It's a cut-throat world in crayfish society. When two unacquainted crustaceans meet, they battle it out to establish their social status and their resulting rank can affect other subsequent behaviours. Sawako Fujimoto, Bunpei Hirata and Toshiki Nagayama from Hokkaido University and Yamagata University, Japan, explain that stereotypical responses can be altered by a wide range of factors. The team were curious to find out how a crayfish's social status might affect one of its stereotypical responses: the avoidance reaction, when they respond to a perceived attack on their tail (p. 2718)

Fujimoto and her colleagues explain that crayfish react in one of two ways to a tap on the last segment of the tailfin. They either flee from the perceived attack or turn to take it on. The level of their response also depends on their social status, with dominant animals more likely to attack and subordinates more likely to escape. Starting out with isolated crayfish, the team tested the crustaceans' responses to the simulated attack and found that 90% of the animals fled. Then they paired crayfish together and allowed them to fight before retesting the animals' reactions. The winners switched their response from flight to fight, with 90% of the dominant crayfish aggressively curling their bodies and turning toward the tail. Next, the team pitted winners against winners to switch the loser's status and the newly subordinate crayfish changed their tail-tap response too, becoming more timid. Finally, when the team measured the spike pattern in the neurones that control the position of appendages on the tail tip, the spike pattern reversed when the crayfish's behaviour switched.

Having shown that the crayfish's avoidance reaction is changeable and dependent on the crustacean's social status, the team says, `The neural mechanisms for this change in aggressiveness and behavioural choice in response to a stimulus are unclear and further neuroethological studies are necessary to clarify this point.'

Dominance hierarchy-dependent behavioural plasticity of crayfish avoidance reactions
J. Exp. Biol.