Evidence for autonomous selfing in grassland Protea species (Proteaceae)

Abstract

It has been assumed that species of the large African genus Protea have strong self-incompatibility systems. However, this assumption was based largely on studies conducted on a clade of bird-pollinated species that occur in the shrubby fynbos vegetation of the Cape region of southern Africa. To test whether self-incompatibility occurs in a grassland/savanna Protea clade, which is largely insect-pollinated, we performed controlled pollination experiments on four species, P. caffra, P. dracomontana, P. simplex and P. welwitschii. Although pollen–ovule ratios of all four species fall within the range for outcrossers, all four species are self-compatible and capable of autonomous seed production. Using fluorescence microscopy, we found that self-pollen tubes had the same probability of reaching ovules as cross-pollen tubes. In the small tree P. caffra, selfed progeny had rates of germination and survivorship that were identical to those of crossed progeny. The grassland Protea spp. studied are likely to have mixed mating systems on account of being both visited by insects and capable of autonomous selfing. If one assumes previous reports of self-incompatibility in Protea to be reliable, there have been at least five losses of self-incompatibility and two gains of autonomous selfing in this genus. However, earlier studies in the genus were often methodologically flawed and a thorough re-analysis of breeding systems in Protea is required. © 2012 The Linnean Society of London, Botanical Journal of the Linnean Society, 2012, 169, 433–446.