Thermal biology of the southernmost lizards in the world: Liolaemus sarmientoi and Liolaemus magellanicus from Patagonia,Argentina

We determined the efficiency of thermoregulation by the southernmost liolaemids Liolaemus sarmientoi and L. magellanicus from Patagonia, Argentina (51°S), by measuring body (T_b), microenvironmental, and operative temperatures in the field, and preferred body temperatures in the laboratory (T_pref). L. sarmientoi was found to be a poor thermoregulator, whereas L. magellanicus was deemed to be a constrained thermoconformer. Among all known species of Liolaemus, L. sarmientoi and L. magellanicus had the lowest T_b's when tested in the field; however, their T_pref's were similar to other liolaemids. These data suggest that these southernmost liolaemid species have not evolved appropriate thermoregulatory behaviors or made adequate physiological adaptations to face the extreme thermal challenges of their environment.     

Thermal responses to environmental constraints in two populations of the oviparous lizard Liolaemus bibronii in Patagonia,Argentina

Ectotherms change their thermoregulation behaviour according to the available temperatures, photoperiod, and radiation present in their local environment. The influences of the abiotic environment not only affect the body temperature but also most life history traits of populations. The thermal biology of one of the southernmost oviparous lizards, Liolaemus bibronii, was studied at high- and low-latitude sites in Patagonia, Argentina, following the methodology of Hertz et al. [1993. Evaluating temperature regulation by field-active ectotherms: the fallacy of the inappropriate question. Am. Nat. 142, 796–818]. Our results show that L. bibronii lives under thermal–environmental constraints, behaves as a moderate thermoregulator, and shows the lowest body temperature (28 °C) for oviparous liolaemids.     

Performance and thermal sensitivity of the southernmost lizards in the world, Liolaemus sarmientoi and Liolaemus magellanicus

Locomotor activity performance of reptiles is largely temperature dependent and, in harsh environments with short activity periods during the day and throughout the year, plays a vital role in the fitness of the species. This particular study focuses on the performance and the thermal sensitivity for running, at different body temperatures, of the two southernmost species of lizards in the world, Liolaemus sarmientoi and Liolaemus magellanicus, studied at two locations in the south of Santa Cruz province, Argentina (51°S, 70°W and 50°S, 72°W; 133 m asl). The speed of sprint and long runs was measured in the field to determine the physiological performance of lizards at different air temperatures. In both species speed increases with the temperature, and they reach the highest performance at high temperatures. The difference between activity and thermal optima suggests that L. magellanicus has colonized its actual environment recently, and that it has not had enough time for its physiological mechanisms to evolve and achieve a maximum performance at the cold temperatures they have to tolerate at present. In contrast, L. sarmientoi achieved a high performance over a wider range of temperatures that included temperatures lower than the preferred temperatures in the lab, which they can generally find in their environment.     

Thermal ecology of two sympatric saxicolous lizards of the genus Phymaturus from the Payunia region (Argentina)

We evaluated the thermal biology of two sympatric saxicolous species of the genus Phymaturus, endemic from the Argentine Payunia region. Taking into account that the distributional range of Phymaturus roigorum (the largest species) is greater than the range of P. payuniae, we evaluated the habitat (type of rocks) used by these species. We recorded body temperature and operative temperatures in different habitats, and we determined the preferred body temperature in the laboratory. We compared the thermal quality of habitats occupied and not occupied by Phymaturus payuniae, and the accuracy and effectiveness of thermoregulation between species.     

Thermoregulatory movement patterns of the lizard Podarcis carbonelli (Lacertilia: Lacertidae)

Using video cameras and motion detection software, we examined sequential positions of the lizard Podarcis carbonelli in a temperature gradient to look for patterns in spatial and temporal thermoregulatory movements. As lizards shuttled between warm and cool areas, their movements were typically slow; punctuated by bursts of speed. The animals were relatively inactive when heating, moved almost continually when cooling, and spent less time heating than cooling. Traditional modeling techniques proved unsuccessful, so we assessed the movement patterns with nonlinear dynamical techniques. The shuttling frequency, and the pattern of velocity changes, both met the qualitative attributes (self similarity, strange attractors, and noisy power spectra) and the quantitative criteria (positive Lyapunov exponent and capacity and/or correlation dimensions less than 5) that suggest deterministic chaos. These movement patterns appear regular, but at unpredictable times the patterns become disturbed before returning to regulation. There are both behavioral and physiological advantages to movements that follow a model of deterministic chaos control.     

Seasonal changes in the thermoregulatory strategies of Rhinella arenarum in the Monte desert, Argentina

We determined and compared the efficiency of thermoregulation of Rhinella arenarum in the Monte desert (Argentina) in two seasons, dry and wet. In the field, we measured body temperatures, micro-habitat temperatures and operative temperatures; while in the laboratory; we measured the selected body temperatures. Our results show a change in the thermoregulatory strategy of R. arenarum that is related to environmental constraints on their thermal niche. R. arenarum has the ability to be plastic and combine two strategies: (i) a moderate thermoregulator in the wet season, where thermal resources are available such that body temperature is maintained within the set points and physiologicial and behavioral processes are optimized; and (ii) a thermoconformer in the dry season where the thermal environment is more homogeneous and there is greater time invested in searching for food.     

Factors affecting the thermal behavior of the sand lizard Liolaemus wiegmannii in natural and modified grasslands of temperate coastal dunes from Argentina

The present study describes and compares the thermal behavior of individuals of Liolaemus wiegmannii, inhabiting patches of natural grassland and modified patches with exotic trees of Acacia longifolia, by analyzing the factors affecting its behavior. Thermal behavior of L. wiegmannii was assessed by radiotracking 22 adult individuals in a coastal dune area from Argentina. In order to account for individual responses we analyzed the factors affecting thermal behavior using Generalized Linear Mixed Models. Thermal behavior of L. wiegmannii was mainly affected by the time of day and the substrate temperature. The individuals basking on bare sand in the morning shifted to filtered sunlight during midday and to the shade of clump and erect stems and herbs during the afternoon. The individuals buried in sand when the substrate temperature was low and the wind speed was high. The use of sub-shrubs and shrubs could not be explained solely by thermal factors. In natural L. wiegmannii regulated its body temperature by shuttling between microhabitats that provided them with different levels of exposure to sunlight during the day. However, in modified patches individuals varied in the choice of plants used as shaded places to mitigate high microenvironmental temperatures and they were also more exposed to full shaded sites and less to warm sand to bask, which could have negative consequences for its thermal biology.     

Temperature dependence of habituation of the initial responses to cold-water immersion

The initial responses to cold-water immersion, evoked by stimulation of peripheral cold receptors, include tachycardia, a reflex inspiratory gasp and uncontrollable hyperventilation. When immersed naked, the maximum responses are initiated in water at 10°C, with smaller responses being observed following immersion in water at 15°C. Habituation of the initial responses can be achieved following repeated immersions, but the specificity of this response with regard to water temperature is not known. Thirteen healthy male volunteers were divided into a control (C) group (n = 5) and a habituation (H) group (n = 8). Each subject undertook two 3-min head-out immersions in water at 10°C wearing swimming trunks. These immersions took place at a corresponding time of day with 4 days separating the two immersions. In the intervening period the C group were not exposed to cold water, while the H group undertook another six, 3-min, head-out immersions in water at 15°C. Respiratory rate (f _R), inspiratory minute volume (V˙ _I) and heart rate (f _H) were measured continuously throughout each immersion. Following repeated immersions in water at 15°C, the f _R, V˙ _I and f _H responses of the H group over the first 30 s of immersion were reduced (P < 0.01) from 33.3 breaths · min⁻¹, 50.5 l · min⁻¹ and 114 beats · min⁻¹ respectively, to 19.8 breaths · min⁻¹, 26.4 l · min⁻¹ and 98 beats · min⁻¹, respectively. In water at 10°C these responses were reduced (P < 0.01) from 47.3 breaths · min⁻¹, 67.6 l · min⁻¹ and 128 beats · min⁻¹ to 24.0 breaths · min⁻¹, 29.5 l · min⁻¹ and 109 beats · min⁻¹, respectively over a corresponding period of immersion. Similar reductions were observed during the last 2.5 min of immersions. The initial responses of the C group were unchanged. It is concluded that habituation of the cold shock response can be achieved by immersion in warmer water than that for which protection is required. This suggests that repeated submaximal stimulation of the cutaneous cold receptors is sufficient to attenuate the responses to more maximal stimulation. Accepted: 6 February 1998     

Effects of thermal environment on sleep and circadian rhythm

ABSTRACT: The thermal environment is one of the most important factors that can affect human sleep. The stereotypical effects of heat or cold exposure are increased wakefulness and decreased rapid eye movement sleep and slow wave sleep. These effects of the thermal environment on sleep stages are strongly linked to thermoregulation, which affects the mechanism regulating sleep. The effects on sleep stages also differ depending on the use of bedding and/or clothing. In semi-nude subjects, sleep stages are more affected by cold exposure than heat exposure. In real-life situations where bedding and clothing are used, heat exposure increases wakefulness and decreases slow wave sleep and rapid eye movement sleep. Humid heat exposure further increases thermal load during sleep and affects sleep stages and thermoregulation. On the other hand, cold exposure does not affect sleep stages, though the use of beddings and clothing during sleep is critical in supporting thermoregulation and sleep in cold exposure. However, cold exposure affects cardiac autonomic response during sleep without affecting sleep stages and subjective sensations. These results indicate that the impact of cold exposure may be greater than that of heat exposure in real-life situations; thus, further studies are warranted that consider the effect of cold exposure on sleep and other physiological parameters.     

Growth and morphological responses of Fargesia angustissima to altitude in the Wolong Nature Reserve, southwestern China

The strong altitudinal gradients leading to dramatic variations in environmental conditions in mountain regions provide unique and sometimes the best opportunities to study plant responses and adaptation to global climate change. We investigated the morphological characteristics, aboveground biomass and its allocation of Fargesia angustissima (Mitford) T.P. Yi along an altitudinal gradient ranging from 1200 m (the lowest distribution boundary of F. angustissima) to 1810 m a.s.l. (the uppermost distribution limit) in the Wolong Nature Reserve, southwestern China. Except for a nearly linear increase in internode number and a linear decrease in shoot biomass with increasing elevation, other parameters studied changed non-linearly with increasing elevation. These results may imply that the local-environmental conditions do not change linearly with altitude. The growth of F. angustissima, as a low-altitude species, may be impacted by precipitation rather than by temperature. Hence, this dwarf bamboo species may be more sensitive to change in the amount and pattern of precipitation caused by rapid global climate change.     

Thermal responses of men and women during cold-water immersion: influence of exercise intensity

The influence of exercise intensity on thermoregulation was studied in 8 men and 8 women volunteers during three levels of arm-leg exercise (level I: 700 ml oxygen (O2).min-1; level II: 1250 ml O2.min-1; level III: 1700 ml O2.min-1) for 1 h in water at 20 and 28 degrees C (Tw). For the men in Tw 28 degrees C the rectal temperature (Tre) fell 0.79 degree C (P less than 0.05) during immersion in both rest and level-I exercise. With level-II exercise a drop in Tre of 0.54 degree C (P less than 0.05) was noted, while at level-III exercise Tre did not change from the pre-immersion value. At Tw of 20 degrees C, Tre fell throughout immersion with no significant difference in final Tre observed between rest and any exercise level. For the women at rest at Tw 28 degrees C, Tre fell 0.80 degree C (P less than 0.05) below the pre-immersion value. With the two more intense levels of exercise Tre did not decrease during immersion. In Tw 20 degrees C, the women maintained higher Tre (P less than 0.05) during level-II and level-III exercise compared to rest and exercise at level I. The Tre responses were related to changes in tissue insulation (I(t)) between rest and exercise with the largest reductions in I(t) noted between rest and level-I exercise across Tw and gender. For mean and women of similar percentage body fat, decreases in Tre were greater for the women at rest and level-I exercise in Tw 20 degrees C (P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)     

Thermal responses to feeding in a secretive and specialized predator (Gila monster, Heloderma suspectum)

We investigate how a unique dietary specialist, the Gila monster (Heloderma suspectum), uses behavioral thermoregulation to elevate body temperature (T_b) after feeding. Lizards in a laboratory thermal gradient were fed rodent meals of three different sizes (5, 10, or 20% of body mass), or sham fed (meal of 0% body mass), and T_bs were recorded for three days before feeding and seven days after feeding. Gila monsters selected a mean T_b of 25.2 °C while fasting (set-point range 23.6–27.1), and increased T_bs after feeding. The magnitude and duration of post-prandial T_b increases are positively related to meal size, and Gila monsters selected mean T_bs up to 3.0 °C higher and maintain elevated T_bs for 3–6 days after feeding. Selection of T_b does not appear to differ between day and night time periods, and because the lizards are both diurnal and nocturnal (at different times of year), photoperiod may not be an important influence on T_b selection.     

Effect of ambient temperature on female endurance performance

Ambient temperature can affect physical performance, and an ambient temperature range of −4 °C to 11 °C is optimal for endurance performance in male athletes. The few similar studies of female athletes appear to have found differences in response to cold between the genders. This study investigated whether ambient temperature affects female endurance performance. Nine athletes performed six tests while running on a treadmill in a climatic chamber at different ambient temperatures: 20, 10, 1, −4, −9 and −14 °C and a wind speed of 5 m s⁻¹. The exercise protocol consisted of a 10-min warm-up, followed by four 5-min intervals at increasing intensities at 76%, 81%, 85%, and 89% of maximal oxygen consumption. This was followed by an incremental test to exhaustion. Although peak heart rate, body mass loss, and blood lactate concentration after the incremental test to exhaustion increased as the ambient temperature rose, no changes in time to exhaustion, running economy, running speed at lactate threshold or maximal oxygen consumption were found between the different ambient temperature conditions. Endurance performance during one hour of incremental exercise was not affected by ambient temperature in female endurance athletes.     

Geographic variation and acclimation effects on thermoregulation behavior in the widespread lizard Liolaemus pictus

Populations at the warm range margins of the species distribution may be at the greatest risks of extinction from global warming unless they can tolerate extreme environmental conditions. Yet, some studies suggest that the thermal behavior of some lizard species is evolutionarily rigid. During two successive years, we compared the thermal biology of two populations of Liolaemus pictus living at the northern (warmer) and one population living at the southern (colder) range limits, thus spanning an 800 km latitudinal distance. Populations at the two range margins belong to two deeply divergent evolutionary clades. We quantified field body temperatures (T_b), laboratory preferred body temperatures (PBT), and used operative temperature data (T_e) to calculate the effectiveness of thermoregulation (E). During one year in all populations, we further exposed half of the lizards to a cold or a hot acclimation treatment to test for plasticity in the thermal behavior. The environment at the southern range limit was characterized by cooler weather and lower T_e. Despite that, females had higher T_b and both males and females had higher PBT in the southernmost population (or clade) than in the northernmost populations. Acclimation to cold conditions led to higher PBT in all populations suggesting that plastic responses to thermal conditions, instead of evolutionary history, may contribute to geographic variation. Lizards regulated moderately well their body temperature (E≈0.7): they avoided warm microhabitats in the northern range but capitalized on warm microhabitats in the southern range. We review literature data to show that Liolaemus species increase their thermoregulation efficiency in thermally challenging environments. Altogether, this indicates that habitats of low thermal quality generally select against thermoconformity in these lizards.     

Mathematical modeling of thermal physiological responses of clothed infants

The objective of this study is to develop a mathematical model for simulating the thermal physiological responses of clothed infants. By modifying and integrating Gagge's two-node model and Stolwijk's multi-node model, and coupled with the model of dynamic couple heat and moisture transfer in functional clothing, a new seven-node thermoregulation model for closed infants was developed. A series of preliminary numerical test were carried out for naked and clothed infant. The prediction of the new model was compared with the published data, the comparison results demonstrate that the model has good potential predictability.     

Seasonal and geographic variation in thermal biology of the lizard Microlophus atacamensis (Squamata: Tropiduridae)

1.

We studied physiological thermal adaptation in the lizard Microlophus atacamensis along a latitudinal range.     

A canine thermal model for simulating temperature responses of military working dogs

Military working dogs (MWDs) are often required to operate in dangerous or extreme environments, to include hot and humid climate conditions. These scenarios can put MWD at significant risk of heat injury. To address this concern, a two-compartment (core, skin) rational thermophysiological model was developed to predict the temperature of a MWD during rest, exercise, and recovery. The Canine Thermal Model (CTM) uses inputs of MWD mass and length to determine a basal metabolic rate and body surface area. These calculations are used along with time series inputs of environmental conditions (air temperature, relative humidity, solar radiation and wind velocity) and level of metabolic intensity (MET) to predict MWD thermoregulatory responses. Default initial values of core and skin temperatures are set at neutral values representative of an average MWD; however, these can be adjusted to match known or expected individual temperatures. The rational principles of the CTM describe the heat exchange from the metabolic energy of the core compartment to the skin compartment by passive conduction as well as the application of an active control for skin blood flow and to tongue and lingual tissues. The CTM also mathematically describes heat loss directly to the environment via respiration, including panting. Thermal insulation properties of MWD fur are also used to influence heat loss from skin and gain from the environment. This paper describes the CTM in detail, outlining the equations used to calculate avenues of heat transfer (convective, conductive, radiative and evaporative), overall heat storage, and predicted responses of the MWD. Additionally, this paper outlines examples of how the CTM can be used to predict recovery from exertional heat strain, plan work/rest cycles, and estimate work duration to avoid overheating.     

Effect of thermal tachypnoea and of its mechanical or pharmacological inhibition on hypothalamic temperature in the sheep

The abrupt inhibition of breathing in the panting sheep, by mechanical blockage of the nostrils or by the injection of noradrenaline or carbachol into a lateral cerebral ventricle, causes an immediate rise in hypothalamic temperature, followed by a rise in that of the carotid artery blood.

This confirms that evaporation from the surfaces of the upper respiratory tract has an immediate and local effect on brain temperature.

The significance of this relation in a species which controls its core temperature particularly well is discussed.     

Effects of acclimation and diapause on the thermal tolerance of the two-spotted spider mite Tetranychus urticae

The two-spotted spider mite, Tetranychus urticae, is a worldwide pest species that overwinters as diapausing females. Cold hardening is presumed to start during diapause development to ensure the successful overwintering of this species. To address this hypothesis, we compared cold tolerance between non-diapausing and diapausing females. We measured supercooling point (SCP) and survival to acute cold stress by exposing the mites at a range of sub-zero temperatures (from −4 to −28 °C for 2 h). The mean SCPs of non-diapausing and diapausing females were −19.6±0.5 and −24.7±0.3 °C respectively, and freezing killed the mites. Diapausing females were significantly more cold tolerant than non-diapausing ones, with LT₅₀ of −19.7 and −13.3 °C, respectively. Further, we also examined the effects of cold acclimation (10 d at 0 or 5 °C) in non-diapausing and diapausing females. Our findings indicated that diapause decreased SCP significantly, while cold acclimation had no effect on the SCP except for non-diapausing females that were acclimated at 5 °C. Acclimation at 5 °C enhanced survival to acute cold stress in diapausing and non-diapausing females, with LT₅₀ of −22.0 and −17.1 °C, respectively. Altogether, our results indicate that T. urticae is a chill tolerant species, and that diapause and cold acclimation elevate cold hardiness in this species.