Abstract
Arctic ungulates usually neither freeze nor starve to death despite the rigours of winter. Physiological adaptations enable them to survive and reproduce despite long periods of intense cold and potential undernutrition. Heat conservation is achieved by excellent insulation combined with nasal heat exchange. Seasonal variation in fasting metabolic rate has been reported in several temperate and sub-arctic species of ungulates and seems to occur in muskoxen. Surprisingly, there is no evidence for this in reindeer. Both reindeer and caribou normally maintain low levels of locomotor activity in winter. Light foot loads are important for reducing energy expenditure while walking over snow. The significance and control of selective cooling of the brain during hard exercise (e.g. escape from predators) is discussed. Like other cervids, reindeer and caribou display a pronounced seasonal cycle of appetite and growth which seems to have an intrinsic basis. This has two consequences. First, the animals evidently survive perfectly well despite enduring negative energy balance for long periods. Second, loss of weight in winter is not necessarily evidence of undernutrition. The main role of fat reserves, especially in males, may be to enhance reproductive success. The principal role of fat reserves in winter appears to be to provide a supplement to, rather than a substitute for, poor quality winter forage. Fat also provides an insurance against death during periods of acute starvation.
Highlights
T h e arctic is a hostile place in winter, yet the cold, dark polar 'wastes' sustain life
Like other arctic homeotherms which maintain a high internal body temperature, the temperature difference between the body core and the environment may be as much as 100°C
Despite an earlier suggestion based on changes in blood levels o f thyroxine which themselves appeared to indicate that the minimum metabolic rate of Svalbard reindeer might fall in winter (Ringberg, 1979), no experimental evidence has been found for such a drop, at least in captive animals (Nilssen, Sundsfjord and Blix, 1984a)
Summary
T h e arctic is a hostile place in winter, yet the cold, dark polar 'wastes' sustain life. Most arctic animals usually neither freeze nor starve to death They are well adapted to the several challenges o f the environment. T h i s paper reviews some o f the physiological adaptations which enable ungulates to survive and reproduce in the arctic, Several species of monogastric mammals circumvent the problem of cold and the scarcity o f food in winter by hibernating. These typically store large quantities o f fat i n summer and autumn and, by reducing their metabolic rate, Rangifer, Special Issue No 3, 1990. Adaptations for survival can, be divided between those which help the animals to reduce their energy expenditure (and, to reduce their food requirements), which are the subject o f this paper, and those which help them to make best use o f what food they find (see Orpin , et al 1985; Mathiesen, et al 1987; Orpin and Mathiesen, 1990)
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