Social learning of escape routes in zebrafish and the stability of behavioural traditions

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Multiple factors potentially influence the formation and longevity of behavioural traditions. In zebrafish, Danio rerio , we investigated whether subjects follow knowledgeable fish escaping from a novel artificial predator, learn this escape response, and maintain the demonstrated escape route and response when knowledgeable fish were removed. A moving ‘trawl’ net forced fish to escape via one of two equidistant escape routes. Groups of four naive fish were placed together with demonstrator fish trained to use either one of the two routes. Observers with demonstrators were faster to escape than observers exposed to untrained fish, and were biased towards the demonstrated route, effects that persisted when demonstrators were removed. Thus zebrafish socially learned escape routes and to escape faster from the approaching trawl. To address whether escape responses were stably transmitted, we used a transmission chain with observers becoming demonstrators for further groups of observers, thus simulating three generations of social learning. Escape times remained stable along the transmission chain, but route preferences slowly collapsed. Thus while the escape response per se was reliably socially transmitted, more arbitrary choices such as route choice decayed rapidly over repeated episodes of social learning. Our results suggest pervasive species and population differences in social-learning propensities.