Figure 1.

Outline of the experimental design. Each test phase was preceded by an experience phase where the focal animal could provide food to its partner an undetermined number of times, over 7 mins, by pulling a baited tray with a wooden stick towards the cage. On the following day, after 18 h of food deprivation, the focal animal was returned into the experimental cage where the roles were reversed and (A) the partner rat could now provide food to the focal subject. In the first control condition (B) the partner from the previous day was present in the neighbouring cage compartment, but no moveable tray with food was present. In the second control condition (C) the focal rat was on the receiving side of the food tray like in condition (A), but no partner was present to move it. Each focal animal went through all three experimental treatments in a random order, each time preceded by the experience phase with a new partner on the previous day. Figure modelled on comparable depiction in Schweinfurth and Taborsky (2018a).