Frequency-dependent success of aggressive mimics in a cleaning symbiosis

Abstract

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.

Figure 1

The density of cleaner wrasse models (black bars) and cleaner wrasse mimics (grey bars; number 25 m⁻²) on four Indonesia reefs. Bars represent mean +s.e.

Figure 2

Proportion of successful attacks (%) by bluestriped fangblennies in relation to (log) ratio of models : mimics (y=41.7+58.8x). Open circles, Kaledupa; filled circles, Hoga; filled triangles, Pak Kasim's; open triangles, Sampela.

Figure 3

Proportion of successful attacks (%) by bluestriped fangblennies on four Indonesian reefs. The reefs are presented in order of (a) increasing ratio of models : mimics and (b) increasing density of reef fish clients. Bars represent mean+s.e. Sample sizes are given in parentheses.