Sensory and Chemical Ecology Group

Crayfish Chemical Ecology
(funded by a NERC fellowship and a grant of the Royal Society)

PI: Thomas Breithaupt

Publications:

Breithaupt, T. & Eger, P. 2002 Urine makes the difference: chemical communication in fighting crayfish made visible. J. Exp. Biol. 205, 1221-1231.

Summary: Chemical communication is a widespread phenomenon in aquatic animals but is difficult to investigate because the signals are not visible. Here, we present the results of a study into chemical communication in blindfolded fighting crayfish (Astacus leptodactylus) in which we employed a new method: visualisation of urine using the dye Fluorescein. The probability of urine release is greater during fights than during non-social activities or inactivity. The eventual winners are more likely to release urine during fights than the eventual losers. In both winners and losers, urine release is coupled to offensive behaviours, and the probability of urine release increases with increasing levels of aggression. In A. leptodactylus, urine is carried to the opponent by the forward-projecting gill currents. During spontaneous release, urine is fanned laterally with the aid of the exopodites of the maxillipeds. Aggressive behaviour is effective in intimidating blindfolded opponents only in conjunction with urine release: receivers decrease offensive behaviour and increase defensive behaviour. Aggressive behaviour alone does not intimidate opponents. The loser of a recent fight is deterred equally well by a familiar and an unfamiliar opponent. Hence, in crayfish, individual recognition of the urine scent of a dominant individual does not appear to be significant for the maintenance of dominance hierarchies. Our results suggest that urine contains information about the fighting ability and/or aggressiveness of the signaller. The chemical signals thus far unidentified appear to be important in determining the outcome of a fight.

Breithaupt, T. 2001 The fan organs of crayfish enhance chemical information flow. Biol. Bull. 200, 150-154.

Summary: Animals as well as autonomous robots need to acquire environmental signals in order to adjust their activity in time and space. Some information is accessible to the sensors only as a result of specific behaviors for stimulus acquisition. Due to the slow rate of molecular diffusion, dispersal of chemical stimuli depends on fluid flow. Aquatic crustaceans can generate directed water currents by specialized appendages. Here I describe the crayfish fan organs, which are feathered flagella of the mouthparts, and their activity in sending and receiving chemical signals in environments with stagnant flow conditions. During the power-stroke, the fan opens and displaces water; during the return stroke, it collapses and thereby minimizes drag. These organs can create a variety of flow fields including water jets, and in many different directions. Bilateral upward fanning draws water horizontally from all directions toward the anterior chemoreceptors. Unilateral upward fanning draws water from only one side towards the body. The versatility of the crayfish fan organ makes it a candidate for biomimetic reconstruction and use in autonomous robots that can search chemical sources.