Influence of black spot disease on shoaling behaviour in female western mosquitofish, Gambusia affinis (Poeciliidae, Teleostei)
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Parasites can fundamentally alter the cost–benefit ratio of living in a group, e.g. if infected individuals increase the predation risk of shoal mates. Here, the effect of an infection with a trematode, Uvulifer sp. (Diplostomatidae) on the shoaling behaviour of female western mosquitofish, Gambusia affinis, was investigated. The parasite examined causes a direct phenotypical change of the host by forming black spots on its body surface. When given a choice between a stimulus shoal and no shoal, we found shoaling tendencies to be significantly reduced in infected focal fish. In another experiment, we tested for association preferences relative to the infection status of the stimulus fish. Given the choice between an infected and a healthy stimulus fish, both infected and healthy focal fish preferred to associate with non-infected stimulus fish. Our results suggest that (1) the cost–benefit ratio of shoaling might be different for infected and non-infected individuals. Infected fish may be more affected by competition for food within a shoal. (2) Associating with infected conspecifics appears to be costly for female mosquitofish, maybe due to increased predation risk.
KeywordsGroup living Predation Parasites Uvulifer Fish behaviour
We thank Martin Plath and two anonymous reviewers for comments on an earlier version of the manuscript, Amber Makowicz and Rüdiger Riesch for help in the field and Wendal Porter for providing equipment. This research project was approved by the Animal Care and Use Committee of the University of Oklahoma (AUS R05-014). Texas Parks and Wildlife kindly issued the permit to collect fish (SPR-0305-045). Financial support came from the Basler Foundation for Biological Research, the Janggen-Poehn-Foundation, the Roche Research Foundation, and the Wolfermann-Nägeli-Foundation (to M. T.) as well as the Faculty Senate of the University of Oklahoma (to I.S.).
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