Abstract
Inbreeding of Japanese wild rats (Rattus norvegicus) resulted in five new strains. The conception rates of wild rat strains were lower than those of inbred laboratory strains, and maternal aggressiveness was observed in some wild strains. The body size of domesticated animals was larger than that of captured ancestors. Two strains have been established as inbred strains; the MITA strain has been tamed to the level of laboratory rats, while the nature of the MITD strain is wild. The MITB strain was derived from the MITA strain as a coat color variant. The MITC and MITE strains have been bred to the F15 and F11 generations, respectively. The new strains can provide new genetic variations against a wild type background and might be useful for physiological and psychological experiments.
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