Floral chemical defences against ants and microorganisms

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Flower odours are known to serve as pollinator attractants. However, apart from mutualists, antagonists strongly affect the reproductive success of a plant and may represent important selective agents for the evolution of phenotypic floral traits. The innovative goal of the proposed project is to understand the defensive role of floral volatiles against ants that represent potential nectar thieves, and against potentially harmful microorganisms. The project will represent the first experimental investigation of the defensive function of floral scents except for a few specific case studies. We recently demonstrated that ants were repelled by specific floral volatiles and entire bouquets of flowers from a number of plant species. Ants could overcome such repellence in some cases by associative learning; this process will be studied in greater detail here and compared to behavioural responses of pollinators. Moreover, the toxic function of these compounds will be tested for ants, bees and microorganisms. Terpenoids, particularly monoand sesquiterpenes, are common among floral odours and are known as an attractive signal for pollinators. Here we hypothesise that terpenoids also play a dominant role in the defensive system. Since plant species vary in their exposition to different antagonists, comparisons between species with variable life histories, using a phylogenetically controlled approach, will facilitate an increased understanding of the evolutionary dynamics of both, attractive and repellent signals.