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Urine makes the difference : chemical communication in fighting crayfish made visible

Thomas Breithaupt^* and Petra Eger

Fakultät für Biologie, Universität Konstanz, Postfach 5560 (M618), D-78457 Konstanz, Germany
^* Present address: Department of Biological Sciences, University of Hull, Hull HU6 7RX, UK

View larger version (128K): [in a new window]   Fig. 1. Astacus leptodactylus (carapace length 45 mm) releasing a plume of urine made visible by intra-vascular injection of Fluorescein.

View larger version (13K): [in a new window]   Fig. 3. The effect of experience on urine release: percentage of time urine is released by winners (filled columns) and losers (open columns) during first (N=16), second (N=15) and third (N=8) fights of winners and spontaneously (Spont.) (N=39). Values are means +1 S.E.M. Asterisks denote significant differences between winner and loser (**P<0.01, *P<0.05; multi-way ANOVA for repeated measures). Crayfish are more likely to release urine in a fight than spontaneously (P<0.01; paired t-test). No difference was found in urine release for winners or for losers between first, second and third fights.

View larger version (38K): [in a new window]   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.

View larger version (20K): [in a new window]   Fig. 4. Duration of different agonistic levels per fight (A,B) and probabilities (P) of urine release at these levels (C,D) in winners (A,C) and losers (B,D). Values are means +1 S.E.M. for 39 fights. Asterisks denote significant differences with respect to the mean probability over all agonistic levels (*P<0.05, **P<0.01; logistic regression analysis). Probabilities at level 0 and 1 are generally lower, while those of levels 3-5 are higher, than the mean probability of urine release as estimated by the logistic model. At levels -2 and -1, probabilities are smaller than the mean only in losers.

View larger version (14K): [in a new window]   Fig. 5. Mean probability (+1 S.E.M., N=39 fights) of activities of antennules and mouthparts accompanying spontaneous urine release and urine release during fights. Activities differed between the two release conditions (**P<0.01; multivariate ANOVA).

View larger version (20K): [in a new window]   Fig. 6. Behavioural response of a receiver to offensive behaviour without urine release (filled columns; O, N=174 bouts) and to offensive behaviour accompanied by urine release (`offensive urine release'; open columns; O+U, N=86 bouts). Responses are measured as changes in the relative frequency of certain agonistic levels (levels -2, -1, defensive behaviour; levels 0, A, neutral behaviour; levels 1-5, offensive behaviour; see Materials and methods) from the preceding to the current time interval. Asterisks denote significant differences between the responses to offensive urine release and responses to offensive behaviour (**P<0.01; multivariate ANOVA). Values are means +1 S.E.M.

View larger version (19K): [in a new window]   Fig. 7. Changes in a signaller's behaviour after agonistic level 2 (threat display) accompanied by urine release (open columns, N=42 bouts) or not accompanied by urine release (filled columns, N=108 bouts). Responses are measured as changes in the relative frequency of certain agonistic levels (level -2, -1, 0, 1, agonistic level lower than the initial level; level 2, agonistic level equal to the initial level; levels 3-5, agonistic level higher than the initial level) from the current to the following time interval. Asterisks denote significant differences between the behaviours following agonistic level 2 with urine release and agonistic level 2 without urine release (*P<0.05, **P<0.01; multivariate ANOVA). Values are means +1 S.E.M.