Seasonal,environmental and anthropogenic influences on nocturnal basking in turtles and crocodiles from North-Eastern Australia

Many ectotherms bask in the sun as a behavioural mechanism to increase body temperature and facilitate metabolism, digestion or gamete production, among other functions. Such behaviours are common during the day, but some nocturnal species are also known to thermoregulate at night, in the absence of solar radiation, through shifts in body posture or microhabitat selection. Additionally, recent work has documented nocturnal basking in freshwater turtles in tropical Australia, though the purpose of the behaviour remains unknown. Here, we have built upon that work to test: 1. seasonal differences, 2. the influence of environmental factors and 3. the influence of anthropogenic development (e.g. river-front houses) on nocturnal basking behaviour. We visually surveyed transects repeatedly at night on the Ross River, Townsville, QLD, Australia from March to November 2020 and documented nocturnal basking in both freshwater turtles (Emydura macquarii krefftii) and freshwater crocodiles (Crocodylus johnstoni). For both taxa, we found significantly more nocturnal basking activity during the hotter months. Likewise, water surface temperature significantly influenced nocturnal basking in both taxa, especially when water temperatures were both high and warmer than air temperatures. We propose that nocturnal basking provides a mechanism for thermoregulatory cooling when water temperatures are high (e.g. 30°C) and above-preferred temperatures. After accounting for availability in basking habitat, both turtles and crocodiles basked more frequently on the undeveloped side of the river, suggesting avoidance of human activity or disturbance. This study is the first to document nocturnal basking activity temporally throughout the year as well as the first to identify the influences of environmental factors. Nocturnal thermoregulation has been documented in many reptiles, however, thermoregulatory cooling in tropical systems is less well-known.     

Leech removal is not the primary driver of basking behavior in a freshwater turtle

Leaving the water to bask (usually in the sun) is a common behavior for many freshwater turtles, with some species also engaging in “nocturnal basking.” Ectoparasite removal is an obvious hypothesis to explain nocturnal basking and has also been proposed as a key driver of diurnal basking. However, the efficacy of basking, day or night, to remove leeches has not been experimentally tested. Therefore, we examined the number of leeches that were removed from Krefft''s river turtles (Emydura macquarii krefftii) after experimentally making turtles bask at a range of times of day, durations, and temperatures. Turtles had high initial leech loads, with a mean of 32.1 leeches per turtle. Diurnal basking under a heat lamp for 3 hr at ~28°C significantly reduced numbers of leeches relative to controls. In diurnal trials, 90.9% of turtles lost leeches (mean loss of 7.1 leeches per turtle), whereas basking for 30 min under the same conditions was not effective (no turtles lost leeches, and all turtles were still visibly wet). Similarly, “nocturnal basking” at ~23°C for 3 hr was not effective at removing leeches. Only 18% of turtles lost leeches (one turtle lost one leech and another lost four leeches). Diurnal basking outdoors under direct sunlight for 20 min (mean temp = 34.5°C) resulted in a small reduction in leeches, with 50% of turtles losing leeches and an average loss of 0.7 leeches per turtle. These results indicate basking can remove leeches if temperatures are high or basking durations are long. However, it was only effective at unusually long basking durations in this system. Our data showed even the 20‐min period was longer than 70.1% of natural diurnal basking events, many of which took place at cooler temperatures. Therefore, leech removal does not appear to be the purpose of the majority of basking events.     

Observations and comments on the body temperatures of some New Zealand reptiles

Abstract

Rectal body temperatures (BTs) of tuataras (Sphenodon punctatus) and of endemic, ovoviviparous gekkonid lizards—mainly Hoplodactylus maculatus (=H. pacificus) and Heteropholis manukanus—were taken together with ambient temperatures during early summer 1970 in areas of central New Zealand. The results, combined with earlier data, enable a number of conclusions to be drawn. (a) The preferred body temperature of heliotherm reptiles is best deduced from the mode of rectal BTS taken in the field, but that of non-heliotherms, when unimodal, from the median or mean. (b) Among Gekkonoidea, specific thermal relations are highly variable in several ways. (c) Sphenodon foraged on cool nights at BTs of 10.5–12.5°c, yet basked in the forest by day at BTs up to 24°c; in pasture it apparently basks within the burrow entrance. (d) Similarly, H. maculatus foraged at night at BTs of 10–13°c, but by day thermoregulated at BTs up to 33°c by ‘indirect basking’ (under thin cover) or ‘protected basking’ (in crevices penetrated by solar radiation). The average BT of females was 2°c higher than that of males, presumably because many females were gravid. (e) H. manukanus is (tertiarily) diurnal, and thermoregulated by basking up to a BT of 31 °c. Towards evening it apparently cooled down voluntarily. (f) Whereas a high daytime BT probably assists digestion in nocturnal foragers, a voluntary low night-time BT in diurnal reptiles may help to conserve energy.     

Thermoconformity strategy in the freshwater turtle Hydromedusa tectifera (Testudines,Chelidae) in its southern distribution area

Ectotherm species are not capable of generating metabolic heat; therefore, they present different strategies for regulating their body temperatures, ranging from a precise degree of thermoregulation to a passive thermoconformity with ambient temperatures. In reptiles, aerial basking is the most common mechanism for gaining heat. However, among aquatic reptiles, such as freshwater turtles, aquatic basking is also frequent. Hydromedusa tectifera is a turtle of exclusively aquatic and nocturnal habits widely distributed in South America. We studied the relationship between body temperature (Tb) of H. tectifera and its habitat, and explored the effects of sex, life stage and body size and mass on Tb. Fieldwork was conducted in two streams of a mountain area of central Argentina. We recorded cloacal temperature, size and mass of 84 turtles. We also determined individuals’ sex and life stage (adult/juvenile). Regarding ambient temperatures, we measured water temperature on the surface (Tsurf) and at depth of turtle capture (Tdepth) and air temperature. Mean Tb was 18.58 °C (Min = 10.20 °C; Max = 25.70 °C). Tsurf and Tdepth were highly correlated. Multi-model analysis using Akaike criterion indicated that Tb was strongly associated with water temperature, whereas air temperature and body size and mass did not show a significant effect. There was also no effect of turtle sex or life stage on Tb. Our results indicate that H. tectifera is a thermoconformer and eurythermal species. A nocturnal pattern of activity and a fully aquatic lifestyle are suggested as determinant factors.     

A new method to determine the energy saving night temperature for vegetative growth of Phalaenopsis

Knowledge of the energy saving night temperature (i.e. a relatively cool night temperature without affecting photosynthetic activity and physiology) and a better understanding of low night temperature effects on the photosynthetic physiology of Phalaenopsis would improve their production in terms of greenhouse temperature control and energy use. Therefore, Phalaenopsis‘Hercules’ was subjected to day temperatures of 27.5°C and night temperatures of 27.0°C, 24.2°C, 21.2°C, 18.3°C, 15.3°C or 12.3°C in a growth chamber. A new tool for the determination of the energy saving night temperature range was developed based on temperature response curves of leaf net CO₂ exchange, chlorophyll fluorescence, organic acid content and carbohydrate concentrations. The newly developed method was validated during a complete vegetative cultivation in a greenhouse environment with eight Phalaenopsis hybrids (i.e. ‘Boston’, ‘Bristol’, ‘Chalk Dust', ‘Fire Fly’, ‘Lennestadt’, ‘Liverpool’, ‘Precious’, ‘Vivaldi’) and day/night temperature set points of 28/28°C, 29/23°C and 29/17°C. Temperature response curves revealed an overall energy saving night temperature range for nocturnal CO₂ uptake, carbohydrate metabolism, organic acid accumulation and photosystem II (PSII) photochemistry of 17.1°C to 19.9°C for Phalaenopsis‘Hercules’. At the lower end of this energy saving night temperature range, a high malate‐to‐citrate ratio switched towards a low ratio and this transition seemed to alleviate effects of night chilling induced photoinhibition. At night temperatures of 24°C or higher, the degradation of starch, glucose and fructose indicated an increased respiratory CO₂ production. During the greenhouse validation experiment, the differences between the eight Phalaenopsis hybrids with regard to their response to the warm day/cool night temperature regimes were remarkably large. In general, the day/night temperature of 29/17°C led to a significantly lower biomass accumulation and less leaves which were in addition shorter, narrower and smaller in size as compared to the day/night temperature regimes of 28/28°C and 29/23°C. During week 25 of the cultivation period, plants matured and flower initiation steeply increased for all hybrids and in each day/night temperature regime. Before week 25, early spiking was only sufficiently suppressed in the 29/23°C and 29/17°C temperature regimes for three hybrids (‘Boston’, ‘Bristol’ and ‘Lennestadt’) but not in the other five hybrids. Although a considerable biochemical flexibility was demonstrated for Phalaenopsis‘Hercules’, inhibition of flowering after exposure to a combination of warm days and cool nights appeared to be largely hybrid dependent.     

A novel method of behavioural thermoregulation in butterflies

Abstract The requirement for efficient thermoregulation has directed the coevolution of specialized morphological and behavioural traits in ectotherms. Adult butterflies exhibit three thermoregulatory mechanisms, termed dorsal, lateral and reflectance basking. In this study, we investigate a potential fourth mechanism whereby individuals perch with their wings fully spread and angled downwards such that the margins are appressed to the substrate. We find that mate‐locating male Hypolimnas bolina (L.) (Nymphalidae) adopt this posture when operational thoracic temperatures are lowest (less than approximately 34 °C). As thoracic temperature increases, males perch with wings increasingly closed and ultimately select shaded microhabitats. Using thermocouple‐implanted dead models, we show that appressed posture individuals warm faster than those adopting the conventional dorsal‐basking (horizontal wing) posture. This thermal advantage is not mitigated by shading of the outer 60–70% of the wing area, which suggests that – as with the conventional dorsal posture – only the basal wing surfaces contribute to heat gain via the absorption of solar irradiation. These investigations suggest that appression represents a novel extension of conventional dorsal basking behaviour in butterflies.     

Effect of acclimation temperature and substrate type on selected temperature,movement and activity of juvenile spiny softshell turtles (Apalone spinifera) in an aquatic thermal gradient

In some turtle species, temperature selection may be influenced by environmental conditions, including acclimation temperature and substrate quality. These factors may be particularly important for softshell turtles that are highly aquatic and often thermoregulate by burying in the substrate in shallow water microhabitats. We tested for effects of acclimation temperature (22 °C or 27 °C) and substrate type (sand or gravel) on the selected temperature and movement patterns of 20 juvenile spiny softhshell turtles (Apalone spinifera; Reptilia: Trionychidae) in an aquatic thermal gradient of 14–34 °C. Among 7–11 month old juvenile softshell turtles, acclimation temperature and substrate type did not influence temperature selection, nor alter activity and movement patterns. During thermal gradient tests, both 22- and 27 °C-acclimated turtles selected the warmest temperature (34 °C) available most frequently, regardless of substrate type (sand or gravel). Similarly, acclimation temperature and substrate type did not influence movement patterns of turtles, nor the number of chambers used in the gradient tests. These results suggest that juvenile Apalone spinifera are capable of detecting small temperature increments and prefer warm temperatures that may positively influence growth and metabolism, and that thermal factors more significantly influence aquatic thermoregulation in this species than does substrate type.     

A heterogeneous thermal environment enables remarkable behavioral thermoregulation in Uta stansburiana

Ectotherms can attain preferred body temperatures by selecting specific temperature microhabitats within a varied thermal environment. The side‐blotched lizard, Uta stansburiana may employ microhabitat selection to thermoregulate behaviorally. It is unknown to what degree habitat structural complexity provides thermal microhabitats for thermoregulation. Thermal microhabitat structure, lizard temperature, and substrate preference were simultaneously evaluated using thermal imaging. A broad range of microhabitat temperatures was available (mean range of 11°C within 1–2 m²) while mean lizard temperature was between 36°C and 38°C. Lizards selected sites that differed significantly from the mean environmental temperature, indicating behavioral thermoregulation, and maintained a temperature significantly above that of their perch (mean difference of 2.6°C). Uta's thermoregulatory potential within a complex thermal microhabitat structure suggests that a warming trend may prove advantageous, rather than detrimental for this population.     

Effect of thermal acclimation on preferred temperatures in two mygalomorph spiders inhabiting contrasting habitats

Variations in the preferred temperatures during the rest periods of Grammostola rosea Walckenaer and Paraphysa parvula Pocock, two mygalomorph spiders occupying different habitats in central Chile, are analyzed. The former inhabits arid and semi‐arid lowland near plant communities, composed of shrubs (evergreens with small leathery leaves) and small trees; the latter is found in the central mountains of the Chilean Andes, above 2000 m.a.s.l. The preferred temperatures of these spiders at different times of day and exposure to cold (15 °C) and warm (25 °C) acclimation temperatures are compared. Body mass does not affect the preferred temperature of the larger spider G. rosea, although P. parvula, a spider with half of the body mass of G. rosea, shows a decrease in preferred temperature with body mass. This can be explained by a higher plasticity and thermal sensitivity of the smaller species as result of increased surface : volume ratio. The preferred temperature increases with the hour of the day under both acclimation conditions in P. parvula and in cold‐acclimated G. rosea, which is likely associated with crepuscular and nocturnal behaviour in both species. Grammostola rosea shows temperature preferences lower than those of P. parvula under both acclimation conditions. The increase of the acclimation temperature from 15 to 25 °C results in an increment of 2–3 °C in the preferred temperature of P. parvula but only 0.2 °C in that of G. rosea. Two contrasting lifestyle strategies are found: a small mygalomorph spider with phenotypic plasticity and adaptation to the fluctuating environment of high altitude, and a large mygalomorph spider with higher thermal inertia adapted to the more stable environment of lowlands.     

Effects of Parturition and Feeding on Thermal Preference of Atlantic Stingray, Dasyatis sabina (Lesueur)

Synopsis Temperature is the most important and least well documented environmental entity affecting reproduction and feeding of elasmobranch fishes, but it is unclear to what extent these fish may exploit behavioral thermoregulation to optimize physiological processes. Laboratory thermal preference determinations are important to understanding behavioral processes because they provide the vital quantitative link between environment, physiology, and adaptive behavior. Temperature preference data were collected on Atlantic stingrays, Dasyatis sabina (Lesueur) to assess the fishs’ ability to behaviorally optimize feeding and reproduction. Groups of male and pregnant female Atlantic stingrays exhibited statistically higher preferred median temperatures (26.2 and 26.1°C, respectively) than non-pregnant females (25.3°C; One-Way ANOVA on ranked data, F _[2,26] = 3.72, p=0.038). Median preferred temperatures in unfed stingrays of both genders ranged from 24.5 to 31.0°C, whereas, fed fish preferred temperatures between 23.5 and 27.5°C. Unfed stingrays preferred a median temperature of 24.5°C; however, after feeding fish preferred significantly warmer water temperatures of 25.7°C (Wilcoxon one-tail, matched-pairs, signed rank analysis; p<0.088). While overall differences were subtle, small preference adjustments can have important physiological consequences. For example, the 1°C increase seen in pregnant females over non-pregnant fish would reduce gestation time by as much as two weeks. Likewise, by moving to cooler water after feeding, stingrays may increase nutrient uptake efficiency by reducing evacuation rates. Our data indicate that movement and distribution of Atlantic stingrays are dictated, in part, by temperature effects on physiology.     

Thermoregulation and daily activity patterns in a black desert grasshopper,Taeniopoda eques

Behavioural thermoregulation was studied in the western horse lubber grasshopper Taeniopoda eques (Burmeister), a native of the Chihuahuan Desert of North America. The grasshoppers regulated their temperature through a series of daily cyclical vertical movements between vegetation and the soil, and by the adoption of four thermoregulatory postures: flanking, crouching, stilting and stem-shading. At dawn, the grasshoppers moved from their nocturnal roost-plants to the ground, returned to bushes during the middle of the day, moved back to the open ground in the afternoon, then reascended vegetation at dusk. The occurrences of the four thermoregulatory postures were synchronized with these microhabitat shifts. During the cooler mornings and afternoons, the insects maximized heat gain by flanking and crouching, achieving thoracic temperatures of up to 16°C above ambient. Throughout the hot middle of the day the insects stilted and shaded, minimizing heat gain. These behaviours effectively kept the grasshoppers' body temperatures near the preferred temperature (36·2°C), but lower than the maximum voluntarily tolerated temperature (41·9°C), critical thermal maximum (45·2°C) and instantaneous lethal maximum (46·5°C). The body size of flanking insects influenced heating and cooling rates, wind effects and temperature excess at equilibrium. Both infrared and visible radiation appeared to elicit flanking. The need and ability to thermoregulate are influenced by this insect's reliance on chemical deterrents for defence.     

Thermoregulatory behavior of the triggerfish Balistes fuscus in an electronic shuttlebox

Ten blue triggerfish,Balistes fuscus, were tested individually for 3 days each in Ichthyotron electronic shuttleboxes to measure their thermoregulatory behavior. The modal thermal preferendum, a species-specific measure of temperature preference which is independent of prior thermal acclimation, was 25 °C. The triggerfish voluntarily occupied a 16–27 °C range of temperature, out of a potentially available range of 0–50 °C. There was no significant difference in preferred temperature between night and day, indicating lack of a thermoregulatory rhythm in this species. The preferred temperature range of this tropical marine reef species is similar to that of cool temperate freshwater and marine fishes; many warm temperate species prefer higher temperatures.     

Intraspecific alkaloid variation in ladybird eggs and its effects on con- and hetero-specific intraguild predators

Sexual size dimorphism (SSD) is a common phenomenon in animals. In many species females are substantially larger than males. Because body size plays a central role in modulating the body temperature (T _b) of ectotherms, intersexual differences in body size may lead to important intersexual differences in thermoregulation. In addition, because SSD is realized by differences in growth rate and because growth rate is strongly temperature dependent in ectotherms, a conflict between male reproductive behaviour and thermoregulation may affect the expression of SSD. In this study, we investigated the thermal implications of SSD in a reptile exhibiting spectacular female-biased SSD: the northern map turtle (Graptemys geographica). Over three seasons, we collected >150,000 measurements of T _b in free-ranging adult and juvenile northern map turtles using surgically implanted miniature temperature loggers. Northern map turtles exhibited seasonal patterns of thermoregulation typical of reptiles in northern latitudes, but we found that large adult females experienced a lower daily maximum T _b and a narrower daily range of T _b than adult males and small juvenile females. In addition, despite more time spent basking, large adult females were not able to thermoregulate as accurately as small turtles. Our findings strongly suggest that body size limits the ability to thermoregulate accurately in large females. By comparing thermoregulatory patterns between adult males and juvenile females of similar body size, we found no evidence that male reproductive behaviours are an impediment to thermoregulation. We also quantified the thermal significance of basking behaviour. We found, contrary to previous findings, that aerial basking allows northern map turtles to raise their T _b substantially above water temperature, indicating that basking behaviour likely plays an important role in thermoregulation.     

Ecophysiology of seed dormancy and the control of germination in early spring‐flowering Galanthus nivalis and Narcissus pseudonarcissus (Amaryllidaceae)

Seed dormancy induction and alleviation in the winter‐flowering, moist temperate woodland species Galanthus nivalis and Narcissus pseudonarcissus are complex and poorly understood. Temperature, light and desiccation were investigated to elucidate their role in the germination ecophysiology of these species. The effect of different seasonal temperatures, seasonal durations, temperature fluctuations, the presence of light during different seasons and intermittent drying (during the summer period) over several ‘years’ on seed germination was investigated with outdoor and laboratory experiments. Warm summer‐like temperatures (20 °C) were necessary for germination at subsequent cooler autumn‐like temperatures (greatest at 15 °C in G. nivalis and 10 °C in N. pseudonarcissus). As the warm temperature duration increased, so did germination at subsequent cooler temperatures; further germination occurred in subsequent ‘years’ at cooler temperatures following a second, and also third, warm period. Germination was significantly greater in darkness, particularly in G. nivalis. Dormancy increased with seed maturation period in G. nivalis, because seeds extracted from green capsules germinated more readily than those from yellow capsules. Desiccation increased dormancy in an increasing proportion of N. pseudonarcissus seeds the later they were dried in ‘summer’. Seed viability was only slightly reduced by desiccation in N. pseudonarcissus, but was poor and variable in G. nivalis. Shoot formation occurred both at the temperature at which germination was greatest and also if 5 °C cooler. In summary, continuous hydration of seeds of both species during warm summer‐like temperatures results in the gradual release of seed dormancy; thereafter, darkness and cooler temperatures promote germination. Cold temperatures, increased seed maturity (G. nivalis) and desiccation (N. pseudonarcissus) increase dormancy, and light inhibits germination. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2015, 177 , 246–262.     

Thermal response in pre‐imaginal biology of Ochlerotatus albifasciatus from two different climatic regions

The biological processes on mosquito could be variable in response to local climatic characteristics. The thermal effects on time and the rate larval development, immature survival and adult size in local populations of Ochlerotatus albifasciatus (Macquart) (Diptera: Culicidae) from cold (Sarmiento) and temperate (Buenos Aires) regions from Argentina were evaluated. This species affects livestock production and human health. Larvae of both regions were placed in breeding thermal baths (11–32 °C range). Development and survival were recorded daily until adult emergence. The development temperature threshold and thermal constant for Sarmiento (4.59 ± 3.08 °C, 204.08 ± 7.83 degree days) was lower and higher than Buenos Aires, respectively (8.06 ± 1.81 °C, 149.25 ± 2.6 degree days). At cold temperatures (11–16 °C), Sarmiento larvae demonstrated 5 days faster development and higher survival (56%) than Buenos Aires (15%), whereas at warm temperatures (20–32 °C) were up to 2 days slower and similar survival (16% vs. 18%). The size did not show differences between populations. An Ochlerotatus albifasciatus population seems to present local thermal responses. The favourable temperature for survival and rate of development would vary within a cold or warm range, and these differential responses would explain the wide geographical distribution in different climatic regions of southern South America.     

Temperature during embryonic and juvenile development influences growth in hatchling snapping turtles,Chelydra serpentina

Embryonic temperature influenced subsequent growth in juvenile snapping turtles, Chelydra serpentina: incubation temperatures of 24 and 26.5°C enhanced growth relative to a temperature of 29°C. Although embryonic temperature normally determines gonadal sex in this species, experimental manipulations revealed that temperature effects on growth were independent of sex. Ambient temperature also affected growth: juvenile turtles grew slowly in a cool (19°C) versus a warm (28°C) environment. In a parallel experiment, turtles from different embryonic temperatures displayed different patterns of temperature choice in response to nutritional status or time of day. We tentatively conclude that embryonic temperature has both direct and indirect (i.e., through temperature choice) effects on growth in snapping turtles.     

Why don't small snakes bask? Juvenile broad‐headed snakes trade thermal benefits for safety

Previous studies have suggested that most small Australian elapid snakes are nocturnal and rarely bask in the open because of the risk of predation by diurnal predatory birds. Because the physiology and behaviour of reptiles is temperature dependent, staying in refuges by day can entail high thermoregulatory costs, particularly for juveniles that must grow rapidly to maximise their chances of survival. We investigated whether the risk of predation deters juveniles of the endangered broad-headed snake ( Hoplocephalus bungaroides ) from basking, and if so, whether there are thermal costs associated with refuge use. To estimate avian attack rates on snakes, we placed 900 plasticine snake replicas in sunny locations and underneath small stones on three sandstone plateaus for 72 h. At the same time we quantified the thermal benefits of basking vs refuge use. On sunny days, juveniles could maintain preferred body temperatures for 4.7 h by basking but only for 2.0 h if they remained inside refuges. Our predation experiment showed that basking has high costs for juvenile snakes. Predators attacked a significantly higher proportion of exposed models (13.3%) than models under rocks (1.6%). Birds were the major predators of exposed models (75% of attacks), and avian predation did not vary across the landscape. By trading heat for safety, juvenile H. bungaroides decreased the potential time period that they could maintain preferred body temperatures by 57%. Thermal costs of refuge use may therefore contribute to the slow growth and late maturation of this endangered species. Our results support the hypothesis that nocturnal activity in elapid snakes has evolved to minimise the risk of avian predation.     

Thermal ecology of the Australian agamid Pogona barbata

This study compares the thermal ecology of male bearded dragon lizards (Pogona barbata) from south-east Queensland across two seasons: summer (1994–1995) and autumn (1995). Seasonal patterns of body temperature (T _b) were explored in terms of changes in the physical properties of the thermal environment and thermoregulatory effort. To quantify thermoregulatory effort, we compared behavioral and physiological variables recorded for observed lizards with those estimated for a thermoconforming lizard. The study lizards' field T _bs varied seasonally (summer: grand daily mean (GDM) 34.6 ± 0.6°C, autumn: GDM 27.5 ± 0.3°C) as did maximum and minimum available operative temperatures (summer: GDM T _max 42.1 ± 1.7°C, T _min 32.2 ± 1.0°C, autumn: GDM T _max 31.7 ± 1.2°C, T _min 26.4 ± 0.5°C). Interestingly, the range of temperatures that lizards selected in a gradient (selected range) did not change seasonally. However, P. barbata thermoregulated more extensively and more accurately in summer than in autumn; lizards generally displayed behaviors affecting heat load nonrandomly in summer and randomly in autumn, leading to the GDM of the mean deviations of lizards' field T _bs from their selected ranges being only 2.1 ± 0.5°C in summer, compared to 4.4 ± 0.5°C in autumn. This seasonal difference was not a consequence of different heat availability in the two seasons, because the seasonally available ranges of operative temperatures rarely precluded lizards from attaining field T _bs within their selected range, should that have been the goal. Rather, thermal microhabitat distribution and social behavior appear to have had an important influence on seasonal levels of thermoregulatory effort. Received: 28 April 1997 / Accepted: 29 December 1997     

Broad thermal capacity facilitates the primarily pelagic existence of northern fur seals (Callorhinus ursinus)

Thermoregulatory capacity may constrain the distribution of marine mammals despite having anatomical and physiological adaptations to compensate for the thermal challenges of an aquatic lifestyle. We tested whether subadult female northern fur seals (Callorhinus ursinus) experience increased thermoregulatory costs in water temperatures potentially encountered during their annual migration in the Bering Sea and North Pacific Ocean. Metabolic rates were measured seasonally in 6 captive female northern fur seals (2.75–3.5 yr old) in ambient air and controlled water temperatures of 2°C, 10°C, and 18°C. Rates of oxygen consumption in ambient air (1°C–18°C) were not related to environmental temperature except below 2.5°C (winter only). However, metabolism was significantly higher during the fall seasonal trials (September–October) compared to other times of year, perhaps due to the costs of molting. The fur seals appeared thermally neutral in all seasons for all water temperatures tested (2°C–18°C) except during the summer when metabolic rates were higher in the 2°C water. Comparing this broad thermal neutral zone to the average sea surface temperatures potentially encountered during annual migrations indicates wild fur seals can likely exploit a large geographic area without added thermal metabolic costs.     

Thermoregulation in premature infants: A mathematical model

PurposeIn 2010, approximately 14.9 million babies (11.1%) were born preterm. Because preterm infants suffer from an immature thermoregulatory system they have difficulty maintaining their core body temperature at a constant level. Therefore, it is essential to maintain their temperature at, ideally, around 37 °C. For this, mathematical models can provide detailed insight into heat transfer processes and body-environment interactions for clinical applications.MethodsA new multi-node mathematical model of the thermoregulatory system of newborn infants is presented. It comprises seven compartments, one spherical and six cylindrical, which represent the head, thorax, abdomen, arms and legs, respectively. The model is customizable, i.e. it meets individual characteristics of the neonate (e.g. gestational age, postnatal age, weight and length) which play an important role in heat transfer mechanisms. The model was validated during thermal neutrality and in a transient thermal environment.ResultsDuring thermal neutrality the model accurately predicted skin and core temperatures. The difference in mean core temperature between measurements and simulations averaged 0.25±0.21 °C and that of skin temperature averaged 0.36±0.36 °C. During transient thermal conditions, our approach simulated the thermoregulatory dynamics/responses. Here, for all infants, the mean absolute error between core temperatures averaged 0.12±0.11 °C and that of skin temperatures hovered around 0.30 °C.ConclusionsThe mathematical model appears able to predict core and skin temperatures during thermal neutrality and in case of a transient thermal conditions.