Cleaner Wrasses Labroides dimidiatus Are More Cooperative in the Presence of an Audience

Abstract

Humans may help others even in situations where the recipient will not reciprocate [1-5]. In some cases, such behavior can be explained by the helpers increasing their image score, which will increase the probability that bystanders will help them in the future [5-7]. For other animals, the notion that many interactions take place in an environment containing an audience of eavesdropping bystanders has also been proposed to have important consequences for social behavior, including levels of cooperation [8]. However, experimental evidence is currently restricted to the demonstration that cleaner fish Labroides dimidiatus can learn to solve a foraging task [9]. The cleaners learned to feed against their preference on artificial clients if that allowed them to access additional artificial clients, which would translate into cooperatively eating ectoparasites rather than cheating by eating client mucus under natural conditions [10]. Here we show that cleaners immediately increase current levels of cooperation in the presence of bystander client reef fish. Furthermore, we find that bystanders respond to any occurrence of cleaners cheating their current client with avoidance. In conclusion, the results demonstrate, for the first time, that image scoring by an audience indeed leads to increased levels of cooperation in a nonhuman animal.

Referential gestures in fish collaborative hunting

“…In the present study, the observed ability of the grouper to wait above a hidden prey for up to 25 min before signalling to a passing predatory partner suggests it may perform at an ape-like level in a memory task commonly used to assess cognitive ability 38 . More generally, fishes may use complex social strategies in the context of intraspecific collaborative hunting 39 , social learning 40,41 and in cleaning interactions [42][43][44] , and demonstrate potentially complex cognitive processes such as transitive inference 45 and the ability to generalize 46 . On the neurophysiological level there is recent evidence that the reward structure of fish brains is similar to that of mammals 47 .…”

Explaining brain size variation: from social to cultural brain

“…When the comparison is extended to non-mammal and non-bird species, the discrepancies become even more marked. Several small fish species show socio-cognitive abilities rivaling those of primates [21,24], despite having relatively minute brains. (Because the fish case can be linked to the modularity debate, its discussion is postponed until the next section.)…”

Signal verification can promote reliable signalling

“…Both their model and ours should have wide applicability. Reliability in the cleaner fish mutualism is further enforced by an audience effect, where cleaner fish are more cooperative in the presence of potential clients that witness their cleaner behaviour [14]. This additional mechanism that could enforce reliability is not expected to occur in plant-animal communication.…”