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Seasonal changes in insulation of fur

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Abstract

Seasonal changes in insulation of the fur have been compared in nine species of arctic and North temperate zone mammals. Relative seasonal changes ranged from 12 to 52% of the winter value. Absolute changes were greatest in the larger mammals with thickest fur. The limited seasonal insulative change in small mammals suggests that changes in heat production may be important in seasonal acclimatization.

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... Adaptation to seasonal thermoregulatory demands in many mammals includes modification of fur insulation (Hart, 1956). Several Arctic and temperate species are seasonally dimorphic with winter pelages having better insulative values than summer ones (c.f. ...
... Several Arctic and temperate species are seasonally dimorphic with winter pelages having better insulative values than summer ones (c.f. Hart, 1956; Underwood & Reynolds, 1980). These seasonal pelage changes have been shown to be photoperiodically controlled (c.f. ...
... In many species fur length of dried pelts has been found to be inversely related to its insulative quality (Scholander et al., 1950; Hart, 1956). In the Arctic fox, fur length is nearly twice as long in winter as in summer. ...
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An examination was made of the moult and seasonal pelage variations in adult and juvenile raccoon dogs, Nyctereutes procyonoides (Gray, 1834) from Eastern Finland. The Arctic fox (Alopex lagopus) served as a reference animal. Raccoon dog pelage is composed of four types of hair: guard hairs, long pile hairs, short pile hairs, and underfur. Whelps moult at the age of 4-5 weeks to a new summer pelage.
... Fur depth, which can be a function of length, may have a role in holding still-air in the fur. The insulation value of fur increases with its depth and it is well known that fur depth undergoes seasonal changes (Scholander et al., 1950; Schmidt-Nielsen, 1990; Hart, 1956; Lentz & Hart, 1960). Deep win¬ ter fur provides greater insulation than short sum¬ mer fur, e.g. , in large mammals summer fur may have only 32% to 52% of the winter insulation value (Hart, 1956). ...
... The insulation value of fur increases with its depth and it is well known that fur depth undergoes seasonal changes (Scholander et al., 1950; Schmidt-Nielsen, 1990; Hart, 1956; Lentz & Hart, 1960). Deep win¬ ter fur provides greater insulation than short sum¬ mer fur, e.g. , in large mammals summer fur may have only 32% to 52% of the winter insulation value (Hart, 1956). Svalbard reindeer fur is unusu¬ ally deep compared to Norwegian reindeer fur (Tyler, 1993). ...
... However, Tregear (1965) observed that, interspecifically , as hair density increased so did insula¬ tion; thus, heat loss was less because wind penetra¬ tion into the fur was reduced. Finally, Lentz & Hart (1960) could observe no direct relation between fur density and heat transfer, although conductance changed with depth and density (Hart, 1956). ...
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Physical characteristics of Svalbard reindeer (Rangifer tarandus platyrhynchus) fur samples were examined with respect to season. A total of 33 dorsal fur sections including adults and calves were investigated. A direct relationship between hair density and heat transfer was not observed, and optimal hair density may depend on an interaction with other fur characteristics. Seasonal changes in fur length and depth were inversely proportional to, and appear to be the main determinants of, seasonal changes in calm air conductance. Fur length and depth, however did not explain the exceptional wind resistance of Svalbard reindeer fur. Since wind has little effect on heat transfer through Svalbard reindeer fur regardless of season or animal age, fur characteristics, which change are not likely critical. Instead, constant physical characteristics, which trap still-air within the fur and resist wind compaction and penetration, are probably responsible. These could include hair stiffness, the crimped wave, hollow hairs, intertwining distal tips and the fine wool fuzz about the hair roots. The extent and means are not well understood at present.
... When animals are exposed to long-lasting seasonal low temperatures, changes in fur properties provide an efficient way to increase the insulation without increasing energy expenditure, because denser and longer pelage reduces both: conductive and convective heat loss ( Harris et al., 1985). Seasonal changes in density, thickness and length of hair fibers that result in changes in thermal conductance, have long been recognized as important adjustments to seasonal variations in climatic conditions in homeotherms, principally in mammals from arctic and subarctic climates ( Scholander et al., 1950;Hart and Heroux, 1953;Hart, 1956;Reynolds, 1993). Although the insulation provided by the pelt is not the most dynamic thermal physiological variable, it is a major determinant of metabolic rate and thermoregulatory capacity (Gordon, 1982). ...
... Seasonal insulative changes have been proposed as of limited value in small mammals from arctic and North temperate zones. Hart (1956) concludes that ''small mammals, which have the greatest metabolic response to temperature changes, have only limited possibilities for seasonal insulative change'' and ''unless these species entirely escape exposure to winter cold, seasonal acclimatization must largely lie in their ability to change heat production''. ...
... Hart and Heroux (1953) reported a winter increase in insulation of 21.1% in Peromyscus maniculatus from Ottawa, Canada. Hart (1956) found a winter increase in insulation between 12% and 52% in arctic mammals in a wide range of body masses. Reynolds (1993) determined a rise of 18% in the heat loss of summer pelts of lemmings. ...
Article
1. Cooling coefficients of cylinders covered with Calomys musculinus skins were significantly different between seasons (F5,75 = 12.36, p<0.001). Winter and spring skins had significantly lower cooling coefficients than summer and fall skins. Cooling coefficients of naked skins were not different between seasons 2. Cooling coefficients were significantly different between hair treatments (F2,75 = 673.98, p <0.001). Fluffed hair skins had lower cooling coefficients than skins with hair laying naturally and naked skins. 3. Body masses of animals were significantly different between seasons (F5,27 = 5.39, P<0.001).
... Response to shortening photoperiod consists of morphological, physiological and behavioral adjustments and results in development of winter phenotype. In winter, small mammals, which are mostly long-day breeders, regress gonads and cease reproduction [1][2][3], decrease body mass (m b ) [4][5][6], some molt to white fur [7][8][9][10], and heterothermic species use torpor [11,12]. These adjustments allow for energy savings and are considered beneficial for winter survival, yet individuals insensitive to changes in day length (nonresponding individuals), or individuals presenting only some of winter traits (partial-responding individuals) also exist in many populations [7,8,[13][14][15][16][17][18][19][20]. ...
... Lack of molting can be regarded as disadvantageous because white fur increases insulation [69], but Boratyński et al. [51] did not find differences in thermal conductance between winter and summer acclimated Siberian hamsters. Although energy savings due to molting in small mammals are considered to be limited [9,70], they may still be present. Here we found that after acclimation to short photoperiod, BMR of white animals was 10% lower than BMR of grey individuals (Fig. 4). ...
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Background The theory of delayed life history effects assumes that phenotype of adult individual results from environmental conditions experienced at birth and as juvenile. In seasonal environments, being born late in the reproductive season affects timing of puberty, body condition, longevity, and fitness. We hypothesized that late-born individuals are more prone to respond to short photoperiod (SP) than early born ones. We used Siberian hamsters Phodopus sungorus , a model species characterized by high polymorphism of winter phenotype. We experimentally distinguished the effect of litter order (first or third) from the effect of exposure to long photoperiod (LP) before winter (3 months or 5 months) by manipulating the duration of LP acclimation in both litters. We predicted that, irrespective of the litter order, individuals exposed to long photoperiod for a short time have less time to gather energy resources and consequently are more prone to developing energy-conserving phenotypes. To assess effect of litter order, duration of acclimation to long days, and phenotype on basal cost of living we measured basal metabolic rate (BMR) of hamsters. Results Individuals born in third litters had faster growth rates and were bigger than individuals from first litters, but these differences vanished before transfer to SP. Litter order or duration of LP acclimation had no effects on torpor use or seasonal body mass changes, but prolonged acclimation to LP inhibited winter molting both in first and third litters. Moreover, individuals that did not molt had significantly higher BMR in SP than those which molted to white fur. Although one phenotype usually predominated within a litter, littermates were often heterogeneous. We also found that over 10% of individuals presented late response to short photoperiod. Conclusions Our data indicate that duration of postnatal exposure to LP may define propensity to photoresponsiveness, regardless of the litter in which animal was born. Existence of littermates presenting different phenotypes suggests a prudent reproductive strategy of investing into offspring of varied phenotypes, that might be favored depending on environmental conditions. This strategy could have evolved in response to living in stochastic environment.
... Our infrared thermal imaging experiments lead us to hypothesize that CR animals display a coat with a higher insulating capacity. In mammals, a layer of air is trapped between the surface of the skin and the outer surface of the hair coat, and the degree of insulation can be altered by increasing or decreasing the thickness of the air layer (Hart, 1956). To measure whether the CR-remodeled fur coat had better insulating properties, we developed an Arduino-based system to simultaneously record the temperature below (bottom) and above (top) the hair coat ( Figure 5B). ...
... As a result, mice housed and/or tested in typical laboratory environments, including those in which CR is found to be beneficial, are subjected to cold stress (Ravussin et al., 2012). Interestingly, sweating and panting are not important thermoregulatory mechanisms for rodents, so these animals may rely heavily on their skin and fur for proper thermoregulation (Hart, 1956;Romanovsky, 2014). In the skin, we found that CR predictably decreases dWAT but also leads to epidermal thickening. ...
... Our infrared thermal imaging experiments lead us to hypothesize that CR animals display a coat with a higher insulating capacity. In mammals, a layer of air is trapped between the surface of the skin and the outer surface of the hair coat, and the degree of insulation can be altered by increasing or decreasing the thickness of the air layer (Hart, 1956). To measure whether the CR-remodeled fur coat had better insulating properties, we developed an Arduino-based system to simultaneously record the temperature below (bottom) and above (top) the hair coat ( Figure 5B). ...
... As a result, mice housed and/or tested in typical laboratory environments, including those in which CR is found to be beneficial, are subjected to cold stress (Ravussin et al., 2012). Interestingly, sweating and panting are not important thermoregulatory mechanisms for rodents, so these animals may rely heavily on their skin and fur for proper thermoregulation (Hart, 1956;Romanovsky, 2014). In the skin, we found that CR predictably decreases dWAT but also leads to epidermal thickening. ...
Article
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Caloric restriction (CR) is the most effective intervention known to enhance lifespan, but its effect on the skin is poorly understood. Here, we show that CR mice display fur coat remodeling associated with an expansion of the hair follicle stem cell (HFSC) pool. We also find that the dermal adipocyte depot (dWAT) is underdeveloped in CR animals. The dermal/vennule annulus vasculature is enlarged, and a vascular endothelial growth factor (VEGF) switch and metabolic reprogramming in both the dermis and the epidermis are observed. When the fur coat is removed, CR mice display increased energy expenditure associated with lean weight loss and locomotion impairment. Our findings indicate that CR promotes extensive skin and fur remodeling. These changes are necessary for thermal homeostasis and metabolic fitness under conditions of limited energy intake, suggesting a potential adaptive mechanism.
... While variation in endotherm body size in relation to climate has been extensively studied and debated, there has been surprisingly little consideration of the interacting role of insulation. This is despite evidence of the significant role of pelage as a modifier of heat exchange in birds and mammals (Scholander et al., 1950a;Herreid & Kessel, 1967;Dawson & Maloney, 2004) and substantial seasonal variation in pelt insulation in many species (Hart, 1956;Reynolds, 1993). In outlining a series of ecogeographical rules, Rensch (1938) suggested that animals in colder regions would have longer and thicker hair, yet few studies have tested this, and studies of geographical variation in pelage have tended to focus instead on coat colour (i.e. ...
... While biogeographical studies of fur in mammals and birds are rare, shorter fur is also associated with warmer climates in bush rats (Rattus fuscipes; Glanville et al., 2012), supporting recent suggestions that heat dissipation is a key limitation for endothermic species (Speakman & Kr ol, 2010). In contrast to some arctic and temperate mammals that vary fur properties to meet seasonal changes in insulative requirements (Hart, 1956), koala fur depths did not vary between seasons. Nevertheless, koalas exhibit considerable variation in insulation across the body (Fig. 1), and are therefore able to posturally vary insulation in response to changing environ- conditions. ...
Article
AimBody size often varies clinally, with dominant explanations centred on how body size influences heat exchange (e.g. Bergmann's rule). However, for endotherms, pelage properties can also dramatically alter heat exchange – a point emphasized by Scholander in the 1950s but which has received little attention in biogeographical analyses. Here, we investigate how geographical variation in both body size and fur properties of the koala (Phascolarctos cinereus) is related to climate.LocationEastern Australia.Methods We measured head length and fur depths of koala museum specimens from across its geographical range, and quantified the relationship between fur depth and insulation. We used linear regression and regression tree analyses to test for associations between morphological traits and climate variables relating to four hypotheses: heat conservation (Bergmann's rule), heat dissipation, fasting endurance/survival of extremes, and productivity.ResultsBoth body size and fur depth of koalas decrease substantially towards the tropics. Consistent with Scholander's view, fur properties showed stronger associations with climate than body size. Males, the larger sex, had shorter fur than females in hot environments but not in more temperate regions, suggesting that shorter fur compensates for sexual size dimorphism. While fur depth and male body size were more strongly associated with variables relating to heat dissipation, female body size was most strongly associated with minimum temperatures.Main conclusionsBody size interacts strongly with other traits, such as fur properties, to influence how animals experience climate. Our results emphasize how the consideration of geographical variation in suites of functionally related traits can provide important insight into how species persist across broad environmental gradients.
... According to H art's formula (Hart 1963) heat loss depends on temperature gradient between body and environment, and on insulation of body surface area. Small mammals limit heat loss by insulative and posture changes, social thermoregulation and building of the nest (Hart 1956, Hensel et al. 1973). Hart's formula suggested that also a reduction of difference between body and ambient temperatures limit heat loss. ...
... Small mammals encounter severe problems of temperature regulation during cold stress. The mechanism reducing heat loss from body by improving insulation becomes functional only in species of greater size (fox or larger -Hart 1956), because in small mammals the relative heat loss is so great that the fur cannot protect them sufficiently. Mammals have an additional thermoregulatory mechanism, an increase of heat production, however, additional heat production results in higher demands for energy restitution in the body. ...
Article
Tegowska E. 1991. Stabilization o f the brain temperature in mammals o f different body size under various am bient temperatures. A cta theriol. 36: 179 -186. Brain tem perature (TbO was measured with accuracy 0.05°C in 9 species o f m ammals weighing from 7 to 3850g. Experiments were performed at am bient temperatures (Ta) ranging from 0 to 35°C. There was found a negative correlation between body size and the dependence o f brain temperature on ambient temperature. However, the pattern o f changes o f TBr and the fact that the increase o f TBr after noradrenaline injection was higher than the drop o f TBr after cold exposure o f animals, suggested that this dependence did not result from low thermal inertia. Results suggested that changes o f TBr may be an adaptation to thermal economy, even at the cost of accuracy o f hom eotherm ia o f the brain.
... It is known that fur insulation qualities undergo significant seasonal changes. Thus, in summer P. maniculatus is 21.4% less insulated than in winter (Hart, 1956). ...
... Adaptive programs are common in mammals. For example, some mammals can change the genetically-specified density and color of their fur coats in response to seasonal changes [29]. This allows the animal to operate over a wider geographic range without migration. ...
Article
As recently as 2002 gerontologists widely thought that an aging program that purposely caused aging in mammals was impossible and therefore scientifically ridiculous because it violated widely accepted concepts regarding the nature of the evolution process. However, a number of modern evolutionary mechanics concepts such as group selection and evolvability suggest that an individually adverse trait like aging can evolve if it creates an advantage (reduced probability of extinction) for a population. Genetics discoveries suggest that aging creates multiple population advantages and therefore, aging programs that purposely cause and regulate aging evolved in mammals. This led to various concepts regarding the nature of the program. One such concept is that aging is a completely genetically specified function of age, essentially a biological clock. However, this article presents evidence and theoretical basis for the idea that the programmed aging function is controlled by an adaptive mechanism that can sense local or temporary conditions that affect the optimum aging function and adjust it to compensate for those conditions. This issue is important for medical research because the sensing mechanisms and associated signaling provide additional points at which intervention in the aging process and associated highly age-related diseases could be attempted.
... It is found in many mammals such as rodents, bears, hedgehogs, bats, marsupials Geiser et al., 2014) and even primates (Dausmann et al., 2004;Blanco et al., 2021). Other strategies used by endothermic mammals for coping with low temperature include increased heat production via shivering and non-shivering thermogenesis, reduction of heat loss from the body surface with the help of fur (Hart, 1956) and/or subcutaneous adipose tissue (Tattersall et al., 2012), or modifications of the blood system such as sequence changes of haemoglobin genes (Campbell et al., 2010), counter-current heat exchange (Ninomiya et al., 2011) or the heart's pumping ability mediated by a missense mutation in the NRAP gene (Buggiotti et al., 2021). Mitogenome adaptations include polymorphisms in mitochondrial genes encoding subunits of the respiratory chain (Balloux et al., 2009;Awadi et al., 2021) and stem-loop formation(s) in the major NCR (Melo-Ferreira et al., 2014). ...
Article
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Enriching mitochondrial DNA (mtDNA) for sequencing entire mitochondrial genomes (mitogenomes) can be achieved by single long-range PCR. This avoids interference from the omnipresent nuclear mtDNA sequences (NUMTs). The approach is currently restricted to the use of samples collected from humans and ray-finned fishes. Here, we extended the use of single long-range PCR by introducing back-to-back oligonucleotides that target a sequence of extraordinary homology across vertebrates. The assay was applied to five hibernating rodents, namely alpine marmot, Arctic and European ground squirrels, and common and garden dormice, four of which have not been fully sequenced before. Analysis of the novel mitogenomes focussed on the prediction of mitochondrial-derived peptides (MDPs) providing another level of information encoded by mtDNA. The comparison of MOTS-c, SHLP4 and SHLP6 sequences across vertebrate species identified segments of high homology that argue for future experimentation. In addition, we evaluated four candidate polymorphisms replacing an amino acid in mitochondrially encoded subunits of the oxidative phosphorylation (OXPHOS) system that were reported in relation to cold-adaptation. No obvious pattern was found for the diverse sets of mammalian species that either apply daily or multiday torpor or otherwise cope with cold. In summary, our single long-range PCR assay applying a pair of back-to-back primers that target a consensus sequence motif of Vertebrata has potential to amplify (intact) mitochondrial rings present in templates from a taxonomically diverse range of vertebrates. It could be promising for studying novel mitogenomes, mitotypes of a population and mitochondrial heteroplasmy in a sensitive, straightforward and flexible manner.
... The primary defense of polar bears against cold temperatures is their thick fur, which in winter provides a thermal insulation of~0.8 m 2 C W À1 , which is similar to that in other Arctic mammals such as grey wolves (Canis lupus) and caribou (Rangifer tarandus) but is less than that of the Arctic fox (Vulpes lagopus) and Dall sheep (Ovis dalli; Scholander et al. 1950;Hart 1956). Polar bear skin is black, and their fur appears white, although individual hairs are translucent and partially hollow . ...
Chapter
Otters are a semiaquatic clade that stands out among carnivorans. Of 13 otter species, only three are known to cooperate, although most species exhibit some form of sociality. The observed variation in social structure among species, especially those in marine environments, makes this taxon suitable for studying the proximate and ultimate factors underpinning sociality. Here we review evidence for social behavior in otters with an emphasis on two species: the North American river otter (an inland and coastal generalist) and the sea otter (a marine specialist). In addition, we provide new information on a marine population of river otters in coastal Alaska using telemetry, camera traps, and social network analysis. Our results provide new insight into the contexts for river otter social behavior, confirm previous observations on individual variation in social behavior, and highlight differences between males and females. We additionally review the published data on sea otter social behavior. We discuss potential directions for hypothesis testing in otter social systems with an emphasis on drivers of individual variation in social behavior, especially potential insights from the fields of sociogenomics and proteomics.
... However, resident species have to endure the winter conditions with physiological, morphological and/or behavioural adaptations. For instance, antifreeze production (Goddard et al. 1992, Duman 2015, hypo metabolism during hibernation and daily torpor (Heldmaier et al. 2004), insulation for low thermal conductance (Hart 1956), body fat reserves and passive rewarming (Signer et al. 2011), altitude change (Mysterud 1999), increased foraging effort (Systad et al. 2000, Grémillet et al. 2005, or social grouping (Vincent et al. 1995, Gardner 2004 can be used in response to the severity of conditions. Nonetheless, winter is reported as a challenging period that increases mortality (Jansson et al. 1981, Barrett 1982, Hurst 2007. ...
Thesis
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Although the cost of reproduction constrains animals to breed during spring/summer when food availability peaks, exception exist in seabirds with few species engaged in breeding during winter months. How their elevated energy needs can be sustained during a period traditionally reported for food shortage and challenging at-sea conditions is poorly understood. In addition, this unusual breeding phenology is adopted by more species in New Zealand than elsewhere in the world, with a concentration on the South island west coast where several winter breeding species are reported to forage with overlap. Therefore, the objectives of this thesis were to: 1) describe the fine-scale foraging behaviour of winter-breeding species from the west coast of New Zealand’s South Island, 2) investigate the intrinsic and extrinsic factors driving their foraging, and 3) quantify their niche overlap as they exploit similar areas during elevated energetically demand. Using bio-logging data (GPS, accelerometer, dive recorder) combined with stable isotopes (carbon and nitrogen from whole blood), the winter foraging strategies of breeding males and females were investigated in a deep diver (Fiordland penguin Eudyptes pachyrhynchus) and two surface-feeders / shallow divers (Westland petrel Procellaria westlandica and southern Buller’s albatross Thalassarche b. bulleri). The tracked individuals foraged close to their colony compared to their summer breeding congenerics, using primarily the nearby shelf-slope and neritic waters. Males and females displayed similar foraging behaviour in penguins and petrels, while spatial sexual differences occurred for albatross. All three species encountered prey at a high rate, allowing raising offspring with good success and without higher foraging effort than their summer-breeding congeners.These findings suggest that winter-breeding species have a phenology matching a winter prey resource on the shelf of the west coast of New Zealand’s South Island. With additional data from literature for little penguin Eudyptula minor and spotted shag Stictocarbo punctatus, this winter-breeding community showed partial overlap of their foraging niche, but an accumulation of small divergences in home ranges, diving behaviour, temporal pattern of foraging, diet and trophic level is likely to explain their coexistence. Hence, winter-breeding can be a favourable phenology for high-level predators, which exploit shelf-slope and inshore waters undergoing winter mixing that insure fish and squids persistence through winter. In addition, winter-breeding also allow the matching of chick-fledging period with the spring (local primary production peak), and before the elevated needs of millions of summer-breeding species back from migration.
... The range of the TNZ is mainly determined by morphological and physiological features relevant for body insulation. In species living in habitats with distinct seasonality, those adaptations include summer and winter fur (Hart 1956), seasonal changing subcutaneous fat layers (Scholander et al. 1950c, Irving and Hart 1957, Thiemann et al. 2006, as well as peripheral AVA in the blood vessels (Schmidt-Nielsen 1990). Species inhabiting tropical zones have a short, less insulating fur throughout the year and do not develop insulating fat layers (Scholander et al. 1950a). ...
Thesis
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The aim of the study was to examine the effect of different meteorological variables on behavioural and autonomic thermoregulatory mechanisms in polar bears (Ursus maritimus) and Malayan sun bears (Helarctos malayanus) and to determine to which degree behavioural thermoregulation complements autonomic mechanisms to keep energy expenditure for the maintenance of body temperature low. The study took place in nine European zoos including a total of 17 polar bears and 10 sun bears. Infrared thermography was used to non‒invasively determine surface temperature distribution in relation to ambient temperature and to detect body surfaces specialized for heat dissipation. Thermographic measurements were made on 10 adult Malayan sun bears at air temperatures between 5 °C and 30 °C and on 11 adult polar bears and two cubs between 0 °C and 20 °C. To assess behaviours that contribute to thermoregulation, observations were conducted by instantaneous scan sampling at ambient temperatures ranging from 5 °C to 34 °C in nine adult sun bears and between −2 °C and 35 °C in 10 adult polar bears. Activity, body posture while resting, selection of substrate to rest on, choice of shady resting places, and the occurrence of shivering and panting were recorded in 60 second intervals for a total of 721 hours of direct observations. Simultaneously, ambient temperature, humidity, wind speed and solar radiation were recorded four times per hour. Thermographic measurements revealed that the thermoneutral zone of sun bears lies between 24 °C and 28 °C. The assumption that polar bears possess body surfaces specialised for the dissipation of excess heat in the shoulder region and limbs, so called thermal windows, could be confirmed. Behavioural data showed that behaviours related to thermoregulation, such as changes in activity, body posture while resting, and the choice of shade and substrates for resting occurred in advance of heat dissipation and panting, which would increase the physiological costs, and were highly correlated to ambient temperature and solar radiation. Temperature thresholds for the initiation of various thermoregulatory behaviours could be defined. The results are discussed with respect to ex‒situ und in‒situ conservation.
... Discrete seasonal molts have evolved as energy-efficient phenological adaptations to regenerate hair layers and produce coats with insulating properties adequate for each season (Geyfman, Plikus, Treffeisen, Andersen, & Paus, 2015;Hart, 1956;Ling, 1972). In at least 20 vertebrate species, seasonal molts are accompanied by the change from summer brown to winter white coats, allowing camouflage in snow-covered environments (Mills et al., 2013. ...
Article
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Abstract Color molts from summer brown to winter white coats have evolved in several species to maintain camouflage year‐round in environments with seasonal snow. Despite the eco‐evolutionary relevance of this key phenological adaptation, its molecular regulation has only recently begun to be addressed. Here, we analyze skin transcription changes during the autumn molt of the mountain hare (Lepus timidus) and integrate the results with an established model of gene regulation across the spring molt of the closely related snowshoe hare (L. americanus). We quantified differences in gene expression among three stages of molt progression—“brown” (early molt), “intermediate,” and “white” (late molt). We found 632 differentially expressed genes, with a major pulse of expression early in the molt, followed by a milder one in late molt. The functional makeup of differentially expressed genes anchored the sampled molt stages to the developmental timeline of the hair growth cycle, associating anagen to early molt and the transition to catagen to late molt. The progression of color change was characterized by differential expression of genes involved in pigmentation, circadian, and behavioral regulation. We found significant overlap between differentially expressed genes across the seasonal molts of mountain and snowshoe hares, particularly at molt onset, suggesting conservatism of gene regulation across species and seasons. However, some discrepancies suggest seasonal differences in melanocyte differentiation and the integration of nutritional cues. Our established regulatory model of seasonal coat color molt provides an important mechanistic context to study the functional architecture and evolution of this crucial seasonal adaptation.
... The present study showed that annual changes in hair coat density and thickness are smaller than the seasonal changes that have been reported in species living in more temperate regions. For example, Hart (1956) observed that winter changes in these coat traits can reach 50% for some wild species. Similar pattern was observed by Dowling (1958) who investigated the winter and summer coats of Holstein cattle managed at 25°S latitude. ...
... colouration, yet there is little evidence that it improves heat retention. Also, unlike other Canadian mammals (Hart 1956), the winter pelage of least weasels (Mustela nivalis) and ...
Thesis
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The purpose of this study was to examine the winter activities and burrow characteristics of North American badgers (Taxidea taxus jeffersonii). At the northern range-limit of these animals (British Columbia, Canada) winter is long and harsh and habitat patchy and atypical; thus, badgers may respond to winter differently here than elsewhere. Using radio-telemetry and remote-cameras, I documented winter activities of 16 badgers (12♀, 4♂) between 2007 and 2011. Similar to limited and anecdotal data collected elsewhere, badgers during winter reduced home range 3.5 (SD = 0.6) km2 and movements 110.5 (SD = 12.2) m /day and intensively used burrows 1.3 (SD = 0.8) burrows per winter. Total winter burrow stay averaged 34 days (SD = 25.0) per winter and this use coincided with the onset of torpor (first week in January). Despite intensive burrow-use, badgers emerged frequently (0.30 ± 0.07 events/camera-night) and displayed foraging behaviour (mean foray length: 46.70 ± 65.44 min). Burrow emergence was not related to temperature or snow depth; rather it was best explained by the amount of time elapsed since the badger entered the burrow in mid-winter (Julian Day). Despite these trends, winter activity was quite variable among individual badgers. I also compared the thermal properties of the burrows used by the badgers to those previously used in summer or for rearing offspring (natal). As expected, all burrow temperatures remained relatively mild and constant throughout the winter; however, winter burrows were significantly cooler during this time than burrows that had been used in the previous summer, albeit a small difference (average 1.9o C). Snow depth at winter burrows did not differ from ‘summer burrows’, yet natal burrows had significantly less snow. Analysis revealed that soil fan size, number of entrances, horizontal cover, presence of infrastructure, and a coarse description of habitat differentiated seasonal burrow types relatively well. I suggest that individual variation (strategies) may be a response to local conditions. Relatively small, patchy, atypical habitat, in combination with extremely large summer home ranges may limit the ability of some animals to gain sufficient fat reserves, thus necessitating additional foraging during winter. Moreover, my research suggests that seasonal burrows differ with respect to measurable habitat features that can be used to identify and protect important burrows (natal and winter burrow). This study has been the vi first dedicated winter ecology study of free ranging North American badgers and has expanded our knowledge about the winter activities, movements and burrow use of this endangered species. As winter is a critical time in the life history of many mammals, an effective management plan will require an understating of species ecology across all seasons.
... Species that are adapted to cold climates, such as the wolverine (Gulo gulo; [23][24][25]), may be particularly vulnerable to rising ambient temperatures associated with global warming [25][26][27]. The need for a framework incorporating ecology and physiology of cold-adapted mammals to identify vulnerability to winter climate change has been emphasized [28], as well as a need for long-term measurements of physiology of mammals in cold environments [29]. ...
Article
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Background Mammals in the far north are exposed to extreme seasonal changes in environmental conditions, such as temperature and photoperiod, which have notable effects on animal physiology and behaviour. The wolverine (Gulo gulo) is a carnivore with a circumpolar distribution and well-adapted to extreme environmental conditions. Still, ecophysiological studies on free-ranging wolverines are lacking. In this study, we used abdominally implanted body temperature loggers in combination with GPS collars with acceleration sensors on 14 free-ranging wolverines in northern Sweden to study daily and seasonal variation in body temperature and activity patterns. We used generalized additive mixed modelling to investigate body temperature patterns over time and Lomb-Scargle periodogram analysis to analyse circadian rhythms. Results We found that wolverines have an average core body temperature of 38.5 ± 0.2 °C with a daily variation of up to 6°C. Body temperature patterns varied between reproductive states. Pregnant females showed a distinct decrease in body temperature during gestation. Wolverines were active both in day and night, but displayed distinct activity peaks during crepuscular hours. However, body temperature and activity patterns changed seasonally, with a gradual change from a unimodal pattern in winter with concentrated activity during the short period of day light to a bimodal pattern in autumn with activity peaks around dusk and dawn. Wolverines were less likely to display 24-h rhythms in winter, when hours of day light are limited. Conclusions The combination of different biologging techniques gave novel insight into the ecophysiology, activity patterns and reproductive biology of free-ranging wolverines, adding important knowledge to our understanding of animals adapted to cold environments at northern latitudes.
... Movement parameters can vary within species, often along gradients of environmental productivity (Duncan, Nilsen, Linnell, & Pettorelli, 2015) such that remote sensing products like NDVI can be used to correct for some of the expected inter-site variation. Similarly, at the 5th order, the heat signature of the animal will be different in different seasons and sites due to better insulation of a winter coat compared to a summer coat (Hart, 1956) and differences in background surface temperature among seasons, sites, and even CT locations. Season also influences weather, temperature, and the denseness of the vegetation (Lesmeister, Nielsen, Schauber, & Hellgren, 2015;Nagy-Reis et al., 2017;Rowcliffe et al., 2011). ...
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Obtaining reliable species observations is of great importance in animal ecology and wildlife conservation. An increasing number of studies use camera traps (CTs) to study wildlife communities, and an increasing effort is made to make better use and reuse of the large amounts of data that are produced. It is in these circumstances that it becomes paramount to correct for the species-and study-specific variation in imperfect detection within CTs. We reviewed the literature and used our own experience to compile a list of factors that affect CT detection of animals. We did this within a conceptual framework of six distinct scales separating out the influences of (a) animal characteristics, (b) CT specifications, (c) CT setup protocols, and (d) environmental variables. We identified 40 factors that can potentially influence the detection of animals by CTs at these six scales. Many of these factors were related to only a few overarching parameters. Most of the animal characteristics scale with body mass and diet type, and most environmental characteristics differ with season or latitude such that remote sensing products like NDVI could be used as a proxy index to capture this variation. Factors that influence detection at the microsite and camera scales are probably the most important in determining CT detection of animals. The type of study and specific research question will determine which factors should be corrected. Corrections can be done by directly adjusting the CT metric of interest or by using covariates in a statistical framework. Our conceptual framework can be used to design better CT studies and help when analyzing CT data. Furthermore, it provides an overview of which factors should be reported in CT studies to make them repeatable, comparable, and their data reusable. This should greatly improve the possibilities for global scale analyses of (reused) CT data.
... Endotherms have evolved several morphological, physiological and behavioural mechanisms to reduce heat loss, particularly during the rest phase of their circadian cycle (Bennett and Ruben 1979;Gilbert et al. 2010;Ruf and Geiser 2015). Morphological mechanisms include the insulation provided by fur or feathers (Hart 1956;Wolf and Walsberg 2000), and physiological mechanisms include heterothermic responses, such as torpor and hibernation [(pronounced reductions in metabolic rate and T b over time scales varying from hours to months (Ruf and Geiser 2015)]. Behavioural mechanisms include social thermoregulation via roosting communally (Gilbert et al. 2010), and roosting in thermally-buffered microsites, such as nests and cavities (Hatchwell et al. 2009). ...
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Small endotherms have evolved behavioural mechanisms for reducing rest-phase energy expenditure, which reduce the likelihood of mismatches between energy supply and demand during periods of cold weather and/or food scarcity. Although the energetic consequences of communal roosting and the use of insulated roosts have been the subject of numerous studies, less is known about the energy savings achieved by species that use these two behaviours simultaneously. We hypothesised that communal roosting in insulated roost nests by a small arid-zone passerine, the Scaly-feathered Finch Sporopipes squamifrons, results in additive energetic benefits that reduce nocturnal energy requirements far below those of individual birds roosting in the open. We measured metabolic rates in finches over air temperatures (Ta) between −5 and 20 °C using flow-through respirometry. Measurements were taken from single finches and groups varying in size from two to 12 individuals, with or without a roost nest. Consistent with our predictions, rest-phase resting metabolic rate (RMR) of finches decreased when the birds roosted communally and decreased further when groups were roosting in a nest. In the absence of a nest, groups of eight or 12 birds reduced RMR by >30% compared with single birds. These energy savings increased further when groups roosted in nests; at Ta = 0 °C, groups of eight or 12 finches approximately halved their RMR compared with that of groups without nests. Our data confirm that Scaly-feathered Finches save considerable energy by roosting communally in roost nests, and these behaviours likely are a key reason why this small species from subtropical latitudes can occur in areas with winter night-time temperatures as low as −10 °C.
... The thermo-neutral zone of harbour porpoises has not been measured; however, our findings imply that it changes seasonally, as in other small endotherms living in habitats with significant ambient temperature fluctuations, such as the arctic fox (Hart, 1956). The low variability in porpoise FMRs within a large range of water temperatures suggests that by building a thick blubber layer during the colder months, and even potentially changing their blubber heat conductivity (Koopman, 2007;Samuel and Worthy, 2004), porpoises can lower their lower critical temperature to counter the increased temperature gradient. ...
Article
Reliable estimates of field metabolic rates (FMRs) in wild animals are essential for quantifying their ecological roles, as well as for evaluating fitness consequences of anthropogenic disturbances. Yet, standard methods for measuring FMR are difficult to use on free-ranging cetaceans whose FMR may deviate substantially from scaling predictions using terrestrial mammals. Harbour porpoises (Phocoena phocoena) are among the smallest marine mammals, and yet they live in cold, high-latitude waters where their high surface-to-volume ratio suggests high FMRs to stay warm. However, published FMR estimates of harbour porpoises are contradictory, with some studies claiming high FMRs and others concluding that the energetic requirements of porpoises resemble those of similar-sized terrestrial mammals. Here, we address this controversy using data from a combination of captive and wild porpoises to estimate the FMR of wild porpoises. We show that FMRs of harbour porpoises are up to two times greater than for similar-sized terrestrial mammals, supporting the hypothesis that small, carnivorous marine mammals in cold water have elevated FMRs. Despite the potential cost of thermoregulation in colder water, harbour porpoise FMRs are stable over seasonally changing water temperatures. Varying heat loss seems to be managed via cyclical fluctuations in energy intake, which serve to build up a blubber layer that largely offsets the extra costs of thermoregulation during winter. Such high FMRs are consistent with the recently reported high feeding rates of wild porpoises and highlight concerns about the potential impact of human activities on individual fitness and population dynamics.
... In most animals occupying temperate and arctic regions, fur/feather composition changes seasonally and provides greater insulation, regardless of the winter colour (Hart, 1956;Walsberg, 1991). Mammalian winter fur is denser and or longer in most species in those regions (e.g. ...
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Animals that occupy temperate and polar regions have specialized traits that help them survive in harsh, highly seasonal environments. One particularly important adaptation is seasonal coat colour (SCC) moulting. Over 20 species of birds and mammals distributed across the northern hemisphere undergo complete, biannual colour change from brown in the summer to completely white in the winter. But as climate change decreases duration of snow cover, seasonally winter white species (including the snowshoe hare Lepus americanus, Arctic fox Vulpes lagopus and willow ptarmigan Lagopus lagopus) become highly contrasted against dark snowless backgrounds. The negative consequences of camouflage mismatch and adaptive potential is of high interest for conservation. Here we provide the first comprehensive review across birds and mammals of the adaptive value and mechanisms underpinning SCC moulting. We found that across species, the main function of SCC moults is seasonal camouflage against snow, and photoperiod is the main driver of the moult phenology. Next, although many underlying mechanisms remain unclear, mammalian species share similarities in some aspects of hair growth, neuroendocrine control, and the effects of intrinsic and extrinsic factors on moult phenology. The underlying basis of SCC moults in birds is less understood and differs from mammals in several aspects. Lastly, our synthesis suggests that due to limited plasticity in SCC moulting, evolutionary adaptation will be necessary to mediate future camouflage mismatch and a detailed understanding of the SCC moulting will be needed to manage populations effectively under climate change.
... The production of different coats provides an adaptation to the disparate demands of each season. For example, coats composed of different hair types and densities provide protection against the varying thermoregulatory challenges of each season (Hart, 1956). Furthermore, several temperate, boreal and arctic species alternate between a white winter coat and brown summer coat (e.g., long-tailed weasels, Bissonnette & Bailey, 1944; snowshoe hares, Severaid, 1945; short-tailed weasels, Rust, 1965; Siberian hamsters, Logan & Weatherhead, 1978; mountain hares, Angerbj€ orn & Flux, 1995;and arctic foxes, V age et al., 2005), to maintain crypsis in seasonally snow-covered environments (Mills et al., 2013). ...
Article
Seasonal coat colour change is an important adaptation to seasonally changing environments but the evolution of this and other circannual traits remains poorly understood. In this study we use gene expression to understand seasonal coat colour moulting in wild snowshoe hares (Lepus americanus). We used hair colour to follow the progression of the moult, simultaneously sampling skin from three moulting stages in hares collected during the peak of the spring moult from white winter to brown summer pelage. Using RNA-sequencing, we tested if patterns of expression were consistent with predictions based on the established phases of the hair growth cycle. We found functionally consistent clustering across skin types, with 766 genes differentially expressed between moult stages. "White" pelage showed more differentially expressed genes that were upregulated relative to other skin types, involved in the transition between late telogen (quiescent stage) and the onset of anagen (proliferative stage). Skin samples from transitional "intermediate" and "brown" pelage were transcriptionally similar and resembled the regressive transition to catagen (regressive stage). We also detected differential expression of several key circadian clock and pigmentation genes, providing important means to dissect the bases of alternate seasonal colour morphs. Our results reveal that pelage colour is a useful biomarker for seasonal change but that there is a consistent lag between the main gene expression waves and change in visible coat colour. These experiments establish that developmental sampling from natural populations of non-model organisms can provide a crucial resource to dissect the genetic basis and evolution of complex seasonally changing traits. This article is protected by copyright. All rights reserved.
... The phases of growth and reduction of the labial lobes and the tongue pad's adhesive structures are thus opposite, and each increases the prey-capture performance in the stage at which they are grown. The most popular examples of phenotypic flexibility in vertebrates in response to environmental fluctuations certainly include seasonal fur and plumage changes in mammals and birds that live in temperate climate zones [37][38][39][40][41][42] . Less known examples might include songbirds that seasonally grow and shrink song control nuclei in their brains [43][44][45] , migratory bats and birds that alter organ-, connective tissue-and muscle mass to cope with the energy demands of long-distance migrations 46,47 , or mammals, sauropsids, amphibians and actinopterygians that undergo structural and physiological changes of the digestive system as response to fluctuating quality and quantity of available food 3,[48][49][50][51][52] . ...
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Many organisms faced with seasonally fluctuating abiotic and biotic conditions respond by altering their phenotype to account for the demands of environmental changes. Here we discovered that newts, which switch seasonally between an aquatic and terrestrial lifestyle, grow a complex adhesive system on their tongue pad consisting of slender lingual papillae and mucus-producing cells to increase the efficiency of prey capture as they move from water onto land. The adhesive system is reduced again as newts switch back to their aquatic stage, where they use suction to capture prey. As suction performance is also enhanced seasonally by reshaping of the mouth due to the growth of labial lobes, our results show that newts are exceptional in exhibiting phenotypic flexibility in two alternating components (i.e. tongue pad and labial lobes) within a single functional system, and suggest that this form of phenotypic flexibility demands complex genetic regulation.
... The presence of fur-game species in bone assemblages has commonly been argued to indicate a winter occupation (Enghoff, 2011). Fur-games can be hunted all year round, but winter pelts from most fur species are more desirable than the summer pelts (Andersson, 2006) because their insulating properties are optimal (Hart, 1956). A higher frequency of fur-game hunting can therefore be expected during the winter season, if there are indications of a sedentary lifestyle with occupation during most of the year. ...
Article
Delayed-return foraging strategies connected with a sedentary lifestyle are known from Late Mesolithic Scandinavian settlements. However, recent evidence from the archaeological site of Norje Sunnansund, in south-eastern Sweden, indicates the presence of sedentism from the Early Mesolithic. By analyzing the faunal assemblage from Norje Sunnansund, patterns of delayed-return strategies were examined for five categories of faunal exploitation/interaction: seal hunting, fishing, ungulate hunting, opportunistic hunting and rodent intrusions. The evidence suggests selective hunting strategies, large catches of fish and all year round seasonality indicators as well as evidence of commensal behavior in non-typical commensal species. The data were related to ethnographic accounts and sedentary foraging societies' modes of subsistence. The evidence suggests an expanding, sedentary, aquatically dependent Early Mesolithic foraging lifestyle in southern Scandinavia, which, it is argued, came to dominate the mode of subsistence, implying larger settlements and a larger prevalent population. This process may have been going on for millennia prior to the rise of the Late Mesolithic Ertebølle culture, implying much larger Late Mesolithic populations than previously realized, perhaps comparable with the native cultures of the north-west coast of America.
... In two instances they detected a faint glow from the entrance of nests after they saw a squirrel depart the nest. Since they easily imaged all red squirrels not in nests and since their fur does not provide significant insulation (Hart, 1956) it was suggested that the nests provide such superior insulation that it minimizes heat loss to the environment. Free-ranging snowshoe hare (Lepus americanus) were easily detected "appearing as glowing silhouettes" when viewed from 20 m away in dense undergrowth but were less distinct from a distance of 40 m. ...
... According to Hart's formula (Hart 1963) heat loss depends on temperature gradient between body and environment, and on insulation of body surface area. Small mammals limit heat loss by insulative and posture changes, social thermoregulation and building of the nest (Hart 1956, Hensel et al. 1973). Hart's formula suggested that also a reduction of difference between body and ambient temperatures limit heat loss. ...
... ermal conductance (mean in calm air: 1.67 W/m 2 C) at various wind speeds on middorsal fur samples from 3 subadult males. No fur depth provided; assuming fur depth was between 30 mm and 50 mm, this would be a calm air thermal conductivity of 0.05 to 0.08 W/mC. Conductance increased linearly (7% for every 1 m/s increase) for wind speeds up to 7 m/s. [53]: Thermal conductivity (mean:,0.05 W/mC) as measured on 6 winter polar bear pelt samples in windless conditions. [54]: Summer head, neck, and leg measurements are our estimations doi:10.1371/journal.pone.0072863.t002 the coastal plain) and allowing bears to seek shade (to simulate inland bears with access to tree shade). ...
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In this study we tested the ability of a mechanistic model (Niche Mapper™) to accurately model adult, non-denning polar bear (Ursus maritimus) energetics while fasting during the ice-free season in the western Hudson Bay. The model uses a steady state heat balance approach, which calculates the metabolic rate that will allow an animal to maintain its core temperature in its particular microclimate conditions. Predicted weight loss for a 120 day fast typical of the 1990s was comparable to empirical studies of the population, and the model was able to reach a heat balance at the target metabolic rate for the entire fast, supporting use of the model to explore the impacts of climate change on polar bears. Niche Mapper predicted that all but the poorest condition bears would survive a 120 day fast under current climate conditions. When the fast extended to 180 days, Niche Mapper predicted mortality of up to 18% for males. Our results illustrate how environmental conditions, variation in animal properties, and thermoregulation processes may impact survival during extended fasts because polar bears were predicted to require additional energetic expenditure for thermoregulation during a 180 day fast. A uniform 3°C temperature increase reduced male mortality during a 180 day fast from 18% to 15%. Niche Mapper explicitly links an animal's energetics to environmental conditions and thus can be a valuable tool to help inform predictions of climate-related population changes. Since Niche Mapper is a generic model, it can make energetic predictions for other species threatened by climate change.
... +Callaghan, 1980) and they are important for the hardening of plants (Sakai and Larcher, 1987 ). The content of carbohydrates is also closely related to the degree of frost hardiness of tissues (Kaurin et al., 1981Kaurin et al., , 1982). Relating vegetation patterns to the depth and duration of I the snow cover alone may be misleading. ...
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In extreme arctic environments, selection forces driving evolution are mainly of the phsyical environment and plant interactions are positive. Elsewhere, biotic factors, such as herbivory, are important and plant interactions become negative through competition. Low winter temperatures rarely affect arctic plants, but snow depth and duration influence species distributions. Deep and persistent snow deforms plants and limits the period of resource acquisition. Cryptogams are common in such snow beds. Little or no snow cover exposes plants to abrasion by wind-blown particles and desiccation. In such fell-field sites, deciduous species and xerophytes, such as evergreen cushion plants, are common. Arctic summers are short and developmental processes are extended beyond one growing season, with perennials predominating. Cushion plants efficiently increase their temperatures above ambient, while evergreen and deciduous ericaceous dwarf shrubs exist and have complementary strategies for intercepting radiation in a low canopy. Tundra soils are generally infertile and may be disturbed by freeze/thaw cycles. Nutrients are conserved by recycling within shoots and between ramets within clones. Vegetative proliferation enhances the survival of young ramets, while physiological integration between ramets enables young ramets to forage across patchy environments. Periodic infestations of moth caterpillars defoliate large areas of mountain birch Betula pubescens tortuosa and stimulate increases in populations of their predators. Periodic population peaks of small rodents graze or kill much vegetation and they may moderate the dynamic structure of plant communities, as the plant species have different abilities to regenerate. -from Authors
... Temperate and arctic mammals prepare for winter by increasing their lipid stores (Young 1976) and (or) the insulative value of their pelage (Scholander et al. 1950;Hart 1956;Ling 1970). However, lipid deposition and molting both require an increase in energy intake and may be adversely affected by a lack of available food (Ling 1970). ...
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Energy storage was examined in relation to the timing of the fall molt in racoons (Procyon lotor) in southwestern Ontario, Canada. Total carcass lipids, corrected for body size, increased curvilinearly over time for juveniles and adults. As well, there were changes in the proportions of the three fall molt categories over time, but these changes were not the same for all four age–sex classes. We suggest that various behavioral and physiological factors are responsible for the differences observed in lipid accumulation and molting over time. Finally, the fall molt had no effect on lipid accumulation by juveniles or adults. For juveniles, lipid stores appeared to have some effect on the start of the fall molt. We suggest that this is due to the need for juveniles to attain a certain level of growth and lipid storage before the fall molt can begin. We conclude that the fall molt and lipid accumulation are occurring simultaneously and that the fall molt is not stressful in adult raccoons. There may be some consequences of growth on the timing of the cycle in juvenile raccoons.
Article
Phenotypic convergence across distantly related taxa can be driven by similar selective pressures from the environment or intrinsic constraints. The roles of these processes on physiological strategies, such as homeothermy, are poorly understood. We studied the evolution of thermal properties of mammalian pelage in a diverse community of rodents inhabiting the Mojave Desert, USA. We used a heat flux device to measure the thermal insulation of museum specimens and determined whether thermal properties were associated with habitat preferences while assessing phylogenetic dependence. Species that prefer arid habitats exhibited lower conductivity and thinner pelage relative to species with other habitat preferences. Despite being thinner, the pelage of arid species exhibited comparable insulation to the pelage of the other species due to its lower conductivity. Thus, arid species have insulative pelage while simultaneously benefitting from thin pelage that promotes convective cooling. We found no evidence of intrinsic constraints or phylogenetic dependence, indicating pelage readily evolves to environmental pressures. Thermoregulatory simulations demonstrated that arid specialists reduced energetic costs required for homeothermy by 14.5% by evolving lower conductivity, providing support for adaptive evolution of pelage. Our study indicates that selection for lower energetic requirements of homeothermy has shaped evolution of pelage thermal properties.
Chapter
Polar bears possess morphologic and physiologic characteristics that reflect their terrestrial lineage as members of the bear family (Ursidae) as well as adaptations to the Arctic marine environment. Among marine mammals, they are the least adapted for aquatic life. They exhibit substantial seasonality in body mass, body condition, and many physiological functions, reflecting the annual cycle of both their Arctic sea ice habitat and the availability of their main prey, ringed seals. This hypercarnivorous diet has likely influenced the polar bear’s craniodental morphology and nutritional physiology. Similar to other marine mammal predators, polar bears exhibit a relatively high resting metabolic rate (RMR) and field metabolic rate (FMR). The polar bear skeleton is well adapted for walking, rather than tree-climbing, and to a lesser degree, for swimming. The large feet provide secure traction on sea ice (aided by sharp claws) and propulsion in the water. Their reproduction, winter hibernation (by pregnant females), and sensory systems resemble those of other bears. Future research should focus on nutrient recycling during fasting, adaptation to a high-fat diet, susceptibility to pathogens, and assessment of the fitness consequences of ongoing sea ice loss and chemical contamination of their habitat.
Thesis
Red deer exhibit a marked seasonal cycle of coat growth and replacement which results in a dense insulatory winter coat and a sparse summer coat that allows evaporative heat loss. The aim of this study was to describe fully this annual cycle and investigate the hormonal control of initiation and growth of the two coats in the species. Analysis of skin biopsies revealed that a complete moult of primary and secondary coat hairs occurred in the spring and autumn. Within the summer coat, in addition to fully developed primary coat follicles, a second 'vestigial' population of primary follicles was identified which failed to produce functional hair fibres. Thus, primary follicle density remained constant from coat to coat throughout the year, but this structural adaptation to the summer coat resulted in reduced fibre density and probably acts to aid heat dispersal from the animal. A strong temporal relationship was established between the spring rise in plasma prolactin levels and the initiation of summer coat growth. Further experiments showed that local infusion of ovine prolactin during the winter induced an advance in summer coat growth. The development of the following winter coat was also affected by prolactin treatment, showing that a local phase shift of the annual pelage cycle was induced. This study identified a seasonal 'window' through which prolactin could adjust the inherent activity rhythm within the population of coat follicles. An in vitro model for hair follicle culture was also developed. This technique was used to show that ovine prolactin administration stimulated growth of fully developed summer coat follicles. This effect on growth was augmented by concomitant administration of triiodothyronine. The fact that summer follicles could be stimulated to further growth suggests that prolactin maybe involved in the maintenance of the summer coat growth. Autoradiographic studies localised high numbers of prolactin receptors in the bulb region of both growing summer and winter coat follicles. The demonstration of target tissues for prolactin in red deer coat follicles together with the results from in vivo and in vitro experiments strongly supports a role for prolactin in seasonal coat growth regulation in this species.
Article
This study aims to address if are there annual changes in the hair coat traits and skin morphology of hair sheep breeds raised in an equatorial semi-arid region? Coat and skin samples were taken from thirty Morada Nova (4 ± 2 years old; red coat; ±SD) and twenty Santa Inês multiparous ewes (5 ± 2 years old; brown and black coat; ±SD) every 3 months over a year. Hair coat traits included thickness (mm), density (number of hairs cm−2), length (mm), and diameter (mm), plus epidermal and dermal thickness (μm), sweat glands and blood capillaries area (μm cm−2) were determined. Means of solar irradiance and ambient air temperature were higher between September and December. Annual changes (P < 0.05) in hair density, diameter, length and thickness, as well as the skin blood capillaries and sweat gland area differed between breeds. The modifications on hair coat traits resulted in minor changes on the effective thermal conductivity of the hair coat surface both for Morada Nova and Santa Ines sheep. Nevertheless, it was clearly evident that the overall cutaneous thermal insulation for Morada Nova sheep was lowest in September that was coupled with lower hair density, coat thickness, and higher sweat gland and blood capillary area (P < 0.05). In conclusion, even in an equatorial region, phenotypic acclimatization on morphological traits of cutaneous surface and skin traits can modify the overall thermal insulation of sheep breeds.
Article
Dicrostonyx has been reported from seven Late Pleistocene localities in Wyoming. All localities are stratified, highly fossiliferous and detail a similar sequence of faunal changes through the late Pleistocene and early Holocene. Three of these are found in the northern Bighorn Mountains: Natural Trap Cave, Prospects Shelter and Shutdown Shelter. Little Box Elder and Bell Caves are found in the Laramie Range while Little Canyon Creek Cave and Bush Shelter are found in the southern Bighorn Mountains. These latter four localities contain sizable samples of Dicrostonyx teeth which have not been previously described. All four of these faunas date older than 12,000 years B.P. A review of the physiology of Dicrostonyx shows the genus is adapted to cold, moist climates and should not be used as an indicator of an environment similar to the modern High Arctic tundra. Preliminary examination of occlusal surfaces of Dicrostonyx teeth from these four localities suggests a taphonomy resulting from both diurnal and nocturnal birds of prey, similar to studies on the Dicrostonyx remains from Natural Trap Cave. There remains a slight possibility for at least some of the Dicrostonyx remains to be accumulated due to mammalian carnivore predation.
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On St. Paul Island, a remnant of the Bering Land Bridge, woolly mammoths persisted until 5,600 yr BP with no known predators or competitors, providing a natural system for studying hypothesized environmental drivers of extinction. These include overheating due to rising temperatures, starvation, and drought. Here, we test these hypotheses using Niche Mapper and LPJ‐GUESS to mechanistically estimate mammoth metabolic rates and dietary and freshwater requirements and, from these, estimate variations in island carrying capacity on St. Paul for the last 17,000 yr. Population carrying capacity may have been several hundred individuals at the time of initial isolation from the mainland. Adult mammoths could have fasted for two to three months, indicating a necessary ability to access snow‐buried forage. During the Holocene, vegetation net primary productivity increased, but shrinking island area overrode increased net primary productivity (NPP), lowering carrying capacity to ~100 individuals. NPP and freshwater availability alternated as critical limiting factors for this island population during the environmental changes of the late Pleistocene and Holocene. Only two or three individuals could have been sustained by the freshwater surplus in crater lakes (up to 18 individuals under the most optimistic parameter sensitivity experiments), suggesting that the St. Paul mammoth population was highly dependent on coastal freshwater sources. The simulations are consistent with the available proxy data, while highlighting the need to retrieve new paleohydrological proxy records from the coastal lagoons to test model predictions. More broadly, these findings reinforce the vulnerability of island megaherbivore populations to resource limitation and extinction.
Article
Purpose Wolverine hairs with superior heat transfer properties have been used as fur ruffs for extreme cold-weather clothing. In order to understand the exclusive mechanism of wolverine surviving in the cold areas of circumpolar, the purpose of this paper is to establish a one-dimensional fractional heat transfer equation to reveal the hidden mechanism for the hairs, and also calculate the fractal dimension of the wolverine hair using the box counting method to verify the proposed theory. The observed results (from the proposed model) found to be in good agreement with the box counting method. This model can explain the phenomenon which offers the theoretical foundation for the design of extreme cold weather clothing. Design/methodology/approach The authors calculated the fractal dimension of the wolverine hair using the box counting method to verify the proposed theory. The observed results (from the proposed model) found to be in good agreement with the box counting method. Findings The box counting method proves that the theoretical model is applicable. Originality/value The authors propose the first heat transfer model for the wolverine hair.
Article
Understanding adaptations of nonhibernating northern endotherms to cope with extreme cold is important because climate-induced changes in winter temperatures and snow cover are predicted to impact these species the most. We compared winter pelage characteristics and heat production of snowshoe hares (Lepus americanus Erxleben, 1777) on the southern edge of their range, in Pennsylvania (USA), to a northern population, in the Yukon (Canada), to investigate how hares might respond to changing environmental conditions. We also investigated how hares in Pennsylvania altered movement rates and resting spot selection to cope with variable winter temperatures. Hares from Pennsylvania had shorter, less dense, and less white winter coats than their northern counterparts, suggesting lower coat insulation. Hares in the southern population had lower pelage temperatures, indicating that they produced less heat than those in the northern population. In addition, hares in Pennsylvania did not select for resting spots that offered thermal advantages, but selected locations offering visual obstruction from predators. Movement rates were associated with ambient temperature, with the smallest movements occurring at the lower and upper range of observed ambient temperatures. Our results indicate that snowshoe hares may be able to adapt to future climate conditions via changes in pelage characteristics, metabolism, and behavior.
Chapter
The heat transfer processes of conduction, convection, radiation, and phase changes are introduced and their influence on the radiative components of heat emanating from an animal and its background are discussed. This chapter also covers the essential modifications that external heat sources can have on animals and their habitat, including changing atmospheric conditions, solar loading, and modifications introduced through phase changes such as evaporation. The heat transfer mechanisms are applied to animals and their backgrounds independently to clearly show how each is affected. This method is desirable because thermal images are formed by comparing the difference in the radiative component from the animal with the radiative component from its background. The difference between the two is used to form the thermal images and in this chapter we learn how to use heat transfer mechanisms to maximize the difference in these two radiative components.
Article
The little red kaluta (Dasykaluta rosamondae) is a small, insectivorous-carnivorous dasyurid marsupial found in and spinifex grasslands of northwestern Australia. Kalutas resemble other dasyurids in many aspects of their physiology. Body temperature (T(b); 33.5 degrees C; 1.5 degrees C lower than predicted), wet thermal conductance (1.6 J g(-1) h(-1) degrees C(-1); 91% of predicted), and dry thermal conductance (1.22 J g(-1) h(-1) degrees C(-1); 55% of predicted) are not significantly different from allometric predictions for marsupials in the thermoneutral zone (26-33 degrees C). A significantly lower-than-expected basal metabolic rate (0.55 ml O(2) g(-1) h(-1); 58% of allometric prediction) and evaporative water loss (1.11 mg g(-1) h(-1); 39% of predicted) can be attributed to the combined effect of low T(b) and phylogeny. Physiological adaptation to aridity is further reflected by a substantially smaller body mass (35 g) than predicted by phylogeny (200 g), a thermolabile T(b) and use of torpor, which confer significant energy and water savings, and a high point of relative water economy (16.1 degrees C).
Article
Metabolism of cold stressed weasels is 50-100 per cent greater than that of normally shaped mammals of the same weight. This can be attributed to their greater surface area, shorter fur, and inability to attain a spherical resting posture. In evolving an elongate shape which enables them to enter confined spaces in search of prey, weasels have sacrificed energetic efficiency. Increased ability to obtain prey, made possible by elongate shape and sexual dimorphism in body size, apparently more than compensates for the energetic cost of being long and thin. The information on weasels indicates that body surface area is an important determinant of heat loss in small homeotherms and suggests that energetic efficiency has played a significant role in the evolution of body shape and size.
Article
Heat loss at various environmental temperatures was examined in colour morphs of the eastern grey squirrel, Sciurus carolinensis, during summer and winter.In winter pelage, melanistic squirrels had significantly (p < 0.05) lower heat losses and lower basal metabolic rates than grey morphs at ambient temperatures between −20 and 25 °C. No such differences were observed between colour morphs in summer pelage.Thermal conductances were significantly higher in summer animals. However, there were no significant differences in conductance associated with pelage colouration in either summer or winter squirrels.Melanistic S. carolinensis thus appear to have a lower energy cost for existence during winter than do grey morphs. This may contribute to the apparent superior fitness of melanistic morphs in the northern portion of the species' range. Lower heat loss by melanistic squirrels during winter, without a concomitant reduction in thermal conductance, may be associated with a lower body core temperature.
Article
The effects of air velocity and direction and of wetness on rate of heat transfer were studied in tests with samples of fur from five caribou calves. The rate of heat transfer through this fur increased by a factor of two to three with increase in air velocity from a negligible level (natural convection) to 23 m/second (direction parallel to sample). The effect of air velocity varied markedly (up to ±50% at 23 m/second) with inclination of the sample to the direction of air movement. Spraying water on the fur increased its rate of heat transfer markedly; addition of water equivalent to 10–12% of the volume of the fur doubled the rate of heat transfer. Other factors, such as erectness of the fur, direction of the hairs or "grain" of the fur with respect to the direction of air movement, and wetness of the skin also affected heat transfer. Differences between samples were large and did not appear to depend directly on the physical characteristics measured.
Article
The energetics of six harbor seals in air at temperatures from 25 °C to −20 °C and in water from 25 °C to 0 °C was studied in animals acclimatized to summer conditions at Woods Hole, Mass. Over the above temperature range, the temperature of skin of the back cooled from about 35° to 1° with lowering temperature of the medium. Temperatures of the flippers were less dependent upon the surroundings than those of the body skin. The dependence of metabolism upon temperature was operative below 2 °C in air and below 20 °C in water (the critical temperatures), but the body skin temperature at these critical temperatures was the same, viz. 21 °C. Metabolism in air and in water was the same over the range of comparable skin temperatures. Body insulation was equal in air and in water at the respective critical temperatures. The insulation index of the air was approximately 20 times that of the water. Heat conductivity of living blubber to water averaged 2.5 cal/cm2/hr/°C, which exceeded that reported for dead blubber by about 50%.When compared with seals tested at St. Andrews during December, summer seals had a higher critical temperature, a lower body insulation index at the critical temperature, and a warmer body skin temperature for the same metabolic rate. No seasonal changes were found in thermoneutral metabolic rate, and no discernible changes in skin temperatures or in thermal gradients in the blubber.
Article
During the winter, wild rats (Rattus norwegicus) develop metabolic adjustments similar to those found in the white rats acclimated to cold in the laboratory. The rate of shivering found in the winter-captured wild rats is lower than that found in the summer-captured rats, indicating the presence of non-shivering thermogenesis. The metabolic response to noradrenaline is enhanced suggesting that non-shivering metabolism in these wild rats, as in the case of white rats, is mediated by noradrenaline. Unlike white rats acclimated to a constant cold temperature in the laboratory, but like white rats acclimatized to cold by group exposure to outdoor winter conditions, wild rats develop a greater pelt insulation in winter.
Article
The cold resistance of deer mice captured during the winter was greater than that of summer mice and was accompanied by a greater pelage insulation and a lower oxygen consumption at 1–2 °C. On the other hand, the enhanced cold resistance of deer mice previously acclimated to cold was not accompanied by differences in pelage insulation. Moreover, in white-footed mice previously acclimated to different temperatures, oxygen consumption was similar at 1–2 °C. These data indicate that the seasonal changes observed in Peromyscus are not identical to changes produced by acclimation in the laboratory. Environmental factors responsible for these differences are discussed.
Article
The thermal resistance of a pile fabric uncovered and covered with thin fabrics of various permeabilities was measured under different conditions of wind velocities and wind direction. Wind velocities up to 30 m.p.h. were used and tests were carried out with winds striking the surface of the material at 0°, 30°, 45°, and 90°. The permeabilities of the covers varied between 0 and 193 cu. ft. per sq. ft. per min., under a pressure difference of in. of water across the fabric. The effects of varying the conditions of the thermal resistance of the boundary air layer are discussed and corrections applied to the results for the resistance of this air layer. The results show that for low wind velocities, the permeability, within wide limits, is relatively of little importance, but with higher wind velocities it is advantageous to employ a covering fabric of as low a permeability as possible.
Article
HITHERTO most work on the photoperiodic behaviour of mammals has been related to their reproductive cycles1,2. Hammond, jun.3, working with mink, was able to demonstrate an effect on the onset of moulting (correlated with new and more rapid growth of hair), when the animals were responding to photoperiodic stimulation by coming into œstrus.
Article
5 In the preceding paper are presented observations and measurements of the body insulation of a series of arctic and tropical mammals and birds. In the present paper we shall describe experiments in which our animals were subjected to gradu ally lowered air temperatures in a respiration chamber, where the heat production was simultaneously determined through the oxygen consumption or carbon dioxide production. Similar experiments have been conducted earlier on many laboratory mammals and birds and a few wild animals. Excellent data were obtained by Theodor ( 1878) , Falloise ( 1900) , Rubner ( 1902) , Martin (1902), Goto (1923), Terroineand Trautmann (1927),Benedictand MacLeod (1929),Giaja(1931), Kayser(1930,1937),BenedictandFox (1933),Gelineo(1934),SwiftandForbes ( 1939), Kendeigh ( 1939, 1944), Kalabukhov (1940), and Herrington (1940). From the earliest investigations it was made clear that down to a certain environ mental temperature (the critical temperature) the body temperature could be main tained, without increasing the metabolism, simply by increasing the insulation (so called physicalheat regulation). Below the critical temperature the body tempera ture could be maintained only by increasing the heat production (so-called metabolic or “¿�chemical” heat regulation). For geese and rabbits it was found that the critical temperature could be as low as 0°C., and from observed fact that eskimo dogs sleep onthesnowatâ€"¿� 400C.orbelowwe couldexpecttofindarctic mammals havinga critical temperature that low or even lower. It was considered likely that cold ex periments on tropical mammals and birds would furnish a valuable contrast to our arctic material, and through the courtesy of the Navy we were granted a six months stay in the Panama Canal Zone for the study of this and other problems. ANIMAL MATERIAL
Article
Insulation measurements on raw skins from 16 arctic and 16 tropical mammals are given. There is, as would be expected, a good correlation between the thickness of the fur and the insulation. The smaller arctic mammals (weasels, lemmings) have much less insulation than the larger and overlap many of the tropical forms. From the size of a fox to the size of a moose there is no correlation between insulation and body size, they all have about the same insulation per surface area. When submerged in ice water, seal blubber retains about the same good insulation, as compared with measurements taken in 0° C. air. In the polar bear, heat transfer through the fur increases 25-50 times when submerged, because of complete wetting of the skin surface and absence of blubber. The beaver is slightly better off when submerged, as it retains an insulating layer of air in the fur next to the skin.
Sur Ics 1:ariations du m6tabolisme du lapin apres exposition au froid. i7ariations saisonnieres du n16tabolisme du lapin et rnodification de la fourrure
  • A Nichita
MAYER, A. ant1 NICHITA, G. Sur Ics 1:ariations du m6tabolisme du lapin apres exposition au froid. i7ariations saisonnieres du n16tabolisme du lapin et rnodification de la fourrure. Ann. physiol. physicochim. biol. 5 : 621-632. 1929.
S~rrvival of PC~ONZ~SCZIS acclimation at high and low temperatures The significance of fur cover and body size of certain species of C., and l I ~ s s o s Jan. If. 133. 1953. L. Hent 1950. in relation to en -ironmental temperature and 1951
  • J A V P Sealander
SEALANDER, J. A. S~rrvival of PC~ONZ~SCZIS acclimation at high and low temperatures. Am. Saturalist, 46 : 257-311. V. P. The significance of fur cover and body size of certain species of C., and l I ~ s s o s , J. Influence 1949. 1954. Jan. If. 133. 1953. L. Hent 1950. in relation to en -ironmental temperature and 1951. Can. J. Zool. Downloaded from www.nrcresearchpress.com by Guangzhou Jinan University on 06/03/13 For personal use only.
and l I ~ s s o s , J . Influence cle I'adaptation sur les r6actions therrnor6g~1latriccs au froitl chez le rat
  • B Irge
  • D ~on
  • i Eox
  • C Icrux-Hbller
B;IRGE,~ON, D., EOX, >I., ICRUX-HBLLER, C., L I B E R ~ I. ~ ~ ~, C., and l I ~ s s o s, J. Influence cle I'adaptation sur les r6actions therrnor6g~1latriccs au froitl chez le rat. J. Physiol. SG : 845-8GO. 1954.
The moulting and fur gro~vth pattern in adult mink
  • C F Bassett
  • L M Lewelles
BASSETT, C. F. and LEWELLES, L. M. The moulting and fur gro~vth pattern in adult mink. Am. Midland Xaturalist, 42 : 751. 1949.
S in relation to en\-ironmental temperature and acclimation a t high and low temperatures
  • J A Sealander
  • P C ~ O N Z ~ S C Z I S~rrvival
SEALANDER, J. A. S~rrvival of P C ~ O N Z ~ S C Z I S in relation to en\-ironmental temperature and acclimation a t high and low temperatures. Am. Saturalist, 46 : 257-311. 1951. Can. J. Zool. Downloaded from www.nrcresearchpress.com by YORK UNIV on 11/23/14 For personal use only.
A cornoarison of some seasonal and telliDerntLlre induced chinges in Perotnyscz~s: Cold resistance, metabol~sm, and pelage ihsulation
HART. I. S. and HEROCS. 0. A cornoarison of some seasonal and telliDerntLlre induced chinges in Perotnyscz~s: Cold resistance, metabol~sm, and pelage ihsulation. Can. J. Zool. 31 : 528-534. 1953.