An Adaptive Change in an Inbred Mouse Strain maintained in a Cold Environment

Abstract

A STRAIN of A2Gmice (Mus musculusL.), maintained for a number of generations in a room kept at −3° C., has progressively improved in ability to cope with the cold. The mice were obtained from Glaxo Laboratories, and had a long history of sib mating. When the breeding was begun in the cold environment, a parallel colony was started at 21° C. (controls). Members of a single litter were used to start the two colonies: one pair was kept at 21° C. and the other transferred to −3° C. These initial pairs were the parents of the first generation of mice studied. All subsequent breeding pairs too were litter mates, and were selected at random at the age of 5 weeks. Reproductive performance was recorded to the age of 28 weeks. There were few barren pairs in the cold, and only one after the fourth generation. One control pair, in the fourth generation, failed to produce young. The methods used, and some of the physiological changes in the mice kept in the cold, have already been described^1–3,5.