9319002 Delph This research addresses the genetic mechanisms that may be responsible for variation in the ability of offspring to survive, for the alpine tundra plant, Silene acaulis. Silene acaulis has a mating system that is termed "gynodioecy", in which there are two types of individuals, females and hermaphrodites. This contrasts with the majority of flowering plant species, in which only hermaphrodites occur. It has been reported that offspring from the female morph are nine times more likely to survive the seedling establishment phase than are offspring whose seed-parents are hermaphrodites. This is in spite of the fact that the seeds from the females are smaller and contain fewer nutrients than those from hermaphrodites. This suggests that genetic mechanisms are involved. Three genetically based hypotheses to explain the higher quality of seeds from females will be tested using field and laboratory experiments. The work funded by this grant will provide insight into (1) how genes that affect more than one trait in an organism are selected for, (2) how matings between related individuals affect offspring fitness,and (3) how competition among pollen grains that differ in their genetic constitution can affect offspring fitness. Furthermore, the genetic basis of sex determination will be investigated, in that the number of cytoplasmic types conferring male-sterility will be determined. Plant species with different mating systems vary in their ability to persist in natural populations, and this work promote understanding of the mechanisms responsible for this difference.
