Animals at the extremes: hibernation and torpor

1 Hibernation and torpor: An introduction

This course examines hibernation, a special kind of adaptation that animals can make to the ecological demands of remaining in a choose habitat in winter. Hibernation is a state which enables energy-efficient survival when ambient temperatures are so moo that foraging or just maintaining normal core body temperature and basal metabolic rate are either energetically excessively dearly-won or impossible. arctic endotherms can maintain a high T b evening when living actively at sub-zero temperatures. such animals have very good thermal insulation and may have a bountiful food add to sustain the increased thermogenesis needed to maintain a big difference between T a and T bel. For many animals, however, the food supply in a cold environment becomes barely or inaccessible below bamboozle or ice rink .

Question 1

What are the options for surviving a very cold winter ?


  1. To remain active. This scheme is possible for an animal with allow insulating material, considerable energy reserves and the ability to compete successfully for a continuing food reservoir. The arctic fox and the emperor penguin are examples of such animals.
  2. To migrate to another habitat for the duration of an inhospitably cold season. This scheme is possible if the animal has sufficient mobility to leave the extreme latitudes as the available food dwindles. many birds and bats adopt this strategy .
  3. To endure the periods of low temperature extremes in the chosen habitat at low metabolic cost – by reducing T b, locomotion and early animation functions at all levels. The manipulation of this approach path, to varying extents, is seen in a huge and diverse group of birds and mammals. It has besides been adopted by poikilothermic vertebrates and invertebrates, though much for unlike reasons .

option 3 is adaptive hypothermia, as seen in torpor and hibernation. modest homeotherms living at latitudes ( or altitudes ) at which they experience long periods of coldness weather and lack of solar radiation have few options. Consider the problems a small animal is probable to encounter compared with a large one. It has a relatively high surface sphere to volume proportion and therefore a high gear potential for heat loss : even at moderate T a, it normally has a high metabolic rate and can not carry enough very effective insulation, whether of fur, feathers or blubber. Some species can survive in burrows if they can emerge regularly and find enough plant material to eat beneath the coke, but even these animals are probably to use energy-conserving strategies for much of the time. frankincense, humble rodents and insectivores, for exercise, have small choice but to exploit choice ( three ) above, uncoupling their homoiothermic mechanisms or resetting the critical body temperature ( Tc ) : in other words adaptive hypothermia. thermal adaptation in animals overcomes the ecological and bioenergetic constraints of live in extreme climates. For warm-blooded vertebrates, development has generated about every conceivable approach to this problem, and the adaptations adopted for each species reflect different approaches to the evolutionary cost-benefit analysis of variations on ceremonious endothermy. Whilst most hibernate endotherms lower the temperature of all or parts of their bodies by between 5 and 25° C, many ectotherms and some mammals are characterized by their ability to depress their T barn to below the freezing point of water. In either site, physiologic adaptations must include :

  1. thermoregulatory systems with control mechanisms different from, or with the ability to override, those which operate in the seasons when the animal is euthermic ;
  2. biochemical and cellular operate mechanisms adequate to of protecting tissues against damage, and compensating for energetic and metabolic disadvantages which are manifested at low body temperatures .

The terminology used to describe the different forms in which adaptive hypothermia is observed in animals is complicated. however, it is well viewed as a way of identifying a more or less persistent entrance into a state of suffer physiological depression and metabolic dormancy. A source of clear definitions which is reasonably contemporaneous at the date of write is provided by Körtner and Geiser ( 2000 ). Torpor is well defined as entrance of the whole animal into a state of matter of hypothermia which is accompanied by behavioral inactivity, regulated by a combination of external and home signals. Hibernation is defined as a confirm and fundamental state of listlessness, entry to and exit from which is governed by internal signals together with entirely seasonal external cues. We can place the methods of reducing soundbox temperature for the purpose of energy saving into the hierarchy below :Hierarchy of methods of reducing body temperature for the purpose of energy saving

Figure 1 Hierarchy of methods of reducing body temperature for the purpose of energy saving

dependable hibernators undergo three definitive and coordinate physiological changes :

  • Thermal dormancy – the ability of an animal to operate its biological functions at very low core torso temperatures .
  • Behavioural suppression – the cessation of activeness of many muscles, which depends upon the ability of the brain to override sensational inputs and endogenous rhythms such as breathe .
  • Metabolic inhibition – the ability of an animal to undergo episodic bradymetabolic changes : the low of energy-related and anabolic reactions .

adaptation to climatic extremes affects organisms at respective levels. In plants, which have little coordination at the level of systems, physiological adaptations to extreme heat, cold and dehydration can occur merely as they do in animals that have such control. Adaptation is manifested not merely at the flush of tissue and organ systems but besides at the grade of genes, proteins, protein complexes and cells. Many of the fundamental responses to hypothermic extremes mirror those seen in estivation – a submit of torpor seen in some ectotherms adapting to arid preferably than cold conditions. In both hibernation and estivation, far adaptations can be seen at the flat of cells and tissues : the being of protective measures that enable rapid convalescence from very cold temperatures, lack of oxygen and low energy supplies .

Question 2

What protective measures might be required to keep cells animated during periods of listlessness ?


such protective measures might include : prevention from freezing of the cytosol and organelles ; maintenance of life functions in the absence of oxygen or energy-yielding substrates ; stay or neutralization of processes which normally eliminate dying cells that may harm tissues if they remain. about all hibernate animals prepare during the summer and fall seasons by eating large amounts of food that they convert into fat, providing extra energy stores. Cellular metabolic processes are linked to a central regulative mechanism, an ‘ home clock ’, that provides the reference degree for entering hibernation and when to resume normal behavior. apart from episodic periods of foreplay to forage and excrete, hibernating animals are passive for several months on end. During this period, the lack of food and water means that physiological processes, blood and cellular biochemistry undergo major changes. Animals may be inactive for shorter periods toward the goal of hibernation periods, as they emerge to access signals ( e.g. light levels, T a ) which trigger the switch to normal activeness. environmental signals are integrated in the genius, pineal gland and other centres implicated in controlling seasonal changes in physiology and behavior. The annual cycle that governs introduction into and die from hibernation is besides under the command of inner physiologic systems. For case, as the bodies of hibernating male squirrels return to convention in the spring, a sustained, increased secretion of sex hormones prevents return to hibernation. result of hibernation is highly sensitive to temperature change. In fact, current global up trends in ambient temperature are having a measurable impression in shortening the hibernation seasons of a number of species, such as the chicken marmot animation in the Rocky mountains of the northwestern USA. Snowfalls have besides increased with the changing climate, so that the ground is calm covered with bamboozle when the marmots arouse from hibernation ( earlier than used to be the case ), making food hard to find. Summary of Section 1

hibernation is a physiological and behavioral adaptation whose function is to maximize energy efficiency in animals remaining in the lapp area the hale year round. It is an option to the provision of sufficient insulation to remain warm, scrounge continuously and sustain a constant eminent metabolic rate. There are three aspects of coordinated rule in hibernating or dormant animals : thermal, behavioral and metabolic. They operate independently, at least to some degree, and at the flush of the whole organism down to that of person molecules. There are besides adaptations that protect the organism against cell and tissue damage. hibernation and listlessness are regulated at the flat of the hale animal by biological rhythm generators that are adjusted by environmental stimuli which initiate rapid transposition signals at the decision of the period of dormancy .

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