Cleaners perform better in front of an audience

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Public image for Cleaner wrasse is everything and they will put on their best behaviour in the presence of other fish, according to a paper published in a recent issue of the journal Current Biology.

Ana Pinto and coauthors found that Cleaner wrasses (Labroides dimidiatus) immediately increase current levels of cooperation in the presence of bystander client reef fish in the hope of attracting more clients.

The authors conducted a series of experiments, first to test the cues client fish may use for the decision to approach or to avoid a cleaner and secondly to test whether Cleaner wrasses spontaneously improved service quality to current clients if a bystander fish was experimentally introduced.

In the first series of experiments, the authors used Lined bristletooth (Ctenochaetus striatus) as clients and Bridled monocle bream (Scolopsis bilineatus) as bystanders.

The authors removed ectoparasites from half of the clients and then allowed a bystander client in a central aquarium to observe through one-way mirrors in one adjacent aquarium a cleaner exposed to a parasitised client and on the other side a cleaner exposed to an unparasitised client.

The same ten cleaner and parasitised client pairs and ten cleaner and unparasitised client pairs were exposed to two different bystanders.

The behaviour of the fishes were then recorded on video for analysis, with the authors quantifying the total time of the interactions in seconds and the number of jolts performed by clients (a jolt is an involuntary short twitch of the client's body in response to oral contact by the Cleaner wrasse, and is an established correlate of cheating by the wrasse).

The authors found that bystanders avoided Cleaner wrasses that produced many jolts in their clients (the preference of the bystanders was recorded by how close they chose to swim to the client-cleaner pair).

In the second series of experiments, the authors used a similar experimental setup to measure the jolt rate of clients in the absence and presence of bystanders.

A parasitised client was allowed to interact with a Cleaner wrasse, with an adjacent aquarium housing a shelter in plain sight. In half of the trials, a bystander was placed in the shelter (with the shelter being left empty in the other half).

The behaviour of the fish was again recorded with a video camera for 10 minutes. In this set of experiments, the authors found that the client jolt frequency was lower when bystanders were present than when they were absent.

Based on the results of the experiments, the authors concluded that potential clients (bystanders) tended to avoid Cleaner wrasses that exhibit cheating behaviour, and that Cleaner wrasses improved their level of service (ie. cheated less often) in the presence of potential clients (bystanders).

For more information, see the paper: Pinto, A, J Oates, AS Grutter and R Bshary (2011) Cleaner wrasses (Labroides dimidiatus) are more cooperative in the presence of an audience. Current Biology 21, pp. 1140-1144.

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