Aggressive mimics profit from a model-signal receiver mutualism

Abstract

Mimetic species have evolved to resemble other species to avoid predation (protective mimicry) or gain access to food (aggressive mimicry). Mimicry systems are frequently tripartite interactions involving a mimic, model and 'signal receiver'. Changes in the strength of the relationship between model and signal receiver, owing to shifting environmental conditions, for example, can affect the success of mimics in protective mimicry systems. Here, we show that an experimentally induced shift in the strength of the relationship between a model (bluestreak cleaner fish, Labroides dimidiatus) and a signal receiver (staghorn damselfish, Amblyglyphidodon curacao) resulted in increased foraging success for an aggressive mimic (bluestriped fangblenny, Plagiotremus rhinorhynchos). When the parasite loads of staghorn damselfish clients were experimentally increased, the attack success of bluestriped fangblenny on damselfish also increased. Enhanced mimic success appeared to be due to relaxation of vigilance by parasitized clients, which sought cleaners more eagerly and had lower overall aggression levels. Signal receivers may therefore be more tolerant of and/or more vulnerable to attacks from aggressive mimics when the net benefit of interacting with their models is high. Changes in environmental conditions that cause shifts in the net benefits accrued by models and signal receivers may have important implications for the persistence of aggressive mimicry systems.

Figure 1

The cleaner-fish–fangblenny mimic study system. (a) Model, juvenile L. dimidiatus; (b) mimic, black and blue form of P. rhinorhynchos; (c) signal receiver, A. curacao.

Figure 2

Box plots showing: (a) percentage of cleaning interactions that were terminated by damselfish, (b) proportion (%) of all attacks by mimics towards damselfish that were successful, and (c) proportion (%) of successful attacks by mimics that led to a retaliatory chase by damselfish. Medians are represented by black line, while grey boxes indicate upper and lower quartiles.

Figure 3

Number of pre-emptive chases by parasitized (black bars) and unparasitized (grey bars) staghorn damselfish towards cleaner fish and fangblenny mimics. Bars are mean ±1 s.e. ^**≤0.01; paired t-test.