Abstract
Direct reciprocity, where individuals apply the decision rule ‘help someone who has helped you’, is believed to be rare in non-human animals due to its high cognitive demands. Especially if previous encounters with several partners need to be correctly remembered, animals might either stop reciprocating favours previously received from an individual, or switch to the simpler generalized reciprocity mechanism. Here we tested the decision rules Norway rats apply when interacting with multiple partners before being able to return received help. In a sequential prisoner’s dilemma situation, focal subjects encountered four different partners that were either helpful or not, on four consecutive days. On the fifth day, the focal subject was paired with one of the previous four partners and given the opportunity to provide it with food. The focal rats returned received help by closely matching the quantity of help their partner had previously provided, independently of the time delay between received and given help, and independently of the ultimate interaction preceding the test. This shows that direct reciprocity is not limited to dyadic situations in Norway rats, suggesting that cognitive demands involved in applying the required decision rules can be met by non-human animals even when they interact with multiple partners differing in helping propensity.
Highlights
As male courtship behaviour in sticklebacks or the choice of migratory routes in birds[13,14,15,16]
Hitherto it is not known whether non-human animals switch from applying direct reciprocity rules to the simpler generalized reciprocity decision rule when memorizing the previous behaviour of individual partners becomes challenging
Here we asked whether female Norway rats (Rattus norvegicus) continue using direct reciprocity rules when experiencing several partners successively that either provided or withheld help in the form of food donations, or whether they would switch to applying the simpler generalized reciprocity rules in such situations
Summary
As male courtship behaviour in sticklebacks or the choice of migratory routes in birds[13,14,15,16]. In comparison to humans[19,20,21], only few studies have yet experimentally scrutinized whether non-human animals use the cognitively less demanding behavioural strategy ‘generalized reciprocity’ when given the chance to reciprocate received help (but see for example: capuchin m onkeys22, chimpanzees[23], domestic d ogs[24], Norway rats[25,26,27,28]) Hitherto it is not known whether non-human animals switch from applying direct reciprocity rules to the simpler generalized reciprocity decision rule when memorizing the previous behaviour of individual partners becomes challenging. We predicted that rats memorize the cooperation level of the four previously unfamiliar partners, the behaviour of which they had experienced only once during a 7 min encounter several days before Their decision would not be determined by their last interaction but by the specific previous help they received from the partner they met during the test, thereby applying direct reciprocity rules
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