Preferential outcrossing in Banksia ilicifolia (Proteaceae)

Abstract

The breeding system of Banksia ilicifolia was assessed by performing controlled hand-pollination manipulations on flowers in a natural population in Perth, Western Australia. The percentage of 2000 flowers per treatment converted to fruits and seeds was assessed across 24 recipient plants following (1) self-pollination, (2) local outcross pollination (same population), (3) non-local outcross pollination (pollen sourced from another population 30 km away), (4) unpollinated but bagged flowers and (5) unpollinated, unbagged flowers (natural pollination). The relative performance of the resulting seeds was assessed by seed weight, germination rates and, in an unplanned component of the study, resistance to a fungal pathogen. The percentage of flowers converted to fruits following self-pollination was low (0.9%), but demonstrated self-compatibility. Fruit set following cross-pollinations (3.6 and 3.3% for non-local and local crosses, respectively) was significantly greater than that following self-pollination, open-pollination (0.4%) and autogamous (0.04%) treatments. Low fruit set for open-pollinated flowers, compared with self- and outcross-pollination treatments, suggests pollen limitation. Pollen tubes were observed in 15 and 20% of upper styles of flowers hand-pollinated with self and local outcross pollen, respectively. Seed germination was dependent on the source of pollen, where fewer selfed seeds germinated (37%) than did both non-local and local outcrossed seeds (83 and 91%, respectively). Selfed seedlings showed poorer survival (33.3%) following fungal attack than both non-local and local outcrossed seeds (69.2 and 68.5%, respectively). Only 13% of selfed seeds survived to be 2-month-old seedlings, compared with 63% for non-local and 57% for local outcrossed seeds. Ultimately, for 2000 flowers hand-pollinated with self pollen, only three seedlings survived to an age of 16 weeks, compared with 37 and 45 seedlings for local-cross and non-local cross treatments on 2000 hand-pollinated flowers, respectively. These results indicate that in this population, B. ilicifolia is self-compatible, but preferentially outcrossing, with strong early acting inbreeding depression. Consequently, the breeding system of B. ilicifolia promotes the maintenance of genetic variation and a high genetic load.

Evidence for autonomous selfing in grassland Protea species (Proteaceae)

“…Thus, even though B. marginata is self‐compatible, selfed seedlings suffer from inbreeding depression and were 62% less fit than open‐pollinated progeny. A similar result was reported by Heliyanto et al . (2005) for Banksia ilicifolia R.Br.…”

A Genetic Assessment of Ecological Restoration Success in Banksia attenuata

“…Seed production by banksias relies on pollinators (insects, mammals and, especially, highly mobile birds), and in their absence seed set can be rare or even nonexistent (Whelan & Burbidge 1980; Whelan & Goldingay 1986; Collins & Rebello 1987; Lamont et al 2007; Phillips et al 2010). As a consequence, Banksia in general displays the highest outcrossing rates seen among plants (Scott, 1980; Carthew et al 1996; Heliyanto et al 2005; Coates et al 2007; Lamont et al 2007; Krauss et al 2009), and it is vital therefore that pollinator services are established for viable restored Banksia populations.…”

Pollination ecology and the possible impacts of environmental change in the Southwest Australian Biodiversity Hotspot

“…Coates et al 2007). Within Grevillea, Banksia and Eucalyptus there is considerable interspecific variation in mating system with species varying from complete selfing to complete outcrossing (Ramsey & Vaughton 1991;Ellis & Sedgeley 1992;Day et al 1997;Kennington & James 1997;Hermanutz et al 1998;Heliyanto et al 2005). Studies of wild populations have shown that bird-pollinated plants in several genera tend to be primarily outcrossing (Hopper & Moran 1981;Day et al 1997;Coates et al 2007).…”