Sexually selected traits have proved to be accurate predictors of male fighting and mating success in many animals. Little attention, however, has been paid to the potential role of non-sexual behavioural traits in predicting individual success. Evidence is growing that an individual’s propensity to take risks in the presence of a predator is correlated to behaviours that can affect individual fitness. We examined whether risk-taking behaviour predicts aggression, surface activity levels and mating success in male fiddler crabs, Uca mjoebergi. Although risk-taking behaviour was independent of sexually selected traits, it accurately predicted male mating success in terms of male competitiveness and mating success.

To increase their chances of attracting mate searching females to their burrows, male fiddler crabs also produce highly synchronized courtship waves. While synchronized courtship has been widely studied in acoustic and bioluminescence signals, the reasons behind this behaviour in a visual system remain unknown. Is it cooperative behaviour because females preferentially approach groups that wave synchronously? Or is it competitive behaviour because females prefer males that wave first, with resultant selection on males that generates synchrony as an epiphenomenon? With the use of robotic crabs, this question is resolved.