Fig. 1.

Worker–parasite separation in a social setting. (A) Behavioral procedure schematics. Cohorts of three rats were trained individually to press a lever and retrieve a food pellet on the opposite side (individual test; 90 min) and then placed together (group test; 90 min). (B) Representative cumulative movement trajectories (5-min period) during individual test and group test sessions (sample I3 and W3 sessions, respectively, in C). (C) Lever-press behavior (n = 34 groups). I1–I3, individual test; S1 and Sn, the first and last days, respectively, of the “stalemate” phase of group test; W1 through W3, “worker–parasite” phase. (D) Time course of lever-press behavior during the first worker–parasite appearing session. (E) Experimental scheme for divider tests. A transparent barrier separated the chamber such that a worker rat could press the lever but not access the feeder. (F) Workers’ lever-pressing behavior during divider tests. Orange, workers; gray, parasites. Thin, soft-colored lines and scattered small circles/squares, individual animal data; large circles/squares and error bars, group means and SEMs. *P < 0.05, **P < 0.01, and ***P < 0.001 (in C and D; workers versus parasites, post hoc Sidak’s test following two-way repeated measures ANOVA). Parasite’s lever-press frequency in this and subsequent figures represents averaged value obtained from two parasites of a group.