No Evidence for Selective Fruit Abortion in the Australian Shrub Grevillea barklyana (Proteaceae)

Plants may increase the average quality of their seed crops by selectively aborting less vigorous progeny when resources are limited. Selective fruit abortion was examined in selfing and outcrossing populations of the Australian proteaceous shrub Grevillea barklyana. Inflorescences were pollinated with cross pollen, self pollen, or a combination of the two pollination types on different flowers. Fruit initiation and maturation were similar on self- and cross-pollinated inflorescences. Self-incompatibility indices indicated that all plants were fully self-compatible. When self and cross fruits competed for limited maternal resources on the same inflorescences, numbers of self and cross fruits did not deviate from a 50:50 ratio. This indicates that differences in the vigor of self and cross progeny were minimal, which may be a consequence of populations having a history of inbreeding. Most fruits aborted early in development, before substantial investment of resources. Results in the selfing and outcrossing populations were similar, indicating that neither selective abortion nor inbreeding depression can account for differences in mating patterns.