Experimental setup. During the experience phase, focal rats were paired with cooperating partners that provided food rewards (R) to them, or defecting partners that did not provide food rewards to them. In one treatment (CCCD), focal rats were paired with three different cooperators on three consecutive days, and a defector on the fourth day. In another treatment (DDDC), focal rats were paired with three different defectors on three consecutive days, and a cooperator on the fourth day. During the test phase, focal rats could provide food rewards to one of the partners they had encountered on the previous four days (partner A, B, C or E in treatment CCCD, and partner F, G, H or D in treatment DDDC).