White spotting in Norway rats selected for tame behavior

Norway rats Rattus norvegicus selected over many generations for positive response toward humans were used as a model for the analysis of spotting emergence, penetrance and expressivity in animals differing in the manifestation of tame behavior and in their progeny. Behavior scores and spotting patterns of parents were considered. Although nearly all combinations of white spot locations (chest, chest+belly and belly) can be found in the progeny regardless of white spotting pattern in parents, the frequencies of these combinations depend on the spotting pattern in parents. The results of reciprocal crosses in which either mothers or fathers were spotted and their mates were wholly pigmented indicate that the percentage of spotted offspring is larger among the progeny of spotted fathers. The frequency of spotted individuals among rats with behavior scores of 3.0 and 3.5 (i.e. rats approaching the tester's hand in the glove test) was higher than among rats with the behavior score of 2.5 (avoiding the contact). The frequency of white spots in the progeny depended on the mother's behavior scores; spotting was more frequent in the progeny of rats tolerant of handling than in the progeny of rats that avoided taking in hands. Our data indicate that not only the selection for elimination of aggressive response to humans is associated with higher frequencies of white spot emergence but also further increase in the degree of tame behavior still affects genetic systems associated with spotting.