Sniff ‘N’ Track Or Run ‘N’ Scan?

In familiar environments, the ‘run-and-scan’ strategy is a more efficient way of finding food, at least according to mathematical models.

AsianScientist (Dec. 4, 2015) – A study published in eNeuro has determined the most efficient strategy for animals to search for food using their sense of smell. The method, dubbed ‘run-and-scan’ was found to be more efficient than attempting to trace scents, that is, the ‘follow your nose’ technique.

The research by Drs. Urvashi Bhattacharyya and Upinder Bhalla from the National Center for Biological Sciences (NCBS)/Tata Institute of Fundamental Research (TIFR) revealed that while searching in a familiar area with limited choices, a run-and-scan strategy is more efficient than a tracking strategy. The research used rats to study how animals choose navigational strategies when presented with an odor signal.

The sense of smell is essential for many animals to track food, mates or predators. Dogs, rats, insects and even humans are known to adopt a zig-zag path while tracking smells, a strategy known as ‘casting’. Under natural conditions in large, unfamiliar environments, casting is thought to be useful when animals search using smell-based cues.

However, what happens when organisms are within familiar environs? With access to more information such as well-known paths to food, or memories of past explorations, how do they optimize their searches?

“The question we asked was, what could be the best strategies an animal might use in terms of either speed, accuracy or both, for target selection?” said Bhattacharyya.

To address this question, Bhattacharyya trained rats within an arena to recognize targets having specific odors. Correct identification of the scent-emitting target would result in the rat receiving a reward.

This was followed by a series of target-recognition tests which included disturbances to the ‘normal environment’ of the arena such as addition of background odors and air turbulence (which disrupts the smell gradient). The rats’ choices and behaviors were observed to analyze the strategies they used in identifying the correct targets.

“We found that rather than casting, rats ran towards a potential target, and then serially scanned across other targets till they found the right one”, said Bhattacharyya.

In human terms, this kind of search is equivalent to picking a likely room where dinner could be served, then peeking into different rooms to find dinner if the first one was wrong, which is a very different approach to actually using one’s sense of smell to pin-point the room with food.

Surprisingly, this strategy seems to assure very good accuracy in locating correct targets. Even in the presence of other background odours or air turbulence, the animals were able to identify the correct targets though they tended to be marginally slower than under normal conditions.

Mathematical modeling of casting and run-and-scan situations suggests that the two modes of searching can be useful in different situations. Although casting is advantageous in free-range searches, the run-and-scan approach seems more efficient in situations with known targets in familiar surroundings.

The article can be found at: Bhattacharyya et al. (2015) Robust and Rapid Air Borne Odor Tracking Without Casting.


Source: TATA Institute of Fundamental Research; Photo: Jean-Jacques Boujot/Flickr/CC.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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