Comp. Biochem. Physiol., 1975, VoL 51A, pp. 361 to 368. Pergamon Press. Printed in Great Britain
SOME FACTORS AFFECTING WATER ECONOMY IN SNAKES ALLEN C. Cotton Department of Biology, Cypress College, Cypress, California 90630, U.S.A.
(Received 17 January 1974) AIrstraet--1. A series of experiments was conducted to determine the importance of the following parameters in the rate of water loss in snakes: (1) exposed surface area, (2) flow rate, (3) temperature, (4) state of snake in shedding cycle, (5) snake's position, (6) respiratory vs. cutaneous water loss, (7) vasodilation and (8) species differences. 2. Water lossin Crotalus cerastes is a function of amount of exposed surface area. 3. Water loss was found to be strongly influenced by temperature and by flow rate of the air used to desiccate the snakes. 4. In non-shedding snakes, the cutaneous loss accounted for 75 per cent of the total water loss. 5. Shedding snakes were found to lose considerably more than non-shedding snakes; the increase in cutaneous water loss accounted for the increase seen in shedding snakes. 6. Rate of water loss in snakes allowed to coil is significantly less than that of snakes that were uncoiled. 7. Snakes injected with a vasodilator significantly increased their rate of water loss. 8. Rate of snakes' water loss was found to be correlated with habitats and food habits.
INTRODUCTION SINCE the discovery that cutaneous water loss constitutes a sizable portion of a reptile's total water loss, there have been several investigations concerning reptilian water e c o n o m y (Claussen, 1967; Gans et al., 1968; Schmidt-Nielsen, 1968; Roberts, 1968; Minnich, 1970). Only one o f these concentrated on snakes (Gans et aL, 1968) and presented data primarily concerning non-xeric snakes. A l t h o u g h it has been noted that water loss increases as a function of progress in the shedding cycle (Maderson, 1966), quantitative information describing this phenomenon is lacking. Further, there has been no attempt to separate the cutaneous f r o m the respiratory water loss during shedding and to measure the site of increased water loss. The present study was undertaken to determine the importance of size, temperature, flow rate, shedding, v a s o m o t o r responses and habitat on the water loss of snakes.
MATERIALS AND M E T H O D S Snakes used in this study, according to habitat, were as follows--xeric; the sidewinder, Crotalus cerastes; the shovelnosed snake, Chionactis occipitalis; the leafnosed snake, Phyllorhynchus decurtatus; the glossy snake, * This paper is a partial fulfillment of the requirements for the M.A. in Biology at California State University, Fullerton.
Arizona elegans; the western diamond back, Crotalus atrox; the Mojave rattlesnake, Crotalus scutulatus; semi-xeric: the red diamond rattlesnake, Crotalus ruber; the Southern Pacific rattlesnake, Crotalus viridis; the Mexican West Coast rattlesnake, Crotalus basiliscus; mesic: the common king snake, Lampropeltis getulus; the gopher snake, Pituophis catenifer; the rubber boa, Charina bottae; aquatic snakes: Thamnophis cyrtopsis, the black-necked garter snake; the checkered garter snake, Thamnophis marcianus; the western aquatic garter snake, Thamnophis couchi. All of the xeric snakes used in the experiment except for C. scutulatus were collected within 20 miles of Indio, Riverside County, California. The C. scutulatus as well as the three species of Thamnophis were collected near the Southwestern Research Station, Cochise County, Arizona. The C. basiliscus used were captive-born snakes whose parents were collected in southern Sonora, Mexico. All of the other snakes used were collected in the Trabuco Canyon area, Orange County, California. Animals were kept in a constant temperature, constant humidity room at 20°C, and at a relative humidity of 50 _+10~. The room was kept on a 13-hr light : 1l-hr dark photoperiod, centered at noon, Pacific Standard Time. The animals, when not involved in the experiments, were fed live mice and lizards (Coleonyx variegatus, Uta stansburiana and Dipsosaurus dorsalis) once every 2 weeks. The aquatie garter snakes were fed frogs (Rana pipiens, P. eatesbeiana and Hyla regilla). They were given water ad lib. Animals used in all experiments were postabsorptive for a minimum of 1 week. Only non-shedding animals that had been feeding and drinking until 7 days prior to the forced post-absorptive period were used, except for the experiments on shedding snakes. With the exception of the shedding snakes, all animals used in these 361
ALLEN C. C_,oI~N
362
experiments were captured no more than 25 days before being used in the experiments. The desiccation system used (Fig. 1) was housed in a constant temperature chamber, maintained at 30°C and at a relative humidity of 5 + 3 ~ (except in those experiments where temperature was the variable and in the coiled vs uncoiled trials). Before introduction to the system, snakes were given a 5-min period of equilibration to the chamber's temperature. Air stored in a compressed air bottle was passed through a series of drierite and glass wool-filled tubes. The flow rate of the air was monitored by flow meters; and except where flow rate was the variable, all trials were done at a flow rate of 300 cmZ/min. Except for the investigation of cutaneous vs respiratory water loss, the water loss of the snakes was assumed to be the same as the weight loss of the snake. In early trials, post-drierite catch tubes and ascarite-faUed tubes were used to check whether or not the weight loss was attributable to a sizable loss of CO2. Less than 0.5 per cent of the total loss was contributed by the carbon dioxide.
(_~
Drierit"e (4 tubes)
"
Drierite I~--~
Iregu
[U [
t
Air supply
1
(a)
Dry air source
I Drierite
I
] Drierite
I#L ~,= = ~ I~I
1 sourceDryair
Ii1
Rubberdom (b) Fig. 1. The apparatus used in the water loss experiments. Figure 1(a) shows the tube used to test uncoiled snakes and the jar used to test coiled snakes. Figure l(b) shows the apparatus used to separate the cutaneous from the respiratory compartments of the snakes. After each trial, snakes were weighed on a Mettler PI60 balance (to the nearest 0.001 g), except for snakes whose weight exceeded 160 g; these animals were weighed on a Mettler P1200 (to the nearest 0.01 g). For the first twenty trials, snake weight loss was compared with weight gain in the post-dierite tube and the correlation
between the two was found to be within 1 per cent error, indicating that the system was leak-free. Size relationships have been shown to be of importance in many physiological studies (Kleiber, 1961), and therefore it was of interest to determine if there was a differential water loss between large and small snakes. A series of C. cerastes ranging from 6 to 169 g were tested in the desiccation system. It was also of interest to determine the relationship of flow rate and temperature to water loss. Ten snakes of weights ranging between 24 and 68 g were each tested at flow rates of 50, 150, 300 and 600 cm3/min. For temperature effects, a series of ten snakes weighing from 15 to 93 g was tested at temperatures ranging from 20 to 40°C. Snakes in various phases of the shedding cycle (as described by Maderson, 1966, 1970) were tested to determine the effects of shedding upon rate of water loss. The snakes were recognized as shedding animals when the ocular scale appeared white. This was found to be the most reliable and convenient method for recognizing shedding snakes although the shedding cycle probably begins earlier than this (see Maderson, 1964). Whenever possible, shedding snakes were subjected to the cutaneous vs respiratory water loss test described below. To determine the effect of body posture (coiled vs uncoiled posture) upon rate of water loss, ten sidewinders were tested at 30°C and eleven were tested at 40°C. The latter temperature was used to insure that the snakes would be under a stress situation. The animals were tested in both tubes as described above and in 1-gal jars with tops fitted with intake and exhaust openings. The intake opening consisted of a rubber tube that extended nearly to the bottom of the jar. The exhaust tube extended to about 2 cm into the jar. This arrangement guaranteed that the air in the jar would remain in constant motion, allowing no dead air spaces around the snake. To determine whether or not the air was flowing at a constant rate, the jar was filled with smoke, and then the snake was observed as the smoke was evacuated from the jar by the flowing air system. All visible traces of smoke cleared within 30 sec (at a flow rate of 300 cm3/min) indicating that the dry air passes over the snake's skin while it is in either system, the tube or the jar. In the tube the snake was unable to fold itself, so it was in an uncoiled (or straight) position throughout the experiment. While these animals were confined so that they must conform to the straight position they were not restrained. Restraints such as tying down might have excited the animals, causing an increase in metabolic rate and a subsequent increase in respiratory water loss. The snakes in the jar, on the other hand, were allowed to coil. To determine the cutaneous and respiratory water loss and to determine which contributed most to the increased rate of water loss in shedding animals, the snakes were placed in two tubes, the head in one, the rest of the body in the other. A rubber dam was fitted over the snake's head. The lips of the two tubes were pressed against one another to seat the system with the rubber dam serving as a gasket (Fig. lb). Individual flow meters and valves permitted control over a balanced air flow for the two separate systems. The air was passed over the two separate portions of the snake (respiratory and cutaneous for the head and body respectively) and then was passed through separate drierite catch tubes. Before and after each run, the tubes were weighed to determine the water gain for each section. It was assumed that the weight
Factors affecting water economy in snakes gain in the drierite tube associated with the head was primarily due to respiratory water loss. Also it was assumed that the weight gain in the tube associated with the body was primarily due to cutaneous water loss. In each trial, the snake was weighed before and after to serve as a check against leaks in the system. Data were discarded for every run that the snake's weight loss did not equal ( + 1 per cent) the total weight gain of the respiratory and cutaneous drierite tubes. To determine the effect of vasodilation upon rate of water loss, eight sidewinders were given the sodium thiosulfate vasodilator that acts specifically upon the capillaries. A 10% solution was injected intraperitoneally at doses of 2 mg/g body weight. Vasomotor effects on capillary beds were determined by direct observation. In each test, a pair of sidewinders was used, one injected with the sodium thiosulfate solution, the other given an equivalent volume of distilled water as a placebo. The snakes were paired according to size so that the same volume could be injected into each snake on each trial. After a minimum of 1 day, the situation was reversed for each snake so that the animal that formerly received the sodium thiosulfate received the placebo. Because of the possibility of damage from the injections or from the sodium thiosulfate, no animals used in these experiments were used in other experiments. To determine whether snakes of different habitats and different food habits had rates of water loss correlated with the availability of free water, a series of snakes was tested under conditions specified above. The snakes include all of the ones mentioned above, according to their habitat type. RESULTS T h e relationship between the log o f the r a t e of water loss a n d the log o f the b o d y weight o f sidewinders is given in Fig. 2. T h e regression line was d e t e r m i n e d b y m e a n s o f least squares, a n d the exp o n e n t i a l e q u a t i o n t h a t c o r r e s p o n d s to the regression line is as follows: water loss (mg/g per hr) = 34"7 weight (g)-0.s3.
363
JE:
1.0 Q 0
3:~ 0"2 0.1
I0 Wt". of snokes,
50
IO0
g
Fig. 2. Rate of water loss as a function of weight in C. cerastes. B o t h flow r a t e a n d t e m p e r a t u r e significantly affect the rate o f w a t e r loss in snakes. T h e m e a n rate o f water loss for the four flow rates 50, 150, 300 a n d 600 c m 3 are 0-69, 0.68, 0.90 a n d 1.02 m g / g per h r respectively (Table 3). Except for the differences between 50 a n d 150's, there is a significant difference in rate o f water loss at different flow rates ( P < 0 . 0 1 in the F-test). W h i l e there is n o significant difference between rates of w a t e r loss between 20 a n d 30°C, there is a significant difference between 30 a n d 40°C ( P < 0.01 in a t-test). However, the m e a n rate o f water loss does n o t linearly follow the s a t u r a t i o n deficits at the three t e m p e r a t u r e s tested. While the water losses a t 20 a n d 30°C follow the s a t u r a t i o n deficits a t those temperatures, at 40°C, the rate o f water loss is d i s p r o p o r t i o n a t e l y high (Table l a , l b a n d Fig. 7). I n the C. occipitalis, w h o s e s h e d d i n g history was followed f r o m 6 days before s h e d d i n g until 6 days after shedding, the rate o f w a t e r loss goes f r o m 1"5
Table la. Rate of water loss as a function of temperature Snake No.
Weight (g)
Loss at 20°C (mg/g per hr)
Loss at 30°C (mg/g per hr)
Loss at 40°C (mg/g per hr)
1 2 3 4 5 6 7 8 9 10
15'4 26.2 27"8 27.9 30"6 35-7 39.7 43.5 82-8 93.3
0'26 0'46 1.20 0"35 0"81 0.75 0.85 1.86 0.79 0.26
1'60 0.99 1 "45 0.90 0-63 0.67 0.57 0.51 0'49 0'44
1-95 2-01 1"83 1 "56 1.86 2"38 2.43 1.44 1"33 2.43
Table lb. Saturation deficits at a relative humidity of 5% 20°C
30°C
40°C
0.70 m m
1.27 mm
2"21 mm
364
ALLEN C. COHEN
Table 2. Rate of water loss with vasodilator and with distilled water placebo in C. cerastes
Snake No.
Weight (g)
1 2 3 4 5 6 7 8
60 30 31 32 40 34 85 60
H~O loss (mg/g per hr) (without vasodilator)
H~O loss (mg/g per hr) (with vasodilator)
water loss of the two compartments in a snake before, during and after shedding (Fig.s and 4 5). The total water loss was high 2 days before shedding, and increased the day before shedding
~
0.63 1"10 0.93 1"61 1"33 0.72 1.73 1.22
0'84 2.28 0'96 3.35 1.67 0.99 2.26 1.66
.t~= 1"16 S = 0"395 P
SOME FACTORS AFFECTING WATER ECONOMY IN SNAKES ALLEN C. Cotton Department of Biology, Cypress College, Cypress, California 90630, U.S.A.
(Received 17 January 1974) AIrstraet--1. A series of experiments was conducted to determine the importance of the following parameters in the rate of water loss in snakes: (1) exposed surface area, (2) flow rate, (3) temperature, (4) state of snake in shedding cycle, (5) snake's position, (6) respiratory vs. cutaneous water loss, (7) vasodilation and (8) species differences. 2. Water lossin Crotalus cerastes is a function of amount of exposed surface area. 3. Water loss was found to be strongly influenced by temperature and by flow rate of the air used to desiccate the snakes. 4. In non-shedding snakes, the cutaneous loss accounted for 75 per cent of the total water loss. 5. Shedding snakes were found to lose considerably more than non-shedding snakes; the increase in cutaneous water loss accounted for the increase seen in shedding snakes. 6. Rate of water loss in snakes allowed to coil is significantly less than that of snakes that were uncoiled. 7. Snakes injected with a vasodilator significantly increased their rate of water loss. 8. Rate of snakes' water loss was found to be correlated with habitats and food habits.
INTRODUCTION SINCE the discovery that cutaneous water loss constitutes a sizable portion of a reptile's total water loss, there have been several investigations concerning reptilian water e c o n o m y (Claussen, 1967; Gans et al., 1968; Schmidt-Nielsen, 1968; Roberts, 1968; Minnich, 1970). Only one o f these concentrated on snakes (Gans et aL, 1968) and presented data primarily concerning non-xeric snakes. A l t h o u g h it has been noted that water loss increases as a function of progress in the shedding cycle (Maderson, 1966), quantitative information describing this phenomenon is lacking. Further, there has been no attempt to separate the cutaneous f r o m the respiratory water loss during shedding and to measure the site of increased water loss. The present study was undertaken to determine the importance of size, temperature, flow rate, shedding, v a s o m o t o r responses and habitat on the water loss of snakes.
MATERIALS AND M E T H O D S Snakes used in this study, according to habitat, were as follows--xeric; the sidewinder, Crotalus cerastes; the shovelnosed snake, Chionactis occipitalis; the leafnosed snake, Phyllorhynchus decurtatus; the glossy snake, * This paper is a partial fulfillment of the requirements for the M.A. in Biology at California State University, Fullerton.
Arizona elegans; the western diamond back, Crotalus atrox; the Mojave rattlesnake, Crotalus scutulatus; semi-xeric: the red diamond rattlesnake, Crotalus ruber; the Southern Pacific rattlesnake, Crotalus viridis; the Mexican West Coast rattlesnake, Crotalus basiliscus; mesic: the common king snake, Lampropeltis getulus; the gopher snake, Pituophis catenifer; the rubber boa, Charina bottae; aquatic snakes: Thamnophis cyrtopsis, the black-necked garter snake; the checkered garter snake, Thamnophis marcianus; the western aquatic garter snake, Thamnophis couchi. All of the xeric snakes used in the experiment except for C. scutulatus were collected within 20 miles of Indio, Riverside County, California. The C. scutulatus as well as the three species of Thamnophis were collected near the Southwestern Research Station, Cochise County, Arizona. The C. basiliscus used were captive-born snakes whose parents were collected in southern Sonora, Mexico. All of the other snakes used were collected in the Trabuco Canyon area, Orange County, California. Animals were kept in a constant temperature, constant humidity room at 20°C, and at a relative humidity of 50 _+10~. The room was kept on a 13-hr light : 1l-hr dark photoperiod, centered at noon, Pacific Standard Time. The animals, when not involved in the experiments, were fed live mice and lizards (Coleonyx variegatus, Uta stansburiana and Dipsosaurus dorsalis) once every 2 weeks. The aquatie garter snakes were fed frogs (Rana pipiens, P. eatesbeiana and Hyla regilla). They were given water ad lib. Animals used in all experiments were postabsorptive for a minimum of 1 week. Only non-shedding animals that had been feeding and drinking until 7 days prior to the forced post-absorptive period were used, except for the experiments on shedding snakes. With the exception of the shedding snakes, all animals used in these 361
ALLEN C. C_,oI~N
362
experiments were captured no more than 25 days before being used in the experiments. The desiccation system used (Fig. 1) was housed in a constant temperature chamber, maintained at 30°C and at a relative humidity of 5 + 3 ~ (except in those experiments where temperature was the variable and in the coiled vs uncoiled trials). Before introduction to the system, snakes were given a 5-min period of equilibration to the chamber's temperature. Air stored in a compressed air bottle was passed through a series of drierite and glass wool-filled tubes. The flow rate of the air was monitored by flow meters; and except where flow rate was the variable, all trials were done at a flow rate of 300 cmZ/min. Except for the investigation of cutaneous vs respiratory water loss, the water loss of the snakes was assumed to be the same as the weight loss of the snake. In early trials, post-drierite catch tubes and ascarite-faUed tubes were used to check whether or not the weight loss was attributable to a sizable loss of CO2. Less than 0.5 per cent of the total loss was contributed by the carbon dioxide.
(_~
Drierit"e (4 tubes)
"
Drierite I~--~
Iregu
[U [
t
Air supply
1
(a)
Dry air source
I Drierite
I
] Drierite
I#L ~,= = ~ I~I
1 sourceDryair
Ii1
Rubberdom (b) Fig. 1. The apparatus used in the water loss experiments. Figure 1(a) shows the tube used to test uncoiled snakes and the jar used to test coiled snakes. Figure l(b) shows the apparatus used to separate the cutaneous from the respiratory compartments of the snakes. After each trial, snakes were weighed on a Mettler PI60 balance (to the nearest 0.001 g), except for snakes whose weight exceeded 160 g; these animals were weighed on a Mettler P1200 (to the nearest 0.01 g). For the first twenty trials, snake weight loss was compared with weight gain in the post-dierite tube and the correlation
between the two was found to be within 1 per cent error, indicating that the system was leak-free. Size relationships have been shown to be of importance in many physiological studies (Kleiber, 1961), and therefore it was of interest to determine if there was a differential water loss between large and small snakes. A series of C. cerastes ranging from 6 to 169 g were tested in the desiccation system. It was also of interest to determine the relationship of flow rate and temperature to water loss. Ten snakes of weights ranging between 24 and 68 g were each tested at flow rates of 50, 150, 300 and 600 cm3/min. For temperature effects, a series of ten snakes weighing from 15 to 93 g was tested at temperatures ranging from 20 to 40°C. Snakes in various phases of the shedding cycle (as described by Maderson, 1966, 1970) were tested to determine the effects of shedding upon rate of water loss. The snakes were recognized as shedding animals when the ocular scale appeared white. This was found to be the most reliable and convenient method for recognizing shedding snakes although the shedding cycle probably begins earlier than this (see Maderson, 1964). Whenever possible, shedding snakes were subjected to the cutaneous vs respiratory water loss test described below. To determine the effect of body posture (coiled vs uncoiled posture) upon rate of water loss, ten sidewinders were tested at 30°C and eleven were tested at 40°C. The latter temperature was used to insure that the snakes would be under a stress situation. The animals were tested in both tubes as described above and in 1-gal jars with tops fitted with intake and exhaust openings. The intake opening consisted of a rubber tube that extended nearly to the bottom of the jar. The exhaust tube extended to about 2 cm into the jar. This arrangement guaranteed that the air in the jar would remain in constant motion, allowing no dead air spaces around the snake. To determine whether or not the air was flowing at a constant rate, the jar was filled with smoke, and then the snake was observed as the smoke was evacuated from the jar by the flowing air system. All visible traces of smoke cleared within 30 sec (at a flow rate of 300 cm3/min) indicating that the dry air passes over the snake's skin while it is in either system, the tube or the jar. In the tube the snake was unable to fold itself, so it was in an uncoiled (or straight) position throughout the experiment. While these animals were confined so that they must conform to the straight position they were not restrained. Restraints such as tying down might have excited the animals, causing an increase in metabolic rate and a subsequent increase in respiratory water loss. The snakes in the jar, on the other hand, were allowed to coil. To determine the cutaneous and respiratory water loss and to determine which contributed most to the increased rate of water loss in shedding animals, the snakes were placed in two tubes, the head in one, the rest of the body in the other. A rubber dam was fitted over the snake's head. The lips of the two tubes were pressed against one another to seat the system with the rubber dam serving as a gasket (Fig. lb). Individual flow meters and valves permitted control over a balanced air flow for the two separate systems. The air was passed over the two separate portions of the snake (respiratory and cutaneous for the head and body respectively) and then was passed through separate drierite catch tubes. Before and after each run, the tubes were weighed to determine the water gain for each section. It was assumed that the weight
Factors affecting water economy in snakes gain in the drierite tube associated with the head was primarily due to respiratory water loss. Also it was assumed that the weight gain in the tube associated with the body was primarily due to cutaneous water loss. In each trial, the snake was weighed before and after to serve as a check against leaks in the system. Data were discarded for every run that the snake's weight loss did not equal ( + 1 per cent) the total weight gain of the respiratory and cutaneous drierite tubes. To determine the effect of vasodilation upon rate of water loss, eight sidewinders were given the sodium thiosulfate vasodilator that acts specifically upon the capillaries. A 10% solution was injected intraperitoneally at doses of 2 mg/g body weight. Vasomotor effects on capillary beds were determined by direct observation. In each test, a pair of sidewinders was used, one injected with the sodium thiosulfate solution, the other given an equivalent volume of distilled water as a placebo. The snakes were paired according to size so that the same volume could be injected into each snake on each trial. After a minimum of 1 day, the situation was reversed for each snake so that the animal that formerly received the sodium thiosulfate received the placebo. Because of the possibility of damage from the injections or from the sodium thiosulfate, no animals used in these experiments were used in other experiments. To determine whether snakes of different habitats and different food habits had rates of water loss correlated with the availability of free water, a series of snakes was tested under conditions specified above. The snakes include all of the ones mentioned above, according to their habitat type. RESULTS T h e relationship between the log o f the r a t e of water loss a n d the log o f the b o d y weight o f sidewinders is given in Fig. 2. T h e regression line was d e t e r m i n e d b y m e a n s o f least squares, a n d the exp o n e n t i a l e q u a t i o n t h a t c o r r e s p o n d s to the regression line is as follows: water loss (mg/g per hr) = 34"7 weight (g)-0.s3.
363
JE:
1.0 Q 0
3:~ 0"2 0.1
I0 Wt". of snokes,
50
IO0
g
Fig. 2. Rate of water loss as a function of weight in C. cerastes. B o t h flow r a t e a n d t e m p e r a t u r e significantly affect the rate o f w a t e r loss in snakes. T h e m e a n rate o f water loss for the four flow rates 50, 150, 300 a n d 600 c m 3 are 0-69, 0.68, 0.90 a n d 1.02 m g / g per h r respectively (Table 3). Except for the differences between 50 a n d 150's, there is a significant difference in rate o f water loss at different flow rates ( P < 0 . 0 1 in the F-test). W h i l e there is n o significant difference between rates of w a t e r loss between 20 a n d 30°C, there is a significant difference between 30 a n d 40°C ( P < 0.01 in a t-test). However, the m e a n rate o f water loss does n o t linearly follow the s a t u r a t i o n deficits at the three t e m p e r a t u r e s tested. While the water losses a t 20 a n d 30°C follow the s a t u r a t i o n deficits a t those temperatures, at 40°C, the rate o f water loss is d i s p r o p o r t i o n a t e l y high (Table l a , l b a n d Fig. 7). I n the C. occipitalis, w h o s e s h e d d i n g history was followed f r o m 6 days before s h e d d i n g until 6 days after shedding, the rate o f w a t e r loss goes f r o m 1"5
Table la. Rate of water loss as a function of temperature Snake No.
Weight (g)
Loss at 20°C (mg/g per hr)
Loss at 30°C (mg/g per hr)
Loss at 40°C (mg/g per hr)
1 2 3 4 5 6 7 8 9 10
15'4 26.2 27"8 27.9 30"6 35-7 39.7 43.5 82-8 93.3
0'26 0'46 1.20 0"35 0"81 0.75 0.85 1.86 0.79 0.26
1'60 0.99 1 "45 0.90 0-63 0.67 0.57 0.51 0'49 0'44
1-95 2-01 1"83 1 "56 1.86 2"38 2.43 1.44 1"33 2.43
Table lb. Saturation deficits at a relative humidity of 5% 20°C
30°C
40°C
0.70 m m
1.27 mm
2"21 mm
364
ALLEN C. COHEN
Table 2. Rate of water loss with vasodilator and with distilled water placebo in C. cerastes
Snake No.
Weight (g)
1 2 3 4 5 6 7 8
60 30 31 32 40 34 85 60
H~O loss (mg/g per hr) (without vasodilator)
H~O loss (mg/g per hr) (with vasodilator)
water loss of the two compartments in a snake before, during and after shedding (Fig.s and 4 5). The total water loss was high 2 days before shedding, and increased the day before shedding
~
0.63 1"10 0.93 1"61 1"33 0.72 1.73 1.22
0'84 2.28 0'96 3.35 1.67 0.99 2.26 1.66
.t~= 1"16 S = 0"395 P
