On the spurious occurrence of Tit for Tat in pairs of predator-approaching fish

David W. Stephens, James P. Anderson, Kari E. Benson

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25 Scopus citations

Abstract

An experimental analysis of the movements of predator-approaching fish is presented. The experiments evaluated two competing hypotheses. (1) Predator-approaching fish play the game-theoretical strategy Tit for Tat. Alternatively, (2) the movements of predator-approaching fish superficially resemble Tit for Tat, because fish independently orient to a predator and simultaneously attempt to stay close together. Experimental subjects were mosquito fish, Gambusia affinis, approaching a green sunfish. Lepomis cyanellus. Two experiments were performed. Experiment 1 replicated results of Milinski (1987) and Dugatkin (1991), showing that Gambusia come closer to a visible predator when a mirror is oriented parallel to their direction of travel. Experiment 2 attempted to separate the effects of common orientation and social cohesion in accounting for the frequency of Tit-for-Tat-like motions in pairs of predator-approaching Gambusia. Results of experiment 2 suggest that a simple additive combination of the effects of (1) social cohesion in the absence of a visible predator and (2) orientation to a visible predator in the absence of a visible companion can account for the observed frequency of Tit-for-Tat-like motions for pairs of predator-approaching Gambusia. It is concluded that predator approach in shoaling fishes is probably a simple by-product mutualism, rather than cooperation maintained by reciprocity in a Prisoner's Dilemma.

Original languageEnglish (US)
Pages (from-to)113-131
Number of pages19
JournalAnimal Behaviour
Volume53
Issue number1
DOIs
StatePublished - Jan 1997

Bibliographical note

Funding Information:
We thank Mike Beecher, Richard Connor, Jennifer Ernisse, John Lazarus, Jennifer Templeton, Jerry Wilkinson and one anonymous referee for critically reading the manuscript. We thank John Lynch for assistance with and advice about fish collection. This work was supported by NSF grant IBN-8958228 to DWS, and an NSF/ EPSCoR grant to the Nebraska Behavioral Biology Group.

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