The effect of the environment on phenotypic variability

Abstract

Mice were raised from birth to 4 weeks of age in three climatic chambers maintained at temperatures of 28 °C (‘hot’), 21 °C (‘temperate’) and 5 °C (‘cold’). Their individual weights were recorded at weeks 1, 2, 3 and 4, and analyzed for the sexes separately. Our object was to test the hypothesis of ‘environmental destabilization’, according to which the mice raised in the extreme climates would be expected to be more variable than those raised in the temperate conditions to which the species has been adapted by natural selection. In overall variability the mice raised in the extreme climates greatly exceeded the temperate level. This was partly due to an exacerbation, particularly in the cold, of the normal tendency for body weight to vary inversely with the number of mice in the litter. But it was in part due to an increase of variability among litter-mates: this effect, which we take to be a genuine example of ‘destabilization’, was more pronounced in the hot environment than in the cold. Members of large litters varied more among themselves than members of small litters. All the effects described above were, in general, more pronounced in the female than in the male The possibility, suggested by this work, that phenotypic variation may be affected by the level of auniformly actingenvironmental influence during development has implications for biometrical genetics, selective breeding and evolution.