The growth of mice in a fluctuating temperature environment

Two inbred strains of mice and the F1 hybrid between them have been reared from 3 to 12 weeks of age in a fluctuating temperature environment. The environment was characterized by temperatures of 90 °F (d.b.) 85 °F (w.b.) and 70 °F (d.b.) 61 °F (w.b.) for the same length of time each day. Mathematical curves of the form y = a + brx have been fitted to body weight and tail length growth. It is shown that in both characters the hybrids display a greater adult size, a more rapid growth and a superior canalization of growth than the inbreds from which they were derived. When the growth in the fluctuating environment is compared with that, previously described, in corresponding constant temperature environments, i.e. either 90 °F (d.b.) 85 °F (w.b.) (heat) or 70 °F (d.b.) 61 °F (w.b.) (control) it is found that hybrid luxuriance is most manifest in constant heat. However, in these conditions, the inbreds tend to disperse their growth rate relatively more rapidly than they do in the other environments. It is also shown that growth in the fluctuating environment is not strictly intermediate between growth in the constant conditions, but much more closely resembles growth in the heat than in the control.