• Despite the conflicting demands imposed by mutualistic (pollination) and antagonistic (for ivory) processes, the relative importance of the key selective pressures influencing floral evolution is not readily apparent. In this study, we quantified a range of floral and foliar traits within the genus Hakea to investigate how pollinator and herbivore selection might influence the evolution of floral attraction and defence attributes.
• Plant material was collected from populations of 51 Australian Hakea species native to southwestern Australia, and measurements were taken of foliage and inflorescence morphology, inflorescence colour and floral chemical defence. Hakeas were separated into a bird- vs insect-pollinated species on the basis of stigma–nectary distance.
• Our results show how the evolution of insect vs bird pollination is closely linked to whether inflorescences are protected by physical (leaf spines, dense foliage) or chemical (floral cyanide) defences, respectively.
• Rather than being constrained by the necessity to attract pollinators, we suggest that pre-existing adaptations to combat florivore and herbivore attacks directed the evolution of floral characteristics employed to attract pollinators and deter folivores. The inter-correlation among bird pollination, red flower colour and floral cyanide indicates floral colouration may signal to vertebrate folivores that the inflorescences are unpalatable despite their high accessibility.
Pollination and plant defense traits co-vary in western Australian Hakeas
Year: 2008
