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Call number: LD2668 .T4 1978 H35 / Master of Science

Call number: LD2668 .T4 1979 W33 / Master of Science

Endothermic homeothermy is a major feature of the adaptive suites of tachymetabolic animals such as mammals and birds. The advantages homeothermy confers on birds and mammals include relative independence from the environment, a stable internal milieu, and possibly the ability to sustain high aerobic activity (Bennett and Ruben 1979). Some mammals in situations of limited water or energy availability, however, depart markedly from homeothermy and instead display patterns of heterothermy. Torpor is a lowering of body temperature (T(b)) to conserve energy and/or water. I studied the energetics of arousal from torpor in two desert pocket mice species. The species differed in warming rates and arousal durations, but used similar amounts of energy to arouse. The smaller species, Perognathus amplus, lost mass more quickly while fasting in the cold, yet waited as long as the larger species, Chaetodipus baileyi, before entering torpor. P. amplus maintained a lower T(b) during topor than C. baileyi. The thermodynamics of arousal indicated that metabolic rate during arousal was a function of T(b) but not ambient temperature (Tₐ), that the animals changed thermal conductance to increase heat gain when Tₐ was greater than T(b), and that Q₁₀ decreased during arousals. In contrast to torpor, adaptive hyperthermia provides desert mammals in dry, hot environments a means to conserve water that would normally be used for evaporative cooling. I modeled the effects of body size on adaptive hyperthermia and discovered that small mammals gain the most in terms of water savings using this strategy, and that small and large mammals can spend larger fractions of the day active than do medium size mammals. I demonstrated that two desert ground squirrel species make use of adaptive hyperthermia during the summer near Tucson, Arizona by following free-ranging squirrels implanted with temperature-sensitive radio transmitters. Ground squirrel T(b) fluctuated almost continuously, ranging from about 35°C to over 42°C, and rarely approached steady state. Of the two species studied, Ammospermophilus harrisii had higher mean T(b), similar maximum T(b), and lower T(b) variability compared to Spermophilus tereticaudus. These results are consistent with the more wide-ranging foraging style of A. harrisii compared to S. tereticaudus.

The current thesis examined whether sex-differences in local and whole-body heat loss are evident after accounting for confounding differences in physical characteristics and rate of metabolic heat production. Three experimental studies were performed: the first examined whole-body heat loss in males and females matched for body mass and surface area during exercise at a fixed rate of metabolic heat production; the second examined local and whole-body heat loss responses between sexes during exercise at increasing requirements for heat loss; the third examined sex-differences in local sweating and cutaneous vasodilation to given doses of pharmacological agonists, as well as during passive heating. The first study demonstrates that females exhibit a lower whole-body sudomotor thermosensitivity (553 ± 77 vs. 795 ± 85 W•°C-1, p=0.05) during exercise performed at a fixed rate of metabolic heat production. The second study shows that whole-body sudomotor thermosensitivity is similar between sexes at a requirement for heat loss of 250 W•m-2 (496 ± 139 vs. 483 ± 185 W•m-2•°C-1, p=0.91) and 300 W•m-2 (283 ± 70 vs. 211 ± 66 W•m-2•°C-1, p=0.17), only becoming greater in males at a requirement for heat loss of 350 W•m-2 (197 ± 61 vs. 82 ± 27 W•m-2•°C-1, p=0.007). In the third study, a lower sweat rate to the highest concentration of acetylcholine (0.27 ± 0.08 vs. 0.48 ± 0.13 mg•min-1•cm-2, p=0.02) and methylcholine (0.41 ± 0.09 vs. 0.57 ± 0.11 mg•min-1•cm-2, p=0.04) employed was evidenced in females, with no differences in cholinergic sensitivity. Taken together, the results of the current thesis show that sex itself can modulate sudomotor activity, specifically the thermosensitivity of the response, during both exercise and passive heat stress. Furthermore, the results of the third study point towards a peripheral modulation of the sweat gland as a mechanism responsible for the lower sudomotor thermosensitivity in females.

Esta tese tem como tema central o conceito de febre comportamental, que tem-se definido como o aumento da temperatura corporal pela efetivação da mudança nas temperaturas preferidas devido ao reconhecimento, por parte do corpo, de uma infecção ou patógeno. O trabalho está composto por três partes. Na Introdução Geral é discutida a febre comportamental em sete pontos fundamentais no entendimento desta resposta dentro da Ecofisiologia, começando pela definição, as pesquisas de laboratório e campo existente até o momento, até as limitações ecológicas dos indivíduos e as implicações do tema na conservação. No capítulo 1, com formato de texto científico, apresentamos a pesquisa na qual estudamos o comportamento e a preferência termal da espécie Proceratophrys boiei em condições experimentais com indivíduos injetados com lipopolisacáridos (LPS), para simular uma infecção, e indivíduos intactos (injetados com salina, grupo controle). Nessa pesquisa consideramos duas alternativas de respostas no comportamento, tal como discutido na introdução geral: a) febre comportamental, que é caracterizada por um aumento da temperatura corporal dos indivíduos pela mudança nas temperaturas preferidas dentro de uma paisagem termal; b) comportamento de doente, que no contexto do desenho experimental seria reconhecido pela diminuição da atividade dos indivíduos. Assim, registramos os seguintes tratamentos durante 24 horas com uma câmara termográfica: 1) indivíduos intactos no gradiente termal desligado, 2) indivíduos intactos no gradiente termal ligado, 3) indivíduos injetados com salina, no gradiente termal ligado 4) indivíduos injetados com LPS no gradiente termal ligado. Para cada um dos tratamentos foi registrada a distância de locomoção e as preferências termais, junto com outros detalhes do comportamento e as preferências termais. A partir de nossos resultados, concluímos que os indivíduos de P. boiei apresentam comportamento de doente como resposta dominante ao ser injetados com LPS, e que as preferências termais destes são consequência do comportamento de doente e não da termorregulação comportamental. Finalmente, a discussão geral explica como o capitulo 1 contribui na discussão de cada um dos sete pontos tratados na introdução geral tentando propor metodologias e estudos mais completos para manter o diálogo entre a fisiologia e a ecologia dos indivíduos no contexto de infecção e doenças / The central theme of this thesis is the concept of behavioral fever, which has been defined as the increase of body temperature by effecting the change in preferred temperatures due to the recognition by the body of an infection or pathogen. The thesis is composed of three parts. In the General Introduction, behavioral fever is presented around seven fundamental points to the understanding of this response within Ecophysiology, starting with the definition, the laboratory and field research until now, to the ecological limitations of individuals and the implications of this theme in conservation. In the first chapter, with scientific text format, we present the research in which we studied the behavior and thermal preference of Proceratophrys boiei species under experimental conditions in individuals injected with lipopolysaccharides (LPS), to simulate an infection, and in intact individuals (injected with Saline, a control group). In this research we considered two alternatives of behavioral responses, as discussed in the General Introduction: a) behavioral fever, which is characterized by an increase in the individuals body temperature by changing the preferred temperatures within a thermal landscape; B) patient behavior, which, in the context of experimental design, would be recognized by the decrease in the activity of individuals. Thus, we recorded the following treatments for 24 hours with a thermographic camera: 1) intact individuals in the thermal gradient switched off, 2) intact individuals in the connected thermal gradient, 3) individuals injected with saline, in the bound thermal gradient 4) individuals injected with LPS in the thermal gradient on. For each of the treatments it was recorded the locomotion distance and the thermal preferences, along with other details of the behavior and the thermal preferences. From our results, we conclude that the individuals of P. boiei present a patient\'s behavior as a dominant response when injected with LPS and their thermal preferences are a consequence of patient behavior and not behavioral thermoregulation. Finally, the general discussion explains how chapter 1 contributes to the discussion of each of the seven points highlighted in the general introduction attempting to propose a complete methodology and studies to maintain the dialogue between the physiology and the ecology of individuals in the context of infection and disease

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Animals have evolved diverse strategies to control solar and thermal radiations so that they can better adapt to their natural habitats. Structured materials utilized by these animals to control electromagnetic waves often surpass analogous man-made optical materials in both sophistication and efficiency. Understanding the physical mechanism behind these structured materials of nature inspires one to create novel materials and technologies. Our optical and thermodynamic measurements of insects (Saharan silver ants and cocoons of the Madagascar comet moth) living in harsh thermal environments showed their unique ability to simultaneously enhance solar reflectivity and thermal emissivity, and to maintain a cool body temperature. Saharan silver ants, Cataglyphis bombycina, forage on the desert surface during the middle of the day. The ants’ conspicuous silvery glance is caused by a coating of hairs with unique triangular cross-sections. The hair coating enhances not only the reflectivity of the ant’s body surface in the visible and near-infrared range of the spectrum, where solar radiation culminates, but also the emissivity of the ant in the mid-infrared. The latter effect enables the animals to efficiently dissipate heat back to the surroundings via blackbody radiation under full daylight conditions. The fibers produced by the wild comet moth, Argema mittrei, are populated with a high density of air voids that have a random distribution in the fiber cross-section but are invariant along the fiber. These filamentary air voids strongly back-scatter light in the solar spectrum, which, in combination with the fibers’ intrinsic high emissivity in the mid-infrared, enables the cocoon to function as an efficient radiative-cooling device, preventing the pupa inside from overheating. The reduced dimensionality of the random voids leads to strong optical scattering in the transverse direction of the cocoon fibers. This enables tightly confined optical modes to propagate along the fibers via transverse Anderson localization. We made the first observation of transverse Anderson localization in a natural fiber and further demonstrated light focusing and image transport in the fibers. This discovery opens up the possibility to use wild silk fibers as a biocompatible and bioresorbable material for transporting optical signals and images. Drawing inspirations from these discoveries, we designed and developed high-throughput fabrication processes to create coatings and fibers with passive radiative-cooling properties. The radiative-cooling coatings consist of various nanoparticles imbedded within a silicone thin film. The sizes and materials of the nanoparticles were chosen to provide simultaneously high solar reflectivity and thermal emissivity. The coating has been implemented in two site studies on real roofs and has demonstrated reduced roof temperature by up to 30oC in the summer and associated reduction of electricity usage by up to 30%. We also made biomimetic fibers from regenerated silk fibroin and a thermoplastic using wet spinning. Spectroscopic measurements showed that these man-made fibers exhibit exceptional optical properties for radiative-cooling applications.

In an attempt to elucidate the mechanism by which ethanol affects vertebrate thermoregulation, the effect of ethanol on temperature selection was studied in the goldfish, Carassius auratus. Ethanol was administered to 10 to 15 g fish by mixing it in the water of a temperature gradient. The dose response curve was very steep between 0.5% (v/v) ethanol (no response) and 0.7% (significant lowering of selected temperature in treated fish). Fish were exposed to concentrations of ethanol as high as 1.7%, at which concentration most experimental fish lost their ability to swim upright in the water. At concentrations higher than 0.7%, the magnitude of the effect did not increase with increasing concentration of ethanol; treated animals continued to select temperatures about 2 C below temperatures selected by controls. Experiments alternating exposure to 1.0% ethanol and water showed that the rate of onset and disappearance of the ethanol effect was rapid (within 10 min). Other experiments exposing fish to 1.0% ethanol for up to 3 hr showed that the effect remained stable for this period of time. The thermoregulatory responses of fish are behavioral, and therefore relatively easy to observe and quantify. Ethanol produces a prompt, stable and reproducible depression of selected temperature in the goldfish. Because the temperature at which fish regulate is controlled by a central nervous system set point and not altered by effects on peripheral effector systems, it appears that ethanol may cause hypothermia in goldfish by directly acting to lower the set point.

The current thesis examined whether sex-differences in local and whole-body heat loss are evident after accounting for confounding differences in physical characteristics and rate of metabolic heat production. Three experimental studies were performed: the first examined whole-body heat loss in males and females matched for body mass and surface area during exercise at a fixed rate of metabolic heat production; the second examined local and whole-body heat loss responses between sexes during exercise at increasing requirements for heat loss; the third examined sex-differences in local sweating and cutaneous vasodilation to given doses of pharmacological agonists, as well as during passive heating. The first study demonstrates that females exhibit a lower whole-body sudomotor thermosensitivity (553 ± 77 vs. 795 ± 85 W•°C-1, p=0.05) during exercise performed at a fixed rate of metabolic heat production. The second study shows that whole-body sudomotor thermosensitivity is similar between sexes at a requirement for heat loss of 250 W•m-2 (496 ± 139 vs. 483 ± 185 W•m-2•°C-1, p=0.91) and 300 W•m-2 (283 ± 70 vs. 211 ± 66 W•m-2•°C-1, p=0.17), only becoming greater in males at a requirement for heat loss of 350 W•m-2 (197 ± 61 vs. 82 ± 27 W•m-2•°C-1, p=0.007). In the third study, a lower sweat rate to the highest concentration of acetylcholine (0.27 ± 0.08 vs. 0.48 ± 0.13 mg•min-1•cm-2, p=0.02) and methylcholine (0.41 ± 0.09 vs. 0.57 ± 0.11 mg•min-1•cm-2, p=0.04) employed was evidenced in females, with no differences in cholinergic sensitivity. Taken together, the results of the current thesis show that sex itself can modulate sudomotor activity, specifically the thermosensitivity of the response, during both exercise and passive heat stress. Furthermore, the results of the third study point towards a peripheral modulation of the sweat gland as a mechanism responsible for the lower sudomotor thermosensitivity in females.