Relative and combined effects of low temperature, poor diet, and short daylength on the productivity of wild house mice.

Abstract

House mice are known to breed either seasonally or continuously depending upon their habitat. The present experiments were designed to identify possible bases for such flexibility by examining the direct and interactive effects of dietary variation, low ambient temperature, and short daylength on productivity as defined in terms of number of litters born. Experimental diets were fed ad libitum and consisted of 1) wheat seeds, 2) rye grass seeds, 3) wheat seeds plus mealworms, or 4) rye seeds plus mealworms, with 5) a balanced, commercial diet serving as a control. With the exception of the wheat diet, any departure from the balanced control diet resulted in a loss of productivity at 23#{176}C. Productivity was markedly reduced by all natural diets at low ambient temperature (3#{176}C). Dietary and low temperature exigencies exerted more pronounced effects on females than on males. Variation in daylength (8L:16D vs 16L:8D LU cycles) yielded no significant effects on productivity either directly or in combination with any of the other variables examined. All of these results, when viewed from an ecological perspective, suggest two generalities regarding the relationship between diet and reproduction in natural populations of house mice. First, house mice, being opportunists, probably often invade habitats that offer only a reproductively marginal diet, and hence most populations of this species probably do not breed at maximum efficiency even at intermediate temperatures. Second, when winter cessations of breeding occur in house mice, they probably typically result from the combined effects of a marginal diet and a low am