|dc.description.abstract||Evolutionary transitions from insect to wind pollination are thought to have occurred many
times during the angiosperm radiation. This transition is commonly associated with a suite
of distinctive floral traits such as reduction of flower size and a transition to dry pollen. In
the dioecious genus, Leucadendron (Proteaceae), evolutionary shifts from insect to wind
pollination have been postulated based on floral morphology features. In this study, I
aimed to experimentally test the potential for wind versus insect pollination in several
Leucadendron species and document a variety of floral traits (pollen size, inflorescence
size, scent, colour, etc.) in order to determine their functional significance whilst utilizing
phylogenetic comparative methods to test the statistical significance of evolutionary
associations between particular floral traits and pollination systems.
Fifteen representative Leucadendron species were investigated to verify insect and
wind pollination in as many clades as possible. Insect exclusion experiments confirmed
that five Leucadendron species, L. rubrum, L. salicifolium, L. dubium, L. coniferum and L.
teretifolium are indeed wind-pollinated. Pria cinerascens (Nititulidae) was found to be the
main pollinator of the insect-pollinated Leucadendron species due to their abundance, high
stigmatic contact and relatively pure Leucadendron pollen loads. Overall, however, the
abundance of insects visiting inflorescences was not significantly different between insectand
wind-pollinated species, which highlights the importance of conducting insect
exclusion experiments to evaluate whether a species is wind- or insect-pollinated.
From the previously determined pollination systems of 17 Leucadendron species,
floral traits associated with the shift to wind pollination were investigated to determine
whether transitions from insect to wind pollination were accompanied by modifications of
pollination-relevant floral traits. In a wind tunnel, pollen grains of wind-pollinated species
were found to be more motile than those of insect-pollinated species. Phylogenetic
analyses suggest that transitions from insect to wind pollination occurred at least four times
during the diversification of Leucadendron and that, compared to insect-pollinated
cogeners, wind-pollinated Leucadendron species are characterized by increased production
of smaller pollen grains, higher inflorescence density, less attractive visual and olfactory
cues, and a greater degree of sexual dimorphism for these visual and olfactory cues.
In conclusion, this study experimentally confirms that there were several shifts
from insect to wind pollination in Leucadendron and identifies floral traits that were
evolutionarily modified during these shifts.||en