Individual recognition after fighting by golden hamsters: a new method.

Individual recognition is crucial for many aspects of social behavior and may be a specially evolved type of learning and memory. Using golden hamsters, we developed a behavioral method for the investigation of individual recognition. After a series of three brief fights, the two males were categorized as winners or losers. In Experiments 1 and 2, the loser was then tested in a Y-maze after four different intervals (30 min, 1 day, 3 days and 7 days). In Experiment 1, the familiar winner was confined in a stimulus compartment at the end of one arm of the Y, whereas no animal occupied the opposite arm. The results showed that the losers in the experimental group spent the most time in the base of the Y (in or near the start box). They also showed hesitancy to approach the winners' odors and spent less time near them than they spent in the same area when tested with no stimulus males present. In contrast, No Fight control males spent the most time near the stimulus males and did not hesitate in approaching them. In Experiment 2, losers spent less time near the odors of a familiar winner than control losers spent near unfamiliar winners, suggesting recognition of a particular winner. In Experiment 3, the losers were tested just once, 7 days after the last interaction. Again, they spent the most time in the base of the Y and avoided the arm with odors of their specific winners. These results suggest that losers learn to recognize individuals during brief interactions and remember this information for both the short term (30 min) and the long term (at least 1 week). This behavioral method will be useful for further investigation of individual recognition and the neural mechanisms underlying this kind of memory.