When deciding to cooperate by direct reciprocity, Norway rats sometimes benefit from olfactory competence and seem not impaired by insufficient cognitive abilities.

Direct reciprocity requires the ability to recognize and memorize social partners, and to remember their previous actions. 'Insufficient cognitive abilities' have been assumed to potentially impair the ability to cooperate by direct reciprocity. Here we compare the propensity of rats to use direct reciprocity with their ability to memorize and recognize sensory cues in a non-social task.

Mickey Mouse's negative affect facing mistakes.

Many of the scientists working in the field of 'animal behaviour' and especially of 'animal cognition' consider the most obvious factors for fitness maximization - for instance, nutritional reward maximization - as the sole motivators when a course of action must be chosen. Sweis, Thomas, and Redish (2018, PLOS Biology, 16(6), e2005853) show that even in a food-restricted environment in which it is vital to maximize food gaining, other factors, not obviously linked to fitness, play a role for decision-making - in the present case, avoidance of a negative affect linked to changing one's mind (a factor which does not improve foraging efficiency), and individual flavour preference (a factor which even impairs foraging efficiency).

Environmental enrichment of young adult rats (Rattus norvegicus) in different sensory modalities has long-lasting effects on their ability to learn via specific sensory channels.

Sensory modalities individuals use to obtain information from the environment differ among conspecifics. The relative contributions of genetic divergence and environmental plasticity to this variance remain yet unclear. Numerous studies have shown that specific sensory enrichments or impoverishments at the postnatal stage can shape neural development, with potential lifelong effects.

Ultimate and proximate mechanisms of reciprocal altruism in rats.

The reciprocal exchange of goods and services among social partners is a conundrum in evolutionary biology because of its proneness to cheating, but also the behavioral and cognitive mechanisms involved in such mutual cooperation are hotly debated. Extreme viewpoints range from the assumption that, at the proximate level, observed cases of "direct reciprocity" can be merely explained by basic instrumental and Pavlovian association processes, to the other extreme implying that "cultural factors" must be involved, as is often attributed to reciprocal cooperation among humans. Here we argue that neither one nor the other extreme conception is likely to explain proximate mechanisms underlying reciprocal altruism in animals.

Norway rats reciprocate help according to the quality of help they received.

Direct reciprocity, according to the decision rule 'help someone who has helped you before', reflects cooperation based on the principle of postponed benefits. A predominant factor influencing Homo sapiens' motivation to reciprocate is an individual's perceived benefit resulting from the value of received help. But hitherto it has been unclear whether other species also base their decision to cooperate on the quality of received help.

Fruit flies learn to avoid odours associated with virulent infection.

While learning to avoid toxic food is common in mammals and occurs in some insects, learning to avoid cues associated with infectious pathogens has received little attention. We demonstrate that Drosophila melanogaster show olfactory learning in response to infection with their virulent intestinal pathogen Pseudomonas entomophila. This pathogen was not aversive to taste when added to food.