Selfed Seed Set and Inbreeding Depression in Obligate Seeding Populations of 'Banksia marginata'

Abstract

Self-compatible species can often produce seeds when pollinators are scarce or unreliable, but any advantage may be lessened if selfed progeny are less fit than outcrossed progeny due to inbreeding depression. We use hand self-pollinations to determine whether Banksia marginata is self-compatible and examine the relative fitness of seeds derived from self- and open-pollination at several early life-cycle stages to gauge the likely impact of inbreeding depression. Substantial numbers of fruits and seeds were produced following selfing, indicating that plants are self-compatible. However, differences between selfand open-pollinated inflorescences indicated that relative self-fertility was less than one. Compared with open-pollinated seeds, selfed seeds were smaller and produced smaller seedlings that were less likely to survive. Percent germination of self- and open-pollinated seeds was similar. Cumulative fitness estimated over several life-cycle stages, including seed production, indicated that selfed progeny were on average only 62% as fit as open-pollinated progeny. These differences in relative fitness indicate that despite self-compatibility, populations have experienced a history of outcrossing. Banksia marginata plants at Gibraltar Range National Park are killed by fire, and self-compatibility may be associated with this trait.