Temperature and the tropical tortoise Kinixys spekii: tests of thermoregulation

The mean body temperature (T_b) of active Kinixys spekii did not vary with sex or type of activity, or between hot days (maximum ambient temperature T_a > 29°C) and cool days. On hot days, T_b increased rapidly in the morning, and was constant during the late afternoon after midday inactivity. On cool days, T_b increased more slowly in the morning, and decreased during the afternoon. The slopes of T_b on T_a overall, and on hot days, were close to one, suggesting that tortoises were thermoconformers; the slope was greater than one on cool days. In a second test of thermoregulation, T_bs were compared with temperatures of null models (T_m). Tortoises were clearly thermoregulators compared to 'active-all-day' models. 'Activity-time' models had T_m more similar to T_b. Nevertheless, detailed comparison showed that tortoises were thermoregulating in the late morning, and that this was by choice of microenvironment, rather than ceasing activity when T_b reached a high level. These results are discussed in relation to E, a measure of the effectiveness of thermoregulation based on comparison of T_b and T_m with the set point range (T_set) selected in a thermal gradient. A set of three indices, which separate the variability of T_b, the difference between T_b and T_m, and between T_b and T_set, is suggested as a more generally applicable summary of thermoregulation in ectotherms.     

Body temperature and foraging behaviour of the Eurasian otter (Lutra lutra), in relation to water temperature

The effects of water temperature (T_w) on core body temperature (T_b) and foraging behaviour were studied in four free-ranging and one captive otter Lutra lutra in NE Scotland. The free-ranging animals were observed in and around two freshwater lochs, and measurements were made of T_w (2–16°C), T_b at the beginning and end of swimming bouts, lengths of swimming bouts, and dive times and intervals. T_b ranged from 35.9 to 40.4°C (mean 38.1°C). At the beginning of a period of activity and of a swimming bout. T_b rose significantly; during swimming it fell at a rate of 2.3°C/h, independent of T_w. Dive intervals were longer in colder waters, but this was probably due to other, seasonal environmental changes (perhaps water level). T_w had no significant effect on length of swimming bouts or on T_b. Although otters entered water with increased T_b, they exited when T_b was not significantly different from the mean resting T_b. The data suggest that otters maintain T_b irrespective of T_w, by increasing it before entering water, then either exiting at a given T_b, or at an earlier time determined by other environmental conditions.     

Thermoregulation, energy metabolism, and torpor in blossom-bats, Syconycteris australis (Megachiroptera)

Since little information is available on torpor in bats of the suborder Megachiroptera, we investigated whether the small (18 g) blossom-bat Syconycteris australis displays torpor in the laboratory. Bats entered daily torpor when food and water were withheld for one night and the air temperature (T_a) was below about 26°. Torpor began shortly after lights went on in the morning and lasted for a maximum of 12 hours. During torpor at T_a18°, metabolic rates fell to a minimum of about 15% of that in resting individuals at the same T_a, and to about 40% of the basal metabolic rate. The body temperature (T_b) during torpor was metabolically defended at or above about T_b 18°. Individuals that did not enter torpor in the morning reduced their T_b from about 34.5°, observed in resting individuals that had been fed during the previous night, to values between 30.2 and 32.8°, and the resting metabolic rate fell by about 25%. The ability to undergo short periods of torpor may explain why the distribution range of S. australis extends much further south than that of other small Australian megachiropteran bats.     

The utilization of patchy thermal microhabitats by the ectothermic insect predator, Cicindela sexguttata

Abstract. 1. Tiger beetles ( Cicindela ) of open habitats have served as model ectotherms in studies of the dependence of activity and habitat utilization on temperature. Potential departures from the cicindelid model were investigated in Cicindela sexguttata , a species inhabiting forests where thermal resources are patchy and ephemeral.
2. Body temperatures (T_b) were determined by inserting thermocouples into beetles immediately after observing specific behaviours in the field. Cicindela sexguttata elevated T_b by basking, foraged at a preferred T_b of 32.8 °C, and stilted, sun-faced, or sought shade when T_b exceeded 35 °C. Although these behaviours were typical of Cicindela , their set points were lower than those of species in more open habitats.
3. Illuminated substrates were utilized for basking and foraging. Beetles were dispersed throughout the forest floor in early spring, but became aggregated in light gaps when the canopy leafed out. Operative temperatures of thermal models indicated that beetles were unable to maintain the preferred T_b in shade and would not be able to maintain a preferred T_b in light gaps during the autumn, when adults are normally in diapause.
4. Beetles were confined to foraging in light gaps once the canopy was closed. Foraging rate and searching speed were independent of T_b, in contrast to other cicindelids. Adults rarely searched for prey, but ambushed small arthropods that alighted in the light gap. Dependence on patches of illumination as thermal resources may increase prey capture, intraspecific encounters, and risk of predation, and preclude foraging in the autumn when Cicindela species of open habitats are also active.     

Prolonged and daily torpor in the feathertail glider, Acrobates pygmaeus (Marsupialia: Acrobatidae)

Deep and prolonged torpor in marsupials is only known from the pygmy possums, family Burramyidae. We investigated the pattern of torpor in the feathertail glider Acrobates pygmaeus (Acrobatidae) to determine whether members of other marsupial families also possess the ability of remaining torpid for several days with body temperatures (T_b) approaching 0°C. At high air temperatures (T_a) of 15 and 20°C, A. pygmaeus usually exhibited daily torpor. Torpor bouts at T_a 12°C usually lasted for about 2˙5 days and at T_a 8°C up to 5˙5 days. The metabolic rate during torpor was reduced to about 1% of that in normothermic, resting individuals. The T_b during torpor was regulated at about 2°C when T_a fell below about 0˙8 °C. Arousal from torpor was rapid and the mean fastest rewarming rate was 0˙88°C/min. While A. pygmaeus exhibited deep and prolonged torpor, its pattern differed somewhat from deep hibernation. Acrobates pygmaeus did not show prehibernation fattening and a subsequent prolonged hibernation period and it appears that prolonged torpor is used only in emergency situations.     

Effects of Temperature and Leaf Weness on the Latent Period of Rbynchosporium Secalis (Leaf Blotch) on Leaves of Winter Barley

Effects of temperature and leaf wetness on the latent period of Rhynchosporium secaits (leaf blotch) on winter barley were examined in controlled environment experiments. At 100% relative humidity (continuous leaf wetness) the mean length of the latent period was c.24 days at 5°C, c. 19 days at 10°C, c. 16 days at l5°C and c. 13 days at 20°C. The mean number of days between the appearance of the first and the last lesions was c. 13 days at 5°C, c. 6 days at 10°C, c. 5 days at 15°C and c. 3 days at 20°C. A negative curvilinear regression of latent period on temperature accounted for 99% of the variance. The mean area of lesions per leaf was 38 mm² at 5°C, 46 mm² at 10°C, 24 mm² at 15°C and 24 mm² at 20°C. At 10°C, after a 48 h wet infection period, the interruption of leaf wetness for 5 or more days at any time during the next 15 days of the latent period did not decrease subsequent lesion area. However, absence of leaf wetness after these 15 days, at the onset of sporuiation, did decrease the area of lesions which developed.     

Seasonal metabolism of a small, arboreal monitor lizard, Varanus scalaris, in tropical Australia

The field metabolic rates (FMR) and water fluxes of Varanus scalaris were measured during the wet and dry seasons by the doubly-labelled water technique. Seasonal measurements of standard (night-time) metabolism (SMR) and resting (daytime) metabolism (RMR) were made in the laboratory at 18, 24, 30 and 36°C, and maximal oxygen consumption was measured at 36°C on a motorized treadmill. This population was active throughout the year. In the wet season, the mean FMR was 7.8 kJ day⁻¹ (128.0 kJkg⁻¹ day⁻¹; mean mass = 66.4 g, n = 13), and during the dry season the mean was 5.0 kJ day⁻¹ (67.6 kJ kg⁻¹ day⁻¹; mean mass = 77.4 g, n = 17). The mean water flux rates for these animals were 3.6 and 1.2 ml day⁻¹, respectively (60.4 and 16.6 ml kg⁻¹ day⁻¹). The seasonal means of FMR and water flux were significantly different by ANCOVA ( P < 0.0001). Measurements of SMR and RMR were significantly higher in the wet season (ANCOVA: P < 0.0001), but we found no difference in the maximal oxygen consumption between seasons (ANCOVA: P = 0.6). The maximal oxygen consumption of the lizards on the treadmill (2.9 ml min⁻¹= 1.8 ml g⁻¹ h⁻¹), mean mass = 97.4 g, n = 16) was 20 times that of the SMR at the same temperature during the dry season, and 11 times that of the SMR during the wet season. The seasonal differences in FMR were attributable to: changes in SMR (12.2%) and RMR (16.4%); differences in night-time body temperatures (11.3) and daytime body temperatures (16.4%); and activity (broadly defined to include locomotion, digestion, and reproductive costs (43.7%).     

Effect of temperature and dissolved oxygen concentration on the metabolic rate of the turbot and the relationship between metabolic scope and feeding demand

Turbot Scophthalmus maximus maximum oxygen uptake following feeding and exhaustive exercise increased from 107 mg O2 kg⁻¹ h⁻¹ at 6° C to c . 218 mg O2 kg⁻¹ h⁻¹ at 18° C, then increased slightly from 18 to 22° C to 224 mg O2 kg⁻¹ h⁻¹. Standard oxygen uptake increased exponentially as a function of temperature from 11 mg O2 kg ⁻¹ h⁻¹ at 6° C to 66 mg O2 kg⁻¹ h⁻¹ at 22° C. Gradual reduction in oxygen concentration to 87–90% air saturation at 6, 10. 18° C and <80% at 14 and 22° C limited the maximum metabolic rate but, supersaturation (>100% saturation) had little effect. Metabolic scope attained a maximum of 176 mg O₂ kg⁻¹ h⁻¹ at 18° C. Interpolation of the results showed that this value changed little between 16 and 20° C. It is suggested that this temperature range is optimal for turbot of c . 500 g. A comparison with a previous study on feeding demand in intensive farming conditions showed a linear relationship between appetite and metabolic scope. It is concluded that the ability of a fish to supply energy (including the energy requirement of digestive metabolism) above a standard level is a limiting factor in the manifestation of its feeding demand.     

Energy balance and temperature relations of Azorella compacta, a high-elevation cushion plant of the central Andes

The environmental relationships and ecophysiology of Azorella compacta, a giant cushion plant, were investigated in Parque Nacional Lauca, Chile (18°10'–18°25' S and 69°16' W, 4400 m asl). The diurnal temperature range can reach 42 °C on some days of the year. The surface temperature of A. compacta was 13 °C below that of the air temperature of −7 °C at dawn, but from midmorning to late afternoon, the plant surface temperature remained within a few degrees of the air temperature. Soil surface temperatures did not differ between north- and south-facing slopes, but a model showed an increase in radiation reception by north-facing slopes throughout most of the year. Gas exchange measurements of A. compacta measured at the onset of the wet season ranged from −0.6662 to 11.4 μmol·m⁻²·s⁻¹, and maximum stomatal conductance (Gs) was 410 mmol·m⁻²·s⁻¹. The estimated light compensation point was 89 μmol·m⁻²·s⁻¹ and estimated light saturation occurred at about 1280 μmol·m⁻²·s⁻¹. Diurnal water potential measurements for A. compacta ranged from −1.67 to −2.65 MPa. This is one of the first ecophysiological studies of a tropical alpine cushion plant.     

Physiological adaptation to aridity in the bushveld gerbil, Tatera leucogaster

Oxygen consumption, rectal temperature, thermal conductance, and evaporative water loss (EWL) were determined in resting captive Tatera leucogaster at ambient temperatures of between 14 and 38 °C. Basal metabolic rate (BMR) was 0.86 ml O₂. min⁻¹ (S.D.=0.15, n = 6), 45% of that expected for a rodent of the same body mass (106.2 g). Minimum wet thermal conductance was 0.21 ml O₂. min⁻¹, °C⁻¹ (S.D. = 0.01, n = 6), 113% of that expected for a mammal of the same body mass. Wet thermal conductance increased exponentially at temperatures greater than 32 °C. Mean rectal temperature was 35.3 °C below 35 °C (S.D. = 0.5, n = 6) and 39.3 (S.D. = 0.6, n = 5) at 38 °C. Mean resting EWL was 1.43 mg. min⁻¹ (S.D. = 0.14, n = 6) between 15 and 32 °C and increased dramatically at temperatures above 32 °C. Combining our data with data from the literature suggests that gerbils (Family Muridae; subfamily Gerbillinae) have, on average, low BMR and average minimum wet thermal conductance when compared to other rodents and other mammals, respectively, of the same body mass. Similarly, rodents (including gerbils) from arid habitats have, on average, lower rates of EWL when at rest below thermoneutrality than do other rodents of the same body mass from mesic habitats.     

Heritability of energetics in a wild mammal,the leaf-eared mouse (Phyllotis darwini)

Abstract.— As a first examination of the additive genetic variance of thermoregulatory traits in a natural population of endotherms, we studied the quantitative genetics of key physiological ecology traits in the leaf-eared mouse, Phyllotis darwini. We measured basal metabolic rate (BMR), nonshivering thermogenesis (NST), maximum metabolic rate for thermoregulation (MMR), thermal conductance (C_T), body temperature (T_b), and factorial aerobic scope (FAS) in individuals acclimated to cold and warm conditions. For comparability with previous studies, we included the following morphological traits: foot length (F_L), total length (T_L), body mass (mb, at birth, sexual maturity, 6 months, and 8 months). Variance components were obtained from two different procedures: the expected variance component in an ANOVA Type III sum of squares and an animal model approach using restricted maximum likelihood. Results suggest the presence of additive genetic variance in F_L (h²= 0.47, P = 0.045), C_T of cold-acclimated animals (h²= 0.66, P = 0.041), and night body temperature, measured in cold-acclimated animals (h²= 0.68, P = 0.080). Heritabilities of m_b were near zero at all ages, but maternal effects and common environment effects were high and significant. We found no evidence of additive genetic variance in BMR, NST, MMR, or FAS (i.e., estimates were not significantly different from zero for all tests). Our results are in general agreement with previous studies of mammals that reported low heritability for: (1) BMR and MMR; (2) daytime body temperature; and (3) body mass for wild, but not laboratory or domestic, populations.     

The effects of temperature, body mass and feeding on metabolic rate in the tsetse fly Glossina morsitans centralis

Abstract.  Metabolic rate variation with temperature, body mass, gender and feeding status is documented for Glossina morsitans centralis . Metabolic rate [mean ± SE; VCO₂= 19.78 ± 3.11 μL CO₂ h⁻¹ in males (mean mass = 22.72 ± 1.41 mg) and 27.34 ± 3.86 μL CO₂ h⁻¹ in females (mean mass = 29.28 ± 1.96 mg) at 24 °C in fasted individuals] is strongly influenced by temperature, body mass and feeding status, but not by gender once the effects of body mass have been accounted for. A significant interaction between gender and feeding status is seen, similar to patterns of metabolic rate variation documented in Glossina morsitans morsitans . Synthesis of metabolic rate-temperature relationships in G. m. centralis , G. m. morsitans and Glossina pallidipes indicate that biting frequency as well as mortality risks associated with foraging will probably increase with temperature as a consequence of increasing metabolic demands, although there is little evidence for variation among species at present. Furthermore, metabolic rate–body mass relationships appear to be similarly invariant among these species. These data provide important physiological information for bottom-up modelling of tsetse fly population dynamics.     

Thermoregulation and metabolism in the Cape golden mole (Insectivora: Chrysochloris asiatica)

The Cape golden mole, Chrysochloris asiatica is an insectivore which excavates superficial foraging burrows as it searches for its food. It has a mean (±S.D.) resting metabolic rate (RMR) when newly captured of 1–17±0.17 cm³ O₂g^-1 h^-1 ( n = 14), within the thermoneutral zone (TNZ) of 30–32°C.
The body temperature (Tb) of the mole in the TNZ is low 32.9 ± 0.36 ( n = 14) and remains stable at ambient temperatures (Tas) from 28–32°C. Above 32°C (range 34–37°C), Tb increases albeit slightly to 36 ± 1.75°C ( n = 14). The conductance is high 0.27 ± 006cm³ O₂g^-1 h^-l°C^-1 ( n = 46) at the lower limit of thermoneutrality. The mean RMR at 9°C (the lowest Ta tested) was 4.82±11 cm³ O₂g^-1h^-1, which is 4.1 times that of the RMR in the TNZ.
At an ambient temperature of 9°C, three of the golden moles entered a state of torpor where the RMR was reduced from 5.9±0.56 to 10 1.0 ± 0.69cm³O₂g^-1h^-1.     

The interaction of temperature and fish size on growth of juvenile halibut

Growth rate of individually tagged juvenile halibut was influenced significantly by the interaction of temperature and fish size. The results suggest an optimum temperature for growth of juvenile halibut in the size range 5–70 g between 12 and 15° C. Overall growth rate was highest at 13° C (1·62% day ⁻¹). At c. 5 g at the beginning of the experiment, fish at 16° C had the highest growth rate (3·2% day ⁻¹), but reduced this rate as they grew bigger. At 9 and 11°p C, growth rates were equal or only slightly lower during the later stages of the experiment, while the fish at 6° C showed significantly lower overall growth rate (0·87% day⁻¹). Optimal temperature for growth decreased rapidly with increasing size, indicating an ontogenetic reduction in optimum temperature for growth. Moreover, a more flattened parabolic regression curve between growth and temperature as size increased indicated reduced temperature dependence with size. Although individual growth rates varied significantly at all times within the experimental temperatures, significant size rank correlations were maintained during the experiment. This indicated an early establishment of a stable size hierarchy within the fish groups. Haematocrit was highest at the highest temperature while Na⁺/K⁺-ATPase activity was inversely related to temperature. There was no difference in plasma Na⁺, Cl⁻ and K⁺ concentrations among the temperature groups.     

Early development and growth of the laboratory reared north-east Atlantic mackerel Scomber scombrus L.

The early development, growth and morphological changes of mackerel Scomber scombrus were investigated at different incubation temperatures (8, 10, 13, 15 and 18° C). Details on the early life history are illustrated with special reference to morphological transformations. Culture techniques to rear larval mackerel stages are described using laboratory cultured foods. Artificially fertilized eggs were hatched after 80·6 h at 18·4° C and 256·8 h at 8·7° C. The standard length ( L _S) of the individuals at first feeding was 4·71 ± 0·18 mm. Four mortality critical periods and cannibalistic behaviour were identified. A maximum average larval size of 37·5 ± 4·41 mm L _S was attained 30 days post-hatch (dph) at 18·4° C. Development and growth were affected significantly by temperature during both endogenous and exogenous feeding periods. Larvae grew more rapidly at high, than at low temperatures. Daily specific growth rate (in mass) ranged from 2·4% at 10·6° C to 16·9% at 18·4° C. Likewise, average growth rate (in length) ranged from 0·05 mm day⁻¹ at 8·4° C to 0·37 mm day⁻¹ at 18·4° C. The allometric relationship of L _S, with several body measurements was not affected by temperature. Comparison with larvae collected in the Bay of Biscay did not show any significant difference in the dry mass and L _S relationship; conversely, the growth rate in length differed significantly between both laboratory and field conditions. The trends observed in the laboratory are described in relation to some aspects of the year-class strength regulation.     

Shifts in the optimal temperature for nocturnal CO2 uptake caused by changes in growth temperature for cacti and agaves

When the day/night air temperatures were raised from 10°C/10°C to 30°C/30°C, the optimal tempearture for nocturnal CO² uptake by six species of cacti and three species of agave shifted from an average of 12°C to an average of 20°C. The maximum rate of CO² uptake was higher for Agave americana at the higher ambient temperature, lower for A. deserti , and much lower for A. utahensis , consistent with the relative mean temperatures of their native habitats. For the cactus Coryphantha vivipara , which had the greatest temperature shift observed (13°C), the halftime was 8 days for the upward shift and 4 days for the downward shift. The halftimes for the comparable shifts averaged 1.6 days for three other species of cacti and less than 1 day for two agave species. The shifts in the optimal temperature for nocturnal CO² uptake were in response to changes in nighttime temperature, at least for C. vivipara , and reflected temperature responses of both the stomates and the chlorenchyma.     

Modulation of mechanosensitive calcium-selective cation channels by temperature

Gating of associations of mechanosensitive Ca²⁺-selective cation co-channels in the plasmalemma of onion epidermis has a strong and unusual temperature dependence. Tension-dependent activity rises steeply as temperature is lowered from 25°C to about 6°C, but drops to a low level at about 5°C. Under the conditions tested (with Mg²⁺ and K⁺ at the cytosolic face of outside-out membrane patches), promotion results both from more bursting at all observed linkage levels and from longer duration of bursts of co-channels linked as quadruplets and quintuplets. Co-channel conductance decreases linearly, but only modestly, with declining temperature. It is proposed that these and related mechanosensitive channels may participate in a variety of responses to temperature, including thermonasty, thermotropism, hydrotropism, and both cold damage and cold acclimation.     

Effect of air temperature upon mean water temperature in streams in the north Pennines and English Lake District

SUMMARY. Water temperatures from six north Pennine streams (approximate mean annual discharges 0.04–1.5 m³ s^-1) and two Lake District streams (mean annual discharges c. 0.04 m³ s^-1) were used to examine the possibility of predicting 5-day or 7-day mean water temperatures from standard meteorological/hydrological data collected at north Pennine stations. The relationship between mean air temperature (X) and mean water temperature (Y) was approximately linear, except in the Pennine streams for periods when mean air temperature was below 0°C. The calculated regressions of mean water temperature upon mean air temperature accounted for 86–96% of the variance of water temperature even when the air and water temperatures were measured at stations some 50 km apart. A negligible improvement was obtained by the use of multiple regressions incorporating rainfall or stream discharge from a nearby metering weir. Predicted water temperatures were rather lower than observed values during the first half of the calendar year and rather higher during the second half, but these seasonal differences could not be adequately quantified for practical application.     

Daily ration estimates for yellowfin sole, Limanda aspera (Pallas), based on laboratory consumption and growth

Several estimates of minimal energy requirements for yellowfin sole were made. Energy expenditures of 1.6, 4.1 and 8.3 cal g⁻¹ day⁻¹ were obtained from starvation weight loss, standard metabolism and maintenance ration procedures, respectively, at 6° C. The temperature effect on energy requirement was reflected in the Q ₁₀ values for starvation weight loss (2.0), standard metabolism (6.3) and maintenance ration (6.5).
Both energy intake and weight of food were linearly related to, and good predictors of, laboratory growth. These relationships were used to estimate the food and energy intake necessary for yellowfin sole to achieve a year's growth in the natural environment. Based on a caloric value of 2.0 kcal g⁻¹ of food (herring fillets), yellowfin would require 0.35 to 0.39% body weight day⁻¹ at 3° C to achieve the mean growth rate exhibited in the Bering Sea. To achieve Gulf of Alaska growth rates at 5 to 6° C, yellowfin would require 0.63% body weight day⁻¹. Based on a caloric value of 0.57 kcal g⁻¹ of food (chopped octopus), yellowfin would require 0.83% body weight per day to achieve the Gulf of Alaska growth rate (6° C). These requirements based on the calorific value of herring fillets, which are three to five times higher than previous estimates of daily ration in this species, are probably conservative estimates since many of their prey species have a lower energy content.     

Effects of temperature and [His7]-corazonin on the body darkening in Locusta migratoria

Abstract.  [His⁷]-corazonin is a neuropeptide that induces dark coloration in locusts. This study examined the effect of temperature on body colour in the migratory locust, Locusta migratoria . L. Injection of a low dose (1 pmol) of [His⁷]-corazonin caused albino nymphs to develop dark coloration at 25–34 °C, but little darkening occurred at 38 and 42 °C. However, injection of a high dose (10 pmol) induced darkening even at these high temperatures. Transfer of nymphs injected with 1 pmol of [His⁷]-corazonin from 30 to 42 °C, and vice versa, indicated that temperature influenced darkening at any time after injection. Measurements of the luminance of the pronotum were made using commercially available computer software to follow continuous changes in darkening of the body. The body colour of nymphs injected with [His⁷]-corazonin was reddish-brown at 25 °C, blackish at 30 and 34 °C, and greyish or whitish at 38 and 42 °C. High temperature also suppressed darkening in a normal (pigmented) strain. Most nymphs transferred from 30 to 42 °C during the first three stadia developed a light colour in the fifth stadium without the striking black patterns that are typically manifested in gregarious nymphs at lower temperatures. Such individuals developed black patterns in the fifth stadium when injected with [His⁷]-corazonin at a mid stage of the previous stadium. These results indicate that high temperature may induce light body coloration by suppressing the release of [His⁷]-corazonin in normal locusts.