Animal Adaptation and Acclimatizationto Cold R.E. Phillips C.A. Watson MANY PEOPLEARE confused by the two terms: adap- tors) and these animals avoid winter conditions by going tation and acclimatization.Adaptation is particularlycon- into a dormancy state. It is primarily the homeotherms Downloaded from http://online.ucpress.edu/abt/article-pdf/39/9/528/35964/4446077.pdf by guest on 02 October 2021 fusing because of its use in a non-scientific way in every- (warm blooded) chioneuphores and chioniophiles that day language. As scientists use the term, adaptation is exhibit some form of adaptation or acclimatization. biotic changes occurring within a population during a period of several generations (Burtonand Edholm 1955). Animal Acclimatization An organism develops adaptation to cold through a Acclimatization to cold, which is exhibited to some natural selection process. The development of heavy fur degree by all animals, can be demonstrated by gradual insulation is a good example of adaptation to cold. exposure of experimental subjects to increasingly cold Acclimatizationto cold is the sum of adjustments that conditions for a specified time. During this period, usually follow repeated and prolonged exposure to cold (Brown from two to six weeks, the organism gradually increases 1957). Exposure time for cold acclimatizationvaries from its abilityto survive in cold temperatures. species to species, but it usually falls within the range of Hart (1960) summarizes the phenomena associated from two to six weeks. Once the stimulus, in this case with cold acclimatization in the following related occur- cold, is removed, a new physiological adjustment is ex- rences: pected to occur. Gordon (1968) cites a classic example of adjustments in acclimatizationto cold in herring gulls. 1. A gradual increase in cold resistance; Cold acclimated gulls can walk on ice at freezing tem- 2. An increase in food consumption; peratures without any visible injury,but warm acclimated 3. An elevation of basal metabolic rate; gulls will immediately freeze their feet on ice. 4. An escalation of peripheral and sometimes core Acclimatization and adaptation, then, differ in two temperatures; major ways. Acclimatizationis a temporary adjustment to 5. A decrease in shivering; and a stimulus, but adaptation becomes established only after 6. An increase in non-shivering heat production; biochemical many generations of natural selection. Acclimatization 7. Other associated physiological and also requires a development period during exposure, changes. considerable but adaptation requires no apparent preparation time. It Each of these related occurrences merits appears likely that acclimatizationis related to adaptation attention when discussing cold acclimation. in that a continuously fixed acclimatization over several generations could result through a natural selection pro- The authors are high school cess in a population into an adaptation; or the abilityof a biology teachers in the St. population species to acclimate could be interpreted as James Assiniboia School a form of adaptation. Division, Winnipeg, Manitoba, Canada. Phillips, who teaches . at Westwood Collegiate, re- Terminology ceived a B.S.A. degree in 1967, a B.Ed. degree in 1974, Formozov (1946) classified animals into three basic and an M.Sc. degree in 1969 types: chionophobes (those that fear snow); chioneu- from the University of Mani- A- phores (those that are tolerant of snow); and chionio- toba. Watson, teaching at John Taylor Collegiate holds a B.Sc. degree (1963) and a B.Ed. degree (1966) from the same university. He com- philes (those that are snow lovers). Because the chiono- pleted his M.Ed. degree in 1976. Phillips and Watson were both mem- phobes escape the snow and winter by migrating the bers of a federally sponsored curriculum development project called latter two groups are of interest for adaptation and ac- Project Canada West (1970-75). They co-authored Environmental Studies: Teacher Resource Manual (Enviro-Concerns, Winnipeg) and climatization studies. Most chioneuphores are poikilo- recently completed another resource manual entitled Winter Investiga- thermic (cold blooded) or heterothermic (true hiberna- tions. 528 THEAMERICAN BIOLOGY TEACHER, DECEMBER 1977 of differences in metabolic rates. Apparently acclimatized rats could maintain a high metabolic rate for a prolonged 40 period of time during cold stress; non-acclimatized rats were metabolically unprepared and could not adjust quickly enough to cold shock. o 30 Metabolic rate increases for cold exposure depend in most instances, on the criticaltemperature of the animal. 00 Once temperatures are lower than the critical temper- atures, the normal metabolism must make adjustments. $4 Increase in metabolism is partially caused by increased muscle activity in the form of shivering. The increase in metabolic rate due to shivering may be as high as 6 to 7 20 2 3 4 V$4 times the basal metabolic rate, for short periods of time U ~ ~ ~ Aelaio eprtr (Burton and Edholm 1955). Because there is such a temperature gradient between the organism and the VoJ~~~ ambient temperature, body shell and core temperature must be maintained for homeotherms. According to Downloaded from http://online.ucpress.edu/abt/article-pdf/39/9/528/35964/4446077.pdf by guest on 02 October 2021 Keller (1960), body core hypothermia is prevented by a series of neural integrationsthroughout the body. Chilling FIGURE1. Upper and lower lethal temperature levels of the goldfish. of peripheral receptors activates hypothalmic activity that Lower limits are adjustable according to extent of acclimatization to cold. stimulates both central and peripheral thermogenesis (heat production) during acclimatizationto cold. Decreased shivering and eventual nonshivering therm- ogenesis results from increased heat production without Development of cold resistance has been shown in detectable muscle activity. Carlson (1960) regards non- some poikilotherms. Studies of cold resistance in goldfish shivering thermogenesis as an acclimatization phenom- (poikilotherms)by Fry (1947) have established upper and date has been shown in rats and to lower lethal temperature levels (fig. 1). The temperature enon, which to clearly in and man. between these two levels represents the temperature some degree rabbits,dogs, and biochemical range within which the acclimated fish can live independ- Numerous associated physiological noted with cold acclimatization. ently. During cold exposure, lower lethal limits can be changes have been adrenals and lowered gradually, thus enabling the fish to survive. Cold Endocrine glands such as the thyroid, pitu- with acclimatization. resistance has also been shown in insects by Asahina itary glands have been linked cold been shown con- (1959). Through a process of gradual acclimation to pre- Noradrenaline and ascorbic acid have and freezing temperatures, insects have eventually been able clusively to interplay with cold resistance. LeBlanc to survive at temperatures below the freezing point of Pouliot (1964) found some cold acclimation accompany- water. ing noradrenaline injections in experimental animals. Food consumption tends to increase significantly 0. Heroux (1960), on the basis of experimental evidence, during cold exposure and acclimatization. Blair et al. believes that noradrenaline plays the role of mediator in for acclimation to cold. (1951) in their study of rabbits at -300 C for many nonshivering thermogenesis research has also been done on ascorbic acid weeks found food intake increased from 60 g at 230 C Extensive to 105 g per day with no appreciable change in weight. in relationship to cold stress and resistance. Increased levels of ascorbic acid in the liver, spleen, and testis have Chinn et al. (1950) found food intake increased 60% to be correlated to in rat experiments at 40 C for 10 days. The type of nutri- been shown highly body adjustment ents also has some bearing on successful cold acclimati- to cold. occurs to some zation. Page (1957) in experiments with rats, noted the In summary, cold acclimatization varies beneficial effects of a high fat diet on acclimation. Fats in degree in all forms of animal life. Its complexity the diet serve as primary fuels for extra heat production according to the thermal status of the organism. Accli- in the cold. matization to cold would appear rather limited for poiki- it would be consid- Sellers et al. (1951b) have clearly shown a relation- lotherms although for homeotherms, ship between cold acclimatization and metabolic rate. ered rather complex. Extensive research, particularly A group of non-acclimatized rats had their coats clipped in the areas related to the intricatephysiological and bio- off and were then subjected to cold conditions. The non: chemical aspects of cold acclimatizationin homeotherms treated control group died within a few hours because of poses a major challenge for the future. excessive cold exposure. In comparison, cold acclima- tized rats were clipped and subjected to cold. In most cases, the test group was able to survive for weeks under Animal Adaptation stress. Experimentalresults were interpreted on the basis When a terrestrialorganism is placed in cold conditions ANIMALSAND COLD 529 species. Lethaltemperatures that could be enduredbe- HOMEOTHERM 40 came higherwith increase of age in all species. Gordon (1968) mentionsone other instanceof heter- othermy in homeotherms in what he calls regional hypothermia.Regional hypothermia exists at poorly 30 insulatedperipheral extremities.