NONRANDOM MATING IN CLARKIA-GRACILIS (ONAGRACEAE) - A CASE OF CRYPTICSELF-INCOMPATIBILITY

In plants capable of both self-fertilization and outcrossing, the self ing rate depends on the proportion of self pollen in pollen loads and on the relative postpollination success of self pollen in siring offsp ring. While the composition of pollen loads is subject to unpredictabl e variation, paternity success of self vs. outcross pollen following p ollen deposition may be controlled by maternal plants. This study exam ined postpollination paternity success in Clarkia gracilis ssp. sonome nsis, in which deposition of self pollen is common. Pure loads of self and outcross pollen produced similar numbers of mature seeds, but equ al mixtures of self and outcross pollen yielded more than three times as many outcrossed offspring as selfed offspring. The finding that the paternity success of self pollen depends on whether it is in competit ion with outcross pollen helps to explain an earlier finding that the selfing rate in experimental populations was highest when pollinator a ctivity was lowest. Cryptic self-incompatibility allows paternity by s elf pollen when outcross pollen is unavailable.