Aim: 

Olfaction in the fruit fly Drosophila melanogaster is increasingly understood, from olfactory receptors to 'higher brain centers'. Drosophila thus offers an excellent opportunity to study the evolutionary and ecological dynamics of olfactory systems. In a previous study we showed that there are shifts at various levels in the olfactory circuitry of D. sechellia related to its sole food source and oviposition site, Morinda citrifolia fruit (Dekker et al., 2006). In the current study we tested if minor and a specific blend of Morinda fruit volatiles could be also relevant for the specialist fruit fly to find its food source.

Methods: 

Gas chromatography coupled with single receptor neuron recording was used for testing if minor of morinda fruit volatiles was biologically relevant for D. sechellia. A free walking bioassay was used to test D. sechellia attractiveness towards some of the morinda volatiles.

Results: 

We identified minor compounds, i.e. 2-heptanone, which triggered a response predominantly on a specific ORNs that is overexpressed in D. sechellia antennae. Behavioral tests showed that D. sechellia was attracted to all concentrations of 2-heptanone tested from pure to 10^-8, whereas the generalist D. melanogaster showed attraction only for intermediate concentrations. Results of behavioural tests also showed that the blend of morinda fruit volatiles, from very high to low concentrations, is a powerful attractant for D. sechellia, differently the mixture was attractive for the generalist D. melanogaster only at midrange concentrations.

Conclusion: 

These findings show that D. sechellia behaviour is remarkably tuned to its sole host, Morinda fruit.