Abstract:
Fermentation is energetically inefficient, but the production of ethanol provides Saccharomyces cerevisiae with an advantage since it poisons competitors in the fruit niche which it is adapted to invade. The fruit fly Drosophila melanogaster has secondarily evolved to locate fruits by following ethanol trails. Volatiles, that include esters, are responsible for the fruity aromas in alcoholic beverages and are also produced by S. cerevisiae during fermentation; however their biological function is unknown. I proposed that the production and modification of volatiles by yeasts serves as a more sophisticated attractant to D. melanogaster which then act as significant vectors of the dispersal of yeast in nature: any yeast traits that encourage dispersal will be operated on by Natural Selection as fruits are ephemeral. This project focused on testing the first hypothesis of attraction: Whether grape juice inoculated with S. cerevisiae is more attractive than grape juice alone. A total of 45 yeasts from New Zealand and international locations were investigated consisting of non- Saccharomyces and Saccharomyces strains associated with wine, non-Saccharomyces strains not associated with fruits and Saccharomyces sensu stricto species. A T-maze was constructed to assay the olfactory behaviour of fruit flies and Attractability Index (AI) was used to measure the attractiveness/repulsion. A total of 80 fruit flies were used and 8 replicates were performed for each test. The yeasts ranged from repulsive to highly attractive. Preliminary analysis of head-space compounds of four yeasts was performed. Future work includes further identification of headspace compounds of the above yeasts and a complementary human sensory test. The findings of this research will contribute to our understanding of co-evolution between two classic model organisms as well as the ecology of yeast dispersal.