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Crayfish weaponry - bigger isn't always better, or is it?

5 Apr 2012
Angilletta, M. J., & Wilson, R. S. (2012). Cryptic asymmetry: unreliable signals mask asymmetric performance of crayfish weapons. Biology Letters, doi:10.1098/rsbl.2012.0029 Details

Customer study highlights

A large number of disputes between crayfish have been settled through signaling of crayfish weaponry. Male crayfish vying for dominance may find themselves unwilling to attack if the opponent happens to wield much larger chelae (pincers) - the basic assumption being that a larger chela will generate more grip force and will therefore pose a greater potential hazard.

However, it has been previously suggested that for any given crayfish, chelae size asymmetries may not always scale with chelae grip asymmetries, creating what is referred to as cryptic asymmetry.

The present study systematically examined cryptic asymmetry in slender crayfish (Cherax dispar). Chela sizes for 97 adult males were measured along with maximum grip force using custom plates attached to strain gauges and a PowerLab. Maximum strength of each chela was estimated from the force produced by the dactylus closing on the fixed propodus. Strain gauges were calibrated to force (N). To control for motivation states, testing was carried out at two temperatures (14°C and 24°C).

Grip forces generated by crayfish (up to 40 N) at either temperature condition were similar – both were associated with unexplained variation in strength with increasing chela size. Thus, size did not necessarily reflect grip strength.

This study demonstrates that the display of strength of crayfish weaponry is unreliable, adding another dimension of uncertainly in crayfish conflict. To what extent this confers additional survival and perhaps mating advantages will be the focus of future studies. In the meantime, a bigger claw may mean more respect, among crayfish.

By Matthew Goddard

Science Manager

Researcher, Dad and motorbike racer.