Most odors in the natural environment are mixtures of several compounds. Olfactory receptors housed in the olfactory sensory neurons (OSNs) detect these odors and transmit the information to the brain, leading to decision making. But whether the olfactory system detects the ingredients of a mixture separately or treat mixtures as different entities is not well understood. Using Drosophila melanogaster as a model system we have demonstrated that fruit flies perceive binary odor mixtures in a manner which is heavily dependent on both the proportion and the degree of dilution of the components, suggesting a combinatorial coding at the peripheral level. This coding strategy appears to be receptor specific and is independent of inter-neuronal interactions.
Significance Statement: Insects rely on olfaction to successfully identify and distinguish between volatile chemical cues that are essential for reproduction and survival. Most naturally occurring olfactory signals are complex mixtures of many chemicals in varying composition and proportion. In the present study, using Drosophila melanogaster, we have shown that the olfactory system can encode the information for binary odor mixtures by exhibiting a strong response towards specific combinatorial concentrations independent of the individual odor intensities. We further found that the ratio coding is receptor specific and is independent of ephaptic interactions. The particular combinations could be relevant in terms of the fly’s ecology. This study can also pave way towards better understanding of the mechanism of host-tracking by insect pests and vectors.
Authors report no conflict of interest.
Authors Contribution: SK, TSC and OS- Designed Research and Analysed Data, SK, AG and AK- Performed Research, SK and TSC- Wrote the paper.
Department of Biotechnology, Government of India- Research Associate Fellowship and National Centre for Biological Sciences (TIFR), Bangalore, India
↵† Dedication: This paper is dedicated to Late Professor Obaid Siddiqi who died on 26th July 2013.