This article is from the WSSF 2008 AFRMA Rat & Mouse Tales news-magazine.

Rats were trained to pull a lever for food for their partner and the receiving rat was found to be 20% more likely to help out an unknown partner than rats who had received no such charity, and 50% more likely to help the specific rat who had helped them. This phenomenon is called generalized reciprocity and has only been seen before in humans.