Body temperature patterns in two syntopic elephant shrew species during winter

We measured body temperature (T_b) in free-ranging individuals of two species of elephant shrews, namely western rock elephant shrews (Elephantulus rupestris) and Cape rock elephant shrews (E. edwardii), during winter in a winter-rainfall region of western South Africa. These syntopic species have similar ecologies and morphologies and thus potential for large overlaps in diet and habitat use. Unexpectedly, they displayed different T_b patterns. Western rock elephant shrews were heterothermic, with all individuals decreasing T_b below 30 °C on at least 34% of nights. The level of heterothermy expressed was similar to other species traditionally defined as daily heterotherms and was inversely related to T_a, as is commonly seen in small heterothermic endotherms. In contrast, Cape rock elephant shrews rarely allowed their T_b to decrease below 30 °C. The level of heterothermy was similar to species traditionally defined as homeotherms and there was no relationship between the level of heterothermy expressed and T_a. In both species, the minimum daily T_b was recorded almost exclusively at night, often shortly before sunrise, although in some individuals minimum T_b occasionally occurred during the day. The interspecific variation in T_b patterns among Elephantulus species recorded to date reiterates the importance of ecological determinants of heterothermy that interact with factors such as body mass and phylogeny.     

Ways to measure body temperature in the field

Body temperature (T_b) represents one of the key parameters in ecophysiological studies with focus on energy saving strategies. In this study we therefore comparatively evaluated the usefulness of two types of temperature-sensitive passive transponders (LifeChips and IPTT-300) and one data logger (iButton, DS1922L) mounted onto a collar to measure T_b in the field. First we tested the accuracy of all three devices in a water bath with water temperature ranging from 0 to 40 °C. Second, we evaluated the usefulness of the LifeChips and the modified iButtons for measuring T_b of small heterothermic mammals under field conditions. For this work we subcutaneously implanted 14 male edible dormice (Glis glis) with transponders, and equipped another 14 males with data loggers to simultaneously record T_b and oxygen consumption with a portable oxygen analyzer (Oxbox). In one individual we recorded T_b with both devices and analyzed recorded T_b patterns.LifeChips are able to measure temperature within the smallest range from 25 to 40 °C with an accuracy of 0.07±0.12 °C. IPTT-300 transponders measured temperature between 10 and 40 °C, but accuracy decreased considerably at values below 30 °C, with maximal deviations of nearly 7 °C. An individual calibration of each transponder is therefore needed, before using it at low T_bs. The accuracy of the data logger was comparatively good (0.12±0.25 °C) and stable over the whole temperature range tested (0–40 °C). In all three devices, the repeatability of measurements was high.LifeChip transponders as well as modified iButtons measured T_b reliably under field conditions. Simultaneous T_b-recordings in one edible dormouse with an implanted LifeChip and a collar-mounted iButton revealed that values of both measurements were closely correlated. Taken together, we conclude that implanted temperature-sensitive transponders represent an appropriate and largely non-invasive method to measure T_b also under field conditions.     

Body temperature variation in free-living and food-deprived yellow-necked mice sustains an adaptive framework for endothermic thermoregulation

In many mammalian species, variation in body temperature (T_b) exceeds the values suitable for defining homeothermy, making it justifiable and even necessary to resort to the term “heterothermic”. However, T_b data are only available for ca. 1% of extant mammalian species. We investigated variations in T_b in wild free-living and experimentally food-deprived yellow-necked mice Apodemus flavicollis, during the temperate-zone autumn-winter period. In line with the adaptive framework for endothermic thermoregulation, we hypothesised that T_b in the mice should be adjustable with the energetic cost-benefit trade-off associated with maintaining homeothermy. In laboratory conditions, mice clearly entered a state of daily torpor when food-deprived. Our study thus makes it clear that A. flavicollis is a heterothermic species in which food deprivation results in switching between endothermic and poikilothermic thermoregulation. We also assumed that, in free-living mice, heterothermy increases with elevated environmental challenges, e.g. when the ambient temperature (T_a) decreases. Consistent with this was the inverse correlation noted between variation in T_b in free-living mice and T_a, with most individuals clearly becoming torpid when T_a decreases below 0 °C. It is the increased cost of food hoarding under cold conditions that most likely triggers a state of torpor as a last result. Overall, our study indicates that yellow-necked mice can provide a further example of species sustaining an adaptive framework for endothermic thermoregulation.     

Interplay between thermal and immune ecology: effect of environmental temperature on insect immune response and energetic costs after an immune challenge

Although the study of thermoregulation in insects has shown that infected animals tend to prefer higher temperatures than healthy individuals, the immune response and energetic consequences of this preference remain unknown. We examined the effect of environmental temperature and the energetic costs associated to the activation of the immune response of Tenebrio molitor larvae following a lipopolysaccharide (LPS) challenge. We measured the effect of temperature on immune parameters including phenoloxidase (PO) activity and antibacterial responses. Further as proximal and distal costs of the immune response we determined the standard metabolic rate (SMR) and the loss of body mass (m_b), respectively. Immune response was stronger at 30 °C than was at 10 or 20 °C. While SMR at 10 and 20 °C did not differ between immune treatments, at 30 °C SMR of LPS-treated larvae was almost 25–60% higher than SMR of PBS-treated and naïve larvae. In addition, the loss in m_b was 1.9 and 4.2 times higher in LPS-treated larvae than in PBS-treated and naïve controls. The immune responses exhibited a positive correlation with temperature and both, SMR and m_b change, were sensitive to environmental temperature. These data suggest a significant effect of environmental temperature on the immune response and on the energetic costs of immunity.     

Energy metabolism and thermoregulation in pygmy lorises (Nycticebus pygmaeus) from Yunnan Daweishan Nature Reserve

The pygmy loris (Nycticebus pygmaeus) is a small prosimian living in Vietnam, Laos, eastern Cambodia and the south part of China. In China it is only found in Pingbian, Hekou, Jinping, Luchun of Yunnan. As N. pygmaeus is seriously threatened by hunting, trade and habitat destruction, it is listed in Appendix II of CITES, and in 2006 the IUCN classified it as “vulnerable”. In order to understand the characteristics of energy metabolism and thermoregulation of N. pygmaeus, the resting metabolic rate (RMR) and body temperature (T_b) at different ambient temperature (T_a) of pygmy lorises, as well as body mass, energy intake, digestable energy intake, digestability and the thermal conductance were measured in captivity. The results obtained mainly are as follows: (1) Pygmy loris feed dry food averaged 12.90 ± 1.02 g/d. They could gain 214.87 ± 16.65 kJ/d from food intake, and earned 200.15 ± 16.36 kJ digestable energy intake per day with 90.13 ± 1.34% of the digestability. (2) The T_b at room temperatures was a little low (35.23 ± 0.16 °C) and varied with T_a from 25 °C to 35 °C. There was a positive relationship between T_b and T_a, which was described as: T_b = 27.22 + 0.34T_a (r = 0.880). (3) The resting metabolic rate (RMR) of the pygmy loris was 0.3844 ± 0.0162 mlO₂/g/h, which was 51.91 ± 1.90% of the previous predicted rate by Kleiber (1961) [21]. (4) The average thermal conductance of the pygmy loris (N. pygmaeus) was 0.0449 ± 0.0031 mlO₂/g/h/°C. These characteristics of energy metabolism and thermoregulation of N. pygmaeus in Yunnan Daweishan Nature Reserve might be considered as the adaptive characteristics to their environment in tropical semi-evergreen forests and secondary forests.     

Body temperature regulation during acclimation to cold and hypoxia in rats

Extreme environmental conditions present challenges for thermoregulation in homoeothermic organisms such as mammals. Such challenges are exacerbated when two stressors are experienced simultaneously and each stimulus evokes opposing physiological responses. This is the case of cold, which induces an increase in thermogenesis, and hypoxia, which suppresses metabolism conserving oxygen and preventing hypoxaemia. As an initial approach to understanding the thermoregulatory responses to cold and hypoxia in a small mammal, we explored the effects of acclimation to these two stressors on the body temperature (T_b) and the daily and ultradian T_b variations of Sprague-Dawley rats. As T_b is influenced by sleep-wake cycles, these T_b variations reflect underlying adjustments in set-point and thermosensitivity. The T_b of rats decreased precipitously during initial hypoxic exposure which was more pronounced in cold (T_b=33.4±0.13) than in room temperature (T_b=35.74±0.17) conditions. This decline was followed by an increase in T_b stabilising at a new level ~0.5 °C and ~1.4 °C below normoxic values at room and cold temperatures, respectively. Daily T_b variations were blunted during hypoxia with a greater effect in the cold. Ultradian T_b variations exhibited daily rhythmicity that disappeared under hypoxia, independent of ambient temperature. The adjustments in T_b during hypoxia and/or cold are in agreement with the hypothesis that an initial decrease in the T_b set-point is followed by its partial re-establishment with chronic hypoxia. This rebound of the T_b set-point might reflect cellular adjustments that would allow animals to better deal with low oxygen conditions, diminishing the drive for a lower T_b set-point. Cold and hypoxia are characteristic of high altitude environments. Understanding how mammals cope with changes in oxygen and temperature will shed light into their ability to colonize new environments along altitudinal clines and increase our understanding of how T_b is regulated under stimuli that impose contrasting physiological constraints.     

Locomotor and energetic consequences of behavioral thermoregulation in the sanguivorous leech Hirudo verbana

Medicinal leeches (Hirudo verbana) thermoregulate with respect to their sanguivorous feeding behavior. Immediate postprandial preferences are for warmer than their initial acclimation temperature (T_a, 21 °C, Petersen et al. 2011), while unfed leeches have a lower preferred temperature (T_pref, 12.5 °C). This may reduce energy expenditure and defer starvation if feeding opportunities are limited. Energetic benefits may have an associated cost if low temperatures reduce mobility and the ability to locate further hosts. These costs could be limited if mobility is unimpaired at low temperatures, or if acclimation can restore locomotor performance to the levels at T_a. The transition from T_a to the unfed T_pref significantly reduced speed and propulsive cycle frequency during swimming, and extension and retraction rates during crawling. Aerobic metabolic rate was also reduced from 0.20±0.03 W kg⁻¹ at T_a to 0.10±0.03 W kg⁻¹ at T_pref. The Q₁₀ values of 1.7–2.9 for energetic and swimming parameters indicate a substantial temperature effect, although part of the decline in swimming performance can be attributed to temperature-related changes in water viscosity. 6 weeks at T_a resulted in no detectable acclimation in locomotor performance or aerobic metabolism. The energetic savings associated with a lower T_pref in unfed leeches effectively doubled the estimated time until depletion of energy reserves. Given that some mobility is still retained at T_pref, and that acclimation is in itself costly, the energetic benefits of selecting cooler temperatures between feedings may outweigh the costs associated with reduced locomotor performance.     

Heterothermy in an Australian passerine, the Dusky Woodswallow (Artamus cyanopterus)

Information regarding passerine heterothermy and torpor is scant, although many species are small and must cope with a fluctuating food supply and presumably would benefit from energy savings afforded by torpor. We studied whether insectivorous Dusky Woodswallows (Artamus cyanopterus; ∼35 g) enter spontaneous torpor (food ad libitum) when held outdoors as a pair in autumn/winter. Woodswallows displayed pronounced and regular daily fluctuations in body temperature (T _b) over the entire study period. The mean T _b ranged from ∼39°C to 40°C (photophase, day time) and ∼33°C to 36°C (scotophase, night time). However, on 88% of bird nights, nocturnal T _b minima fell to < 35°C. The lowest T _b observed in air was 29.2°C. However, when a bird fell into water its T _b dropped further to ∼22°C; this T _b was regulated for several hours and the bird survived. Our observations suggest that heterothermy is a normal part of the daily thermal regime for woodswallows to minimise energy expenditure. Spontaneous nocturnal torpor in captive woodswallows suggests that torpor in the wild may be more pronounced than recorded here because free-living birds are likely challenged by both low food availability and adverse weather.     

Thermoregulation in free‐ranging ground woodpeckers Geocolaptes olivaceus: no evidence of torpor

Heterothermic responses characterised by pronounced hypometabolism and reductions in body temperature (T_b) are one of the most effective ways in which small endotherms can offset the energetic cost of endothermic homeothermy. It remains unclear, therefore, why daily torpor and hibernation are restricted to only a subset of avian lineages. To further our understanding of the phylogenetic distribution of avian torpor, we investigated winter thermoregulation in the southern African ground woodpecker Geocolaptes olivaceus. We considered this species a good candidate for heterothermy, because it is resident year‐round in mountainous regions with cold winters and reliant on small ectothermic prey. We recorded T_b patterns in free‐ranging individuals and measured T_b and metabolic rates in captive individuals. Neither free‐ranging nor captive woodpeckers showed any indication of daily torpor or even shallow rest‐phase hypothermia. All birds maintained bimodally distributed T_b characteristic of classic endothemic homeothermy, with a mean rest‐phase T_b of 37.9 ± 0.2°C and no data below 37.0°C. The mean circadian amplitude of T_b was 4.2°C, equivalent to approximately twice the expected value. There was some evidence of seasonal acclimatisation in T_b, with a small decrease in rest‐phase T_b with the onset of the austral winter. Captive birds showed patterns of resting metabolic rate and T_b consistent with the classic model of endothermic homeothermy. The apparent absence of torpor in G. olivaceus supports the notion that, unlike the case in mammals, many avian taxa that may a priori be expected to benefit from deep heterothermy do not use it.     

Climate change and animals in Saudi Arabia

Global warming is occurring at an alarming rate and predictions are that air temperature (T_a) will continue to increase during this century. Increases in T_a as a result of unabated production of greenhouse gases in our atmosphere pose a threat to the distribution and abundance of wildlife populations worldwide. Although all the animals worldwide will likely be affected by global warming, diurnal animals in the deserts will be particularly threatened in the future because T_as are already high, and animals have limited access to water. It is expected that Saudi Arabia will experience a 3–5 °C in T_a over the next century. For predicting the consequences of global warming for animals, it is important to understand how individual species will respond to higher air temperatures. We think that populations will not have sufficient time to make evolutionary adjustments to higher T_a, and therefore they will be forced to alter their distribution patterns, or make phenotypic adjustments in their ability to cope with high T_a. This report examines how increases in T_a might affect body temperature (T_b) in the animals of arid regions. We chose three taxonomic groups, mammals, birds, and reptiles (Arabian oryx, Arabian spiny-tailed lizard, vultures, and hoopoe larks) from Saudi Arabia, an area in which T_a often reaches 45 °C during midday in summer. When T_a exceeds T_b, animals must resort to behavioral and physiological methods to control their T_b; failure to do so results in death. The observations of this study show that in many cases T_b is already close to the upper lethal limit of around 47° C in these species and therefore allowing their T_b to increase as T_a increases are not an option. We conclude that global warming will have a detrimental impact on a wide range of desert animals, but in reality we know little about the ability of most animals to cope with change in T_a. The data presented should serve as base-line information on T_b of animals in the Kingdom for future scientists in Saudi Arabia as they explore the impact of global warming on animal species.     

Daily and annual patterns of thermoregulation in painted turtles (Chrysemys picta marginata) living in a thermally variable marsh in Northern Michigan

The capacity for an ectothermic reptile to thermoregulate has implications for many components of its life history. Over two years, we studied thermoregulation in a population of Midland painted turtles (Chrysemys picta marginata) in a shallow, thermally variable wetland during summer in Northern Michigan. Mean body temperature (T_b) of free-ranging turtles was greater in 2008 (25.8 °C) than in 2010 (19.7 °C). Laboratory determined thermoregulatory set point (T_set) ranged from 25 °C (T_set-min) to 31 °C (T_set-max) and was lower during the fall (17–26 °C). Deviations of T_b distributions from field measured operative temperatures (T_e) and indices of thermoregulation indicated that C. picta marginata were capable of a limited degree of thermoregulation. Operative temperatures and thermal quality (d_e=|T_set-min−T_e| and |T_e−T_set-max|) cycled daily with maximal thermal quality occurring during late morning and late afternoon. The accuracy of thermoregulation (d_b=|T_set-min−T_b| and |T_b−T_set-max|) was maximal (d_b values were minimal) as T_b declined and traversed T_set during the late afternoon–early evening hours and was higher on cloudy days than on sunny days because relatively low T_e values decreased the number of T_b values that were above T_set. Our index of thermal exploitation (E_x=frequency of T_b observations within T_set) was 36%, slightly lower than that reported for an Ontario population of C. picta marginata. Regression of d_b (thermal accuracy) on d_e (thermal quality) indicated that turtles invested more in thermoregulation when thermal quality was low and when water levels were high than when they were low. There were no intersexual differences in mean T_b throughout the year but females had relatively high laboratory determined T_b values in the fall, perhaps reflecting the importance of maintaining ovarian development prior to winter.     

Daily variation of thermoregulatory costs in laboratory mice selected for high and low basal metabolic rate

Most mammals are known to have clear circadian rhythms of body temperature (T_b) and metabolic rate. Large parts of the rhythms correspond to the oscillation of nonshivering thermogenesis (NST), dependent on visceral organ mass, and, affected by mass of brown adipose tissue (BAT). I tested whether: (1) a different levels of BMR result in respective changes of T_b values and the magnitude of daily RMR oscillations both within and below thermoneutrality; (2) the amplitude of daily variation of RMR depends on ambient temperature (T_a). I studied: (1) daily variation of body temperature at T_a of 23 °C, and (2) the rate of resting metabolism (RMR) within and below thermoneutrality at the time of minimum and increasing T_b (minimum and maximum NST capacity), in two lines of laboratory mice subjected to divergent, artificial selection toward high (HBMR) and low (LBMR) basal rate of metabolism (BMR). All mice had a clear circadian rhythm of T_b with minimum of 36.4±0.2 °C at 7:00 and maximum of 37.8±0.2 °C at 21:00. Their RMR measured below thermoneutrality exhibited significant daily variation, with the maximum between 16:00 and 19:00, when T_b was rising. Within thermoneutral zone (TNZ) I found between-line, but not between-time, differences in RMR. All between-line differences in RMR could be explained by the magnitude of BMR. I did not find any between-line differences of RMR value in temperatures below thermoneutrality. The amplitude of daily variation of RMR measured below TNZ depended neither on the T_a value nor on level of BMR (or visceral organs).     

Evidence for the involvement of eicosanoids in the regulation of normal body temperature

(1) In CD-1 mice and Sprague–Dawley rats, dark-induced elevation of body temperature (T_b) was accompanied by an increase in hypothalamic prostaglandin E₂ (PGE₂) production. (2) Indomethacin, a cyclooxygenase inhibitor, at a dose (5 mg/kg) that did not affect the daytime values of T_b, prevented the increase of T_b after the onset of darkness. (3) Pretreatment of mice with the inhibitor of leukotriene synthesis, MK-886 (1 mg/kg), prevented the decrease of daytime T_b. (4) The results suggest the involvement of PGE₂ and leukotrienes in the regulation of normal daily variations of T_b.     

Polysaccharide peptide induces a tumor necrosis factor-α-dependent drop of body temperature in rats

Polysaccharide peptide (PSP) extracted from the Coriolus versicolor mushroom is frequently suggested as an adjunct to the chemo- or radiotherapy in cancer patients. It improves quality of the patients' life by decreasing pain, fatigue, loss of appetite, nausea, and vomiting. However, the effect of PSP on body temperature has not thus far been studied, although it is well known that treatment with other polysaccharide adjuvants, such as lipopolysaccharides, may induce fever. The aim of the present study, therefore, was to investigate the influence of PSP on temperature regulation in rats. We report that intraperitoneal injection of PSP provoked a dose-dependent decrease of temperature in male Wistar rats equipped with biotelemetry devices to monitor deep body temperature (T_b). The response was rapid (i.e., with latency of 15–20 min), transient (lasting up to 5 h post-injection), and accompanied by a significant elevation of the blood tumor necrosis factor-α (TNF-α) level. Pretreatment of the rats with anti-TNF-α antibody prevented the PSP-induced drop in T_b. Based on these data, we conclude that rats may develop an anapyrexia-like response to the injection of peptidopolysaccharide rather than fever, and the response was TNF-α-dependent.     

Staying cold through dinner: cold-climate bats rewarm with conspecifics but not sunset during hibernation

For temperate endotherms (i.e., mammals and birds) energy costs are highest during winter but food availability is lowest and many mammals depend on hibernation as a result. Hibernation is made up of energy-saving torpor bouts [periods of controlled reduction in body temperature (T _b)], which are interrupted by brief periodic arousals to normothermic T _b. What triggers these arousals in free-ranging hibernators is not well understood. Some temperate bats with intermittent access to flying insects during winter synchronize arousals with sunset, which suggests that, in some species, feeding opportunities influence arousal timing. We tested whether hibernating bats from a cold climate without access to food during winter also maintain a circadian rhythm for arousals or whether cues from conspecifics in the same cluster are more important. We used temperature telemetry to monitor skin temperature (T _sk) of free-ranging little brown bats (Myotis lucifugus) hibernating in central Manitoba, Canada, where temperatures from 22 October to 22 March were too cold for flying insects. We found no evidence bats synchronized arousals with photoperiod but they did arouse synchronously with other bats in the same cluster. Thus, in the northern part of their range where flying insects are almost never available during winter, little brown bats exhibit no circadian pattern to arousals. Warming synchronously with others could reduce the energetic costs of arousal for individuals or could reflect disturbance of torpid bats by cluster-mates.     

Dehydration,with and without heat,in kangaroos from mesic and arid habitats: different thermal responses including varying patterns in heterothermy in the field and laboratory

Field data showing the daily patterns in body temperature (T _b) of kangaroos in hot, arid conditions, with and without water, indicate the use of adaptive heterothermy, i.e. large variation in T _b. However, daily T _b variation was greater in the Eastern Grey Kangaroo (Macropus giganteus), a species of mesic origin, than in the desert-adapted Red Kangaroo (Macropus rufus). The nature of such responses was studied by an examination of their thermal adjustments to dehydration in thermoneutral temperatures (25°C) and at high temperature (45°C) via the use of tame, habituated animals in a climate chamber. At the same level of dehydration M. rufus was less impacted, in that its T _b changed less than that for M. giganteus while it evaporated significantly less water. At a T _a of 45°C with water restriction T _b reached 38.9 ± 0.3°C in M. rufus compared with 40.2 ± 0.4°C for M. giganteus. The ability of M. rufus to reduce dry conductance in the heat while dehydrated was central to its superior thermal control. While M. giganteus showed more heterothermy, i.e. its T _b varied more, this seemed due to a lower tolerance of dehydration in concert with a strong thermal challenge. The benefits of heterothermy to M. giganteus were also limited because of thermal (Q₁₀) effects on metabolic heat production and evaporative heat loss. The impacts of T _b on heat production were such that low morning T _b’s seen in the field may be associated with energy saving, as well as water saving. Kangaroos respond to dehydration and heat similarly to many ungulates, and it is apparent that the accepted notions about adaptive heterothermy in large desert mammals may need revisiting.     

Estimation of the core temperature control during ambient temperature changes and the influence of circadian rhythm and metabolic conditions in mice

It has been speculated that the control of core temperature is modulated by physiological demands. We could not prove the modulation because we did not have a good method to evaluate the control. In the present study, the control of core temperature in mice was assessed by exposing them to various ambient temperatures (T_a), and the influence of circadian rhythm and feeding condition was evaluated. Male ICR mice (n=20) were placed in a box where T_a was increased or decreased from 27 °C to 40 °C or to −4 °C (0.15 °C/min) at 0800 and 2000 (daytime and nighttime, respectively). Intra-abdominal temperature (T_core) was monitored by telemetry. The relationship between T_core and T_a was assessed. The range of T_a where T_core was relatively stable (range of normothermia, RNT) and T_core corresponding to the RNT median (regulated T_core) were estimated by model analysis. In fed mice, the regression slope within the RNT was smaller in the nighttime than in the daytime (0.02 and 0.06, respectively), and the regulated T_core was higher in the nighttime than in the daytime (37.5 °C and 36.0 °C, respectively). In the fasted mice, the slope remained unchanged, and the regulated T_core decreased in the nighttime (0.05 and 35.9 °C, respectively), while the slopes in the daytime became greater (0.13). Without the estimating individual thermoregulatory response such as metabolic heat production and skin vasodilation, the analysis of the T_a–T_core relationship could describe the character of the core temperature control. The present results show that the character of the system changes depending on time of day and feeding conditions.     

Development response of Spodoptera exigua to eight constant temperatures: Linear and nonlinear modeling

Temperature-dependent development of Spodoptera exigua (Hübner) were evaluated at eight constant temperatures of 12, 15, 20, 25, 30, 33, 34 and 36 °C with a variation of 0.5 °C on sugar beet leaves. No development occurred at 12 °C and 36 °C. Total developmental time varied from 120.50 days at 15 °C to 14.50 days at 33 °C. As temperature increased from 15 °C to 33 °C, developmental rate (1/developmental time) of S. exigua increased but declined at 34 °C. The lower temperature threshold (T_min) was estimated to be 12.98 °C and 12.45 °C, and the thermal constant (K) was 294.99 DD and 311.76 DD, using the traditional and Ikemoto–Takai linear models, respectively. The slopes of the Ikemoto–Takai linear model for different immature stages were different, violating the assumption of rate isomorphy. Data were fitted to three nonlinear models to predict the developmental rate and estimate the critical temperatures. The T_min values estimated by Lactin-2 (12.90 °C) and SSI (13.35 °C) were higher than the value estimated by Briere-2 (8.67 °C). The estimated fastest development temperatures (T_fast) by the Briere-2, Lactin-2 and SSI models for overall immature stages development of S. exigua were 33.4 °C, 33.9 °C and 32.4 °C, respectively. The intrinsic optimum temperature (T_Φ) estimated from the SSI model was 28.5 °C, in which the probability of enzyme being in its native state is maximal. The upper temperature threshold (T_max) values estimated by these three nonlinear models varied from 34.00 °C to 34.69 °C. These findings on thermal requirements can be used to predict the occurrence, number of generations and population dynamics of S. exigua.     

Spontaneously reduced body temperature and gasping ability as a mechanism of extreme tolerance to asphyxia in neonatal rats

The aim of the investigation was to verify our hypothesis that extreme tolerance of newborn rodents to anoxia is determined by their ability to maintain reduced body temperature and to keep on gasping.Newborn Wistar rats were used. In separate experiments we checked (1) effect of extreme thermal conditions on rectal temperature (T_re) of the newborns in their nests; (2) effect of ambient temperature (T_a) on oxygen consumption; (3) effects of controlled changes in T_re on thermoregulatory and respiratory responses to anoxia and on anoxia tolerance.In their nests rat pups controlled T_re at 32–36 °C while the T_re–T_a difference changed within a range of 1–20 °C. The lowest oxygen consumption of ∼24 ml O₂ kg⁻¹ min⁻¹ was recorded at T_a of 32 °C. Pups, exposed to anoxia at their normal T_re of 33 °C, were able to decrease T_re by another 1.7 °C and they kept on extremely slow and quiescent gasping for scheduled 25 min. In contrast, rats at T_re of 37 °C and 39 °C reached a critical phase of accelerated and shallow gasping after 14.95±0.40 min and 9.25±0.30 min, respectively.In conclusion, reduced T_re and unique gasping ability make newborn rats extremely tolerant to asphyxia.