not
resource limitation, may limit female success. We will also look at
the effect of inflorescence-unit size on geitonogamous pollinations in
natural populations. We will manipulate umbels in the field to create
five treatments ranging in size (5, 15, 25, 35, 45 flowers per umbel),
and then measure effects of size on pollen export and selfing rate
with AFLP analysis of inserted pollinia. This will be the most direct
study of pollen export and geitonogamy in a natural population
conducted to date.
Key words: Asclepias speciosa, geitonogamy, inflorescence design, pollination