Mimics make cleaning business harder

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Aggressive copycats are sharply curtailing business for Bluestreaked cleaner wrasses (Labroides dimidiatus), according to a study to be published in a forthcoming issue of the journal Biology Letters.

The Bluestriped fangblenny (Plagiotremus rhinorhynchos) mimics juvenile Bluestreaked cleaner wrasses in overall shape and colour pattern. However, instead of removing ectoparasites, these cleaner mimics nip at passing reef fish to remove scales, pieces of fin or body tissue.

The fangblennies benefit from this mimicry in gaining increased access to reef fish victims, while the cleaner wrasses lose out in losing potential customers.

But does the mere presence of a mimic lead to reduced feeding opportunities for the cleaner wrasses, or does the behaviour of the mimic play a role? This was the question Karen Cheney sought to answer in her study.

If reef fish clients use the mere presence of a fangblenny to avoid or cut short a cleaning interaction once it is detected, then the penalty the wrasses suffer should be independent of the extent of aggression shown by the fangblenny. However, if clients modify their behaviour in response to the aggressive levels of the fangblenies, then the penalty to the wrasses should be correlated with increased aggression by the fangblennies.

The author conducted her research on coral reefs in the Great Barrier Reef. She carried out a focal observations for 20 minutes on a fangblenny, an observation for 20 minutes on the juvenile cleaner wrasse with which the fangblenny mimic was associated, and a third 20-minute observation on a lone cleaner wrasse located on a similar section of the reef nearby.  

After carrying out 25 sets of observations (each on different individuals) and analysing the results, the author found that cleaner wrasses suffered a reduction in cleaning activity when they were associated with the cleaner mimic, and cleaning activity was reduced in relation to the number of times that mimics attacked coral reef fish.

From the results of this study, it appears that the mimics need to strike a very fine balance in their behaviour lest the mimicry system break down. If they are too aggressive, the cleaner wrasses may relocate or turn on the fangblennies and chase them away, but if they show too much reserve, then the fangblennies do not get enough to eat.

This suggests that the maintenance of such an aggressive mimicry system may rely on a balance between learning and forgetting in reef fishes.

For more information, see the paper: Cheney, KL (2011) Cleaner wrasse mimics inflict higher costs on their models when they are more aggressive towards signal receivers. Biology Letters doi:10.1098/rsbl.2011.0687

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