Wild Mice in the Cold: Some Findings on Adaptation

Abstract

The house mouse, Mus domesticus, can thrive in natural environments much below its optimum temperature. Thermogenesis is then above that at more usual temperatures. In addition, body weight, and the weights of brown adipose tissue and the kidneys, may be higher than usual. In free populations of house mice cold lowers fertility and may prevent breeding. Other possible limiting factors on breeding are food supply, shelter for nesting and social interactions. In captivity, wild-type house mice exposed to severe cold (around 0 degrees C) at first adapt ontogenetically by shivering and reduced activity. But raised thermogenesis is soon achieved without shivering; nest-building improves; and readiness to explore may be enhanced. Endocrine changes probably include, at least initially, a rise in adrenal cortical activity and in catecholamine secretion. Some females become barren, but many remain fertile. The maturity of fertile females is, however, delayed and intervals between births are lengthened; nestling mortality rises. A limiting factor during lactation may be the capacity of the gut. Similar adaptive changes are observed during winter in some species of small mammals that do not hibernate. But neither the house mouse nor other species present a single, universal pattern of cold-adaptation. Wild-type mice bred for about 10 generations in a warm laboratory environment (20-23 degrees C) change little over generations. In cold they become progressively heavier and fatter at all ages; they mature earlier, and nestling mortality declines. The milk of such 'Eskimo' females is more concentrated than that of controls. If 'Eskimo' mice are returned to a warm environment, they are more fertile, and rear heavier young, than controls that remained in the warm. Despite the heavier young, litter size is not reduced: it may be increased, probably as a result of a higher ovulation rate. Parental effects have been analyzed by cross-fostering and hybridizing. Survival, growth and fertility are all favourably influenced by the intra-uterine and nest environments provided by 'Eskimo' females. 'Eskimo' males are also better fathers. Hence after ten generations the phenotype of cold-adapted house mice shows the combined effects of (a) an ontogenetic response to cold, (b) a superior parental environment and (c) a change genotype. The secular changes in the cold that lead to this phenotype give the appearance of evolution in miniature; but it is equally possible that they represent a genetical versatility that allows rapid, reversible shifts in response to environmental demands.(ABSTRACT TRUNCATED AT 400 WORDS)

Effect of food restriction on energy budget in warm-acclimated striped hamsters

“…T a has significant effects on both BMR and NST max in many small mammals including striped hamsters [9,[17][18][19][20][21]40,41]. In the present study, striped hamsters significantly decreased BMR and NST max after being acclimated to a warm condition (30°C), which were lower by 30.3% and 53.8% at 30°C than those at 21°C, respectively.…”

“…GEI, digestive energy intake (DEI) and digestibility were measured over the last three days of experiment (days [40][41][42], and calculated as follows [26][27][28],.…”

Group housing and nest building only slightly ameliorate the cold stress of typical housing in female C57BL/6J mice

“…It should be noted that these mice were raised at 30°C and first experienced 20°C (either singly, with nesting, or with cage mates) at the initiation of this experiment. As these mice were not acclimated to the cooler temperature, the elevated noise on the ECG tracing is likely only acute in nature as shivering diminishes over time with acclimation to 20°C housing (3,8).…”

Mouse (Mus musculus) stocks derived from tropical islands: new models for genetic analysis of life‐history traits

“…However, the sample of mammals from which this trend was deduced was decidedly biased toward temperate, as opposed to tropical, islands and may not hold when the effects of latitude are controlled for. For instance, in house mice Mus musculus, the mammal most broadly characterized in terms of latitudinal trends in insular body size, populations at low latitudes are frequently small (typically 9±14 g: Tomich, Wilson & Lamourex, 1968;Berry, Sage et al, 1981) and at high latitudes are frequently large (20+ g: Berry, Jakobson & Peters, 1978;Barnett & Dickson, 1989), although exceptions occur (Tomich et al, 1968;Berry & Peters, 1975) possibly as a result of founder effects and/or unusual combinations of predator or competitor species (Angerbjorn, 1986;Berry, 1996). Because animals from populations with statistically distinct body sizes are seldom reared under standardized conditions, the extent to which observed size differences represent genetic or environmental differences is unclear.…”