Scientists have already observed that rats will voluntarily share food with other rats who are hungry. A new study now suggests that they do so not just based on what the other rat does, but also on how it smells.

It had previously been noted that hungry rats will beseech their fellow rats via vocalizations and gestures, in hopes of getting a food handout. However, how could a rat with food know that the requesting rat really was hungry, as opposed to just being greedy? Wildlife biologist Dr. Karin Schneeberger set out to see if there was more of an "honest cue" involved.

Her study was conducted with help from colleagues at Switzerland's University of Bern and Germany's University of Potsdam, both of which she's affiliated with.

The scientists placed either a hungry or well-fed Norway rat in one room, then directed air from its cage into a cage in another room. That other cage was divided in two by a wire mesh barrier, and contained two other Norway rats – each one located on either side of the barrier. An external tray of food was accessible by one of these rats, who could pull it to within reaching distance of its cage-mate if desired.

An overhead view of the food-sharing cage, in which the rat at right is able to pull the food tray to within reach of the rat on the left Res Schmid

It was observed that when a hungry rat was in the cage from which the air was flowing, the rat with food access was much quicker to share it than when the air flow came from a satiated rat.

Upon analyzing air samples from around both the hungry and well-fed rats, the researchers found significant differences between levels of seven different volatile organic compounds. These compounds could be emitted by recently-digested food, by the metabolic processes involved in digestion, or they may be intended to serve specifically as olfactory cues for food-sharing behaviour.

A paper on the research was recently published in the journal PLOS Biology.

Source: PLOS via EurekAlert

