EFFECTS OF THE LIGHT-DARK CYCLE ON A WATER TANK SOCIAL-INTERACTION TEST IN MICE

Mice were exposed to a water tank interaction test in which food could be obtained either by wading in the water or by attacking littermates . A tank with progressively rising water levels caused mice in groups of four to differentiate into those willing to wade (carrier mice) fro m those unwilling to wade (noncarrier mice). Noncarrier mice could onl y obtain food by stealing it from carrier mice or from other noncarrie r mice. It was found that mice during the dark period of the light-dar k cycle were more willing to wade in the search for food rather than a ttempt to steal food from other mice. Because mice are generally more active during the dark period, this result suggests that higher activi ty levels increase the willingness to share the work load, a form of a ltruism, rather than promote parasitic behavior and aggression.