A crayfishs urine scares off its enemies.
The left-hand crayfish fans green urine at its opponent
© T. Breithaupt
A well-timed blast of urine is the key to winning a crayfish fight, say researchers. The chemical aggression intimidates opponents into backing down.
Ecologist Thomas Breithaupt injected freshwater crayfish with a dye that made their urine glow green. He and his colleague Petra Eger staged fights between blindfolded crayfish (Astacus leptodactylus), to replicate the animals nocturnal habits1.
Freshwater crayfish fight a lot. They live in dense groups of up to 20 individuals per square metre, and squabble over food, shelter and mates.
Brawls involve a ritualized escalation of violence - from posturing, to gripping, arm wrestling and finally attempting to wrench each others limbs off. Urination increases as the animals become more aggressive, the researchers found.
Chemical signals in the urine tell each party how likely it is to win, reducing the number of extreme fights. If urine release is blocked, fights are longer and more violent.
Crayfish waft the glowing urine towards opponents with their gills. "As far as I know, this is the first time that anyones seen chemical communication underwater," says Breithaupt, although the water probably hums with such messages.
But chemical posturing still needs something to back it up, says Atema, and most encounters do get physical. "Violence is always the reinforcer."
JOHN WHITFIELD | © Nature News Service
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