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- PublicationAccès libreSpatial Group Structure as Potential Mechanism to Maintain Cooperation in Fish Shoals of Unrelated IndividualsIn public goods games, group members share the benefits created through individual investments. If benefits are shared equally, individual contributions readily become altruistic, and hence, a social dilemma arises in which group interests and individual interests oppose each other. However, contributions to public goods can be self-serving if each investor gains a disproportionate benefit from its own contribution. This scenario may hold for our study system, the interactions of shoaling-unrelated scalefin anthias Pseudanthias squamipinnis and the ectoparasitic blenny Plagiotremus tapeinosoma. The blenny bites off pieces of skin, mucus and scales from anthias that in return may chase the blenny. Chasing the blenny represents a public good as it makes the parasite change victim species for its next attack. Laboratory experiments using artificial Plexiglas hosts suggest that one reason why individuals contribute to the public good is that the blenny may specialise on non-punishing ‘free-riders’. Here, we investigated how far a spatial structure within the shoal and limited space use by the blenny may contribute to punishment being self-serving. Field observation reveals that anthias indeed live in spatially structured groups and that blennies have preferred areas for attacks. Thus, some anthias individuals are consistently more exposed to blennies than others and hence may gain disproportional benefits from their punishment. In conclusion, spatial structure may contribute to the maintenance of punishment in blenny–anthias interactions even when groups are large.
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- PublicationAccès libreInteractions Between Sabre-Tooth Blennies and Their Reef Fish Victims: Effects Of Enforced Repeated Game Structure and Local Abundance on Victim AggressionThe conditions under which humans benefit from contributing to a public good have attracted great interest; in particular the potential role of punishment of cheaters is hotly debated. In contrast, similar studies on other animals are lacking. In this study, we describe for the first time how the course of interactions between parasitic sabre-tooth blennies (the cheaters) and their reef fish victims can be used to study both punishment and the emergence of public goods. Sabre tooth blennies (Plagiotremus sp.) sneak up from behind to bite off small pieces of scales and/or mucus from other fish. Victims regularly show spontaneous aggression as well as aggressive responses to blenny attacks. In a between species comparison, we tested how the probability of chasing a blenny is affected by (1) the option of avoiding interactions with a blenny by avoiding its small territory, and (2) variation in local abundance of conspecifics. We found that resident victim species are more aggressive towards blennies than visiting species. This difference persisted when we controlled for victim size and territoriality, suggesting that it is the enforced repeated game structure that causes residents to chase blennies. In residents, we also found a negative correlation between aggression towards blennies and local abundance, which suggests that the benefits of chasing are diluted with increasing local abundance. We discuss the implication of these results for future studies.
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