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The effect of the rate of change of temperature on the resistance of Asellus aquaticus (L.) to high lethal temperatures
J. Thermal Biology. Vol. 3. pp. 121 to 123 © Pergamon Press Ltd 1978. Printed in Great Britain
0306-4565/78/0701-0121502.00/0
THE EFFECT OF THE RATE OF CHANGE OF T E M P E R A T U R E ON THE RESISTANCE OF ASELLUS AQUATICUS (L.) TO HIGH LETHAL TEMPERATURES T. M. SALIH* and J. N. R. GRAINGER Department of Zoology, Trinity College, Dublin 2, Ireland
(Received 29 July 1977: accepted 9 November, 1977) Abstract--1. The heat resistance of adult Asellus aquaticus increased with increasing acclimation temperature. 2. 20°C acclimated animals heated to 35°C at a rate of I°C per 4 min were less resistant at 35°C than similar individuals placed directly at 35°C. Similarly acclimated animals which were slowly heated to 30OC and then suddenly placed at 35°C showed increased heat acclimation in the more resistant individuals. 3. The results indicate that when 20°C acclimated individuals are subjected to a steadily rising temperature, further acclimation takes place (especially in the more resisIant individuals). When 30:C is reached a little further acclimation takes place in heat sensitive individuals. Above 30°C the animals are adversely affected and this becomes progressively more marked as 35°C is approached.
INTRODUCTION
RESULTS
THIS PAPER IS one of a series investigating the effect of temperature and other factors o n the heat resistance of Asellus aquaticus. The purpose of the present paper is to investigate the effect of rate of change of temperature on survival at high lethal temperatures. Most of the literature concerning heat resistance in poikilotherms is summarised in Precht et al. (1973). The commonest p h e n o m e n o n a m o n g poikilotherms is 'reasonable heat adaptation'; in other words, the heat resistance increases with increasing acclimation temperature.
The percentage survival of adult Asellus acclimated to 5 °, 10°, 20 ° and 25°C and tested at a series of high lethal temperatures for 10 min at each temperature is s h o w n in Fig. 1. The curves obtained are more or less reversed sigmoid in shape, and they shift to the right as the acclimation temperature is increased. This is the normal pattern (termed reasonable heat adaptation by Precht et al., 1973). Since the time of exposure to the high temperature can also be variable, a similar series of experiments were carried out in which animals acclimated to various constant temperatures were tested at 35°C for varying
MATERIALS AND METHODS ioo
Adult Asellus aquaticus (L.) were collected from the Grand Canal, Dublin. They were kept in the laboratory in plastic aquaria containing 10 litres of canal water, and a handful of vegetation from the natural habitat was given as food. The water in each aquarium was aerated continuously. For lower temperatures these tanks were placed in a cold room. The temperature of the water in the aquaria was checked daily and did not vary more than + 0.1°C from the desired temperature. All tanks were kept under conditions of 12 h light followed by 12 h dark, this being controlled by a time clock. At 25 ° and 20°C animals were acclimated for 2 weeks; at 15°, 10° and 5°C animals were acclimated for 3, 4 and 6 weeks respectively. Experiments were carried out throughout the year. Animals were tested in groups of 20 individuals. In all the experiments, the animals were allowed a recovery period of 24 h at 18°C after the test and then the number alive was counted. In the experiments shown in Figs. 3-5 the survival time was measured from the time when 35°C was reached.
80
_ 6o
ar
3-5 5~ 3-9 ET "C Fig. I. Percentage survival of Asell~ aquoticus acclimated to 5°, 10°, 15°, 20° and 25°C (A, B, C, D and E respectively) after being tested for l0 rain at various high lethal ternperatures (ET).
* Present address: Department of Biology, University of Mosul, Iraq. T.B.
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T.M. SALIH AND J. N. R. GRAINGER I00
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80
80
60
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60
40--
40
2C
20
20
40
so
-
ao
40
20
~5o
Fig. 2. Percentage survival of Asellus aquaticus acclimated to 5°, 10°, 15°, 20° and 25~C (A, B, C, D and E respectively) after being tested at an experimental lethal temperature of 35°C for different periods (min). periods of time. The results are shown in Fig. 2. It is evident here too, that the animals gain resistance to the lethal temperature as their acclimation temperature is increased. In the experiments already described the heat resistance was determined by testing the animals abruptly at the lethal temperature. In order to investigate the effect of rate of increase in temperature, three sets of experiments were carried out on 20°C adapted animals. (i) Gradual change from 20 ° to 35°C at the rate of I°C per 4 min. (ii) Gradual change from 20 ° to 35°C at a rate of I°C per min. (iii) Abrupt change 20 ° to 35°C. The results are shown in Fig. 3. These suggest that the animals are being adversely affected before 35°C is reached, since those which were slowly heated to
~oo
60
80
tOO
rain
rain
Fig.4. Percentage survival of 20°C acclimated animals tested at 35°C for different periods (min) after the temperature was raised from 20° t o 30°C at different rates: (A) abrupt change 20° to 35~C, (B) I°C per 4 min up to 30: and (C) I°C per 30 min up to 30=C. 35 '~ (Fig. 3A) all died in a shorter time (at all survival levels) at 35°C than those subjected to a sudden change (Fig. 3C) to 35°C. In veiw of these results a further series of experiments were carried out (using 20:C acclimated animals) in which the temperature was raised gradually to 30°C at two different rates (i) I°C per 4 min and (ii) I°C per 30min. The animals were then suddenly placed at 35°C and tested for different periods of time at 35°C along with 20°C acclimated animals tested abruptly at 35°C. The results are shown in Fig. 4. It appears that in the more resistant individuals some additional acclimation has taken place. A further series of experiments was carried out in which 20°C acclimated animals were placed suddenly at 30°C, kept there for 30 min, 1 h and 2 h respectively and then suddenly placed at 35°C for varying lengths of time. The results are shown in Fig. 5. The only difference between the groups are that the heat sensitive individuals become somewhat more sensitive.
IOO[~
'°f}, \ I
A~B
C
ET 3 5 " C
60
4O 40 20 20
min
20
Fig. 3. Percentage survival of 20°C acclimated a nima]s tested at 35°C for different periods (min) after the temperature was raised from 20°C to 35°G at different rates: (A) 1°C per 4rain, (B) t°G per one min and (C) abrupt change
20°
to
35°C.
40
60-
20
40
60
2o 40
60
rain Fig.5. Pereentage survivalof20°Cacclimated animals tested at 35°G for different periods (min) after being placed directly from 20°G to 30°G and kept at 30:G for (A) 30mirL
(B) one h and (C) two h.
Resistance of Asellus aquaticus (L.) to high lethal temperatures For instance, survival after 20 min at 35°C is 50, 65 and 85% following prior exposures of 30 rain, 1 h and 2 h at 30°C. DISCUSSION
As is seen from Figs. 1 and 2, Asellus aquaticus shows an increase in heat resistance as acclimation temperature increases. This type of acclimation has been found commonly among poikilotherms. Sprague (1963) reported that four species of crustacea including Asellus intermedius show this type of heat acclimation. Many examples have been given by Precht et al. (1973). It has been argued that bringing animals gradually to the lethal temperature enables an additional acclimation to take place which results in higher resistance to heat than those tested abruptly at the same lethal temperature. For instance Bovee (1949) working on the crustacean Hyallela azteca stated that while bringing H. azteca gradually to the lethal temperature, temporary acclimation took place, which allowed the animals to survive longer at the lethal temperature than those of a similar group placed directly at the same lethal temperature. The results in Fig. 3 seem to show that in Asellus this is not the case as the animals which had been subjected to a sudden change survived longer at 35°C than those of a similar group heated up to 35°C at two different rates. These results suggest that the animals were being adversely affected before 35°C was reached and that the damage inflicted on the animals during the course of raising the temperature, overcomes any temporary additional acclimation gained during the period. As is clear in Figs. 3A and B, animals heated up at the slow rate (I°C per 4 min) to 35°C were less resistant to 35°C than those heated up at the faster rate (I°C per min). So it would appear that the duration of exposure to the gradually increasing temperature affects survival at 35°C and suggests that more damage has taken place. This latter result is in total agreement with the findings of Rees (1941) who showed that the flatworm Monocelis fusca died at 37°C when heated up at a rate of l°C/day, but
123
when the rate was l°C/30min the animals survived up to 44°C, Evans (1948) gives similar results in three species of Patella. The results given in Fig. 4 show that there is a marked increase in survival at 35°C in the more resistant individuals when the temperature is slowly raised to 30°C, with perhaps even a slight decrease in survival of the more sensitive individuals. Such a differential effect has been described by Ushakov & Bugayeva (1975) and Bovee (1949). The results given in Fig. 5 show that a period of up to 2 h at 30°C has little effect on survival at 35°C. This together with the earlier results leads one to the conclusion that when 20°C acclimated Asellus are subjected to rising temperature further acclimation takes place up to about 30°C and this is most marked in the more resistant individuals. Above 30°C the animals ai'e adversely affected and this becomes progressively more intense as the temperature rises to 35°C. REFERENCES BOVEEE. C. (1949) Studies on the thermal death of Hyalella azteca. Biol. Bull. Wood's Hole, 96, 123-128. EVANSR. G. (1948). The lethal temperatures of some common British littoral molluscs.J. Anim. Ecol. 17, 165-173. PRECh"r H., CHRISTOPHERSENJ., HENSEL H. & LARCHER W. (1973). Temperature and Life. 779 pp. Springer-Verlag, Berlin. REES G. (1941) The resistance of the flatworm Monocelis fusca to changes in temperature and salinity under natural and experimental conditions. J. Anita. Ecol. 10, 121-145. SPRAGUEJ. B. (1963) Resistance of four freshwater crustaceans to lethal high temperatures and low oxygen. J. Fish. Res. Bd Can. 20, 387-415. USHAKOVB. P. & BUGAYEVAE. A. (1975). The environmental temperature and physiological polymorphism of populations I. The effect of heat acclimation on variability and survival of a population at elevated temperature. J. Therm. Biol. 1, 1-6.
Key Word Index--Asellus aquaticus; resistance acclimation; heat death; temperature change.
0306-4565/78/0701-0121502.00/0
THE EFFECT OF THE RATE OF CHANGE OF T E M P E R A T U R E ON THE RESISTANCE OF ASELLUS AQUATICUS (L.) TO HIGH LETHAL TEMPERATURES T. M. SALIH* and J. N. R. GRAINGER Department of Zoology, Trinity College, Dublin 2, Ireland
(Received 29 July 1977: accepted 9 November, 1977) Abstract--1. The heat resistance of adult Asellus aquaticus increased with increasing acclimation temperature. 2. 20°C acclimated animals heated to 35°C at a rate of I°C per 4 min were less resistant at 35°C than similar individuals placed directly at 35°C. Similarly acclimated animals which were slowly heated to 30OC and then suddenly placed at 35°C showed increased heat acclimation in the more resistant individuals. 3. The results indicate that when 20°C acclimated individuals are subjected to a steadily rising temperature, further acclimation takes place (especially in the more resisIant individuals). When 30:C is reached a little further acclimation takes place in heat sensitive individuals. Above 30°C the animals are adversely affected and this becomes progressively more marked as 35°C is approached.
INTRODUCTION
RESULTS
THIS PAPER IS one of a series investigating the effect of temperature and other factors o n the heat resistance of Asellus aquaticus. The purpose of the present paper is to investigate the effect of rate of change of temperature on survival at high lethal temperatures. Most of the literature concerning heat resistance in poikilotherms is summarised in Precht et al. (1973). The commonest p h e n o m e n o n a m o n g poikilotherms is 'reasonable heat adaptation'; in other words, the heat resistance increases with increasing acclimation temperature.
The percentage survival of adult Asellus acclimated to 5 °, 10°, 20 ° and 25°C and tested at a series of high lethal temperatures for 10 min at each temperature is s h o w n in Fig. 1. The curves obtained are more or less reversed sigmoid in shape, and they shift to the right as the acclimation temperature is increased. This is the normal pattern (termed reasonable heat adaptation by Precht et al., 1973). Since the time of exposure to the high temperature can also be variable, a similar series of experiments were carried out in which animals acclimated to various constant temperatures were tested at 35°C for varying
MATERIALS AND METHODS ioo
Adult Asellus aquaticus (L.) were collected from the Grand Canal, Dublin. They were kept in the laboratory in plastic aquaria containing 10 litres of canal water, and a handful of vegetation from the natural habitat was given as food. The water in each aquarium was aerated continuously. For lower temperatures these tanks were placed in a cold room. The temperature of the water in the aquaria was checked daily and did not vary more than + 0.1°C from the desired temperature. All tanks were kept under conditions of 12 h light followed by 12 h dark, this being controlled by a time clock. At 25 ° and 20°C animals were acclimated for 2 weeks; at 15°, 10° and 5°C animals were acclimated for 3, 4 and 6 weeks respectively. Experiments were carried out throughout the year. Animals were tested in groups of 20 individuals. In all the experiments, the animals were allowed a recovery period of 24 h at 18°C after the test and then the number alive was counted. In the experiments shown in Figs. 3-5 the survival time was measured from the time when 35°C was reached.
80
_ 6o
ar
3-5 5~ 3-9 ET "C Fig. I. Percentage survival of Asell~ aquoticus acclimated to 5°, 10°, 15°, 20° and 25°C (A, B, C, D and E respectively) after being tested for l0 rain at various high lethal ternperatures (ET).
* Present address: Department of Biology, University of Mosul, Iraq. T.B.
3/3--a
1
121
aa"
122
>
>
T.M. SALIH AND J. N. R. GRAINGER I00
lOG
80
80
60
- -
60
40--
40
2C
20
20
40
so
-
ao
40
20
~5o
Fig. 2. Percentage survival of Asellus aquaticus acclimated to 5°, 10°, 15°, 20° and 25~C (A, B, C, D and E respectively) after being tested at an experimental lethal temperature of 35°C for different periods (min). periods of time. The results are shown in Fig. 2. It is evident here too, that the animals gain resistance to the lethal temperature as their acclimation temperature is increased. In the experiments already described the heat resistance was determined by testing the animals abruptly at the lethal temperature. In order to investigate the effect of rate of increase in temperature, three sets of experiments were carried out on 20°C adapted animals. (i) Gradual change from 20 ° to 35°C at the rate of I°C per 4 min. (ii) Gradual change from 20 ° to 35°C at a rate of I°C per min. (iii) Abrupt change 20 ° to 35°C. The results are shown in Fig. 3. These suggest that the animals are being adversely affected before 35°C is reached, since those which were slowly heated to
~oo
60
80
tOO
rain
rain
Fig.4. Percentage survival of 20°C acclimated animals tested at 35°C for different periods (min) after the temperature was raised from 20° t o 30°C at different rates: (A) abrupt change 20° to 35~C, (B) I°C per 4 min up to 30: and (C) I°C per 30 min up to 30=C. 35 '~ (Fig. 3A) all died in a shorter time (at all survival levels) at 35°C than those subjected to a sudden change (Fig. 3C) to 35°C. In veiw of these results a further series of experiments were carried out (using 20:C acclimated animals) in which the temperature was raised gradually to 30°C at two different rates (i) I°C per 4 min and (ii) I°C per 30min. The animals were then suddenly placed at 35°C and tested for different periods of time at 35°C along with 20°C acclimated animals tested abruptly at 35°C. The results are shown in Fig. 4. It appears that in the more resistant individuals some additional acclimation has taken place. A further series of experiments was carried out in which 20°C acclimated animals were placed suddenly at 30°C, kept there for 30 min, 1 h and 2 h respectively and then suddenly placed at 35°C for varying lengths of time. The results are shown in Fig. 5. The only difference between the groups are that the heat sensitive individuals become somewhat more sensitive.
IOO[~
'°f}, \ I
A~B
C
ET 3 5 " C
60
4O 40 20 20
min
20
Fig. 3. Percentage survival of 20°C acclimated a nima]s tested at 35°C for different periods (min) after the temperature was raised from 20°C to 35°G at different rates: (A) 1°C per 4rain, (B) t°G per one min and (C) abrupt change
20°
to
35°C.
40
60-
20
40
60
2o 40
60
rain Fig.5. Pereentage survivalof20°Cacclimated animals tested at 35°G for different periods (min) after being placed directly from 20°G to 30°G and kept at 30:G for (A) 30mirL
(B) one h and (C) two h.
Resistance of Asellus aquaticus (L.) to high lethal temperatures For instance, survival after 20 min at 35°C is 50, 65 and 85% following prior exposures of 30 rain, 1 h and 2 h at 30°C. DISCUSSION
As is seen from Figs. 1 and 2, Asellus aquaticus shows an increase in heat resistance as acclimation temperature increases. This type of acclimation has been found commonly among poikilotherms. Sprague (1963) reported that four species of crustacea including Asellus intermedius show this type of heat acclimation. Many examples have been given by Precht et al. (1973). It has been argued that bringing animals gradually to the lethal temperature enables an additional acclimation to take place which results in higher resistance to heat than those tested abruptly at the same lethal temperature. For instance Bovee (1949) working on the crustacean Hyallela azteca stated that while bringing H. azteca gradually to the lethal temperature, temporary acclimation took place, which allowed the animals to survive longer at the lethal temperature than those of a similar group placed directly at the same lethal temperature. The results in Fig. 3 seem to show that in Asellus this is not the case as the animals which had been subjected to a sudden change survived longer at 35°C than those of a similar group heated up to 35°C at two different rates. These results suggest that the animals were being adversely affected before 35°C was reached and that the damage inflicted on the animals during the course of raising the temperature, overcomes any temporary additional acclimation gained during the period. As is clear in Figs. 3A and B, animals heated up at the slow rate (I°C per 4 min) to 35°C were less resistant to 35°C than those heated up at the faster rate (I°C per min). So it would appear that the duration of exposure to the gradually increasing temperature affects survival at 35°C and suggests that more damage has taken place. This latter result is in total agreement with the findings of Rees (1941) who showed that the flatworm Monocelis fusca died at 37°C when heated up at a rate of l°C/day, but
123
when the rate was l°C/30min the animals survived up to 44°C, Evans (1948) gives similar results in three species of Patella. The results given in Fig. 4 show that there is a marked increase in survival at 35°C in the more resistant individuals when the temperature is slowly raised to 30°C, with perhaps even a slight decrease in survival of the more sensitive individuals. Such a differential effect has been described by Ushakov & Bugayeva (1975) and Bovee (1949). The results given in Fig. 5 show that a period of up to 2 h at 30°C has little effect on survival at 35°C. This together with the earlier results leads one to the conclusion that when 20°C acclimated Asellus are subjected to rising temperature further acclimation takes place up to about 30°C and this is most marked in the more resistant individuals. Above 30°C the animals ai'e adversely affected and this becomes progressively more intense as the temperature rises to 35°C. REFERENCES BOVEEE. C. (1949) Studies on the thermal death of Hyalella azteca. Biol. Bull. Wood's Hole, 96, 123-128. EVANSR. G. (1948). The lethal temperatures of some common British littoral molluscs.J. Anim. Ecol. 17, 165-173. PRECh"r H., CHRISTOPHERSENJ., HENSEL H. & LARCHER W. (1973). Temperature and Life. 779 pp. Springer-Verlag, Berlin. REES G. (1941) The resistance of the flatworm Monocelis fusca to changes in temperature and salinity under natural and experimental conditions. J. Anita. Ecol. 10, 121-145. SPRAGUEJ. B. (1963) Resistance of four freshwater crustaceans to lethal high temperatures and low oxygen. J. Fish. Res. Bd Can. 20, 387-415. USHAKOVB. P. & BUGAYEVAE. A. (1975). The environmental temperature and physiological polymorphism of populations I. The effect of heat acclimation on variability and survival of a population at elevated temperature. J. Therm. Biol. 1, 1-6.
Key Word Index--Asellus aquaticus; resistance acclimation; heat death; temperature change.