Thermoregulatory Capabilities Research Articles

Biomimetic Structurally Colored Film for High‐Performance Radiative Cooling

AbstractIn recent years, passive radiative cooling has garnered considerable attention as a sustainable thermal regulation without relying on external energy sources, thus mitigating pollutants generation. However, an intrinsic limitation of these cooling systems lies in the reflective glare, often characterized by an ivory or silvery appearance. This drawback limits their practical application, especially where both functional efficiency and aesthetic appeal are pivotal. Herein, a biomimetic approach inspired by Saharan silver ants' thermoregulatory capabilities is adopted. These ants, equipped with distinctive triangular‐shaped hair, maintain body temperature lower than the ambient air. Leveraging insights from this natural model, a reusable silicon template is employed to fabricate a metasurface structural colored film with a triangular prism array structure using thermoplastic polyurethane (TPU) and the phase separation technique. The film demonstrates an average emissivity of 96% within the atmospheric window and an average solar reflectivity of 93%, leading to a maximum temperature reduction of 8.6 °C during daytime and 5.9 °C at night. Furthermore, the film displays stretchability and mechanical resilience, bolstered by the microscale prismatic structure enhancing superhydrophobicity. This work introduces a biomimetic strategy aimed at augmenting thermal emission while reconciling the challenge of achieving visual appealand high radiative cooling performance.

Preclinical validation of NeoWarm, a low-cost infant warmer and carrier device, to ameliorate induced hypothermia in newborn piglets as models for human neonates.

Approximately 1.5 million neonatal deaths occur among premature and small (low birthweight or small-for gestational age) neonates annually, with a disproportionate amount of this mortality occurring in low- and middle-income countries (LMICs). Hypothermia, the inability of newborns to regulate their body temperature, is common among prematurely born and small babies, and often underlies high rates of mortality in this population. In high-resource settings, incubators and radiant warmers are the gold standard for hypothermia, but this equipment is often scarce in LMICs. Kangaroo Mother Care/Skin-to-skin care (KMC/STS) is an evidence-based intervention that has been targeted for scale-up among premature and small neonates. However, KMC/STS requires hours of daily contact between a neonate and an able adult caregiver, leaving little time for the caregiver to care for themselves. To address this, we created a novel self-warming biomedical device, NeoWarm, to augment KMC/STS. The present study aimed to validate the safety and efficacy of NeoWarm. Sixteen, 0-to-5-day-old piglets were used as an animal model due to similarities in their thermoregulatory capabilities, circulatory systems, and approximate skin composition to human neonates. The piglets were placed in an engineered cooling box to drop their core temperature below 36.5°C, the World Health Organizations definition of hypothermia for human neonates. The piglets were then warmed in NeoWarm (n = 6) or placed in the ambient 17.8°C ± 0.6°C lab environment (n = 5) as a control to assess the efficacy of NeoWarm in regulating their core body temperature. All 6 piglets placed in NeoWarm recovered from hypothermia, while none of the 5 piglets in the ambient environment recovered. The piglets warmed in NeoWarm reached a significantly higher core body temperature (39.2°C ± 0.4°C, n = 6) than the piglets that were warmed in the ambient environment (37.9°C ± 0.4°C, n = 5) (p < 0.001). No piglet in the NeoWarm group suffered signs of burns or skin abrasions. Our results in this pilot study indicate that NeoWarm can safely and effectively warm hypothermic piglets to a normal core body temperature and, with additional validation, shows promise for potential use among human premature and small neonates.

The Influence of Roost Type and Diet on Energy Expenditure in Bats

Bats spend most of their lives resting, socializing, and raising their young in roosts. Roost conditions may affect the lifetime energy expenditure of bats, and this could, in turn, influence fitness of individuals. Different kinds of roosts impose different microclimatic conditions that can affect the thermal balances of bats that use them. Bats thermoregulate by using both physiological mechanisms (such as changes in conductance) and behavioral responses (huddling or active search of certain microclimates). We hypothesized that the contribution of these thermoregulatory strategies would differ depending on the roost type that bats use. To test this idea, we collated data from the literature on metabolic rate (MR), body temperature (Tb), ambient temperature at which MR and Tb were collected, roost type, and diet for 43 species of bats spanning eleven families. From these data, we calculated, for each species, the wet conductance and the area of the thermoregulatory polygon (TRP) as a proxy for the physiological thermoregulatory capabilities of bats. We found that, after controlling for phylogeny, wet conductance and the area of the TRP were higher in bats that use more exposed roosts than in those bats who use roosts that can buffer environmental conditions. Our results suggest that energy expenditure is similar for all species, but in bats that live in more exposed roosts, the contribution of physiological responses was more important than behavior at the entire range of environmental temperatures, whereas bats in more protected roosts seem to rely more on behavioral responses to thermoregulate. Considering that roosts represent valuable resources, the availability of roosts with the proper microclimatic conditions could determine the patterns of distribution of bat populations.

Octopamine drives honeybee thermogenesis.

In times of environmental change species have two options to survive: they either relocate to a new habitat or they adapt to the altered environment. Adaptation requires physiological plasticity and provides a selection benefit. In this regard, the Western honeybee (Apis mellifera) protrudes with its thermoregulatory capabilities, which enables a nearly worldwide distribution. Especially in the cold, shivering thermogenesis enables foraging as well as proper brood development and thus survival. In this study, we present octopamine signaling as a neurochemical prerequisite for honeybee thermogenesis: we were able to induce hypothermia by depleting octopamine in the flight muscles. Additionally, we could restore the ability to increase body temperature by administering octopamine. Thus, we conclude that octopamine signaling in the flight muscles is necessary for thermogenesis. Moreover, we show that these effects are mediated by β octopamine receptors. The significance of our results is highlighted by the fact the respective receptor genes underlie enormous selective pressure due to adaptation to cold climates. Finally, octopamine signaling in the service of thermogenesis might be a key strategy to survive in a changing environment.

Thermal ecology of Northern Water Snakes (Nerodia sipedon) in a northern wetland in central Michigan

Semi-aquatic north-temperate reptiles experience challenging environmental conditions for thermoregulation on both seasonal and daily bases. We studied the thermal biology of north-temperate Northern Water Snakes (Nerodia sipedon) in central Michigan by remote radiotelemetry monitoring of snake body temperature (Tb) using surgically implanted thermally-sensitive radio-transmitters and by measuring operative temperatures (Te) across a range of microhabitats using biophysical models. Our goals included evaluation of thermoregulatory capabilities at a locality that we viewed to be a fine-grained thermal environment, seasonal variations in patterns of thermoregulation, and the effects of sex on thermoregulation. During summer, snakes showed diel Tb cycling apparently using the open Sphagnum mat for late morning warming and shuttling among different microhabitats until early evening when a monotonic decline in Tb ensued and continued through the early morning hours. Snakes attained Tb within their laboratory-determined preferred body temperature range (Tset = 28–33 °C) mostly during late afternoon and with average percentages of Tb values for individual snakes within Tset range when permitted by operative temperatures (Ex) between 68 and 70% of the time depending on method of measurement. Relatively high investment in thermoregulation when thermal conditions were poor occurred only during September but declined thereafter as snakes prepared to overwinter. We did not detect differences in thermoregulation among reproductive females, non-reproductive females, and males. Relative to a population of N. sipedon at a higher latitude in Ontario our snakes showed a relatively high Tset range and thermoregulated more effectively, particularly during the daylight hours. It remains unclear how much inter-population variation in thermoregulation is due to potential adaptations to latitude, to habitat differences, or variations in methodologies.

Phenotypic variation in male Calopteryx splendens damselflies: the role of wing pigmentation and body size in thermoregulation

Abstract For ectothermic insects, their colour and size are important determinants of body temperature: larger bodies require more heat to reach a certain temperature, and dark colours absorb heat more efficiently. These dark colours are expressed using melanin, which has been intimately linked with the thermoregulatory capabilities of insects. Melanin is also linked with immune defence and is often used as a secondary sexual character in insects. There is a potential trade-off situation between thermoregulatory capabilities, immune defence and secondary sexual characters, all of which use melanin. Some Calopteryx damselflies, such as Calopteryx splendens, have melanin-based wing pigmentation that is sexually selected and drives intra- and interspecific territorial aggression. Our goal was to study experimentally how the wing pigmentation and body size of C. splendens males affect their thermoregulation and, especially, their ability to become active (hereafter, ‘activate’) after being cooled down. Our results were in line with our hypotheses, showing that individuals with larger wing spots had significantly faster activation times than those with smaller wing spots, and that individuals with larger body size had significantly slower activation times than those with smaller body size. Both variables showed an interaction and are therefore important in damselfly warm-up and activation. We discuss the role of wing pigmentation and thermoregulation in the behavioural patterns observed in Calopteryx species.

The down color of day old chicks of russian white hens population as a selection trait

As a result of long-term selection of Russian White hens in the RRIFAGB population for thermal resistance to low temperatures during chicks raising, as well as increased resistance to Marek's disease, carcinomas and diseases of the leukemia-sarcoma complex, genotypes with color of the down of day-old chicks appeared. Currently, a line of snow-white hens, homozygous for the recessive allele of down gene, has been segregated. Research objective was to study the traits of Russian hens with yellow down at day-old age comparing to snow-white hens in embryonic and early neonatal periods for thermoresistivity in low temperatures of raising, and also at the output level and the biological activity of the allantoin-amniotic fluid of their embryos. The influence of a single cooling during the sensitive period of embryogenesis (+20 o C for 6 hours on 5.5 days of incubation) on the output of extraembryonic fluid of 12.5-day-old embryos was studied; the thermoregulatory capabilities of 7-day-old chicks under the influence of a stress factor (cooling at +10 o C for 30 minutes for 7 days) and raising at a low temperature (+22 o C) were studied. The level of allantois-amniotic fluid yield and biological activity of Newcastle disease viruses, infectious bronchitis and chicken reovirus infection in it in embryos of Russian White hens with different color of down was evaluated. In response to the dosed effect of low temperatures during the sensitive period of embryogenesis, 12.5-day-old embryos of hens with down color increased the volume of extraembryonic fluid. However, the incubation rates in the line of snow-white hens were worse than in hens with yellow color of down. Snow white chicks also responded more to hypothermic stress in the first week of raising and had less volume and biological activity of the extraembryonic fluid of their embryos. It is concluded that to use hens that are homozygous for the gene of down as producers of raw materials for the Bio-Industry is not advisable.

Coping with heat in the arid interior – what can feather structure reveal about the ecology of Australia’s desert-living Grey Falcon Falco hypoleucos?

ABSTRACTThe Grey Falcon (Falco hypoleucos) is a desert-living species restricted to the dry centre of Australia. These falcons have a number of unique life-history adaptations that may be crucial for their survival in this harsh environment, but these may, conversely, confine them to these arid regions. In this study we investigated what Grey Falcon feather structure can reveal about the ecology of the species. Specifically, we tested UV reflectance and structural waterproofing of Grey Falcon feathers, and compared these properties across other Australian Falco species. Grey Falcon feathers did not reflect unique UV peaks, nor show any significant difference in structural waterproofing when compared with closely-related sympatric falcon species. This suggests that Grey Falcon feathers have no specific adaptations to prevent the impact of UV or water on their plumage, so feather structure evidently does not help explain the persistence of this species in arid Australia. We suggest that an exploration of the physiological and behavioural thermoregulatory capabilities of this species should provide further insights in understanding how these birds cope with their extreme environment and are confined there.

Pediatric Thermoregulation: Considerations in the Face of Global Climate Change.

Predicted global climate change, including rising average temperatures, increasing airborne pollution, and ultraviolet radiation exposure, presents multiple environmental stressors contributing to increased morbidity and mortality. Extreme temperatures and more frequent and severe heat events will increase the risk of heat-related illness and associated complications in vulnerable populations, including infants and children. Historically, children have been viewed to possess inferior thermoregulatory capabilities, owing to lower sweat rates and higher core temperature responses compared to adults. Accumulating evidence counters this notion, with limited child–adult differences in thermoregulation evident during mild and moderate heat exposure, with increased risk of heat illness only at environmental extremes. In the context of predicted global climate change, extreme environmental temperatures will be encountered more frequently, placing children at increased risk. Thermoregulatory and overall physiological strain in high temperatures may be further exacerbated by exposure to/presence of physiological and environmental stressors including pollution, ultraviolet radiation, obesity, diabetes, associated comorbidities, and polypharmacy that are more commonly occurring at younger ages. The aim of this review is to revisit fundamental differences in child–adult thermoregulation in the face of these multifaceted climate challenges, address emerging concerns, and emphasize risk reduction strategies for the health and performance of children in the heat.

The Effect of Convective Pre-warming on Intra-operative Thermoregulatory Capabilities

The Effect of Convective Pre-warming on Intra-operative Thermoregulatory Capabilities

Foraging strategies and physiological adaptations in large carpenter bees.

Large carpenter bees are charismatic and ubiquitous flower visitors in the tropics and sub-tropics. Unlike honeybees and bumblebees that have been popular subjects of extensive studies on their neuroethology, behaviour and ecology, carpenter bees have received little attention. This review integrates what is known about their foraging behaviour as well as sensory, physiological and cognitive adaptations and is motivated by their versatility as flower visitors and pollinators. This is evident from their extremely generalist foraging and adeptness at handling diverse flower types as legitimate pollinators and as illegitimate nectar robbers. They purportedly use traplining to forage between isolated patches and are long-distance flyers over several kilometres suggesting well-developed spatial learning, route memory and navigational capabilities. They have a broad range of temperature tolerance and thermoregulatory capabilities which are likely employed in their forays into crepuscular and nocturnal time periods. Such temporal extensions into dim-light periods invoke a suite of visual adaptations in their apposition optics. Thus, we propose that carpenter bees are an excellent though understudied group for exploring the complex nature of plant-pollinator mutualisms from ecological and mechanistic perspectives.

Tailoring of bifunctional microencapsulated phase change materials with CdS/SiO2 double-layered shell for solar photocatalysis and solar thermal energy storage

A novel type of bifunctional microcapsules was tailored by encapsulating an n-eicosane phase-change material (PCM) into a CdS/SiO2 hybrid via the interfacial polycondensation of silica precursors, followed by an in-situ precipitation between Cd2+ and S2− ions. Structural characterizations indicated that a double-layered shell based on an amorphous SiO2 inner layer and a crystalline CdS outer layer was fabricated successfully onto the n-eicosane core. Transmission and scanning electron microscopy demonstrated that the n-eicosane@SiO2/CdS double-layered microcapsules had a regularly spherical morphology with a perfect core-shell structure. Thermal analysis revealed that the n-eicosane@SiO2/CdS microcapsules achieved high energy-storage efficiency and reliable phase-change properties. Most of all, the n-eicosane@SiO2/CdS microcapsules not only exhibited good solar thermal energy-storage and thermoregulatory capabilities but also showed a high solar photocatalytic activity to organic dyes under the natural sunlight. Additionally, the microcapsules presented a fluorescent function due to the CdS outer layer. With these unique bifunctional characteristics, the n-eicosane@SiO2/CdS double-layered microcapsules developed by this work can serve for energy efficiency, sustainable chemistry and green processes, and therefore they exhibit an application potential for solar thermal energy collection and storage, solar photocatalytic depuration of industrial waste water, the solar photochemical detoxification of organic water pollutants, etc.

Avian thermoregulation in the heat: evaporative cooling capacity and thermal tolerance in two Australian parrots.

Avian orders differ in their thermoregulatory capabilities and tolerance of high environmental temperatures. Evaporative heat loss, and the primary avenue whereby it occurs, differs amongst taxa. Although Australian parrots (Psittaciformes) have been impacted by mass mortality events associated with extreme weather events (heat waves), their thermoregulatory physiology has not been well characterized. We quantified the upper limits to thermoregulation under extremely hot conditions in two Australian parrots: the mulga parrot (Psephotellus varius; ∼55 g) and the galah (Eolophus roseicapilla; ∼265 g). At air temperatures (Ta) exceeding body temperature (Tb), both species showed increases in Tb to maximum values around 43-44°C, accompanied by rapid increases in resting metabolic rate above clearly defined upper critical limits of thermoneutrality and increases in evaporative water loss to levels equivalent to 700-1000% of baseline rates at thermoneutral Ta Maximum cooling capacity, quantified as the fraction of metabolic heat production dissipated evaporatively, ranged from 1.71 to 1.79, consistent with the known range for parrots, similar to the corresponding range in passerines, and well below the corresponding ranges for columbids and caprimulgids. Heat tolerance limit (the maximum Ta tolerated) ranged from 44 to 55°C, similar to the range reported for passerines, but lower than that reported for columbids and caprimulgids. Our data suggest that heat tolerance in parrots is similar to that in passerines. We argue that understanding how thermoregulatory capacity and heat tolerance vary across avian orders is vital for predicting how climate change and the associated increase in frequency of extreme weather events may impact avian populations in the future.

Classification of Heat-Related Illness Symptoms Among Florida Farmworkers.

Farmworkers working in hot and humid environments have an increased risk for heat-related illness (HRI) if their thermoregulatory capabilities are overwhelmed. The manifestation of heat-related symptoms can escalate into life-threatening events. Increasing ambient air temperatures resulting from climate change will only exacerbate HRI in vulnerable populations. We characterize HRI symptoms experienced by farmworkers in three Florida communities. A total of 198 farmworkers enrolled in 2015-2016 were asked to recall if they experienced seven HRI symptoms during the previous work week. Multivariable logistic regression was used to estimate odds ratios (ORs) and 95% confidence intervals (CIs) for the association between selected sociodemographic characteristics and reporting three or more symptoms. Latent class analysis was used to identify classes of symptoms representing the HRI severity range. We examined sociodemographic characteristics of the farmworkers across the latent classes. The mean age (±SD) of farmworkers was 38.0 (±8) years; the majority were female (60%) and Hispanic (86%). Most frequently reported symptoms were heavy sweating (66%), headache (58%), dizziness (32%), and muscle cramps (30%). Females had three times the odds of experiencing three or more symptoms (OR = 2.86, 95% CI 1.18-6.89). Symptoms fell into three latent classes, which included mild (heavy sweating; class probability = 54%), moderate (heavy sweating, headache, nausea, and dizziness; class probability = 24%), and severe (heavy sweating, headache, nausea, dizziness, muscle cramps; class probability = 22%). Farmworkers reported a high burden of HRI symptoms that appear to cluster in physiologic patterns. Unrecognized accumulation of symptoms can escalate into life-threatening situations if untreated. Our research can inform interventions to promote early recognition of HRI, on-site care, and appropriate occupational health policy. Administrative or engineering workplace controls may also reduce the manifestation of HRI. This study advances the current knowledge of HRI symptoms in farmworkers and moves beyond reporting individual symptoms by utilizing latent class analysis to identify how symptoms tend to co-occur together in this population. It acknowledges multiple symptoms occurring as a result of occupational heat exposure and highlights the importance of symptom recognition.

Keeping it regular: Development of thermoregulation in four tropical seabird species

The thermoregulatory capacity of a species can determine which climatic niche it occupies. Its development in avian chicks is influenced by numerous factors. Furthermore, it is suggested that altricial chicks develop their thermoregulatory capacity post-hatching, while precocial chicks develop aspects of this in the egg. We investigated the development of thermoregulation of four co-occurring seabird species in the Seychelles; namely white, ground-nesting white-tailed tropicbirds (Phaethon lepturus) and tree-nesting fairy terns (Gygis alba); and dark plumaged, tree-nesting lesser noddies (Anous tenuirostris) and ground- and tree-nesting brown noddies (A. stolidus). White-tailed tropicbirds have semi-altricial chicks, while the remaining species have semi-precocial chicks. Cloacal temperatures (Tb) were measured at five day intervals from newly hatched chicks and compared over time, and with adult Tbs. Initial Tbs of all chicks, except fairy terns, were lower than those taken when chicks were older. Brooding cessation generally coincided with feather development, as did an increase in Tb. Mean chick Tb was significantly lower than mean adult Tb for all species, but only white-tailed tropicbird and brown noddy chicks in tree nests differed significantly from mean adult Tb when chick Tb at five day intervals were considered. There was a significant interactive effect of nest site and age on brown noddy chick Tb, but chick colour did not have a significant effect on Tb. However, brown noddy chicks on dune crests maintained a constant Tb sooner than chicks in tree nests. Our results demonstrate that tropical seabird species have a more delayed onset of thermoregulatory capabilities when compared with those in temperate environments, perhaps as nest sites are less thermally challenging. Nest microhabitats and behavioural thermoregulation, are likely more important during early chick development for these species.

Temperature influences the activity patterns of armadillo species in a large neotropical wetland

In this study, we characterized the activity patterns and estimated the activity overlap between two armadillo species (Dasypus novemcinctus and Euphractus sexcinctus) in the Pantanal wetlands of Brazil. We report the effect of daily mean ambient temperature on activity onset and duration of these armadillos. We captured seven yellow armadillos and three nine-banded armadillos and fitted them with very high frequency radios and temperature loggers. By monitoring the temperature of the environment (air temperatures and burrow temperatures), we inferred when the armadillo was active (above ground) or inactive (inside the burrow). Yellow armadillos were active mainly during the daytime and in the beginning of the night, while nine-banded armadillos were active mainly during the night. However, nine-banded armadillos presented a bimodal activity pattern, becoming active for a short period in the middle of the morning and/or afternoon. The proportion of activity overlap was 0.28 between the species, occurring primarily at the beginning of the night. At lower temperatures, yellow armadillos tended to leave their burrows earlier and were active for longer periods. This is probably an adaptation to their physiological constraints and limited thermoregulatory capabilities. Xenarthrans could be used as models to obtain valuable information about how physiology affects mammal behavior.

Lipid mobilization and milk production in lactating northern elephant seals

Northern elephant seals (Mirounga angustirostris) incorporate fasting into several life history stages: post weaning development, molting, breeding and lactation. The mobilization and utilization of particular fatty acids may impact both the mother and pup. This study investigated the mobilization of fatty acids from blubber to understand partitioning of fatty acids between maternal use and milk in northern elephant seals. Blubber and milk fatty acid samples were taken from lactating northern elephant seals in early and late lactation. Overall, patterns of specific fatty acid mobilization conformed closely to previously established patterns in laboratory studies. Proportions of milk and blubber were found to display a high degree of similarity both early and late in lactation. Monounsaturated fatty acids (MUFAs) were the least mobilized from the blubber and increased in the proportion it comprised of the milk across lactation. Polyunsaturated fatty acids (PUFA) and saturated fatty acids (SFA) were more mobilized from the blubber, but proportions decreased in the milk. This suggests that of the MUFA mobilized, the majority is directed to milk synthesis and PUFA and SFA may be partitioned for mother's metabolism. MUFA designation to milk may impact milk viscosity to facilitate secretion from the mammary gland, as well as contribute to the development of diving and thermoregulatory capabilities in the pup.

Fluctuations in oxygen influences facultative endothermy in bumblebees

Bumblebees are facultative endotherms, having the ability to elevate thorax temperature above ambient temperature by elevating metabolism. Here we investigated the influence of hypoxia on metabolic demands and thermoregulatory capabilities of the bumblebee Bombus terrestris. We measured thorax temperature, oxygen consumption, carbon dioxide production, and ventilation rates of bees exposed to oxygen levels of 21, 15, 10, and 5 kPa at 26°C. Under normoxia, bumblebees maintained an elevated thorax temperature of 35.5 °C. There was no significant change in thorax temperature at 15 kPa oxygen (33.4°C). Mean thorax temperature decreased significantly at 10 kPa (31.6 °C) and 5 kPa (27.3 °C). Bees were able to maintain an elevated metabolic rate at 15 kPa and 10 kPa. In normoxia, thermoregulating bees exhibited periods of rapid abdominal pumping (327 s−1) interspaced by periods of no abdominal pumping. At 10 kPa oxygen, abdominal pumping rate deceased (255 s−1) but became continuous. Upon exposure to 5 kPa, metabolic rate and abdominal pumping rate (152 s−1) dropped rapidly although the animals continued abdominal pumping at the reduced rate throughout the exposure period. Bumblebees are able to meet the energetic demands of endothermy at 15 kPa oxygen, but begin to become compromised at levels of 10 kPa oxygen.

Thermal biology and temperature-based habitat selection in a large aquatic ectotherm, the alligator snapping turtle, Macroclemys temminckii

Ectotherms in water experience rates of heat transfer at least two orders of magnitude greater than in air, seriously constraining their thermoregulatory capabilities. Yet, even in water, individuals may exert control over body temperature ( T b ) via behaviors such as selecting thermally favorable microhabitats. The interactions among body size, physiology, and behavior on the thermal biology of large, entirely aquatic, ectotherms is poorly understood. We tested the hypothesis that alligator snapping turtles ( Macroclemmys temminckii) selected microhabitats based on temperature by comparing temperatures at sites used by turtles to temperatures at randomly selected sites. These large turtles selected a narrow range of microhabitats that were significantly warmer and less variable in temperature than random sites. Cooling trials in the laboratory indicated larger turtles equilibrated more slowly to ambient temperature ( T a ) than smaller turtles. We recorded T a and body temperature ( T b ) of turtles in the field continuously throughout the year. The T b generally conformed to T a but there were periods when T b − T a differences were great. These results suggest that while physiology and size of aquatic turtles can affect T b transiently, microhabitat selection may be the only meaningful mechanism for large, entirely aquatic, turtles to control T b .

Does the Thermal Advantage of Melanism Produce Size Differences in Color-dimorphic Snakes?

Despite extensive research, the function and adaptive significance of melanism remain controversial.In snakes, melanistic individuals enjoy a thermal advantage compared with normal-colored individuals due to superior thermoregulatory capabilities. The hypothetical consequences of this thermal advantage are that melanistic individuals have longer daily and seasonal active periods, and thus collect more food, resulting in a higher growth rate and larger body size. To test the generality of this hypothesis, I made intermorph comparisons of body size using a melanistic/striped color-dimorphic snake (Elaphe quadrivirgata) on Yakushima Island, Japan. Melanistic individuals were not significantly larger in body size than striped individuals in either males or females, and the largest individual was a striped morph in both sexes. Thus, the pattern predicted based on the hypothetical consequences of the thermal advantage of melanism was not observed in E. quadrivirgata on Yakushima Island. Based on this coupled with the results of a previous survey on the thermal ecology of the snake, I conclude that melanistic individuals of E. quadrivirgata on Yakushima Island may benefit from fast body warming, which shortens the time of basking, but this benefit is not sufficient to realize larger body size compared to that of striped individuals, and/or such a benefit is not realized in the hypothesized way. The thermal advantage of melanism in nature may be more limited in scope than has been assumed.