Thermoregulation in Vertebrates

Abstract

Body temperature is one of the most important factors influencing animal function. Vertebrate animals generally regulate their body temperatures within quite narrow limits, but use different mechanisms to achieve this stability. In some circumstances, maintaining a high stable body temperature is not possible and several vertebrate groups have involved adaptive responses, such as torpor and hibernation, to overcome these problems.

Keywords: body temperature; endothermy; exothermy; homeothermy; poikilothermy

Figure 1.

Variation in energy requirement to keep a body at a fixed body temperature (Tb) as a function of ambient temperature. Theoretical energy requirements are shown in (a) for a body that has high thermal conductance (red line) and a body with low thermal conductance (blue line). These lines cross the abscissa at Tb. Endothermic animals are able to modulate their surface conductance by altering the properties of their pelage. The effect on energy requirements depends on the manner in which thermal conductance is modulated with changes in ambient temperature. Hence in (b) the animal decreases its thermal conductance as temperature declines from i to ii. The resultant line (thick green line) tracing the relation between energy requirement and ambient temperature follows a shallower curve than the lines for fixed thermal conductance and this line also extrapolates to a much higher temperature on the abscissa than Tb. In (c) the animal modulates its thermal conductance in the opposite direction – increasing conductance as temperature declines from i to ii. The resultant line relating energy requirement to ambient temperature is steeper (thick green line) and intersects the abscissa below Tb. Panel (d) illustrates the interaction between basal metabolic rate (BMR) and the thermal conductance. Where basal metabolism intersects the thermal conductance line, the animal is in energy balance (requirements met by demands) without the need to expend further energy on thermoregulation. These intersection points, called the lower critical temperatures (Tlcs), are at lower ambient temperatures when BMR is higher and when thermal conductance is lower.

Figure 2.

Relationships between energy requirements and ambient temperature for animals regulating their body temperatures (Tb) at different levels (red line: Tb regulated at euthermic levels; blue line: torpid Tb regulated at 20°C; and orange line: torpid Tb regulated at 5°C). In all cases the patterns of variation in energy requirements as a function of temperature are similar, reflecting the fact that torpor is a regulated state of energy metabolism. The metabolic rate of torpid animals (TMR) reaches a minimum at an ambient temperature (Ta) below the point where Ta = Tb. Higher and lower ambient temperatures result in higher metabolic rates. Lower energy requirements follow the lines defined by torpid conductance. Abbreviation: Tlc, lower critical temperature.

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Further Reading

Cossins A and Bowler K (1980) Temperature and Life. London: Chapman and Hall.

Davenport C (1996) Low Temperature Adaptations of Animals. Cambridge, UK: Cambridge University Press.

Schmidt Nielsen K (1998) Environmental Physiology of Animals: Adaptation and Environment. Cambridge, UK: Cambridge University Press.

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How to Cite close
Speakman, John R(Apr 2001) Thermoregulation in Vertebrates. In: eLS. John Wiley & Sons Ltd, Chichester. http://www.els.net [doi: 10.1038/npg.els.0001824]