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Endotherms, unlike ectotherms, generate metabolic heat to meet their thermoregulatory demands. As homeotherms their body temperature stays within a certain range of body temperature, often higher than the environment. This ability to maintain a biochemically optimal body temperature bestows protection against unfavourable thermal conditions for endotherms. The energetic costs associated with thermoregulatory metabolism and the limits for thermoregulatory capacity will, however, still set a boundary upon the range and duration of conditions that are tolerated by an endotherm. Especially within the context of global climate change, the effect of ahistorically high ambient temperatures on endotherms will depend heavily on the cost the new conditions will impose upon them. Despite various statistical and mechanistic evaluations of endotherm energy metabolism and heat exchange, these costs and limits are poorly known on the interspecific level. In the first chapter, we review and summarise current understanding of endotherm thermal physiology, identify the unresolved questions and examine the conceptual and methodological challenges to a consensus. The field metabolic rate (FMR) of an endothermic animal represents its energy expenditure in a natural environment, or its energy budget, and the field water flux of an animal reflects the animal’s water requirements. In the second chapter, we examined FMR of 97 avian species and field water flux of 76 species for adults from direct field measurements by the doubly-labelled water (DLW) method, and conducted a phylogenetically informed, comprehensive analysis of the relationship between FMR and field wtaer flux, and multiple environmental and biological variables. FMR was strongly associated with body mass with an allometric exponent of 0.6, and seabirds had lower FMR than terrestrial birds. Birds consuming plant matter had lower FMR compared to omnivores, carnivores or nectarivores, and low ambient temperature was associated with higher FMR. Unlike for BMR, there was scarce evidence for phylogenetic covariance in FMR. Life history traits such as fecundity and migration were also not strongly associated with FMR. Field water flux was strongly associated with body mass with an allometric exponent of 0.6, and seabirds, breeding birds and birds from relatively humid habitats had higher field water flux. There was considerable evidence for phylogenetic covariance, but granivory and mean temperature were not associated with field water flux. Endotherms maintain a stable body temperature at high ambient temperatures by continuous dissipation of metabolic heat to the environment. This requires endotherms to maintain a balance between heat dissipation and water conservation at multiple temperatures. Birds are relatively small, contain a large amount of metabolically expensive tissue, and are mostly diurnal. As a result, they are severely affected by physiological challenges. In the third chapter, we compiled evaporative water loss measurements for birds exposed to different temperatures and examined their relationships with ambient temperature, precipitation, diet and circadian cycles. While evaporative water loss at normothermic conditions was associated with precipitation and water content in diet, ambient temperature in their natural habitat was important when birds were exposed to heat stress. Additionally, the circadian cycle had an effect on water evaporation. Activephase birds that had higher resting metabolic rates lost more water through evaporation than resting-phase birds. The direction and magnitude of relationship between ambient temperature and evaporative water loss at a high temperature also differed between active- and resting-phase birds. These results suggest that birds do not experience a tradeoff between water conservation at lower temperatures and efficient heat dissipation under heat stress, and that the activity level of a bird may affect the ability to dissipate heat through water evaporation. The upper critical temperature (UCT) of an endotherm represents the temperature that requires it to actively dissipate mettabolic heat through increased energy consumption. Endotherms have relatively low variation in UCT compared to the variation in the lower critical temperature (LCT), but environmental conditions are also linked to intraspecific and interspecific variation in UCT. Difficulty in estimating UCT and differences in data quality complicate the comparative analysis of this variation in UCT. In the fourth chapter, we compiled estimates of UCT for 210 bird species, categorised the information by data quality, and evaluated the relationship between UCT and ambient temperature, precipitation, seasonality, migration and circadian cycle. UCT was positively correlated with maximum temperature in the natural range and negatively correlated with body mass, long-distance migration and summer precipitation. Birds in the resting phase of the circadian cycle had lower UCT compared to birds in the active phase. Including the studies that did not include temperatures well above UCT resulted in slightly reduced coefficient estimates for UCT and thus lower accuracy. However, data quality did not severely impact the precision of estimates.

The Arctic is warming at approximately twice the global rate, with well-documented indirect effects on wildlife. However, few studies have examined the direct effects of warming temperatures on Arctic wildlife, leaving the importance of heat stress unclear. Here, we assessed the direct effects of increasing air temperatures on the physiology of thick-billed murres (Uria lomvia), an Arctic seabird with reported mortalities due to heat stress while nesting on sun-exposed cliffs. We used flow-through respirometry to measure the response of body temperature, resting metabolic rate, evaporative water loss and evaporative cooling efficiency (the ratio of evaporative heat loss to metabolic heat production) in murres while experimentally increasing air temperature. Murres had limited heat tolerance, exhibiting: (1) a low maximum body temperature (43.3°C); (2) a moderate increase in resting metabolic rate relative that within their thermoneutral zone (1.57 times); (3) a small increase in evaporative water loss rate relative that within their thermoneutral zone (1.26 times); and (4) a low maximum evaporative cooling efficiency (0.33). Moreover, evaporative cooling efficiency decreased with increasing air temperature, suggesting murres were producing heat at a faster rate than they were dissipating it. Larger murres also had a higher rate of increase in resting metabolic rate and a lower rate of increase in evaporative water loss than smaller murres; therefore, evaporative cooling efficiency declined with increasing body mass. As a cold-adapted bird, murres' limited heat tolerance likely explains their mortality on warm days. Direct effects of overheating on Arctic wildlife may be an important but under-reported impact of climate change., Summary: Thick-billed murres have limited heat tolerance, displaying low evaporative cooling efficiencies and increases in physiological traits associated with heat stress at low air temperatures relative to desert birds.

In the following chapters the interaction between large body size and climate and the resulting influence of this interaction at the level of the tissue, the whole body, and at the landscape level are investigated. In chapter one, tissue level adaptations of Asian (Elephas maximus)(Loxodonta africana)oC range of ambient temperatures were used to construct climate dependent thermal and water budgets. In chapter three, these budgets were used to construct a coupled biophysical and dynamic programming model to investigate how climate together with thermal, water, and energy demands, interact to produce landscape level patterns of habitat use. At the tissue level, the integument of elephants has a high water and low lipid content and its thermal conductivity (0.19±0.01 to 0.23±0.13 W m--10C) approaches the upper limit of previously measured mammalian values. The integument's resistance to water loss is also low and is comparable to or less than that of some amphibians. At the whole body level, low integumental resistance results in high rates of cutaneous evaporative water loss (E.m.: 0.31 and 8.9 g min-1m-2; L.a.: 0.26 and 6.5 g min-1m-2) and at temperatures between 28-30oC, elephants are fully dependent on evaporative cooling to dissipate heat produced from resting metabolism. At the landscape level, simulations under six combinations of climate and primary productivity demonstrated that under cool and moderate climates, primary productivity was the strongest determinate of home range size, however, at temperatures above 24-27oC, ambient temperature was limiting as elephants were more tightly tethered to water with less access to food. Climate appears to have a non-linear influence on landscape use because evaporative cooling increases exponentially with ambient temperature. Although the drivers of landscape use by large herbivores are complex, the results of this work demonstrate the importance of interactions between body size and climate spanning three levels of biological organization, in setting the fundamental spatial and temporal patterns of landscape use reported for elephants.

International audience; Chronic changes in climate conditions may select for acclimation responses in terrestrial animals living in fluctuating environments and beneficial acclimation responses may be key to the resilience of these species to global changes. Despite evidence that climate warming induces changes in water availability, acclimation responses to water restriction are understudied relative to thermal acclimation. In addition, acclimation responses may involve different modes, paces and trade-offs between physiological and behavioral traits. Here, we tested the dynamical acclimation responses of a dry-skinned terrestrial ectotherm to a chronic water restriction. Yearling common lizards (Zootoca vivipara) were exposed to a sub-lethal water restriction during 2 months of the summer season in laboratory conditions, then released in outdoor conditions for 10 additional months. Candidate behavioral (exploration, basking, and thermal preferences) and physiological traits (metabolism at rest and standard water loss rate) potentially involved in the acclimation response were measured repeatedly during and after water restriction. We observed a sequential acclimation response in water restricted animals (yearlings spent less time basking during the first weeks of water deprivation) which was followed by delayed sex-specific physiological consequences of the water restriction during the following months (thermal depression in males and lower standard evaporative water loss rates in females). Despite short-term negative effects of water restriction on body growth, annual growth, survival and reproduction were not significantly different between water restricted and control yearlings. This demonstrates that beneficial acclimation responses to water restriction involve both short-term flexible behavioral responses and delayed changes in thermal and water biology traits.

Marsupials have relatively low body temperatures and metabolic rates, and are therefore considered to be maladapted for life in cold habitats such as alpine environments. We compared body temperature, energetics and water loss as a function of ambient temperature for 4 Antechinus species, 2 from alpine habitats and 2 from low altitude habitats. Our results show that body temperature, metabolic rate, evaporative water loss, thermal conductance and relative water economy are markedly influenced by ambient temperature for each species, as expected for endothermic mammals. However, despite some species and individual differences, habitat (alpine vs non-alpine) does not affect any of these physiological variables, which are consistent with those for other marsupials. Our study suggests that at least under the environmental conditions experienced on the Australian continent, life in an alpine habitat does not require major physiological adjustments by small marsupials and that they are physiologically equipped to deal with sub-zero temperatures and winter snow cover.

In terrestrial endotherms, evaporation is a significant mechanism of water loss in hot environments. Although water is passively lost by evaporation, individuals can regulate it at different levels. Inhabiting a relatively stable environment characterized by mild ambient temperature (Ta) and high humidity can ensure a balanced water budget. Many fossorial rodents are well adapted to live in such conditions. In this study, evaporative water loss (EWL) of fossorial rodent species with different degree of adaptations to underground life (from strictly subterranean to those with regular surface activity) was evaluated. By measuring EWL, the specific contribution of either evaporative or non-evaporative components of heat loss can be determined. With the exception of the silvery mole-rat (Heliophobius argenteocinereus), in all tested rodents EWL is relatively stable below and within the thermoneutral zone (TNZ). As Tas increase above TNZ, EWL increases as does total thermal conductance, but conductance increases several times more than EWL. In addition, non-evaporative routes seem to be more important than evaporative heat loss in the analyzed species. No clear pattern of EWL in relation to a species degree of fossoriality or sociality was detected. In this context, atmosphere of burrows could affect EWL, since the high humidity found inside tunnels can establish limits on evaporation to favor water rather than thermal balance. Fil: Luna, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Šumbera, Radim. University of South Bohemia; República Checa Fil: Okrouhlík, Jan. University of South Bohemia; República Checa Fil: Mladěnková,Nella. University of South Bohemia; República Checa Fil: Antenucci, Carlos Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencias Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

Brushtail possums have a wide geographical distribution. Possums from warmer, drier habitats have more frugal energy and water use and increased heat loss capacity at high temperatures. Consideration of geographical patterns in physiological attributes of source populations will likely improve the success and welfare outcomes of translocations., Identifying spatial patterns in the variation of physiological traits that occur within and between species is a fundamental goal of comparative physiology. There has been a focus on identifying and explaining this variation at broad taxonomic scales, but more recently attention has shifted to examining patterns of intra-specific physiological variation. Here we examine geographic variation in the physiology of brushtail possums (Trichosurus), widely distributed Australian marsupials, and discuss how pertinent intra-specific variation may be to conservation physiology. We found significant geographical patterns in metabolism, body temperature, evaporative water loss and relative water economy. These patterns suggest that possums from warmer, drier habitats have more frugal energy and water use and increased capacity for heat loss at high ambient temperatures. Our results are consistent with environmental correlates for broad-scale macro-physiological studies, and most intra-generic and intra-specific studies of marsupials and other mammals. Most translocations of brushtail possums occur into Australia’s arid zone, where the distribution and abundance of possums and other native mammals have declined since European settlement, leading to reintroduction programmes aiming to re-establish functional mammal communities. We suggest that the sub-species T. vulpecula hypoleucus from Western Australia would be the most physiologically appropriate for translocation to these arid habitats, having physiological traits most favourable for the extreme Ta, low and variable water availability and low productivity that characterize arid environments. Our findings demonstrate that geographically widespread populations can differ physiologically, and as a consequence some populations are more suitable for translocation to particular habitats than others. Consideration of these differences will likely improve the success and welfare outcomes of translocation, reintroduction and management programmes.

Made available in DSpace on 2018-11-26T20:04:44Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-12-15 Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Many adult mammals and birds respond to high surrounding temperatures with thermal tachypnea - an increase in breathing frequency accompanied by shallow tidal volume, with minimal increase in oxygen consumption (VO2). This pattern favors heat dissipation by evaporative water loss (EWL) through the respiratory tract. We asked to what extent this response was apparent at the earliest stages of development, when pulmonary ventilation initiates. Measurements of pulmonary ventilation (V. E; barometric technique), VO2 (open-flow methodology) and EWL (water scrubbers) were performed on chicken embryos at the earliest appearance of pulmonary ventilation, during the internal pipping stage. Data were collected, first, at the normal incubation temperature (37.5 degrees C); then, ambient and egg temperatures were increased to approximately 44 degrees C over a 2 h period. Other embryos of the same developmental stage (controls) were maintained in normothermia for the whole duration of the experiment. During heat exposure, the embryo's VO2 and carbon dioxide production increased little. In contrast, V. E more than doubled (similar to 128% increase), entirely because of the large rise in breathing frequency (similar to 132% increase), with no change in tidal volume. EWLdid not change significantly, probably because, within the egg, the thermal and water vapor gradients are almost nonexistent. We conclude that chicken embryos respond to a major heat load with tachypnea, like many adult mammals and birds do. Its appearance so early in development, although ineffective for heat loss, signifies that thermal tachypnea represents an important breathing response necessary to be functional from hatching. Sa Paulo State Univ, Dept Anim Morphol & Physiol, Coll Agr & Vet Sci, BR-14884900 Jaboticabal, SP, Brazil INCT Fisiol Comparada, Natl Inst Sci & Technol Comparat Physiol, BR-14884900 Jaboticabal, SP, Brazil McGill Univ, Dept Physiol, Montreal, PQ H3G 1Y6, Canada

Made available in DSpace on 2018-11-26T17:24:24Z (GMT). No. of bitstreams: 0 Previous issue date: 2017-05-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) Because of their permeable skin, terrestrial amphibians are constantly challenged by the potential risk of dehydration. However, some of the physiological consequences associated with dehydration may affect aspects that are themselves relevant to the regulation of water balance. Accordingly, we examined the effects of graded levels of dehydration on the rates of evaporative water loss and water absorption through the skin in the terrestrial Neotropical toad, Rhinella schneideri. Concomitantly, we monitored the effects of dehydration on the mass of visceral organs; hematocrit and hemoglobin content; plasma osmolality; and plasma concentration of urea, sodium, chloride, and potassium. We found that dehydration caused an increase in the concentration of body fluids, as indicated by virtually all the parameters examined. There was a proportional change in the relative masses of visceral organs, except for the liver and kidneys, which exhibited a decrease in their relative masses greater than the whole-body level of dehydration. Changesor the preservationof relative organ masses during dehydration may be explained by organ-specific physiological adjustments in response to the functional stress introduced by the dehydration itself. As dehydration progressed, evaporative water loss diminished and water reabsorption increased. In both cases, the increase in body fluid concentration associated with the dehydration provided the osmotic driver for these changes in water flux. Additionally, dehydration-induced alterations on the cutaneous barrier may also have contributed to the decrease in water flux. Dehydration, therefore, while posing a considerable challenge on the water balance regulation of anurans, paradoxically facilitates water conservation and absorption. Univ Estadual Paulista, Inst Biociencias, Dept Zool, Sao Paulo, Brazil Univ Estadual Paulista, Ctr Estudos Ambientais, Sao Paulo, Brazil Univ Estadual Paulista, Inst Biociencias, Dept Zool, Sao Paulo, Brazil Univ Estadual Paulista, Ctr Estudos Ambientais, Sao Paulo, Brazil FAPESP: 10/20061-6 FAPESP: 13/04190-9 CNPq: 302045/2012-0 CNPq: 306811/2015-4 CNPq: 13/14-25780

Adequate water intake, supporting both cardiovascular function and evaporative cooling, is a critical factor in mitigating the effects of heat waves, which are expected to increase with global warming. However, the regulation of water intake during periods of intermittent heat exposure is not well understood. In this study, the effects of access to water or no access during intermittent heat exposure were assessed using male Sprague‐Dawley rats exposed to 37.5°C for 4 h/day. After 7 days of intermittent heat exposure, reductions in evaporative water loss were observed in all animals and reductions in water intake following heat exposure occurred as the days of heat exposure increased. Rats that were not allowed water during the 7 days of exposure had decreased rehydration levels, however, rats allowed access to water increased water intake during exposure and exhibited higher overall rehydration levels over the same time period. Peripheral administration of angiotensin II, mimicking activation of volemic thirst, or hypertonic saline solution, activating intracellular thirst, did not result in alteration of water intake in rats exposed to heat with access to water compared to control rats. In contrast, rats exposed to heat without access to water had reduced water intake after administration of hypertonic saline and increased water intake after administration of angiotensin II compared to control rats. These experiments demonstrate that thirst responses to intermittent heat exposure are altered by providing water during heat exposure and that intermittent heat exposure without access to water alters drinking responses to both intracellular and extracellular thirst challenges.

Subterranean rodents face unique thermoregulatory challenges. Evaporative water loss (EWL) is a crucial mechanism for maintaining heat balance in endotherms subjected to heat stress but also leads to potential dehydration. EWL depends on gradients of temperature and humidity between the surface of the individual and the surrounding environment. Underground burrows generally provide a stable water vapor saturated atmosphere which may impede evaporative heat loss (EHL). This will mainly occur when ambient temperature exceeds the upper limit of individual's thermoneutral zone, or when body temperature rises as result of digging activities. Here we evaluate the effect of ambient temperature on EWL and energy metabolism in the subterranean rodent Ctenomys talarum (tuco-tucos), which inhabits sealed burrows, but makes an extensive use of the aboveground environment. We observed that EWL is increased when ambient temperature rises above thermoneutrality; below this point, evaporation remains stable. Though EWL contributes to total heat loss by increasing ~1.3 times at 35 °C, dry thermal conductance is raised four times. In tuco-tucos' burrows both non-evaporative and, to some extent, evaporative and behavioral mechanisms are essential for body temperature regulation, preventing overheating at high ambient temperatures in a water vapor-saturated atmosphere. Fil: Baldo, María Belén. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Antenucci, C. Daniel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina Fil: Luna, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones Marinas y Costeras. Universidad Nacional de Mar del Plata. Facultad de Ciencia Exactas y Naturales. Instituto de Investigaciones Marinas y Costeras; Argentina

We investigated the applicability of 2H to measure the amount of body water (TBW) and water fluxes in relation to diet type and level of food intake in a mollusk-eating shorebird, the Red Knot ( Calidris canutus). Six birds were exposed to eight experimental indoor conditions. Average fractional 2H turnover rates ranged between 0.182 day−1 (SD = 0.0219) for fasting birds and 7.759 day−1 (SD = 0.4535) for birds feeding on cockles ( Cerastoderma edule). Average TBW estimates obtained with the plateau method were within the narrow range of 75.9–85.4 g (or between 64.6 and 70.1% of the body mass). Those obtained with the extrapolation method showed strong day-to-day variations (range 55.7–83.7 g, or between 49.7 and 65.5%). Average difference between the two calculation methods ranged between 0.6% and 36.3%, and this difference was strongly negatively correlated with water flux rate. Average water influx rates ranged between 15.5 g/day (fasting) and 624.5 g/day (feeding on cockles). The latter value is at 26.6 times the allometrically predicted value and is the highest reported to date. Differences in 2H concentrations between the blood and feces (i.e., biological fractionation) were small but significant (−3.4% when fed a pellet diet, and −1.1% for all the other diets), and did not relate to the rate of water flux (χ2 1 = 0.058, P < 0.81). We conclude that the ingested water equilibrated rapidly with the body water pool even in an avian species that shows record water flux rates when living on ingested marine bivalves.

We integrated population, climate, and physiological data to investigate Fynbos birds' vulnerability to recent climate change. Species occupying cool ranges with warming trends showed greatest declines. However, physiological thermal thresholds varied and, with the exception of Cape Rockjumper, were not clearly the cause of decline in most species., We investigated whether observed avian range contractions and population declines in the Fynbos biome of South Africa were mechanistically linked to recent climate warming. We aimed to determine whether there were correlations between preferred temperature envelope, or changes in temperature within species' ranges, and recent changes in range and population size, for 12 Fynbos-resident bird species, including six that are endemic to the biome. We then measured the physiological responses of each species at air temperatures ranging from 24 to 42°C to determine whether physiological thermal thresholds could provide a mechanistic explanation for observed population trends. Our data show that Fynbos-endemic species occupying the coolest regions experienced the greatest recent reductions in range and population size (>30% range reduction between 1991 and the present). In addition, species experiencing the largest increases in air temperature within their ranges showed the greatest declines. However, evidence for a physiological mechanistic link between warming and population declines was equivocal, with only the larger species showing low thermal thresholds for their body mass, compared with other birds globally. In addition, some species appear more vulnerable than others to air temperatures in their ranges above physiological thermal thresholds. Of these, the high-altitude specialist Cape rockjumper (Chaetops frenatus) seems most at risk from climate warming. This species showed: (i) the lowest threshold for increasing evaporative water loss at high temperatures; and (ii) population declines specifically in those regions of its range recording significant warming trends. Our findings suggest that caution must be taken when attributing causality explicitly to thermal stress, even when population trends are clearly correlated with rates of warming. Studies explicitly investigating the mechanisms underlying such correlations will be key to appropriate conservation planning.