Fig. 2. Time course of agonistic behaviours (levels -2 to 5; see Materials and methods), of urine release (UR) and of the activity of anterior appendages (MX, maxilliped endopodites extended upwards; AF, antennule flicking; AD, antennules pointing downwards) during a fight. Behaviour was recorded at 5 s intervals. Only intervals in which animals fought and/or released urine are shown. The ethograms of the eventual winner (upper trace) and the eventual loser (lower trace) show four bouts of interactions. Positive agonistic levels denote offensive behaviours; negative agonistic levels denote defensive behaviours (see Table 1). Level A denotes activity at some distance from the opponent. Level 0 denotes no activity. The vertical broken line indicates lifting of the divider screen that separated the animals.