Behavioural differentiation of rats confronted to a complex diving-for-food situation.

Previous studies have shown that a behavioural differentiation appeared in groups of rats subjected to an experimental design in which access to the feeder was made difficult. Some rats brought back food pellets to the cage (divers) while the others (non-divers) stayed in the sole home cage and obtained food only by stealing it from divers. In this study, we elaborated a more complex diving-for-food device which allowed divers to consume the food in a second cage away from non-divers. As a result, the expected lack of suppliers should not allow the emergence of the non-diver status. Unexpectedly, our results showed the apparition of non-divers and the persistence of divers (divers c1) bringing food back to the initial cage. Two new categories of rats appear: individuals which consume the food in the second cage where they stay once they have reached it (divers c2), or occasionally go back to the initial cage throughout the experiment (divers c1c2). Our results show the influence of spatial environment on social organization of rats and suggest that social pressure strongly determines the emergence of specialized roles in a group.