Frequency-dependent success of aggressive mimics in a cleaning symbiosis

Batesian mimics—palatable organisms that resemble unpalatable ones—are usually maintained in populations by frequency-dependent selection. We tested whether this mechanism was also responsible for the maintenance of aggressive mimicry in natural populations of coral reef fishes. The attack success of bluestriped fangblennies ( Plagiotremus rhinorhynchos ), which mimic juvenile bluestreaked cleaner wrasses ( Labroides dimidiatus ) in colour but tear flesh and scales from fishes instead of removing ectoparasites, was frequency-dependent, increasing as mimics became rarer relative to their model. However, cleaner mimics were also more successful on reefs with higher densities of potential victims, perhaps because a dilution-like effect creates few opportunities for potential victims to learn to avoid mimics. Further studies should reveal whether this second mechanism is specific to aggressive mimicry.