Fig. 2.

Different social dominance between worker and parasite rats. (A) Schematics for the three social dominance tests used in the present study. (Left) Feeder test in the Skinner box. Small food pellets were delivered to the feeder in a fixed 10-s interval schedule, and the number of pellet consumption was compared across three rats. An opaque barrier (blue) blocked rat’s access to the lever. (Middle) Cylinder test. A large food pellet was introduced to the center, and the duration of pellet possession was compared across three rats. (Right) Tube test. Two rats competed to run through a tube from the opposite sides to obtain a piece of cereal. (B) Group data showing the ranks of worker (orange) and parasite (gray) rats (n = 5 groups) during the stable behavioral phase. (Top) Individual animal data. (Bottom) Rank proportions of worker (orange) and parasite (gray) rats.