POLLEN-MEDIATED GENE FLOW IN CUCURBITA-FOETIDISSIMA (CUCURBITACEAE)

Pollen-mediated gene flow along a linear series of patches of the functionally gynodioecious, bee-pollinated Cucurbita foetidissima was assessed using electrophoretic analysis of seed allozymes. Gene flow was documented at distances up to 0.7 km. For the 13 patches examined, interpatch pollen must have sired from 0% to 48.3% (XBAR = 8.5%) of the seeds of monoecious plants (hermaphrodites). Rates of interpatch siring of seeds of pistillate plants (females) averaged 20.4% (range 8.6% - 40%) for the three patches examined. Heterogeneity among fruits in seeds sired by interpatch pollen indicates that the arrival of interpatch pollen is clumped with respect to stigmas. Within patches, plants of the same sex type usually shared identical five-locus genotypes, suggesting that clonal propagation predominates. Since approximately 90% of seeds are sired by intrapatch pollen, seeds of monoecious plants appear to result primarily from geitonogamous (self-) fertilization. This may help explain the existence of female plants in natural populations, since self-fertilization has been shown to severely reduce the survival of seedlings in this species.