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Thermoregulatory importance of the beaver's tail
Comp. Biochem. Physiol., 1965, Vol. 15, pp. 267 to 270. Pergamon Press Ltd. Printed in Great Britain
SHORT COMMUNICATION T H E R M O R E G U L A T O R Y I M P O R T A N C E OF T H E BEAVER'S T A I L I N G E R S T E E N and J. B. S T E E N * Institute of Zoophysiology, University of Oslo, Blindern, Norway
(Received 10 February 1965) A b s t r a c t - - 1 . When totally surrounded by air, the beaver is able to maintain a normal body temperature at ambient temperatures below 20°C. Above this temperature it becomes hyperthermic. 2. If the air-surrounded beaver is allowed to keep its naked tail in cool water the animal's body temperature is maintained at a normal level also at an ambient air temperature of 25°C. In this situation heat loss from the tail to water amounts to about 20 per cent of the total heat production. 3. It is concluded that the beaver's tail, like poorly insulated body parts of many other animals, has an important secondary function as an organ for controlled heat dissipation. INTRODUCTION IT HAS been demonstrated that the naked extremities of many homoiothdrms with good body insulation are used as controlled heat dissipators. Kahl (1963) and Steen & Steen (1965) have shown that some birds are dependent upon heat loss from their legs for maintenance of normal body temperature during heat stress. In the heron up to 50 per cent of the total heat production may be lost through one foot immersed in water. Johansen (1961) demonstrated that the muskrat's naked tail has a similar function. At ambient temperature above 25°C, blood flow through the tail was 100-180 times higher than at 15°C. If the tail blood flow was occluded, the animal's rectal temperature rose to 41-42°C as against 37-39°C with tail circulation intact. Last s u m m e r we had the opportunity to perform a few experiments on a beaver (Castor fiber) in order to establish if its naked tail might have a similar function. Our single specimen was very co-operative and maintained its weight of 2.8 kg during its brief stay in the laboratory. EXPERIMENTS AND RESULTS T h e beaver was equipped with thermocouples on the tip of the tail and 2 cm into the rectum. If the entire animal was placed in air of 16°C it maintained a normal rectal temperature of 37 _ 0.2°C and a tail temperature slightly above the environmental temperature. If the air temperature was increased to 25°C, however, the rectal temperature * Present address: Institute of Physiology, University of Oslo, Karl Johansgt. 47, Norway. 267
268
INGER STEEN AND J. B. SaXEN
increased and reached, within 30 min, a new steady level about 2°C above normal (Fig. 1). Under these conditions the skin temperature near the tip of the tail increased from 16°C to 35°C (Fig. 1). Unlike other homoiotherms under heat stress, the beaver did not pant. At an intermediate air temperature of 20°C, the tail temperature showed transient waves of increased temperature and the rectal temperature was normal (Fig. 1). The profound hyperthermia at 25°C did not occur if the animal was allowed to dip its tail in cool water. The experimental arrangement was as in Fig. 2. The beaver was placed on a piece of plywood and the naked part of its tail was completely immersed in a thermos bottle containing well stirred water with an initial temperature of 6°C. Temperatures were recorded simultaneously from the water in the thermos, from the animal's rectum and from the skin near the tip of the beaver's tail. At an air temperature of 16°C, the average heat loss from the tail (details of method see Steen & Steen (1965)) was below 0.1 kcal/hr and the beaver maintained its normal rectal temperature (Fig. 1). When the air temperature was increased to 25°C the heat loss from the tail increased to about 1.2 kcai/hr. Under these conditions, with the tail in water, the beaver maintained a normal rectal temperature at air temperature of 25°C (Fig. 2). DISCUSSION The beaver lives partly on land and partly in fresh-water streams or ponds. Our data indicate that the beaver's naked tail is most markedly influencing thermoregulation when the animal stays in water. The muskrat, when placed in warm air, increases the tail temperature and the resulting increased heat loss enables it to maintain normal body temperature. The beaver does the same, but achieves less thermoregulatory effect probably due to the relatively small surface of its tail. In water, however, heat transfer is more efficient. In this habitat the beaver resembles the fur seals which also have a well insulating fur coat and which regulate body temperature by varying heat loss from their flippers (Irving et al., 1962). According to the "Mouse to Elephant" curve of Benedict (1938) the beaver's resting metabolism is approximately 6 kcal/hr. This means that at 25°C the heat loss from the tail represents about 20 per cent of the total heat production. It has been shown by Johansen (1961) that the changes in heat loss from the muskrat's tail are achieved by vasomotoricaUy controlled variations in blood flow. This is most likely the case also for the beaver's tail, although heat exchange in vascular counter-current bundles may also be involved to achieve a compromise between adequate oxygen supply and sufficient heat loss e.g. during cold conditions. The naked tail of the beaver thus represents another example of a versatile body appendage with large variations in its heat dissipation and consequently of great importance for the maintenance of body temperature.
AcknowledgementoWe wish to acknowledge financial support from Norsk Varekrigsforsikrings Fond.
THERMOREGULATORY
IMPORTANCE
269
OF T H E BEAVER'S TAIL TAIL IN AIR
TAIL IN WATER
RECTAL
35
:~'~'TA IL"",, "', ;
/
25 a:
. . . . AMBIENT
/ '*,
/
:'"
= AMBIENT
.__,'_ '
/
I
. . . .
.=,;;;,~:--'--:'"'%
- "°"
Kcal hr
15
j 30
MiN
30
60
MiN
6
'0
FIG. 1. Importance of the water-immersed tail in the thermoregulation of the beaver. Changes in rectal temperature, tail temperature and heat loss from the tail with alterations in the ambient temperature. Left: Animal's tail in water. Right: Animal's tail in air. (Note that two experiments are described with the animal's tail in air, - . . . . . . . . and .) A m b i e n t t t m p . ,= ?.,5'C
.
57"C
,-%
.j
39"C
FIG. 2. Experimental arrangement for tests on the effect of water immersion of the beaver's tail.
270
INGER STEEN AND J. B. S T ~ REFERENCES
BENEDICT F. G. (1938) Vital Energetics. Carnegie Inst., W'ashington, Publ. 503. IRVING L., P~YTON L. J., BAHN C. H. & PETERSONR. S. (1962) Regulation of temperature in fur seals. Physiol. Zool. 35, 275-284. JOHANSEN K. (1961) Heat exchange through the skin in the tail of the muskrat, Ondatra zibethicus. Fed. Proc. 20, 110. KARL M. P. (1963) Thermoregulation in the wood stork with special reference to the role of the legs. Physiol. Zool. 6, 667-680. STEEN INaER & STEEN J. B. (1965) The importance of the legs in the thermoregulation of birds. Acta Physiol. Scand. In press.
SHORT COMMUNICATION T H E R M O R E G U L A T O R Y I M P O R T A N C E OF T H E BEAVER'S T A I L I N G E R S T E E N and J. B. S T E E N * Institute of Zoophysiology, University of Oslo, Blindern, Norway
(Received 10 February 1965) A b s t r a c t - - 1 . When totally surrounded by air, the beaver is able to maintain a normal body temperature at ambient temperatures below 20°C. Above this temperature it becomes hyperthermic. 2. If the air-surrounded beaver is allowed to keep its naked tail in cool water the animal's body temperature is maintained at a normal level also at an ambient air temperature of 25°C. In this situation heat loss from the tail to water amounts to about 20 per cent of the total heat production. 3. It is concluded that the beaver's tail, like poorly insulated body parts of many other animals, has an important secondary function as an organ for controlled heat dissipation. INTRODUCTION IT HAS been demonstrated that the naked extremities of many homoiothdrms with good body insulation are used as controlled heat dissipators. Kahl (1963) and Steen & Steen (1965) have shown that some birds are dependent upon heat loss from their legs for maintenance of normal body temperature during heat stress. In the heron up to 50 per cent of the total heat production may be lost through one foot immersed in water. Johansen (1961) demonstrated that the muskrat's naked tail has a similar function. At ambient temperature above 25°C, blood flow through the tail was 100-180 times higher than at 15°C. If the tail blood flow was occluded, the animal's rectal temperature rose to 41-42°C as against 37-39°C with tail circulation intact. Last s u m m e r we had the opportunity to perform a few experiments on a beaver (Castor fiber) in order to establish if its naked tail might have a similar function. Our single specimen was very co-operative and maintained its weight of 2.8 kg during its brief stay in the laboratory. EXPERIMENTS AND RESULTS T h e beaver was equipped with thermocouples on the tip of the tail and 2 cm into the rectum. If the entire animal was placed in air of 16°C it maintained a normal rectal temperature of 37 _ 0.2°C and a tail temperature slightly above the environmental temperature. If the air temperature was increased to 25°C, however, the rectal temperature * Present address: Institute of Physiology, University of Oslo, Karl Johansgt. 47, Norway. 267
268
INGER STEEN AND J. B. SaXEN
increased and reached, within 30 min, a new steady level about 2°C above normal (Fig. 1). Under these conditions the skin temperature near the tip of the tail increased from 16°C to 35°C (Fig. 1). Unlike other homoiotherms under heat stress, the beaver did not pant. At an intermediate air temperature of 20°C, the tail temperature showed transient waves of increased temperature and the rectal temperature was normal (Fig. 1). The profound hyperthermia at 25°C did not occur if the animal was allowed to dip its tail in cool water. The experimental arrangement was as in Fig. 2. The beaver was placed on a piece of plywood and the naked part of its tail was completely immersed in a thermos bottle containing well stirred water with an initial temperature of 6°C. Temperatures were recorded simultaneously from the water in the thermos, from the animal's rectum and from the skin near the tip of the beaver's tail. At an air temperature of 16°C, the average heat loss from the tail (details of method see Steen & Steen (1965)) was below 0.1 kcal/hr and the beaver maintained its normal rectal temperature (Fig. 1). When the air temperature was increased to 25°C the heat loss from the tail increased to about 1.2 kcai/hr. Under these conditions, with the tail in water, the beaver maintained a normal rectal temperature at air temperature of 25°C (Fig. 2). DISCUSSION The beaver lives partly on land and partly in fresh-water streams or ponds. Our data indicate that the beaver's naked tail is most markedly influencing thermoregulation when the animal stays in water. The muskrat, when placed in warm air, increases the tail temperature and the resulting increased heat loss enables it to maintain normal body temperature. The beaver does the same, but achieves less thermoregulatory effect probably due to the relatively small surface of its tail. In water, however, heat transfer is more efficient. In this habitat the beaver resembles the fur seals which also have a well insulating fur coat and which regulate body temperature by varying heat loss from their flippers (Irving et al., 1962). According to the "Mouse to Elephant" curve of Benedict (1938) the beaver's resting metabolism is approximately 6 kcal/hr. This means that at 25°C the heat loss from the tail represents about 20 per cent of the total heat production. It has been shown by Johansen (1961) that the changes in heat loss from the muskrat's tail are achieved by vasomotoricaUy controlled variations in blood flow. This is most likely the case also for the beaver's tail, although heat exchange in vascular counter-current bundles may also be involved to achieve a compromise between adequate oxygen supply and sufficient heat loss e.g. during cold conditions. The naked tail of the beaver thus represents another example of a versatile body appendage with large variations in its heat dissipation and consequently of great importance for the maintenance of body temperature.
AcknowledgementoWe wish to acknowledge financial support from Norsk Varekrigsforsikrings Fond.
THERMOREGULATORY
IMPORTANCE
269
OF T H E BEAVER'S TAIL TAIL IN AIR
TAIL IN WATER
RECTAL
35
:~'~'TA IL"",, "', ;
/
25 a:
. . . . AMBIENT
/ '*,
/
:'"
= AMBIENT
.__,'_ '
/
I
. . . .
.=,;;;,~:--'--:'"'%
- "°"
Kcal hr
15
j 30
MiN
30
60
MiN
6
'0
FIG. 1. Importance of the water-immersed tail in the thermoregulation of the beaver. Changes in rectal temperature, tail temperature and heat loss from the tail with alterations in the ambient temperature. Left: Animal's tail in water. Right: Animal's tail in air. (Note that two experiments are described with the animal's tail in air, - . . . . . . . . and .) A m b i e n t t t m p . ,= ?.,5'C
.
57"C
,-%
.j
39"C
FIG. 2. Experimental arrangement for tests on the effect of water immersion of the beaver's tail.
270
INGER STEEN AND J. B. S T ~ REFERENCES
BENEDICT F. G. (1938) Vital Energetics. Carnegie Inst., W'ashington, Publ. 503. IRVING L., P~YTON L. J., BAHN C. H. & PETERSONR. S. (1962) Regulation of temperature in fur seals. Physiol. Zool. 35, 275-284. JOHANSEN K. (1961) Heat exchange through the skin in the tail of the muskrat, Ondatra zibethicus. Fed. Proc. 20, 110. KARL M. P. (1963) Thermoregulation in the wood stork with special reference to the role of the legs. Physiol. Zool. 6, 667-680. STEEN INaER & STEEN J. B. (1965) The importance of the legs in the thermoregulation of birds. Acta Physiol. Scand. In press.