rat eating banana
Rats base how much help they provide on the quality of help received.Vassilissa Dolivo

Rats remember their friends and return favours based on how much help they received from them, scientists have discovered.

In a study of rats in Norway, researchers found they not only offer help to those that have helped them before, but the quality of help provided is adjusted according to the perceived value of what they will get in return.

Vassilissa Dolivo and her team from the Institute of Ecology & Evolution at the University of Bern created a series of experiments where rats were able to help one another.

In one, a rat was able to provide another with a carrot by pulling on a stick. In another, the rat could provide a banana. The rats preferred bananas to carrots.

Findings showed the rats would reciprocate help far more to the rat that provided the banana in comparison to the carrot giver.

Published in the journal Biology Letters, the researchers said their findings show that animals can consider the value of previously-received help when it comes to deciding whether to help a social partner – a result that could have implications for understanding cooperation in nature.

Speaking to IBTimes UK, Dolivo said: "The rats are not just acting but adapting their help to the value of the co-operator independently of what the co-operator has done. This is important because it means they are not just copying what the other is doing, but really adapting their helping behaviour to individuals they have never even met before. It means they are able to remember individual acts very quickly."

As well as showing a preference for the banana-giving rats, findings also showed the results became more pronounced over consecutive days: "In the second phase over two consecutive days, they disassociated the banana or carrot giver to a greater extent.

"That was interesting because it shows they remember even without any interactions with individuals in between and that there is reinforcement that they will help banana providers more than carrot providers."

While the rats did help the poor carrot givers, it was with less enthusiasm: "They helped them back too, but less than those who were providing bananas." However, over time "they decreased help to carrot providers".

"You can imagine that after several days they would not help the carrot providers anymore, but would continue to help the banana providers."

In the future Dolivo said she would like to see if perceived effort would have an effect on the level of help provided, how many individuals they can recognise and how long the rats remember the help for: "It would be interesting to see differential response over time.,"