Objectives
The student will be familiar with one area of environmental physiology - gas exchange - from HBZ213 Animal Physiology. The first part of this course examines another area; temperature. The energy relations of animals are covered in the second part of the course, which also examines the ecological consequences of thermoregulation. The course is thus designed to provide a link between animal physiology and areas of ecology such as foraging and life history.

Syllabus. Temperature and its physiological effects; Thermal classifications of animals; Processes of heat exchange; Heat balance equation; Exponential and logarithmic equations and Q₁₀; Critical and lethal temperatures; Tolerance of high and low temperature; Temperature adaptation and acclimation; Behavioural and physiological thermoregulation in ectotherms (reptiles and insects); Thermoregulation in endotherms (birds and mammals) in heat and cold; Physiology and ecology of heterothermy; The evolutionary approach to physiological ecology; Digestion in herbivores; Optimal foraging - a simple model; Optimizing digestion; Productive uses of energy - growth, storage and reproduction; Energy use in respiration; Calculation of energy budgets; Energetics of ectotherms and endotherms, and ecological consequences.

Course Assessment: Theory. Write an essay on "Behavioural thermoregulation in insects". To be handed in by 22 May 1995; no late submissions will be accepted. Give a specific reference for any factual statements made: a list of books consulted is inadequate.

1. Avery, R. A. (1979). Lizards - a study in thermoregulation. London: Arnold. (QL 666.L2 AVE)
   
2. Bartholomew, G. A. (1982). Physiological control of body temperature and thermoregulation. p 93-166 in Gans, C. & Pough, F. H. (Eds). Biology of the Reptilia, Volume 12 Physiology. London: Academic Press.
   
3. Begon, M., Harper, J. L. & Townsend, C. R. (1986). Ecology: individuals, populations and communities. Oxford: Blackwell. Parts of chapters 3, 9 and 14. (QH 541 BEG)
   
4. Bligh, J. (1973). Temperature regulation in mammals and other vertebrates. Amsterdam: North Holland. (QP 135 BLI)
   
5. Brafield, A. E. & Llewellyn, M. (1982). Animal energetics. Glasgow: Blackie. (QH 510 BRA)
   
6. Cossins, A. R. & Bowler, K. (1987). Temperature biology of animals. London: Chapman & Hall. (QP 135 COS)
   
7. Finch, V. A. (1972). Energy exchanges with the environment of two East African antelopes, the eland and the hartebeest. p 315-326 In Maloiy, G. M. (Ed) Comparative physiology of desert animals. Symp. Zool. Soc. Lond. Volume 31.
   
8. Grodzinski, W., Klekowski, R. Z. & Duncan, A. (1975). Methods for ecological bioenergetics. (IBP handbook 24). (QH 510 GRO)
   
9. Hardy, R. N. (1979). Temperature and Animal Life. Studies in Biology. London: Edward Arnold. (QP 82 HAR)
   
10. Heinrich, B. (1974). Thermoregulation in endothermic insects. Science 185, 747-756.
    
11. Hochachka, P. W. & Somero, G. N. (1984). Biochemical adaptation. Princeton, N.J.: Princeton University Press. Chapter 11. (QP 82 HOC)
    
12. Humphreys, W. F. (1979). Production and respiration in animal populations. J. Anim. Ecol. 48, 427-453.
    
13. Ingram, D. L. & Mount, L. E. (1975). Man and animals in hot environments. New York: Springer. (QP 82.2 H4 ING)
    
14. Krebs, J. R. & Davies, N. B. (Eds) (1984). Behavioural ecology: an evolutionary approach. Oxford: Blackwell. Chapter 4. (QL 751 BEH)
    
15. Petrusewicz, K & Macfadyen, A. (1970). Productivity of terrestrial animals: principles and methods. (IBP handbook 13). (QL 752 PET)
    
16. Pough, F. H. (1980). The advantages of ectothermy for tetrapods. Amer. Nat. 115, 91-112.
    
17. Somero, G. N. and Hochachka, P. W. (1976). Biochemical adaptations to temperature. p 125-190 In
18. Newell, R. C. Ed) Adaptation to environment. Butterworth.
    
19. Townsend, C. R. & Calow, P. (Eds). (1981). Physiological ecology: an evolutionary approach to resource use. Oxford: Blackwell. Chapters 1,2,4,5,8,9,10,12. (QH 366.2 TOW)
    
20. Whittow, G. C. (Ed.) (1971-3). Comparative physiology of thermoregulation. Academic Press. (QP 135 WHI)
    
21. Wiegert, R. G. (Ed.). (1976). Ecological energetics. (Benchmark papers Vol. 4). Stroudsburg, Pennsylvania: Dowden, Hutchinson & Ross. (QH 510 WIE)

Temperature affects many rate processes in an animal, but perhaps the most fundamental is the catalytic activity of its enzymes. In this practical, you will investige the effect of temperature on the velocity of an enzyme-catalysed reaction in an ectotherm and an endotherm. You will studying the hydrolysis of starch (which stains blue/black with iodine) to maltose and glucose (which do not give a colour change with iodine) in the presence of amylase.

Amylase will be obtained from the digestive glands of the snail Helix, and from human saliva. The first stage of the practical is to prepare extracts of digestive gland and saliva, and determine by iteration the quantities required to give a suitable rate of reaction at 30^OC. The second stage is to measure the rate of reaction at a range of temperatures, from 10-70^OC, and compare the thermal sensitivity of the enzyme from the ectotherm and the endotherm.

Your own body temperature should be familiar. Helix is a thermoconforming ectotherm and its body temperature will vary with environmental conditions. The range of temperatures accepted can be found using the thermal gradient. Snails will move away from areas which are too hot or too cold, but should not thermoregulate between these limits. This can be investigated by introducing a group of snails into the thermal gradient at the beginning of the practical, and noting their distribution at intervals throughout the afternoon.

Write-up
Express your results as relative rates of hydrolysis of starch for each extract at each temperature. Relate differences in the thermal sensitivity of amylases from Helix and Homo to their body temperatures.

Thermal acclimation is the process by which organisms are physiologically accustomed to higher or lower environmental temperatures by previous laboratory exposure. The equivalent process in the wild is called acclimatisation. Acclimation may affect many rate functions of the animal, such as metabolism or heart rate, and also tolerance of extreme temperatures. In this experiment you will examine acclimation for high temperature tolerance in the water flea, Daphnia (a small crustacean).

The measure of high temperature tolerance used is the lethal limit TL₅₀, i.e. the temperature at which half the animals die. This can be measured by interpolation from a plot of cumulative mortality against increasing temperature, in order to minimise the number of animals used in the experiment. The TL₅₀ depends on (a) the length of the acclimation period, and (b) the exposure time to the extreme temperature. This experiment investigates (a); it is important to reduce variation due to (b) by standardising the rate at which temperature is increased among different members of the class.

You are provided with Daphnia which have been acclimated to constant 10^OC or to constant 30^OC for either 1, 4, 8 or 16 days. A further group of Daphnia are from the wild, in other words 0 days of acclimation. Each student will investigate the effect of acclimation to 10^OC and 30^OC for one acclimation period, using 10 Daphnia in each of 10 test tubes of pond water, while temperature is gradually increased in a water bath.

Write-up
1. Construct curves of mortality on temperature for both acclimation temperatures for the acclimation period which you investigated.
2. Find the TL₅₀ for each acclimation temperature.
3. Compile data from the whole class to investigate the effect of the period of acclimation on the upper lethal temperature.

Lizards are ectotherms, and most of them thermoregulate behaviourally. Thermoregulatory behaviour should vary with environmental conditions; lizards should spend longer in the sun in cool weather. During these two practicals you will observe and quantify the behaviour of lizards in hot and cool conditions, and predict their body temperatures using information from models.

The common flat lizard Platysaurus intermedius is widely distributed in Zimbabwe. It lives on smooth outcrops of granite or sandstone, taking refuge under exfoliating rock flakes. These lizards often form dense colonies, and become rather tame at sites frequented by people. Their open habitat and ease of approach makes flat lizards ideal for behavioural work. Adult males are territorial; a territory usually contains one adult male and a few females and subadults. Adult males are brightly coloured; females and subadults are dark with three pale longitudinal stripes.

Two visits will be made to the whaleback granite rock at Domboshawa, one at midday in hot weather, and one in cool conditions (either early in the morning, or during cloudy weather). Behaviour will be quantified using the focal individual technique, i.e. watching one lizard intensively. The times of movements between sun and shade, or into and out of crevices, will be recorded, together with any basking or feeding behaviour or social interactions. Lizards should be observed for about 90 minutes in total under each set of conditions. It is best to choose an adult male, as different females and subadults in the area may cause confusion.

A Yellow Springs Instrument Co. telethermometer will be used to measure environmental temperatures and those of model lizards. The heating rates of models in the sun, and cooling rates in the shade, should be measured. The body temperatures of the observed lizards can then be predicted by combining these data with the recorded behaviour.

Write-up
On each day, calculate the proportion of the total time spent in sun and shade; does this vary with conditions ? Do the lengths of the periods in sun and/or shade change with the conditions ? Draw graphs showing the temperatures of models heating in the sun and cooling in the shade on both days. You can estimate the fluctuating body temperature of your lizard by assuming that it had a body temperature of 38^OC on its first voluntary (i.e. undisturbed) movement into the shade. Use body temperatures estimated at two minute intervals to calculate the mean and variance of body temperature in both hot and cool conditions. Discuss the probable importance of the different processes of heat exchange when the lizard is active and when it is in a crevice.

Foods which are difficult to digest must be retained in the gut for longer periods. To achieve the same rate of absorption of energy, an animal feeding on a low quality diet must therefore retain more food in the gut at any time, and so have a larger digestive system. In this practical you will investigate the relation between diet and gut morphology in a variety of fish. The species available should include Tilapia and Labeo (herbivores), Clarias (omnivore), and Hydrocynus (carnivore), depending on the catch available at the fisheries station on Lake Chivero the preceding day.

Each student will dissect one of each species of fish, after measuring its mass and standard length (i.e. the length excluding the caudal fin). The presence of feeding structures such as teeth, pharyngeal teeth and gill rakers should be recorded. The digestive tract will be removed entire, and drawn displayed in linear form. The parts of the gut should be identified and their lengths measured. The gut should then be divided into the major regions, and weighed before and after the contents have been removed. The contents and the gut wall will then be examined using a microscope.

Write-up
Present drawings of the digestive system of each species of fish, and a table of the dimensions (relative to body mass and length) and characteristics (internal surface, wall muscularity) of each region. Discuss in relation to the diets of the fish.

The absorption efficiency is simply the proportion of the food consumed (C) that is absorbed (A) across the gut wall: A/C. It may be measured for any component of the food, for example energy, protein, cellulose, or in this case, ash-free dry mass (AFDM), a measure of the organic content of the food. There are basically two ways to do this. The simpler method in principle is to measure the food absorbed from the gut as C-F, that is the difference between the food consumed and the faeces produced (F). This requires that the amounts of food consumed and faeces produced are measured accurately, and that the faeces can be related to a particular batch of ingested food.

The ratio method is simpler in practice. This depends on a marker in the food which passes unchanged into the faeces. Such markers may be part of the food, such as lignin, or a chemical added to the food, such as chromic oxide. The amount of AFDM per gram of marker is measured in both the food and the faeces. The absorption efficiency (as a proportion) of AFDM is then calculated as:

1-(g AFDM g marker^-1 in faeces / g AFDM g marker^-1 in food)

This method does not require that the food consumed or the faeces produced be measured, or related to each other. It does require that the concentration of the marker be measured accurately, and that the marked food be fed for long enough for the level in the faeces to reach a stable level. In this practical you will measure the level of chromic oxide, a non-toxic and indigestible green powder, in faeces from mice and in the food which they have been eating for several days.

Measuring the chromic oxide content involves weighing the sample, then burning it in a crucible to obtain the ash (which is also weighed, and used to calculate the AFDM). The ash contains the chromic oxide, which must be oxidised from chrome III (which is insoluble) to chrome VI (which forms dichromate ions in solution). This is achieved by fusing the ash with sodium peroxide in a crucible. When water is added the dichromate ions are dissolved, and any remaining peroxide decays to release ozone. The fusion also oxidises part of the metal crucible, to produce a suspension of rust particles which are removed by centrifuging. The optical density of the solution is then measured with a colorimeter, and compared with a calibration series produced from different masses of a standard having a known (15.99%) chromic oxide content.

Write-up
Calculate the g AFDM g marker^-1 in the food and faeces, and then the absorption efficiency of ash-free dry mass. Compare the result with other values of absorption efficiency of animals fed different diets. What was the likely composition of the food the mice had been eating ?