SEED SET AND SEED MASS IN IPOMOPSIS-AGGREGATA - VARIANCE PARTITIONINGAND INFERENCES ABOUT POSTPOLLINATION SELECTION

Events that follow pollination, such as pollen-tube growth and seed ma turation, comprise an important phase of angiosperm reproduction. Diff erential success during this ''postpollination'' phase may represent p henotypic selection, including sexual selection, or interaction betwee n parents caused, for example, by their genetic similarity. By providi ng a detailed partitioning of variance in success, diallel crossing de signs offer great potential to determine which processes are occurring and their relative magnitudes. We performed three partial diallels wi th the montane herb Ipomopsis aggregata, using a large sample of paren tal plants (69 total). Embedded in the designs were crossing-distance treatments of 1 m, 10 m, and 100 m, reflecting a range of parental gen etic similarity. We partitioned phenotypic variance in seed set per fr uit into six components using restricted maximum-likelihood (REML) ana lysis. For one diallel, we also partitioned variance in seed mass into five components, and estimated two components of covariance between s eed set and mass. Variance caused by maternal effects (V(m)at) compris ed 12%-35% of total variance in seed set and 62% of variance in seed m ass, and there was a significant negative environmental covariance bet ween seed set and seed mass. Parental interaction made no detectable c ontribution to phenotypic variance in either of our measures of postpo llination success, although crossing distance did contribute slightly but significantly to fit of the model in some cases. Finally, there wa s no detectable paternal variance (V(p)at) in seed set or seed mass. T hese results are in keeping with reports from other studies of natural plant populations. The finding of little or no paternal variance in p articular suggests little scope for postpollination sexual selection t hrough the male function of cosexual plants such as I. aggregata.