Experiments with robots explain synchronized courtship in fiddler crabs

Male fiddler crabs (Uca mjoebergi) produce highly synchronized courtship waves. Is this a cooperative behaviour because females preferentially approach groups that wave synchronously? Or is it a competitive behaviour because of female choice for males that wave first, with the resultant selection on males generating synchrony as an epiphenomenon [1]? To find an answer we used robotic male crabs to measure female mating preferences. We show that females do not prefer males waving in synchrony, but they strongly prefer males that wave first ('leaders'). Synchrony therefore appears to be a by-product of competitive interactions between males.