Body temperature affects physiological processes and, consequently, has a large impact on fitness. Lizards need to thermoregulate behaviourally to maintain their body temperature within a range that maximizes performance, but there are costs associated with thermoregulation. The thermal quality of an environment is a major cost of thermoregulation because it directly affects the time and energy that must be invested by an individual to achieve and maintain an optimal body temperature for performance. According to the cost-benefit model of thermoregulation, lizards should only thermoregulate when the benefits outweigh the costs of doing so. Thus, in habitats of poor thermal quality, individuals should thermoregulate less. Using two systems, an elevational gradient and a pair of habitats that vary in the amount of solar radiation they receive, I tested the hypothesis that investment in thermoregulation by lizards is dictated by the associated costs of thermoregulating. Temperature, and thus thermal quality, decreases with elevation. I found a significant positive relationship between elevation and effectiveness of thermoregulation of Yarrow’s spiny lizards (Sceloporus jarrovii). When comparing thermoregulation of ornate tree lizards (Urosaurus ornatus) living in the thermally superior open-canopy wash habitat or the closed-canopy upland habitat, I found that habitat type was a significant predictor of accuracy of body temperature. In the poorer quality habitat, lizards had smaller deviations of body temperature from their preferred temperature range. Overall, I conclude that the thermal quality of a lizards’ environment impacts their thermoregulation in the opposite direction than predicted by the cost-benefit model of thermoregulation. This suggests that the disadvantages of thermoconformity may be greater than the costs thermoregulating as habitats become more thermally challenging.

As abelhas sociais são classificadas como animais heterotérmicos, ou seja, podem ser endotérmicas ectotérmicas de acordo com a necessidade do ninho ou do indivíduo. As abelhas sem ferrão eram conhecidas por apresentarem uma termorregulação passiva, onde o invólucro, seria o responsável pela manutenção da temperatura na área de cria. Entretanto, acreditava-se em uma produção de calor ativo como apresentado em abelhas Apis mellifera, embora nunca tenha sido estudado. O objetivo principal do presente trabalho foi verificar a produção de calor ativo por meio das operárias adultas e da cria e relacionar essa produção de calor com a termorregulação passiva e o consumo de oxigênio. Foram utilizadas colônias de abelhas sem ferrão Melipona scutellaris, Frieseomelitta varia e Plebeia droryana mantidas em laboratório. Os resultados obtidos mostraram que a temperatura na área de cria foi sempre maior que na periferia do ninho. Foi verificado que os imaturos produzem calor metabólico e que o invólucro é o responsável pelo isolamento do calor produzido. Além disso, as operárias presentes nas áreas de cria apresentaram temperaturas superficiais torácicas elevadas, sugerindo um incremento na produção de calor na área de cria. Foi observado que as abelhas consomem menos oxigênio quando estão em grupo do que individualmente, sugerindo uma cooperação entre as abelhas ou uma redução de stress em grupo entre as abelhas que pode estar relacionada com a termorregulação colonial. Este trabalho traz novas possibilidades para os estudos de termorregulação, pois confirma a produção de calor ativo em abelhas sem ferrão, até no momento desconhecido / Social bees are classified as heterothermic animals, may be both endothermic and ectothermic according to the necessity of the colony or the individual. The stingless bees are known because the passive thermoregulation, which the involucrum would be responsible for maintenance of the brood area temperature. However, it has been believed in an active heat production as shown in honeybees, although it not studied so far. The aim of the present study was to verify the active heat production through adult workers and brood, and to correlate the heat production with the passive thermoregulation and the oxygen consumption. We used colonies of stingless bees Melipona scutellaris, Frieseomelitta varia and Plebeia droryana maintained in laboratory. Our results showed that the brood area temperature was higher than the nest periphery temperature. We also verified that the immature produces metabolic heat, and that the involucrum is responsible by the isolation of the produced heat. Furthermore, the workers engaged on the brood area had their thoracic surface temperatures higher than other workers, which suggest the increasing of the heat production in the brood area. Bees consumed less oxygen in group than when they are individually tested. This study brings new possibilities to the thermoregulation studies, because it confirms the active heat production in stingless bees

Anfíbios tem a habilidade de manifestar febre comportamental em ambientes heterotermais durante infecção a um custo metabólico associado à elevação da temperatura corpórea e à ativação do sistema imune. Apesar do custo metabólico, a temperatura corpórea febril otimiza a resposta imune no combate à infecção e aumenta as chances de sobrevivência do indivíduo. Contudo, devido à limitada capacidade de termorregular, os anfíbios enfrentam variações diárias e sazonais na temperatura corpórea e na resposta metabólica de reação à infecção. O nosso objetivo foi medir a variação da resposta metabólica à infecção dentro da variação de temperaturas ecológicas relevantes do sapo Cururu. Testamos a hipótese de que a infecção aumenta as taxas metabólicas do sapo Cururu, mas o custo energético da resposta imune deve ser menor na temperatura febril dos sapos infectados. Para testarmos as hipóteses, nós medimos a temperatura operacional dos sapos no campo, a preferencia termal dos sapos hígidos e a temperatura preferencial dos sapos infectados. Depois, medimos a taxa metabólica e a resposta metabólica dos sapos antes e depois da infecção por LPS nessas temperaturas. Nossos resultados mostraram que as temperaturas ecológicas relevantes dos sapos variaram entre 17°C e 26°C. A temperatura influenciou a taxa metabólica dos sapos, mas só na temperatura preferencial dos sapos hígidos houve custo metabólico associado à infecção. Contudo, na temperatura corpórea dos sapos infectados a resposta metabólica de reação à infecção foi menor, indicando que o controle regulado no ponto de ajustes \"set-point\" da temperatura corpórea durante a infecção coevoluiu com um custo energético otimizado da resposta imune / Anphibians have the ability of manifested behavioral fever in heterothermal environments during infection with a metabolic cost associated to elevated body temperature set-point and due to activation of immune system. Despite the metabolic cost, fever body temperature optimizes immune response to combat infection and increase the survival of the host. However, because of the limited capacity for thermoregulation, amphibians can confront daily and seasonal variation in body temperature and in the metabolic response of reaction to combat infection. So, we measured the variation in metabolic response of reaction to infection at ecology relevant body temperature range in Cururu toads. We hypothesized that infection increases metabolic rates of the Cururu toads due to the activation of the immune system at different temperatures, but the energetic cost of immune response is lower at preferred body temperature of infected toads (behavioral fever). To test these hypotheses we measured the operative body temperature in the field, the preferred body temperature of higid toads, and the preferred body temperature of infected toads. After, we measured metabolic rate and metabolic response of the toads before and after injection of LPS at these temperatures. Our results showed that the ecology relevant temperature range of Cururu toads (R. icterica) varies between 17°C and 26°C, respectively, at operative temperature and at preferred body temperature in infected toads when exposed to heterothermal environment. The temperature had the major impact on metabolic rate of the toads during infection. But, at fever body temperature toads decrease the metabolic response of reaction to infection, indicating that the regulated control of body temperature set-point during infection coevolved with an optimized energetic cost of immune response

O objetivo deste estudo foi avaliar a tolerância ao calor de ovinos de corte das raças Santa Inês, Dorper e Merino Branco através do teste de capacidade termolítica (exposição ao sol). Foram utilizadas um total de 97 fêmeas vazias, com idade média de 3 anos. O estudo decorreu no verão, onde foram registradas as variáveis fisiológicas temperatura retal (TR), temperatura superficial (TS), frequência respiratória (FR), mensuradas depois de duas horas sob a sombra (1), uma hora sob o sol (2), quinze (3) e trinta (4) minutos após a exposição ao sol, e a taxa de sudação (Sud), no tempo 2. Posteriormente foram realizadas observações de comportamento a pasto durante três dias, no período das 11 às 14 horas, para as variáveis: tempo ao sol; tempo em pé; pastejo/alimentação, ruminação e ócio. As médias de TR1 foram semelhantes para as ovelhas Santa Inês e Dorper e superior para as ovelhas Merino Branco (P<0,05). Para TR2, TR3 e TR4 as ovelhas da raça Merino Branco tiveram os maiores valores, seguidos das ovelhas da raça Santa Inês e com os menores aumentos de temperatura retal nas ovelhas da raça Dorper (P<0,05). Estes resultados refletiram na capacidade termolítica individual, sendo menor para a raça Santa Inês (P<0,05). Após exposição ao sol observaram-se diferenças entre as TS, sendo as da raça Merino Branco mais elevadas, seguidas pelas da raça Dorper e da Santa Inês (P<0,05). A raça Merino Branco apresentou as maiores FR, seguida das raças Dorper e Santa Inês, todas diferentes entre si (P<0,05). Todos os animais expostos por uma hora ao sol apresentaram aumento nas TR, TS e FR (P<0,05), e se aproximaram dos níveis encontrados antes da exposição ao sol após trinta minutos de descanso sob a sombra (Santa Inês e Dorper P<0,05; Merino Branco P>0,05). A taxa média de sudação para as ovelhas da raça Santa Inês foi superior a encontrada para as ovelhas da raça Dorper (P<0,05). Houve diferença entre os animais dentro de cada raça (P<0,05), confirmando a hipótese de grande variabilidade entre os indivíduos e diferenças entre as raças. Com relação ao comportamento, as ovelhas da raça Santa Inês continuaram em pastejo mesmo nas horas mais quentes do dia, tendo sido encontrada uma correlação positiva de 0,64 entre a capacidade termolítica individual e o pastejo ao sol, enquanto as ovelhas da raça Dorper preferencialmente permaneceram à sombra devido ao manejo semiconfinado. No presente trabalho o tipo de manejo alimentar influenciou no tempo de uso da sombra. Sob as condições climáticas encontradas no experimento os animais estudados tiveram seus parâmetros fisiológicos alterados devido à exposição ao sol, e os animais das raças Dorper e Merino Branco mostraram maior capacidade termolítica do que os animais da raça Santa Inês, sendo este um fator que pode influenciar na tolerância ao calor individual. / The aim of this study was to evaluate the heat tolerance of three meat sheep breeds, Santa Ines, Dorper and White Merino using Thermolysis capacity test. 97 non pregnant females (3 years old) were used in the study that took place in the summer. Physiological variables as rectal temperature (RT), surface temperature (ST), respiratory rate (RR) were measured after two hours under the shade (1), after one hour under the sun (2), fifteen (3) and thirty (4) minutes after sun exposure, and sweating rate (SR) on time 2. Were also collected behavioral data during three days in the period from 11:00 to 14:00 hours: say in the sun, standing posture, eating, ruminating and idling. RT1 means were equal Santa Ines and Dorper, and greater for White Merino (P<0.05). White Merino also had greater values for RT2, RT3 e RT4, followed by Santa Ines and Dorper (P<0.05). These results reflected the thermolysis capacity, being lower for Santa Ines breed (P<0.05). After sun exposure differences between ST were observed, and greater values were found for White Merino, followed by Dorper and Santa Ines breeds (P<0.05). In the same way, White Merino had the highest RR, followed by Dorper, which had higher RR compared to Santa Ines (P<0.05). All animals exposed to the sun for an hour showed increased RT, ST, RR values (P<0.05), and approached the levels found before exposure to the sun after thirty minutes of rest in the shade (Santa Ines and Dorper P<0.05; White Merino P>0.05). Sweating rate for Santa Ines breed was higher than those found for Dorper breed (P<0.05). There were differences among animals within each race (P<0.05), confirming the hypothesis of great variability among individuals and differences between the breeds. With respect to behavior, Santa Ines ewe grazed even during the hottest hours of the day, and a positive correlation of 0.64 between the individual thermolysis capacity and grazing in the sun was found, while the Dorper ewes remained preferentially under the shade due to the semi-confined management. In the present study, feedin management influenced the time under the shade. Under experimental climatic conditions, the studied ewes had theirs physiological parameters increased due to sun exposure, and Dorper and White Merino breeds showed a greater thermolisys capacity than the animals of the Santa Ines breed, which is a factor that can influence individual heat tolerance.

The social organization of insect colonies has long fascinated naturalists. One of the main features of colony organization is division of labor, whereby each member of the colony specializes in a subset of all tasks required for successful group functioning. The most striking aspect of division of labor is its plasticity: workers switch between tasks in response to external challenges and internal perturbations. The mechanisms underlying flexible division of labor are far from being understood. In order to comprehend how the behavior of individuals gives rise to flexible collective behavior, several questions need to be addressed: We need to know how individuals acquire information about their colony's current demand situation; how they then adjust their behavior according; and which mechanisms integrate dozens or thousands of insect into a higher-order unit. With these questions in mind I have examined two examples of collective and flexible behavior in social bees. First, I addressed the question how a honey bee colony controls its pollen collection. Pollen foraging in honey bees is precisely organized and carefully regulated according to the colony's needs. How this is achieved is unclear. I investigated how foragers acquire information about their colony's pollen need and how they then adjust their behavior. A detailed documentation of pollen foragers in the hive under different pollen need conditions revealed that individual foragers modulate their in-hive working tempo according to the actual pollen need of the colony: Pollen foragers slowed down and stayed in the hive longer when pollen need was low and spent less time in the hive between foraging trips when pollen need of their colony was high. The number of cells inspected before foragers unloaded their pollen load did not change and thus presumably did not serve as cue to pollen need. In contrast, the trophallactic experience of pollen foragers changed with pollen need conditions: trophallactic contacts were shorter when pollen need was high and the number and probability of having short trophallactic contacts increased when pollen need increased. Thus, my results have provided support for the hypothesis that trophallactic experience is one of the various information pathways used by pollen foragers to assess their colony's pollen need. The second example of collective behavior I have examined in this thesis is the control of nest climate in bumble bee colonies, a system differing from pollen collection in honey bees in that information about task need (nest climate parameters) is directly available to all workers. I have shown that an increase in CO2 concentration and temperature level elicits a fanning response whereas an increase in relative humidity does not. The fanning response to temperature and CO2 was graded; the number of fanning bees increased with stimulus intensity. Thus, my study has evidenced flexible colony level control of temperature and CO2. Further, I have shown that the proportion of total work force a colony invests into nest ventilation does not change with colony size. However, the dynamic of the colony response changes: larger colonies show a faster response to perturbations of their colony environment than smaller colonies. Thus, my study has revealed a size-dependent change in the flexible colony behavior underlying homeostasis. I have shown that the colony response to perturbations in nest climate is constituted by workers who differ in responsiveness. Following a brief review of current ideas and models of self-organization and response thresholds in insect colonies, I have presented the first detailed investigation of interindividual variability in the responsiveness of all workers involved in a collective behavior. My study has revealed that bumble bee workers evidence consistent responses to certain stimulus levels and differ in their response thresholds. Some consistently respond to low stimulus intensities, others consistently respond to high stimulus intensities. Workers are stimulus specialists rather than task specialists. Further, I have demonstrated that workers of a colony differ in two other parameters of responsiveness: response probability and fanning activity. Response threshold, response probability and fanning activity are independent parameters of individual behavior. Besides demonstrating and quantifying interindividual variability, my study has provided empirical support for the idea of specialization through reinforcement. Response thresholds of fanning bees decreased over successive trials. I have discussed the importance of interindividual variability for specialization and the collective control of nest climate and present a general discussion of self-organization and selection. This study contributes to our understanding of individual behavior and collective structure in social insects. A fascinating picture of social organization is beginning to emerge. In place of centralized systems of communication and information transmission, insect societies frequently employ mechanisms based upon self-organization. Self-organization promises to be an important and unifying principle in physical, chemical and biological systems. / Ein besonderes Merkmal sozialer Insekten ist die Arbeitsteilung. Die Mitglieder einer Kolonie führen jeweils unterschiedliche Arbeiten aus und wechseln, je nach Bedarfslage der Kolonie, flexibel zwischen den verschiedenen Tätigkeiten. Die Mechanismen dieser flexiblen Arbeitsteilung sind bislang weitgehend unverstanden. Wie erfahren einzelne Arbeiterinnen welche Tätigkeiten gerade notwendig sind? Nach welchen Regeln ändern sie ihr Verhalten, wenn sich die Anforderungen an die Kolonie ändern? Wie wird das Verhalten vieler Einzelindividuen so koordiniert, daß die Kolonie als Ganzes sinnvoll auf eine sich verändernde Umwelt reagieren kann? In der vorliegenden Arbeit bin ich diesen Fragen an zwei unterschiedlichen Systemen nachgegangen. Im ersten Kapitel dieser Arbeit untersuchte ich die Regulation des Pollensammelns bei Honigbienen. Pollen ist für Honigbienen eine wichtige Proteinquelle zur Aufzucht der Brut. Sowohl die Menge an Brut als auch die bereits im Stock vorhanden Menge an Pollen beeinflußt die Sammelaktivität. Bislang ist unklar, wie die Sammelbienen Information über den Pollenbedarf ihrer Kolonie erhalten und wie sie ihr Verhalten dementsprechend ändern. Meine Versuche zeigten, daß Pollensammlerinnen ihr Arbeitstempo der aktuellen Bedarfslage anpassen: Ist der Pollenbedarf der Kolonie hoch, verbringen sie wenig Zeit im Stock, ist ausreichend Pollen vorhanden, gehen sie ihrer Sammeltätigkeit langsamer nach. Während ihres Aufenthalts im Stock haben die Sammlerinnen eine Vielzahl trophallaktischer Kontakte mit anderen Bienen. Die Anzahl solcher Kontakte änderte sich mit dem Pollenbedarf der Kolonie: Bei hohem Pollenbedarf sind die trophallaktischen Kontakte kürzer und die Anzahl sehr kurzer Kontakte hoch. Diese Ergebnisse unterstützen die Hypothese, daß Änderungen in der trophallaktischen Erfahrung eine wichtige Informationsquelle über den aktuellen Pollenbedarf einer Kolonie darstellen. Das zweite Beispiel flexibler Arbeitsteilung, welches ich in dieser Arbeit untersucht habe, ist die Regulation des Nestklimas in Hummelkolonien. Dieses System unterscheidet sich von dem oben dargestellten grundlegend, da Information über Änderungen im Bedarf an Arbeitskraft jedem Koloniemitglied zugänglich ist. Jedes Koloniemitglied im Nest kann direkt erfahren wie sich das Nestklima ändert. Ich konnte zeigen, daß Hummelkolonien auf einen Temperaturanstieg und eine Zunahme der Kohlendioxidkonzentration im Nest mit Ventilationsverhalten reagieren. Einzelne Hummeln fächeln dabei mit ihren Flügeln und sorgen so für Evaporationskühlung bzw. eine verstärkte Belüftung des Nestes. Erhöhte Luftfeuchtigkeit löste diese Reaktion nicht aus. Die Anzahl fächelnder Hummeln war abhängig von den Temperatur/CO2 Werten, die Kolonie reagierte fein abgestimmt auf die aktuellen Bedingungen. Unabhängig von ihrer Größe investierten die untersuchten Kolonien einen bestimmten Anteil ihrer Arbeiterinnen in die Ventilation des Nestes. Große Kolonien unterschieden sich jedoch von kleinen Kolonien in ihrer Antwortgeschwindigkeit: Große Kolonien antworten schneller auf einen Temperatur / CO2 Anstieg als kleine. Die flexible und fein abgestimmte Kolonieantwort auf Veränderungen im Nestklima basiert auf dem Verhalten vieler Einzelindividuen. Im dritten Kapitel dieser Arbeit stellte ich aktuelle Ideen und Hypothesen zu Selbstorganisation und dem Einfluß interindividueller Variabilität auf Kolonieverhalten dar. Regulation des Nestklimas in Hummelkolonien ist ein ideales System um interindividuelle Variabilität und ihre Auswirkungen zu untersuchen. Ich konnte zum ersten Mal Unterschiede im Antwortverhalten aller an einem kollektiven Verhalten beteiligten Koloniemitglieder quantifizieren. Neben Unterschieden in Antwortschwellen, die in der Literatur zwar viel diskutiert, aber noch nie schlüssig nachgewiesen wurden, konnte ich zeigen, daß sich Arbeiterinnen einer Kolonie in zwei weiteren Parametern unterscheiden: Die Wahrscheinlichkeit auf einen Stimulus zu reagieren und die Dauer, mit der die Arbeiterinnen das Verhalten ausführen (Aktivität) ist zwischen Individuen unterschiedlich. Diese drei Parameter (Reaktionsschwelle, Antwortwahrscheinlichkeit und Aktivität) sind vermutlich unabhängige Parameter individuellen Verhaltens. Neben diesen interindividuellen Unterschieden konnte ich nachweisen, daß sich die Antwortschwellen verändern, je häufiger eine Hummel fächelt: Arbeiterinnen reagieren von Mal zu Mal auf niedrigere Stimulusintensitäten. Diese Ergebnisse sind für unser Verständnis von Arbeitsteilung und Spezialisierung bei sozialen Insekten von besonderer Bedeutung. In dieser Arbeit habe ich sowohl das Verhalten individueller Arbeiterinnen als auch die daraus resultierende kollektive Antwort der Kolonie untersucht. Es wird zunehmend deutlicher, daß dem faszinierenden Verhalten sozialer Insekten häufig nicht zentrale Informationsverarbeitung sondern Selbstorganisation zugrunde liegt.

Current knowledge indicates that nonthermal muscle metaboreflex activity plays a critical role in the modulation of skin vasodilation and sweating. However, the mechanisms of control have primarily been studied during isometric handgrip exercise in which muscle metaboreceptor activation is induced by a brief post-exercise ischemia of the upper limb. While the reflex increase in mean arterial pressure associated with this period of ischemia is consistent with the activation of muscle metaboreceptors, the change in baroreflex activity may in itself modulate the response. Thus, we sought to understand how these nonthermal stimuli interact in modulating the control of skin perfusion and sweating under conditions of elevated hyperthermia. Furthermore, we examined the mechanisms responsible for the maintenance of arterial blood pressure under varying levels of heat stress during isometric handgrip exercise. Our study findings indicate that the parallel activation of muscle metaboreceptors and baroreceptors during post-exercise ischemia causes divergent influences on the control of skin blood flow and sweating; and these nonthermal stimuli are dependent on the level of hyperthermia. Moreover, we report that heat stress reduces the increase in arterial blood pressure during isometric handgrip exercise and this attenuation is attributed to a blunted increase in peripheral resistance, since cardiac output increased to similar levels for all heat stress conditions. These results provide important insight and understanding into the role of muscle metabo- and baroreflex activity on the control of skin blood flow and sweating; along with further knowledge into the cardiovascular mechanisms responsible for the regulation of arterial blood pressure during hyperthermia.

Thermoregulation is considered a top priority in neonatology due to the fact that relative to adults, neonates have a morphological susceptibility to excessive heat exchange with the environment, and exhibit limited physiological/behavioural responses to thermal strain. Consequently, the environmental conditions in which they are nursed must be tightly regulated to maintain body temperature stable. Neonatal intensive care units (NICU) use radiant warmers (RW) to thermally manage many newborns. However, recent evidence suggests that RW induce intermittent bouts of thermal strain that could adversely affect patients. This warrants further investigation of neonatal heat balance and the pertinent factors affecting it. Conducting an exhaustive audit of heat exchanges affecting the body during standard care under a RW could yield important information that would lead to the improvement of clinical practice in NICUs. The present thesis focuses on neonatal thermoregulatory responses, various body heat exchange mechanisms and processes during standard care under RW.

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.

Current knowledge indicates that nonthermal muscle metaboreflex activity plays a critical role in the modulation of skin vasodilation and sweating. However, the mechanisms of control have primarily been studied during isometric handgrip exercise in which muscle metaboreceptor activation is induced by a brief post-exercise ischemia of the upper limb. While the reflex increase in mean arterial pressure associated with this period of ischemia is consistent with the activation of muscle metaboreceptors, the change in baroreflex activity may in itself modulate the response. Thus, we sought to understand how these nonthermal stimuli interact in modulating the control of skin perfusion and sweating under conditions of elevated hyperthermia. Furthermore, we examined the mechanisms responsible for the maintenance of arterial blood pressure under varying levels of heat stress during isometric handgrip exercise. Our study findings indicate that the parallel activation of muscle metaboreceptors and baroreceptors during post-exercise ischemia causes divergent influences on the control of skin blood flow and sweating; and these nonthermal stimuli are dependent on the level of hyperthermia. Moreover, we report that heat stress reduces the increase in arterial blood pressure during isometric handgrip exercise and this attenuation is attributed to a blunted increase in peripheral resistance, since cardiac output increased to similar levels for all heat stress conditions. These results provide important insight and understanding into the role of muscle metabo- and baroreflex activity on the control of skin blood flow and sweating; along with further knowledge into the cardiovascular mechanisms responsible for the regulation of arterial blood pressure during hyperthermia.

Heat acclimation increases the local heat loss responses of sweating and skin blood flow which is thought to persist for up to 3 weeks post-acclimation. However, the extent to which increases in local heat loss affect whole-body heat loss as a function of increasing levels of heat stress remains unresolved. Using direct calorimetry, we examined changes in whole-body evaporative heat loss (EHL) during progressive increases in metabolic heat production 1) prior to (Day 0), during (Day 7) and following a 14-day heat acclimation protocol (Day 14) – Induction phase, and; 2) at the end of a 1-week (Day 21) and 2-week decay period (Day 28) – Decay phase. Ten males performed intermittent exercise (3 x 30-min (min) bouts of cycling at 300 (Ex1), 350 (Ex2), and 400 watts•meters2 (W•m2) (Ex3) separated by 10 and 20 min rest periods, respectively). During the induction period, EHL at Day 7 was increased at each of the three exercise bouts (Ex1: + 6%; Ex2 +8%; Ex3: +13%, all p≤0.05) relative to Day 0 (EHL at Ex1: 529 W; Ex2: 625 W; Ex3: 666 W). At Day 14, EHL was increased for all three exercise bouts compared to Day 0 (Ex1: 9%; Ex2: 12%; Ex3: 18%, all p≤0.05). As a result, a lower cumulative change in body heat content (ΔHb) was measured at Day 7 (-30%, p≤0.001) and Day 14 (-47%, p≤0.001). During the decay phase, EHL at Day 21 and 28 was only reduced in Ex 3 (p≤0.05) compared to Day 14. In parallel, ΔHb increased by 39% (p=0.003) and 57% (p≤0.001) on Day 21 and Day 28 relative to Day 14, respectively. When Day 28 was compared to Day 0, EHL remained elevated in each of the exercise bouts (p≤0.05). As such, ΔHb remained significantly lower on Day 28 compared to Day 0 (-16%, p=0.042). We show that 14 days of heat acclimation increases whole-body EHL during exercise in the heat which is maintained 14 days post-acclimation.