The biology of pollination and seed dispersal in Clivia (Amaryllidaceae)

Abstract

Pollinator shifts have been implicated as drivers of angiosperm diversification. The hypothesis that a transition from bird to butterfly pollination took place in Clivia was tested, and floral traits investigated to determine which may have mediated the putative shift. Linking pollination systems with available phylogenies indicated a shift occurred from bird to butterfly pollination, accompanied by the evolution of upright trumpet-shaped flowers, scent emission and nectar volume reduction, whilst floral colouration and nectar chemistry remain unmodified. Results support the idea that pollinator shifts may explain major floral trait modifications during plant diversification. Breeding systems of Clivia were investigated, with the aims of demining the site and functional consequences of putative late-acting self-incompatibility (LSI). Results suggest that Clivia species are largely self-sterile as a result of LSI or severe inbreeding depression, but ovule discounting caused by self-pollination is not a major limitation on fecundity, and seed production appears to be mostly resource limited. Clivia miniata is pollinated virtually exclusively by butterflies. Functional significance of C. miniata floral traits were examined, with the aim of determining butterfly floral preferences and the functional basis of traits responsible for butterfly pollination. Colour is a key advertising signal, with orientation facilitating alighting, whilst size, scent, and shape also influence butterfly attraction. Dispersal mechanisms of numerous fleshy seeded Amaryllidaceae have been an enigma as seeds are unorthodox, toxic and unable to survive ingestion, yet packaged in brightly coloured fruits suggestive of animal dispersal. Dispersal and germination of Clivia miniata seeds was investigated. Results indicated consumption of fruit by primates which disperse seeds through non-ingestive spitting behaviour. The short distance of seed dispersal by primates is predicted to lead to restricted gene flow and genetic subdivision of populations. I conclude that shifts in pollination systems and the associated modification of suites of functional floral traits led to floral diversification in Clivia. Self-infertility in Clivia highlights pollinator dependence and pollination syndrome conformity reflects functional advertising signals. Gene flow appears to be governed by pollen flow and facilitated by pollinators rather than seed dispersal. Mating and breeding system evolution are likely a consequence of adaptation to isolated forest habitats.