The Evolution and Maintenance of Mixed Mating Systems
Stephenson, Andrew G. , Mena-Ali, Jorge , Brown, Sarah , Good-Avila, Sara V. .
The Causes of Partial SI and Its Consequences for the Mating System.
Many species are known to exhibit partial self-incompatibility (SI) in which individuals in a population vary in the strength of SI. We have been investigating the genetic causes and evolutionary consequences of partial SI in two species, Campanula rapunculoides and Solanum carolinense. In C. rapunculoides, there is variability in the strength of SI among individuals in two populations; older flowers on most individuals are more self fertile than younger flowers; and partial SI is heritable and determined by 3-5 mostly recessive genetic modifiers that are unlinked to the S-locus (the locus that determines SI). Recently we have shown that when pollinator access is varied in experimental populations with natural (bee)pollination, the selfing rate for weak SI genotypes is greater than for strong SI genotypes. In Solanum carolinense, we have also found that there is variability in the strength of SI among individuals in two populations and that older flowers on most individuals are also more self fertile than younger flowers. To determine the genetic basis of partial SI in S. carolinense, we performed a series of self and cross pollinations on 16 plants and sequenced the S-alleles in 192 progeny (6 self and 6 cross progeny from each of the 16 plants) and scored the progeny for their strength of SI. This study revealed that partial SI in S. carolinense is determined by leaky and strong S-alleles. In both species, self pollen grows more slowly in the styles of the flowers (even old flowers) than cross pollen, consequently partial SI in these species will result in self seed only when cross pollen limits seed production. Thus it appears that partial SI tilts the mating system toward outcrossing but allows some self seed to set when there are few pollinators or few S-alleles in the population.
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1 - Pennsylvania State University, Department of Biology, 202 Mueller Lab, University Park, Pennsylvania, 16802-5301, USA
2 - Amherst College, Department of Biology, Amherst, MA, 01002, USA
3 - Pennsylvania State University, Department of Biology, 208 Mueller Lab, University Park, PA, 16802, USA
4 - Acadia University, Department of Biology, Wolfville, Nova Scotia, BOP 1X0, Canada
Presentation Type: Symposium or Colloquium Presentation
Location: Stevens 5/Hilton
Date: Monday, July 9th, 2007
Time: 8:15 AM