Figure 1.

(a) Pictograms illustrating the escalating levels of aggression that characterize cricket fights (adopted from [6]): level 0 mutual avoidance, non-aggressive interaction. Level 1 pre-established dominance, one cricket attacks, the other retreats. This level is in accordance with the avoiding behaviour of losers. Level 2 antennal fencing, the two crickets fence with their antennae. Level 3 mandible spreading (unilateral), one cricket displays broadly spread mandibles. Level 4 mandible spreading (bilateral), both crickets display their spread mandibles. Level 5 mandible engagement, the mandibles of both contestants interlock. Level 6 grappling, all-out fighting involving repetitive biting, mandible pushing, and opponent flipping. (b) Pictograms illustrating the intruder–resident paradigm. (i) Contests were first staged between pairs of previously isolated, fight-inexperienced and weight-matched adult male crickets. (ii) For each pair, the resulting submissive loser was separated from the aggressive winner via an opaque door dividing the area. (iii) The loser was then provided with a shelter, either immediately (t = 0) or after a delay (up to 15 min), which it immediately occupied (control, no shelter). (iv) The dividing door was removed 15 min after separation in all cases and the interactions between resident-winners and intruding-winners evaluated. (iv) (alternative) In some experiments, the losers all experienced 15 min occupancy in the shelter, followed by a delay (0–15 min) before removing the door (t = 15–30 min).