Thermal parameters of four species of Gerbillurus

1. 1.Thermal parameter of the four Gerbillurus species measured in the laboratory were examined in relation to their micro-environments in a xeric habitat.

2. 2.Basal metabolic rates (BMR) were lower than predicted, while thermoneutral zonds (TNZ) were narrow and exceeded burrow temperatures.

3. 3.Body temperatures (T_b) were regulated over a range of ambient temperatures (T_a). Evaporative water loss was used as a short-term cooling mechanism to reduce hyperthermia above the TNZ.

4. 4.Conductance was low below the TNZ to reduce heat loss.

5. 5.Adaptation to low temperatures is important for gerbils when active at night.

6. 6.The adaptive significance of the thermal biology of Gerbillurus is discussed in relation to phylogeny, distribution, food availability and nocturnal activity.

Development of thermoregulation in Hawaiian brown noddies (Anous stolidus pileatus)

1. 1.|Oxygen consumption ( ) and body temperture (T_b) of Hawaiian brown noddies (Anous stolidus pileatus [Aves: Laridae]) during late incubation and in the first 24 h after hatching were measured at ambient temperatures (T_a) between 28 and 38°C and between 15 and 43°C, respectively. Evaporative cooling by hatchings at T_a of 36–43°C was also measured.

2. 2.|Throughout the late incubation stages studied, and T_b both varied directly with T_a in an ectothermic pattern.

3. 3.|The hatchlings successfully regulated T_b at T_a between ca. 29 and 43°C.

4. 4.|The functional basis of the abrupt increase in thermoregulatory capacity with hatching is discussed.

Shifts in thermoregulatory patterns with pregnancy in the poikilothermic mammal—The naked mole-rat (Heterocephalus glaber)

1. 1. The naked mole-rat (Heterocephalus glaber) is a poikilothermic mammal. During gestation metabolic shifts that differ from both mammalian and reptilian thermoregulatory patterns occurred.

2. 2. Body temperature was directly dependent on ambient temperature. At low ambient temperatures the temperature differential (T_b − T_a) was approximately 3°C, whereas at higher ambient temperatures the temperature differential diminished.

3. 3. In early pregnancy (prior to week 3) oxygen consumption at low ambient temperatures was greater than that of non-reproductive animals. A maximal metabolic rate (3.2 ± 1.0 ml O₂ . g⁻¹ . h⁻¹) occurred at an ambient temperature of 27°C. Thereafter the endothermic pattern of metabolism with increasing ambient temperatures was evident. Oxygen consumption decreased with increasing ambient temperature to minimal rates of 1.2 ± 0.1 ml O₂ . g⁻¹ . h⁻¹ over the ambient temperature range of 31–34°C.

4. 4. Oxygen consumption in late pregnancy (1.8 ± 0.1 ml O₂ . g⁻¹ . h⁻¹) was not correlated with ambient temperature over the entire ambient temperature range measured (24–36°C).

5. 5. Differences in thermoregulation in early and late pregnancy may be attributed to different rates of heat loss as a consequence of (a) changes in surface area and body mass or (b) vascular changes. Furthermore the thermoregulatory changes in late pregnancy may indicate that maximal overall metabolic capacity had been reached, for peak resting metabolism (expressed per animal rather than per gram body mass) in early pregnancy was similar to observed metabolism in late pregnancy.

6. 6. The dissociation of metabolism from both ambient temperature and body temperature in late pregnancy could confer an energetic advantage to this arid dwelling underground inhabitant; for it may enable the breeding female to partition a greater portion of available energy into reproduction.

Development of autonomic and behavioural thermoregulation in turkeys (Meleagris gallopavo)

1. 1.|Heat production (HP) and body temperature (T_b) measurements were conducted at ambient temperatures (T_a) between 10 and 40°C. In addition preference temperatures (PT) were determined in a temperature channel and T_b was measured at preferred T_a

2. 2.|The influence of age on T_b at constant, as well as at PT, was proved. Increasing age was accompanied by an elevation of T_b whereas HP remained constant in the mid-range of T_a

3. 3.|The lower T_b in the first days of life is suggested to result from a lower thermoregulatory set point during the postnatal period.

4. 4.|The PT were different for the observed types of behaviour. The PT at rest was higher than the PT during locomotion, food intake and drinking.

Metabolism and thermoregulation in Maximowiczi's voles (Microtus maximowiczii) and Djungarian hamsters (Phodopus campbelli)

1 Metabolic rates (Vo₂), body temperature (T_b), and thermal conductance (C) were first determined in newly captured Maximowiczi's voles (Microtus maximowiczii) and Djungarian hamsters (Phodopus campbelli) from the Inner Mongolian grasslands at a temperature range from 5 to 35 °C.

2 The thermal neutral zone (TNZ) was between 25 and 32.5 °C for Maximowiczi's voles and between 25 and 30 °C for Djungarian hamsters. Mean T_b was 37.0±0.1 °C for voles and 36.2±0.1 °C for hamsters. Minimum thermal conductance was 0.172±0.004 ml O₂/g h °C for voles and 0.148±0.003 ml O₂/g h °C for hamsters.

3 The mean resting metabolic rate within TNZ was 2.21±0.05 ml O₂/g h in voles and 2.01±0.07 ml O₂/g h in hamsters. Nonshivering thermogenesis was 5.36±0.30 ml O₂/g h for voles and 6.30±0.18 ml O₂/g h for hamsters.

4 All these thermal physiological properties are adaptive for each species and are shaped by both macroenvironmental and microenvironmental conditions, food habits, phylogeny and other factors.

Thermal responses of the fresh water turtle Mauremys caspica to step-function changes in the ambient temperature

1. 1.|The turtle Mauremys caspica cools significantly faster than it heats in air. The heating/cooling ratio is 0.49.

2. 2.|The variation of body temperature in relation to time-course in response to a step-function change of environmental temperature, fitted to a second-order system improves that of a first-order system.

3. 3.|The gradient between ambient temperature (T_a) and equilibrium body temperature (T_b) increases significantly and progressively when ambient temperature rises over 25°C.

4. 4.|At 40°C thermoregulatory hyperventilation was detected, implying an increase in air convection requirement (ventilation relative to O₂ consumption, ).

Body temperature in arboreal and nonarboreal anuran amphibians: Differential effects of a small change in water vapor density

1. 1.|Body temperatures (T_b) and contaneous evaporative water loss rates (CWL) were measured in tree frogs (Hyla cinerea) and toads (Bufo valliceps) exposed to cyclical ramp changes in water vapor density (WVD) between 7.5 and 9.8 gm⁻³ (1 cycle h⁻¹ at an air temperature of 27.0°C.

2. 2.|CWL was 3.3 times greater in toads than in tree frogs.

3. 3.|T_b in toads cycled directly with WVd; WVD accounted for 98% of the variation in toad T_b.

4. 4.|T_b in tree frogs was independent of WVD, probably due to changes in skin resistance to water loss.

Behavioural and autonomic thermoregulation in hamsters during microwave-induced heat exposure

1. 1.|Preferred ambient temperature (T_a) and ventilatory frequency were measured in free-moving hamsters exposed to 2450 MHz microwaves. A waveguide exposure system which permits continuous monitoring of the absorbed heat load accrued from microwave exposure was imposed with a longitudinal temperature gradient which allowed hamsters to select their preferred T_a. Ventillatory frequency was monitored remotely by analysing the rhythmic shifts in unabsorbed microwave energy passing down the waveguide.

2. 2.|Without microwave exposure hamsters selected an average T_a of 30.2°C. This preferred T_a did not change until the rate of heat absorption (SAR) from microwave exposure exceeded approx. 2 W kg⁻¹. In a separate experiment, a SAR of 2.0 W kg⁻¹ at a T_a of 30°C was shown to promote an average 0.5°C increase in colonic temperature. Hamsters maintained their ventilatory frequency at baseline levels by selecting a cooler T_a during microwave exposure. In contrast, hamsters maintained at a T_a of 30°C (without a temperature gradient) underwent a sharp increase in ventilatory frequency compared to animals allowed to select their own T_a.

3. 3.|These data support previous studies suggesting that during thermal stress behavioural thermoregulation (i.e. preferred T_a) takes prescedence over autonomic thermoregulation (i.e. ventilatory frequency). It is apparent that selecting a cooler T_a is a more efficient and/or effective than autonomic thermoregulation for dissipating a heat load accrued from microwave exposure.

Perinatal epigenetic temperature adaptation in avian species: comparison of turkey and Muscovy duck

1. Heat production (HP) and body core temperature (CT) where measured in 1- to 10-day old Muscovy ducklings and turkey chick, incubated during the last week before hatching at a lower (34.5 °C, LT-group) or at higher (38.5 °C, HT-group), than the normal temperature of 37.5 °C (control C-group).

2. In Muscovy ducklings, on the 1st day post-hatching HP was affected by exposure to low T_a of 10 °C T_a 28.2±3.9 W kg⁻¹ in the LT-group vs. 18.1±2.4 W kg⁻¹ in normal controls. On the same day, CT was higher (39.5±1.1 °C) in the HT- than in the CT-group (37.5±2.9 °C).

3. In turkeys, the relationships between T_a and HP could be described by parabola-like functions. Apart from the first day of life, the HP of the LT-group and the HT-group was higher than of the CT-group.

4. The low prenatal temperature of incubation resulted in a decrease of the preferred temperature in the LH-group and in an increase in the HT-group.

5. It is concluded that changes in incubation temperature at the end of embryonic development may induce an epigenetic temperature adaptation, which results in a long-lasting cold- and warm-adaptation in ducks but not in turkeys.

Behavioural and autonomic thermoregulation in lean and genetically obese (ob/ob) mice

1. 1.|The capacity for behavioural thermoregulation has been assessed in lean and genetically obese (ob/ob) mice, using operant conditioning.

2. 2.|After 30 min at an initial air temperature (T_a) of 0°C, total thermal reinforcements and T_a were greater in ob/ob than lean mice; deep body temperature increased in both genotypes. Without a heater, body temperature in the ob/ob fell markedly in the cold.

3. 3.|Behavioural thermoregulation also depended on food intake and test temperature. i]4.|The capacity for behavioural thermoregulation is thus unimpaired in the ob/ob mouse, unlike that for autonomic thermoregulation, suggesting separate sets of central controls for the two thermoregulatory systems.

Polar bear thermoregulation: Effect of oil on the insulative properties of fur

1. 1.|Oil caused a substantial decrease in the insulative value of polar bear (Ursus maritimus) pelts measured in vitro.

2. 2.|Following oil contamination the calm air heat transfer coefficient increased by a factor of 2 to 5: the wind coefficient averaged 290% greater and the solar utilization increased by 55%.

3. 3.|Conductance through oil-covered furs remained high at winter temperatures (T_a = 0.6°C) but decreased with time at summer temperatures (T_a = 24.7°C).

4. 4.|The most viscous of the three oils tested had a more consistently negative effect on insulation.

Temperature dependence of the germination of tomato seeds

1. 1.|The germination of tomato “C38” seeds exposed to periodical white incandescent light occurs from 6.0° ± 0.2°C to 37.5° ± 0.2°C, being rate-limited for 10.3° T 25.9°C, and elsewhere limited by the germination capacity.

2. 2.|Rate averages are linearly T-dependent outside their optimum range (25.9° T 29.5°C) and rate variances are typically heterogeneous.

3. 3.|The smooth curvilinear Arrhenius plot indicates that diffusion processes cannot be rate-limiting outside the interval 25.9° T 29.5°C, whereas phase transitions and (or) transconformation of proteins may limit the rate above 34.9°C and, by opposite effects, below 15.3°C.

4. 4.|The thermal communication between the environment and the germinating seed proceeds by a temperature signal which is quenched by random thermal noise at T 11.2°C and at T 34.0°C.

Skin temperatures, thermosensory and pleasantness estimates in case of heterogeneity in the thermal environment

1. 1. Seven thermal conditions were imposed on male sitting subjects (slightly clothed: 0.6 clo).

2. 2. A thermal mannikin was also used to determine the exact operative temperature, T₀.

3. 3. Conditions were: uniform (UN: all parameters at 24.5°C, air velocity at 0.15 ms⁻¹), heated ceiling (HC at 45°C), heated floor (HF at 34°C), cold floor (CF at 14°C), two conditions of one cold wall at 6°C (CW1 and CW2 respectively with and without air temperature compensation) and increased air velocity (AV at 0.4 ms⁻¹).

4. 4. Local skin temperatures and answers to questionnaires were obtained.

5. 5. Skin temperature variations were affected by conditions and slight T₀ changes.

6. 6. Comfort judgments were fairly well related to T₀, especially when expressed as differences between actual non-uniform environment and the uniform one.

7. 7. It is concluded that, in case of non-uniform environments close to thermoneutral zone, thermal comfort or discomfort reflects the climate alterations better than the thermal sensation does.

Exercise in the heat: Effects of dinitrophenol administration

1. 1.|Dinitrophenol (DNP) was administered to rats in two equal dosages (20 mg/kg, 30 min interval); the second injection was followed immediately by exercise (9.14 m/min) in the heat (30°C) or at room temperature (21°C).

2. 2.|At 21°C control (saline-treated) rats manifested a mean endurance of 94 min which was reduced to 32 min among DNP-treated animals.

3. 3.|At 30°C, control rats ran for 65 min (δT_re/min = 0.05°C) while DNP-treated animals had a mean endurance of only 12 min (δT_re/min = 0.22°C).

4. 4.|DNP-treated rats (30°C) manifested no decrements in tail-skin heat loss (δT_sk/min = 0.17°C vs 0.10°C) or saliva secretion (0.78 g/min, DNP vs. 0.19 g/min, control) for their brief treadmill duration.

5. 5.|The increased metabolic heat production of DNP severely reduced performance.

Daphnia development and reproduction: Responses to temperature

1. 1.|The development times and reproduction were measured for Daphnia pulex and Daphnia magna from 5 to 30°C at 5°C increments.

2. 2.|The general trends for D. pulex and D. magna were for the duration of all juvenile instars to be less than that of adults and for the last juvenile (or adolescent) instar to be longer than all previous juvenile instars.

3. 3.|The number of juvenile instars both species pass through before adulthood is influenced by temperature with increasing numbers occurring at temperature extremes.

4. 4.|Duration of development time decreased over the entire range of increasing temperatures measured for D. pulex but increased for D. magna at 30°C in relation to 25°C.

5. 5.|Quadratic models were less desirable than simple linear logarithmic transformations of the form ln Y = ln a + b ln X for describing the temperature/development relationship.

6. 6.|The greatest young production occurs at 15 and 20°C with significant decreases occurring at temperatures above and below these.

7. 7.|The observed temperature-dependent phenomena an the ecological relationships for the two species are discussed.

The importance of microhabitat in thermoregulation and thermal conductance in two namib rodents—a crevice dweller, Aethomys namaquensis, and a burrow dweller, Gerbillurus paeba

1. 1.|Thermoregulatory measurements of two Nambi rodents; Gerbillurus paeba, a burrow dweller, and Aethomys namaquensis, a crevice dweller were compared. Both were similar to other small arid-adapted rodents in that basal metabolic rates were reduced, thermoneutral zones narrow and evaporative water losses low. Rates of conductance and thermal lability, however, at ambient temperatures (T_a) below thermoneutral zone, were significantly different (P 0.01).

2. 2.|The rock rat A. namaquensis, living in a microclimate characterized by a large diel range and low humidities, compensates for a reduced basal metabolic rate by having a low rate of conductance. In this way it maintains precise thermoregulatory control. G. paeba, on the other hand, living in a thermally-stable milieu, does not control body temperature precisely. This animal instead utilizes a high rate of conductance to remove metabolic heat produced within the body. This would be advantageous to an animal living in a plugged burrow where the high humidities encountered impede the rate of evaporative cooling.

3. 3.|The energetic responses of both species, above the thermoneutral zone, appear to reflect very closely the environmental conditions which occur in the microhabitat that they rest in during the day. G. paeba shows less tolerance to temperature fluctuations than A. namaquensis, but shows more marked increases in short-term cooling mechanisms at high T_as.

4. 4.|Despite the increased use of evaporative cooling through salivation and panting in addition to pulmocutaneous evaporation, exposure to T_as above 38°C is rapidly lethal to G. paeba.

A central excitatory serotonergic or serotonergic-like synapse on the pathway to heat production in the sheep

1. 1.|Intraventricular injections of serotonergic agonists and receptor blockers were given to sheep to determine whether the central nervous pathway mediating the drive to heat production involves serotonergic synapses.

2. 2.|At 15°C ambient temperature (T_a), 5-hydroxytryptamine (5-HT) at all doses tested, and norfenfluramine (NF) in low doses increased heat loss and decreased rectal temperature (T_re); lysergic acid diethylamide (LSD-25) and methysergide prevented these effects.

3. 3.|AT 0°C T_a, 5-HT, even in high doses failed to increase heat production but NF increased heat production and T_re.

4. 4.|The results suggest the effects of NF and LSD-25 on heat production may be related to synapses activated by an indoleamine other than 5-HT.

Thermoregulatory responses of old men to gradual changes in ambient temperature

1. 1. Thermoregulatory respones to gradual rise and fall in the ambient temperature (T_a) were compared between 8 old (68–78 years) and 8 younger (20–25 years) male subjects.

2. 2. Starting at T_a of 31.5°C (r.h. 40%), T_a was raised to 39.5°C, then lowered to 21.5°C, and raised back to 31.5°C at a constant rate of 0.3°C/min.

3. 3. Noticeable differences in responses between the age groups were as follows: decline of sweating rate and reduction of acral blood flow during room cooling were retarded in the aged group, with wider variations among individuals, compared with those in the younger group; the tympanic and oesophageal temperatures fell considerably during cooling in the elderly group, failing to return to the level at start during the rewarming of the room, in contrast to the younger group.

4. 4. Such sluggish responses may be attributed largely to reduced cutaneous thermal perception with advancing age.

Errors resulting from linear approximations in energy balance equations

1. 1.|Linearization techniques commonly used to solve energy budget equations of animals and plants can result in inaccurate estimates of body temperature(T_b).

2. 2.|Errors can be large when actual T_bs differ from the temperature used in linearization techniques; this is especially true for wet-skinned animals.

3. 3.|Iterative solutions of linearized equations can give accurate calculations of T_b.

Day-night variation of thermoregulatory responses to intraperitoneal electric heating in rats

1. 1.Hypothalamic temperature (T_hy), nonevaporative heat loss (R + C + K), evaporative heat loss (E), thermal conductance (k), metabolic heat production (M) and heat storage (S) of rats were simultaneously measured by direct and indirect calorimetry during internal heat loading (2 W per rat) with an intraperitoneal electric heater.

2. 2.The tests were made twice a day; once during the day (1000–1200 h) and once at night (2200–2400 h) at an ambient temperature of 24°C.

3. 3.The resting values of T_hy, colonic temperature, (R + C + K), E, M and heart rate, and the T_hy threshold for tail skin vasodilation (T_th) during internal heat load were significantly higher at night than during the day.

4. 4.The slopes showing the relationshiop between (R + C + K), k or M and T_hy were significantly steeper during the day than at night after T_hy exceeded T_th.

5. 5.The slopes showing the relationship between E or S and T_hy were not different during the day and at night.

6. 6.These results indicate that the responses of nonevaporative heat loss and heat production to internal heat load vary with the time of day in rats.