J. M. Z. Kamau

Transpiratory water loss and metabolism of beetles from arid areas in East Africa

Abstract 1. 1. Carabid beetles have rates of transpiratory water loss and metabolic rates which are higher than those of tenebrionid beetles. Within each family, dry habitat beetles have lower rates of water loss than beetles from mesic or hygric habitats, but no habitat-related difference was observed with regard to metabolic rates. 2. 2. When rates of transpiratory water loss of beetles of the two families are plotted as a function of metabolic rates, it appears that for dry habitat beetles, the metabolic rate is the single determinant of transpiratory water loss. 3. 3. This is interpreted as indicating that respiratory water loss is the dominating component of water loss in both carabids and tenebrionids in dry habitats, and that the difference between the families with respect to rates of water loss reflects the difference in metabolic rates. 4. 4. Carabid beetles have considerably higher extracellular concentrations of sodium than the tenebrionids. Seen in the light of the high energetic cost claimed to be involved in sodium transport, this observation is interpreted as indicating that the high rates of water loss and metabolism of the carabids are due to active extrusion of sodium from the cells of the beetles. 5. 5. The ecophysiological significance of these differences is discussed.

A comparative study of basal metabolism and thermoregulation in a folivorous (Colobus guereza) and an omnivorous (Cercopithecus mitis) primate species.

1. Abdominal temperatures (Tab) and oxygen consumption (VO2) were measured in two males each of colobus and Sykes monkeys. 2. Tab in both species had the same range (36 38.5 C), but there were marked differences in the daily rhythms. 3. Low ambient temperatures (Ta) had little effect on Tab; at Ta = 33.5 35.5 C. however, Tab rose quickly to above 40 C. 4. The thermoneutral zone (TNZ) extended from about 5 to 28 C in both species. 5. In the colobus monkeys the basal metabolic rate (BMR) was considerably lower than in the Sykes monkeys: 85% vs 113% of the value predicted from body mass.

O2-uptake, thermoregulation and heart rate in the springhare (Pedetes capensis)

Summary1.O2-consumption (O2), rectal temperature (Tre) and heart rate were measured in two adult springhares (♂,♀; body mass 2.2–2.4 kg) at ambient temperatures (Ta) from 6–35 °C. Abdominal temperature in the female and heart rate in both animals were determined by telemetry.2.AtTas from 23–28 °C rectal temperature in both animals ranged between 35.5–36.3 °C. This range was well maintained at lowTas. Exposure to highTas, however, led to a considerable rise of the rectal temperature (to above 39 °C atTa=35 °C).3.The lowest oxygen uptake (0.32–0.37 ml O2·g−1·h−1) was found between 23–33 °C. This is only 65–75% of the predicted value in similar sized mammals. Below 23 °C O2-consumption increased rapidly up to approximately 2,5 times (6–7 °C) the value in the thermoneutral zone (23–33 °C). AtTas above 33 °C the heat dissipating capacities of the springhares proved to be inadequate and consequentlyTre rose steadily.4.Basal heart rate (75–85 beats·min−1) was about 30% below the standard value for similar sized mammals. During exposure to cold the heart rate sometimes exceeded 200 beats·min−1.5.The measured parameters are discussed with special regard to the extent of the springhares adaptation to arid conditions. It is concluded that these rodents are physiologically adapted to fossorial habits rather than to life in desert environments and are thus restricted to semi-arid areas.

The relationship between rate of oxygen consumption, heart rate and thermal conductance of the dik-dik antelope (Rhynchotragus kirkii) at various ambient temperatures.

1. The extent of cardiovascular adjustments to heat and cold were investigated between ambient temperatures of 5 and 45 degrees C by measuring conductance and the rates of oxygen consumption and heart beats. 2. Minimum heart rate was observed at 25 degrees C (114 +/- 9 beats/min). In the heat at 45 degrees C heart rate was observed to increase only slightly (127 +/- 12 beats/min) but in the cold -5 degrees C heart rate nearly doubled that at 25 degrees C. 3. Thermal conductance was on average 0.031 mlO2 (g. hr. degrees C)-1 below 25 degrees C but increased by more than 20 times at 40 degrees C. 4. A positive correlation between heart rate and rate of oxygen consumption was demonstrated below 25 degrees C and the relation may be of practical use.

Metabolism and evaporative heat loss in the dik-dik antelope (Rhynchotragus kirki).

1. Under controlled conditions, the rate of oxygen consumption (VO2) respiratory frequency, evaporative water loss, heat balance, rectal (Trec) and surface temperatures were determined in the dik-dik antelopes at ambient temperatures (Ta) ranging from 1 to 44 degrees C. 2. The thermal neutral zone was found to be between 24 and 35 degrees C. 3. Respiratory frequency ranged between 27 and 630 breaths/min. 4. At a Ta of 44 degrees C, 95% of the heat produced by the dik-dik was lost via respiratory evaporation. Despite an increase in Trec, cutaneous evaporation did not increase. 5. During panting, VO2 increased in accordance with the expected Q10 effect, contrary to earlier findings. 6. Measurements of circadian rhythm [LD 12:12 (7-19) CT26 degrees C] in VO2 showed that the minimum VO2 (0.42 ml O2/g/hr) occurred at midnight while the maximum (0.78 ml O2/g/hr) occurred at midday. The 24 hr mean VO2 was 0.61 ml O2/g/hr. 7. These measurements suggest that in nature, determinants other than light may be responsible for triggering the variations observed in VO2.

Adaptations of carabid beetles to dry habitats in East Africa

The rates of water loss and humidity preference of carabids from dry tropical habitats have been studied and compared with corresponding data from temperate carabids and tropical tenebrionids. Within each group of beetles the rate of relative water loss decreases with increasing body size. Carabids from dry tropical areas have rates of water loss which are lower than those of temperate species, but considerably higher than the values for tenebrionids from dry tropical habitats. Small temperate carabids can stay in dry air for only a few hours, whereas large tropical tenebrionids may survive for weeks without becoming critically dehydrated. Given the choice between a dry and a humid atmosphere, well hydrated beetles of all groups will initially choose the dry atmosphere. Most temperate carabids will switch to humid atmosphere after a few hours and tropical carabids after 1–3 days, whereas tropical tenebrionids may remain in dry air for almost 3 weeks. The temperate carabids are very sensitive to dehydration and will shift to a humid atmosphere when dehydrated by only 2–5%. Tropical carabids and tenebrionids will shift first when they are dehydrated by 7–20% of their body weight in a hydrated state, implying that these beetles are considerably less sensitive to water loss than temperate carabids.

Thermoregulation and heat balance in the dik-dik antelope Rhynchotragus kirki: A field and laboratory study

Experiments were conducted in the field to study the physiological responses of dik-dik antelope to direct solar radiation and shade. The results were compared to those obtained in the laboratory. The rates of metabolic heat production when the animals were exposed either to the sun or the shade were identical. Dik-dik antelopes lost about 50% more heat evaporatively when exposed to the sun compared to the shade at an ambient temperature (Ta) of 28 degrees C or a Ta of 40 degrees C in a climatic chamber. Heat storage in the laboratory at Ta 40 degrees C or at Ta 28 degrees C in the shade accounted for between 30 and 35% of the total heat production. The corresponding value in the sun was 55%. The net rate of heat gain under the sun was four times greater than under shade at 28 degrees C or in the laboratory at 40 degrees C. Behavioural mechanisms for avoidance of high insolation must constitute important adaptations that the dik-dik uses to avoid dehydration and dependence on drinking water in their natural environment.

Temperature regulation and water balance of day-active Zophosis congesta beetles in East Africa

East African tenebrionid beetles of the species Zophosis congesta are active on sun-exposed surfaces in dry habitats during the hottest part of the day, when most other ani- mals have retreated to protected areas. They remain on the surface at ambient temperatures up to 650C which is 150C above their highest tolerated body temperature. The beetles appear to regulate their body temperature behaviourally. They frequently rest and cool in the shade, and after each cooling period they remain on the sun-exposed surface until the heat influx from the environment has caused the body temperature to rise close to the lethal level. They have relatively low rates of transpiratory water loss, and appear unable to depress their body tem- perature by means of evaporative heat loss. The rate of metabolic production of water amounts to only about 20% of the rate of transpiratory water loss. Thus, the beetles depend strongly on water intake from dietary sources. The advantage of this type of activity pattern is probably avoidance of predators.

The entrainment of breathing rhythm to stride frequency in the dik-dik antelope (Rhynchotragus kirki) with observations on the thermoregulatory consequences.

1. Three adult dik-dik antelopes with an average weight of 4.5 kg were used to investigate the rate of oxygen consumption (VO2) during exercise and the entrainment of respiratory rate with stride frequencies at running velocities between 2-11 km/hr. 2. The results of VO2 and the metabolic cost of horizontal locomotion were found to agree with what would be expected of an animal of this size. 3. Respiratory frequencies recorded during the most strenuous exercise were approximately 50% below the value observed when dik-diks are exposed to an ambient temperature (Ta) of 42 degrees C. 4. Respiratory evaporative heat loss was estimated to account for only 4% of the total heat production during exercise. 5. Respiratory frequencies were found to be entrained quite strongly to stride frequencies. The thermoregulatory consequences of this entrainment is discussed.

Changes in thyroxine, triiodothyronine and metabolic rate in the dik-dik antelope (Rhynchotragus kirkii): effects of temperature and dehydration

Summary1.Changes in plasma total thyroxine, triiodothyronine (T3) and metabolic rate were investigated in both hydrated and dehydrated dik-diks after prolonged exposure to ambient temperatures (Ta) of 25°C, 35°C and 15°C.2.AtTa of 25°C, metabolic rate, T3 and T4 were 2.58 W·kg−1, 56.3 ng ml−1 and 0.93 ng ml−1 for the hydrated group, and 1.95 W·kg−1, 70.0 ng ml−1 and 0.85 ng ml−1 for the dehydrated group, respectively.3.Exposure to 15°C increased metabolic rate and total hormonal concentrations in both groups.4.Following dehydration and exposure toTa of 35°C a significant decrease in metabolic rate occurred in the presence of a significant increase in both T3 and T4 concentrations.5.Levels of total plasma T3 and T4 alone are unlikely to be responsible for the decrease in metabolic rate observed in the dehydrated dik-dik antelopes.