Flies Sniff Out Smells
Blind flies find the elusive origins of odor plumes
Background
Odor plumes are clusters of odor molecules spread by the wind over a wide area from their original source. They are often carried downwind, following the direction of wind flow and tend to expand outward. Many species of animals are able to track odor plumes to locate food, potential mates, and nesting sites.
However, following a plume to its origin can be incredibly difficult, because odor plumes are constantly disturbed by air flow as it is naturally unstable. Encounters with odors on their own do not provide any information about their source, because odor plumes contain empty patches with no odor at all where animals are typically unable to continue following the odor.
Summary
A study done by Nirag Kadakia, and a team of researchers found evidence that fruit flies can detect odors with their two antennae by sensing the movement of an odor, which enables the fly to follow it to its source.
Kadakia conducted his study using optogenetics, a technique utilized in neuroscience. It allows scientists to control how nerve cells communicate through the use of light signals. Flashes of light penetrate the antennae and activate the area in the fly’s brain that triggers the olfactory receptors, causing the flies to respond as if smelling a physical odor. The light mimicked the motion and patterns of an odor plume. Kadakia used blind flies to prevent them from seeing the light source.
Odor molecules in an odor plume move in different directions, either with or away from the wind flow. Kadakia wanted to know if the fly's ability to track an odor would be affected by wind flow, so they added a flow of fresh air in the space the flies walked in. The researchers were able to change the light and the direction of the wind flow, so it simulated an odor traveling upwind or downwind. The researchers wanted the flies to walk in the area containing the flashes of light and air flow instead of flying, because they could more accurately measure how the fly is reacting in the controlled environment when they move at a slower pace.
Results
The study showed that the neurons in one antenna can activate independently of the other and they use them to detect odor plumes. Fruit flies do not rely on the wind to track the origin of an odor plume.
Kadakia estimated that flies use the direction and size of an odor plume to determine the position of an odor. Sensing the direction and size of a plume enables the fly to know when they are inside the full extent of the plume even if they are not near a dense area of odor molecules. It enables the flies to stay within the odor and follow where the smell began.
Kadakia estimated that flies use the direction and size of an odor plume to determine the position of an odor.
A few limitations of the study are the inability to control how an odor is experienced by fruit flies outside of a contained experiment. In the wild the fruit flies can track a plume for one hundred meters or more. The study does not account for how well a fly could follow a larger plume found naturally in the wild where there are more barriers for the fly to navigate. Scientists have much left to discover, and some evidence has been found to suggest that flies are not the only animals who can sense the movement of odors.
If you are interested in reading more research on this topic, you can find similar research in PLoS Computation Biology.
Grove City College students can find any of these journals by simply searching the journal name in Discover on the Henry Buhl Library’s homepage. And don’t forget — if you’d like to find more related resources, the library maintains a list of A-Z Databases with an entire tab dedicated to biology!
