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- PublicationMétadonnées seulementFrom parasitism to mutualism: partner control in asymmetric interactions(2002)
;Johnstone, RufusIntraspecific cooperation and interspecific mutualism often feature a marked asymmetry in the scope for exploitation. Cooperation may nevertheless persist despite one-sided opportunities for cheating, provided that the partner vulnerable to exploitation has sufficient control over the duration of interaction. Here we develop a simple, game theoretical model of this form of partner control. We show that as a victim's ability to terminate an encounter increases, selection can favour reduced exploitation, resulting in a switch from parasitism to mutualism. For a given level of control, exploitation is likely to be less intense and the interaction to last longer when there are greater mutualistic benefits to be gained, and when the benefits of cheating are lower relative to the costs inflicted on the victim. Observations of interactions between cleaner-fish and non-predatory species of client are shown to match these predictions.
- PublicationAccès libreSignalling by the cleaner shrimp Periclimenes longicarpus(2010)
;Chapuis, LucilleSignals increase the fitness of a sender by altering the behaviour of receivers. For cooperative interactions biological market theory proposes that signalling strength may be linked to supply and demand. In this context, a recent laboratory experiment demonstrated that cleaner shrimps may advertise their service to client reef fish and that the advertisement is linked to hunger levels. We investigated signalling by the cleaner shrimp Periclimenes longicarpus in the field to test more detailed predictions of biological market theory. Shrimps often clapped with their pair of claws in response to approaching clients. In line with both theory and the previous study, the probability of clapping increased when the shrimps had been food deprived and clapping shrimps were more likely to clean than nonclapping individuals. However, we found no evidence for the market theory prediction that signalling was targeted specifically to visiting client species with the option to choose other cleaning stations. Instead, shrimps signalled more frequently towards predatory clients than towards nonpredatory clients. We conclude that the signal does not serve primarily to attract the choosy clients but to convey information about identity as preconflict management to avoid predation.
- PublicationAccès libreMutualism, market effects and partner control(2008)
;Johnstone, Rufus A.Intraspecific cooperation and interspecific mutualism often feature a marked asymmetry in the scope for exploitation. Cooperation may nevertheless persist despite one-sided opportunities for cheating, provided that the partner vulnerable to exploitation has sufficient control over the duration of interaction. The effectiveness of the threat of terminating an encounter, however, depends upon the ease with which both the potential victim and the potential exploiter can find replacement partners. Here, we extend a simple, game-theoretical model of this form of partner control to incorporate variation in the relative abundance of potential victims and exploiters, which leads to variation in the time required for individuals of each type to find a new partner. We show that such market effects have a dramatic influence on the stable level of exploitation (and consequent duration of interaction). As the relative abundance of victims decreases, they become less tolerant to exploitation, terminating encounters earlier (for a given level of exploitation), whereas exploiters behave in a more cooperative manner. As a result, the stable duration of interaction actually increases, despite the decreasing tolerance of the victims. Below a critical level of relative victim abundance, the model suggests that the cost of finding a replacement partner becomes so great that it does not pay to exploit at all.
- PublicationAccès libreStrategic adjustment of service quality to client identity in the cleaner shrimp, Periclimenes longicarpus(2009)
;Chapuis, LucilleCleaning mutualism, in which cleaning organisms remove ectoparasites from cooperating ‘clients’, is widespread among marine animals. Until now, research has focused on fishes as cleaners, whereas cleaner shrimps have received little attention. The aim of this study was to investigate the cleaning behaviour of the cleaner shrimp, Periclimenes longicarpus, and to compare the results directly to data on the sympatric and well-studied cleaner wrasse, Labroides dimidiatus. We first compared the time spent cleaning and client diversity as indicators of the potential importance of the cleaner shrimp to client health and found strong similarities between shrimp and wrasse. We further looked at three correlates of service quality: duration of interactions, tactile stimulation of clients, and jolt rates as correlates of mucus feeding (=cheating). We specifically predicted that shrimps would cheat clients less frequently than the wrasses because they should be more vulnerable to aggressive responses by clients. Although the results partly support our hypothesis, they also suggest that both species strategically adjust cheating rates according to risk, as predatory clients jolted less frequently than nonpredatory clients. In conclusion, the results suggest that the shrimps play an important role in client health but that nonpredatory clients have to control the shrimps' behaviour to receive a good service.