Dominant males exploit the courtship effort of subordinate males in an Amazonian fish

Males signal their breeding burrow characteristics to females in the fiddler crab Austruca perplexa

Females often choose mates based on their courtship signals. Males may signal their heritable genetic quality, defended resources, or parental care efforts; however, the reasons why females choose males based on their signals are often not clear. Here, we show that, in the fiddler crab Austruca perplexa, male signals (major-claw waving rates) were correlated with important characteristics of their defended resources (width and depth of breeding burrows). By using the male signals, females may be able to roughly predict the burrow quality and decide whether to enter and check the burrow characteristics. The signals are predicted to be honest because the female’s final decision is based on burrow quality. Since females can reject males if their burrow quality is insufficient for breeding, the courtship efforts of deceptive males will be dismissed. The honesty of the signals is beneficial for both sexes and thus easily evolved in their signalling system.