WASHINGTON, May 28 (Xinhua) -- British scientists found that dwarf mongooses, Africa's smallest meet-eaters, could remember previous cooperative acts by their group mates and reward them later.
A study, published on Monday in the journal Proceedings of the National Academy of Sciences, provided the experimental evidence in a wild non-primate population for delayed contingent cooperation: providing a later reward to an individual for the amount of cooperation it has performed.
It also offered convincing evidence of cross-commodity trading, whereby individuals reward one type of cooperative behavior with a different cooperative act, as dwarf mongooses traded grooming for sentinel behavior, which involves an individual adopting a raised position to look out for danger and warning foraging group mates with alarm calls.
Andy Radford from Bristol University's School of Biological Sciences, the paper's senior author, said, "Humans frequently trade goods and can track the amount they owe using memories of past exchanges. While nonhuman animals are also known to be capable of trading cooperative acts immediately for one another, more contentious is the possibility that there can be delayed rewards."
Over three-hour periods when mongoose groups were foraging, the researchers simulated extra sentinel behavior by a subordinate group member using playbacks of its surveillance calls: vocalizations given to announce it is performing this duty.
At the sleeping burrow that evening, they monitored all grooming events, especially those received by the individual who had had their sentinel contribution up-regulated.
The researchers found that on days when an individual was perceived to conduct more sentinel duty, it received more evening grooming from group mates than on control.
Grooming has long been considered an important tradable commodity in social species, being used as a reward in various contexts.
The new work showed that this grooming reward did not need to occur immediately after the relevant cooperative act since the increased grooming by mongooses took place at the end of the day when the mongooses had finished foraging and returned to their sleeping burrow.
Dwarf mongooses are Africa's smallest carnivore, living in cooperatively breeding groups of 5 to 30 individuals.
