Thermoregulation by the short-horned lizard (Phrynosoma douglassi) at high elevation

The short-horned lizard Phrynosoma douglassi was studied in a montane habitat (elevation of 2290 m) in the Guadalupe Mountains of Texas. The body temperatures (T_b) of active lizards were consistently between 35–36°C (grand mean=35.5°C) in the period from 0900 to 1800 h during the months of May through September. The lizards began their spring activity during April when environmental temperatures were still low. Although T_bs in April were significantly lower than during May through September, on sunny April days the lizards were able to maintain T_bs near 30°C even when air temperatures were as low as 1.5°C. P. douglassi at this site thermoregulated very effectively whenever they were not limited by the physical environment.     

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.

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.

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.

Evaluation of the cold strain index (CSI) for peripheral cold environmental stress

The purpose of this study was to evaluate the cold strain index (CSI) for peripheral environmental stress using data from a previous footwear study. Eight men (20±2 yr) dressed in protective cold weather clothing with varying footwear underwent 5 days of cold air (−23.4 °C) testing while attempting to sit for 240 min. Rectal, skin, and toe temperatures (T_toe) were continuously measured. All test exposures were ended after 50–165 min due to cold foot discomfort or T_toe<5 °C. However, CSI values indicated little cold strain. Therefore, we revised CSI to include peripheral cold assessment, which was found to be consistent with subject behavior and measured low T_toe.     

Heat tolerance of short-beaked echidnas (Tachyglossus aculeatus) in the field

(1) Echidnas occur throughout the hot arid zone of Australia yet laboratory studies have concluded that they are ill equipped physiologically to manage T_a higher than 35°C. (2) Consequently, it is generally assumed that echidnas must rely on behavioural thermoregulation, being nocturnal in hot weather and seeking less extreme microclimates during the day. (3) By monitoring T_b of echidnas in the field and relating these to T_a within their day time shelters in Western Queensland during summer, this study showed that echidnas are able to tolerate T_a of 35–40°C in hollow logs for up to 10 h. (4) Further, as T_b remains < T_a in these situations, echidnas may have physiological mechanisms for dealing with the heat after all.     

Geographic variation in field body temperature of sceloporus lizards

1. Using data from the literature, I assessed how broad climatic patterns affected field body temperatures (T_b’s) of lizards in the genus Sceloporus.

2. Sceloporus at temperate latitudes had mean T_b’s of 35°C throughout their elevational range. This pattern is associated with “tropical” temperatures that extend into high north latitudes during the summer and the relatively low elevations occupied by the lizards.

3. At tropical latitudes, mean T_b declined from 35°C at low elevations to 31°C at high elevations. This pattern is associated with low seasonal variation in temperature at tropical latitudes and the relatively high elevations occupied by the lizards.     

Intramuscular temperatures during exercise in the heat following pre-cooling and pre-heating

Pre-cooling improves heat tolerance and time to exhaustion in the heat. We tested the possibility that reduced tissue temperatures may explain this phenomenon, using three whole-body treatments: pre-cooling, thermoneutral (control) and pre-heating. Pre-cooling reduced muscle temperature (T_m) by 6.3 °C while pre-heating increased T_m 3.4 °C, relative to control. Despite this offset, T_m climbed towards a common asymptote, with pre-cooling offering no thermal protection beyond 40 min. Following pre-cooling, exercising oesophageal temperature (T_es) initially increased at 0.09 °C min⁻¹, being significantly faster than control (0.05 °C min⁻¹) and pre-heated conditions (0.03 °C min⁻¹). Pre-cooling lowered the sweat threshold and also resulted in a reduced cardiac frequency across the exercise-heat exposure. Our observations do not support the hypothesis that pre-cooling reduces T_m at the end of an exercise-heat exposure, thereby delaying the development of fatigue.     

Daily rhythms of nonshivering thermogenesis in common spiny mice Acomys cahirinus under short and long photoperiods

Daily rhythms of nonshivering thermogenesis NST were studied in common spiny mice Acomys cahirinus, acclimated to different photoperiod regimes (16L:8D and 8L:16D) at a constant ambient temperature of 26°C. Noradrenaline NA (1.5 mg/kg subcutaneous) was injected at: 06:00, 12:00, 18:00 and 24:00 h (±15 min). NST was measured as the ratio between the maximal oxygen consumption (VO₂) as response to NA — VO₂NA and VO₂ measured at 26°C — VO_{2 min}. Rectal temperatures T_bNA and T_{b min} respectively were recorded at the end of VO₂ measurements. Significant variations in T_{b min}, T_bNA, and NST were revealed, under the two different photoperiod regimes. Significant differences in VO_{2 min}, NST, T_{b min} and T_bNA were also recorded within each photoperiod acclimation group. These results suggest that daily and photoperiod depended variations in the brown adipose tissue activity, presumably emerge from amount of unoccupied receptors or changes in the receptors affinity to NA.     

Daily rhythms of nonshivering thermogenesis and responses to photoperiod manipulations in Apodemus mystacinus from two different ecosystems

Comparative physiology is an important tool for understanding adaptation to environment. Regulatory nonshivering thermogenesis (NST) is an essential mechanism in small mammals for coping with low ambient temperatures. Because of its geographical location and its sharp climatic changes across short distances, Israel offers conducting comparative studies between different populations of the same species. The aims of this study were: (1) to compare NST-capacity daily rhythms, between the two populations of the broad-toothed field mouse Apodemus Mystacinus—that of Mount Carmel (Mediterranean) and that of Mount Hermon (Subalpinic), (2) to compare the thermoregulatory daily rhythms response to photoperiod manipulations of mice from the two populations.

Mice were acclimated for at least 3 weeks to long scotophase (16D:8L-LS) and then to long photophase (16L:8D-LP) at a constant ambient temperature (T_a) of 24±1 °C. The following variables were compared at four different times of the day (06, 12, 18, 24 h): minimal body temperature (T_bMin), minimal oxygen consumption (VO₂Min) measured at the lower critical point and their response to noradrenaline (NA), 1.5 mg/1 kg.W_b injected s.c., (VO₂NA and T_bNA). NST-capacity was calculated as the ratio between VO₂NA and VO₂Min. The measurements were carried out at T_a of 28 °C and in light conditions matching those of acclimation. NA was injected after establishing VO₂Min and T_bMin. The values mean±SD are given for each measurement for n=6.

A three-way ANOVA revealed a significant difference between the two populations. Significant differences were revealed at different hours within populations under the different photoperiod regimes for different measured variables.     

Responses of core and peripheral temperatures to chronic cold stress in transiently goitrous goats

Thyroid hormones play a major role in controlling basal metabolic rate, body temperature and hemodynamics. Responses of core and peripheral body temperatures to transient use of thyreostatic drugs are seldom measured simultaneously under chronic experimental settings. We developed a technique to attain this goal. Eighteen Damascus goat kids (initial Avg. BW=44±0.7 kg) underwent a minor invasive surgical procedure to implant two miniature temperature data loggers, intraperitoneally and subcutaneously, to assess core (T_core) and subcutaneous (T_sq) temperature changes when subjected to chronic (47 days) cold (< 10 °C) environment along with or without oral administration of the reversible goitrogen 6-N-propyl-2-thiouracil (PTU; 20 mg/kg BW/day). Nine animals served as controls whereas the remaining nine were treated with PTU for 31 out of total 47-day trial period. The PTU treatment significantly (P<0.05) depressed circulating free thyroxine (FT4), followed by a rebound after termination. Prior to initiation of PTU treatment, all animals displayed similar daily means of T_core and T_sq. Subsequently, both temperatures precipitously declined (P<0.01) with the gradual drop in ambient temperature (T_a) overtime. However, PTU caused an immediate and further drop in T_sq, suggesting a reduction in cutaneous perfusion. Interestingly, on the other hand, a delayed downregulation of T_core by PTU occurred 14 days post-treatment, indicating a relatively slower depression in metabolic thermogenesis after suppression of circulating thyroxine. Upon termination of PTU, T_core but not T_sq, returned to simulate control levels. Results from the current study show the practicality of our technique to concurrently record core and peripheral temperatures in chronically-instrumented animals, and that PTU causes a marked depression in thermoregulatory ability during cold stress with no indication for a reduction in the temperature set-point.     

Avian embryonic thermoregulation: role of Q10 in interpretation of endothermic reactions

1. Incubated chicken eggs (D14 to D21) were placed separately in transparent acrylic glass chambers which were immersed in a 37.5°C water bath for 3 h. The chambers were then moved for 3 h to another water bath controlled at 34.5°C. Oxygen consumption and temperature of the allantoic fluid (T_af) were measured at 5-min intervals for the whole experiment using an oxygen analyzer and CrNi–Ni-thermocouples, respectively. Heat production (HP) was calculated, using an assumed RQ of 0.72.

2. At 37.5°C the relationship between HP and embryonic age follows a sigmoid curve. Between D18 (HP 7.25 J g⁻¹ h; 2.01 W kg⁻¹) and D19 (HP 7.21 J g⁻¹ h⁻¹; 2.00 W kg⁻¹) this function had a plateau phase with a duration of about 24 h.

3. During the cooling process, HP decreased continuously and the relationship between T_a and HP could be described by an exponential function. From the results, it was possible to calculate the relationships between T_af, as a measure of body core temperature, and Q₁₀; the lower the T_af the higher the Q₁₀.

4. Because the actual measured HP is the result of the negative effect of Q₁₀ on HP and the stimulating influence of the CNS-generated HP, a Q₁₀ of more than 2.0 demonstrates the absence of endothermy. Chicken embryos aged between 14 and 21 d have a Q₁₀ of less than 2.0 at body temperatures (T_af) between 34 and 30°C. It is postulated that in chicken embryos of this age endothermic reactions may occur.

5. The Q₁₀-method is suitable for investigating the prenatal development of endothermic reactions in avian embryos.     

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

1. 1. The response of oxygen consumption (VO₂), thermal conductance (C_d and C_min, body temperature (T_b), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures (T_a) from 5–35°C.

2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O₂ g⁻¹ h⁻¹ and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O₂ g⁻¹ h⁻¹). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents.

3. 3. D. auricularis and T. leucogaster regulated T_b over the range T_a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T_a = 30°C.

4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

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, ).

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.

Daily rhythms of oxygen consumption, body temperature, activity and melatonin in the Norwegian lemming Lemmus lemmus under northern summer photoperiod

Rodents inhabiting high latitudes, close to the Arctic Circle or above it, are exposed to near 24 h daylight during the summer season. An example to such rodent species is the Norwegian lemming Lemmus lemmus, which is distributed in northern Fennoscandia. We measured daily rhythms of heat production (VO₂), body temperature (T_b), motor activity and melatonin secretion (measured from its metabolite 6-sulfatoximelatonin 6-SMT) in individuals exposed to natural day light, Oulu Finland, in August 1997 and at a controlled ambient temperature of 22 °C. Our results show a daily rhythm of VO₂ with an acrophase at 04:00 h and minimal values measured at 16:00 h, with a significant difference (p<0.001) between mean day and night values. 6-SMT also shows a daily rhythm with maximal secretion during the dark phase 24:00 and 06:00 h in which total 6-SMT values were 2.92±1.1 and 3.87±1.2 ng, respectively. The lowest values were recorded at 12:00 h; 0.86±0.63 ng. These results suggest that lemmings show a VO₂ and melatonin daily rhythms, which seem to correlate with each other and it appears that melatonin secretion increases heat production.     

Dynamic changes in sweat rates and evaporation rates through clothing during hot exposure

Dynamic changes in local sweat rates (S_w) and local evaporation rates from clothing (E_cl) have been observed during hot exposure. Four young male subjects wearing a cotton T-shirt and half shorts were exposed to 40 °C/50% for 1 h following exposure to 28 °C/50% for 30 min. Amount of water absorbed in clothing (M_sw), clothing surface temperatures (T_cl), local heat flow rates, skin temperatures, body weight, rectal temperature, S_w and E_cl were continuously measured. Upon exposure to the heat, decrease in heat gain to the skin was observed as opposed to increase in S_w, E_cl, M_sw and heat gain to the clothing surface.     

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.

Yield stress components of waxy corn starch–xanthan mixtures: Effect of xanthan concentration and different starches

Yield stress of 6% (w/w) waxy maize (WXM), cross-linked waxy maize (CLWM), and cold water swelling (CWS) starches in xanthan gum dispersions: 0%, 0.35%, 0.50%, 0.70%, and 1.0% was measured with the vane method at an apparent shear rate of 0.05 s⁻¹. The intrinsic viscosity of the xanthan gum was determined to be: 112.3 dL/g in distilled water at 25 °C. Values of the static (σ_0s) and dynamic (σ_0d) yield stress of each dispersion were measured before and after breaking down its structure under continuous shear, respectively. The WXM and CWS starches exhibited synergistic behavior, whereas the CLWM starch showed antagonistic effect with xanthan gum. The difference (σ_0s − σ_0d) was the stress required to break the inter-particle bonding (σ_b). The contributions of the viscous (σ_v) and network (σ_n) components were estimated from an energy balance model. In general, values of σ_b of the starch–xanthan gum dispersions decreased and those of σ_n increased with increase in xanthan gum concentration.     

Correlated changes in thermotolerance traits and body color phenotypes in montane populations of Drosophila melanogaster: analysis of within- and between-population variations

Thermotolerance traits vary across geographical gradients but there is a lack of clinal variation in some Drosophila species. Thus, it is not clear whether thermotolerance or other correlated traits are the target of natural selection. In order to test selection responses, we investigated body melanization and thermotolerance traits in six altitudinal populations of Drosophila melanogaster . Based on rearing different geographical populations under uniform growth conditions at 21 °C (common garden experiments), clinal variations for cold resistance are in the direction opposite to heat resistance along an altitudinal gradient, that is darker flies from highland populations evidenced higher levels of cold resistance while lowland populations showed higher heat resistance. Phenotypic plastic responses for body melanization at 17–28 °C showed significant correlations with thermotolerance traits. At 17 °C, regression coefficients as a function of altitude are highly significant and positive for cold resistance but negative for heat knockdown. However, for flies reared at 28 °C, there is no elevational change in melanization as well as thermotolerance traits. Thus, both genetic and plastic changes of body melanization and thermotolerance traits suggest a correlated selection response. Further, within-population analyses of body melanization (based on dark, intermediate and light color phenotypes) showed significant associations with thermotolerance traits. Correlated variations in body melanization and thermal tolerances are associated with climatic thermal variability ( T _cv) but not with T _min. or T _max. along an altitudinal gradient.