Behavioral Thermoregulation Research Articles

Thermal niches of specialized gut symbionts: the case of social bees.

Responses to climate change are particularly complicated in species that engage in symbioses, as the niche of one partner may be modified by that of the other. We explored thermal traits in gut symbionts of honeybees and bumblebees, which are vulnerable to rising temperatures. In vitro assays of symbiont strains isolated from 16 host species revealed variation in thermal niches. Strains from bumblebees tended to be less heat-tolerant than those from honeybees, possibly due to bumblebees maintaining cooler nests or inhabiting cooler climates. Overall, however, bee symbionts grew at temperatures up to 44°C and withstood temperatures up to 52°C, at or above the upper thermal limits of their hosts. While heat-tolerant, most strains of the symbiont Snodgrassella grew relatively slowly below 35°C, perhaps because of adaptation to the elevated body temperatures that bees maintain through thermoregulation. In a gnotobiotic bumblebee experiment, Snodgrassella was unable to consistently colonize bees reared at 29°C under conditions that limit thermoregulation. Thus, host thermoregulatory behaviour appears important in creating a warm microenvironment for symbiont establishment. Bee-microbiome-temperature interactions could affect host health and pollination services, and inform research on the thermal biology of other specialized gut symbionts.

Long-Term Acoustic Monitoring Reveals Site Fidelity, Reproductive Migrations, and Sex Specific Differences in Habitat Use and Migratory Timing in a Large Coastal Shark (Negaprion acutidens)

Knowledge of the movement patterns of the lemon shark Negaprion acutidens is poor in contrast to the allopatric N. brevirostis. Using acoustic telemetry, we investigated daily (diel and tidal) and seasonal patterns in residency, fidelity, home range, habitat preference, and migratory patterns along the Ningaloo coast, Australia. Thirty eight adult N. acutidens were monitored for up 6.1 years (mean 2.5 y) with 19 animals detected for more than 3 years and 5 for more than 5 y. Approximately 50% of the tagged animals remained within 10 km of their tagging location for more than 12 months (average core home range of 1.7 km2). Surprisingly, residency of adults was greater than juveniles in this known nursery area. Adults showed a strong preference for lagoon habitats and moved into shallow nearshore habitats at high tide and at night. During winter months, female sharks shifted their core home range 0.45 km further offshore into deeper lagoon areas, a shift which is likely due to behavioral thermoregulation. Space use by males and females within core areas was asynchronous indicating sexual segregation by resident sharks. Both resident and non-resident sharks were detected up to 140 km away. These highly directional (southerly) and rapid movements (140 km in 2 days) were largely correlated with the parturition and mating periods with males departing 1–2 months earlier than females. In females, periodicity of migrations was variable with evidence of annual and biannual patterns. Negaprion acutidens are highly susceptible to over-fishing and movement data are essential to quantify spatio-temporal overlap with fisheries and assist with developing spatially explicit stock assessment models.

Changes in dive patterns of leatherback turtles with sea surface temperature and potential foraging habitats

AbstractMarine mesotherms are able to occupy broader thermal niches than ectotherms; however, this means they must thermoregulate according to diverse thermal conditions across the ocean. Knowledge remains limited about how differences in thermal conditions within the selected habitats affect the behavior and associated ecological traits in mesotherms. Here, we tested if a marine mesotherm, leatherback turtles (Dermochelys coriacea) generally maintain their body temperature by diving to greater depths to expose themselves to cold waters as sea surface temperature becomes warmer. Moreover, we investigate how such behavioral thermoregulation may influence their ecological traits (e.g., foraging and migration). We analyzed 49,461 dive profiles and 16,255 temperature‐depth profiles from 17 leatherback turtles migrating across the North Pacific using satellite‐linked data loggers. Our results showed that leatherbacks changed their dive behavior regionally, in response to sea surface temperature and potential foraging habitats. Dive type classification revealed that V‐shaped, presumably gliding dives, became deeper when the surface water was warmer, likely because leatherbacks dive to deep cold waters to avoid overheating. We found five hotspots of wiggle (up‐and‐down undulations in the depth profile) dives that are indicative of foraging behavior, ranging from tropical to cool‐temperate regions in the North Pacific. The dive patterns in potential foraging hotspots indicate that leatherbacks engage in behavioral thermoregulation in warmer regions. Such bioenergetics may affect the time available for foraging activity during migration phases. In cool‐temperate foraging areas, leatherbacks are indeed able to spend more time foraging due to mesothermy. However, the trade‐off between energy gain by foraging activity and additional migration cost of moving to higher latitude areas might not result in greater reproductive output for leatherbacks foraging in distant cool‐temperate regions. These patterns highlight that mesothermy represents a trade‐off: Leatherbacks can utilize cooler waters but must engage in additional behavioral thermoregulation (i.e., extremely deep dives) in warmer waters. Thus, mesothermy might not provide a direct fitness advantage to all individual leatherback turtles; rather, it affords a species‐level fitness advantage by allowing a greater diversity of habitats to be utilized.

Interaction of hydric and thermal conditions drive geographic variation in thermoregulation in a widespread lizard

AbstractBehavioral thermoregulation is an efficient mechanism to buffer the physiological effects of climate change. Thermal ecology studies have traditionally tested how thermal constraints shape thermoregulatory behaviors without accounting for the potential major effects of landscape structure and water availability. Thus, we lack a general understanding of the multifactorial determinants of thermoregulatory behaviors in natural populations. In this study, we quantified the relative contribution of elevation, thermal gradient, moisture gradient, and landscape structure in explaining geographic variation in thermoregulation strategies of a terrestrial ectotherm species. We measured field‐active body temperature, thermal preferences, and operative environmental temperatures to calculate thermoregulation indices, including thermal quality of the habitat and thermoregulation efficiency for a very large sample of common lizards (Zootoca vivipara) from 21 populations over 3 yr across the Massif Central mountain range in France. We used an information‐theoretic approach to compare eight a priori thermo‐hydroregulation hypotheses predicting how behavioral thermoregulation should respond to environmental conditions. Environmental characteristics exerted little influence on thermal preference with the exception that females from habitats with permanent access to water had lower thermal preferences. Field body temperatures and accuracy of thermoregulation were best predicted by the interaction between air temperature and a moisture index. In mesic environments, field body temperature and thermoregulation accuracy increased with air temperature, but they decreased in drier habitats. Thermoregulation efficiency (difference between thermoregulation inaccuracy and the thermal quality of the habitat) was maximized in cooler and more humid environments and was mostly influenced by the thermal quality of the habitat. Our study highlights complex patterns of variation in thermoregulation strategies, which are mostly explained by the interaction between temperature and water availability, independent of the elevation gradient or thermal heterogeneity. Although changes in landscape structure were expected to be the main driver of extinction rate of temperate zone ectotherms with ongoing global change, we conclude that changes in water availability coupled with rising temperatures might have a drastic impact on the population dynamics of some ectotherm species.

Limited heat tolerance in an Arctic passerine: Thermoregulatory implications for cold-specialized birds in a rapidly warming world.

Arctic animals inhabit some of the coldest environments on the planet and have evolved physiological mechanisms for minimizing heat loss under extreme cold. However, the Arctic is warming faster than the global average and how well Arctic animals tolerate even moderately high air temperatures (T a) is unknown.Using flow‐through respirometry, we investigated the heat tolerance and evaporative cooling capacity of snow buntings (Plectrophenax nivalis; ≈31 g, N = 42), a cold specialist, Arctic songbird. We exposed buntings to increasing T a and measured body temperature (T b), resting metabolic rate (RMR), rates of evaporative water loss (EWL), and evaporative cooling efficiency (the ratio of evaporative heat loss to metabolic heat production).Buntings had an average (±SD) T b of 41.3 ± 0.2°C at thermoneutral T a and increased T b to a maximum of 43.5 ± 0.3°C. Buntings started panting at T a of 33.2 ± 1.7°C, with rapid increases in EWL starting at T a = 34.6°C, meaning they experienced heat stress when air temperatures were well below their body temperature. Maximum rates of EWL were only 2.9× baseline rates at thermoneutral T a, a markedly lower increase than seen in more heat‐tolerant arid‐zone species (e.g., ≥4.7× baseline rates). Heat‐stressed buntings also had low evaporative cooling efficiencies, with 95% of individuals unable to evaporatively dissipate an amount of heat equivalent to their own metabolic heat production.Our results suggest that buntings’ well‐developed cold tolerance may come at the cost of reduced heat tolerance. As the Arctic warms, and this and other species experience increased periods of heat stress, a limited capacity for evaporative cooling may force birds to increasingly rely on behavioral thermoregulation, such as minimizing activity, at the expense of diminished performance or reproductive investment.

Variation in leaf temperatures of tropical and subtropical trees are related to leaf thermoregulatory traits and not geographic distributions

AbstractTo help predict the effects of global warming on plants, previous studies have investigated how the distributions and physiological performances of plants relate to environmental temperatures. This approach implicitly assumes that leaf temperatures are tightly linked to regional air temperatures. However, the thermoregulatory behaviors and physical properties of leaves can differ greatly between species, leading to different plants having different leaf temperatures even when they occur under similar conditions. It is important to understand this variation in leaf thermoregulatory traits and temperatures in order to predict how individual species will be impacted by global warming. We measured the thermal properties of leaves from >50 tropical and subtropical tree species grown at the Gifford Arboretum (Florida, USA). For each species, we measured maximum leaf temperature and rate of leaf warming using a new standardized protocol to control for both environmental variation and select plant thermoregulatory behaviors. We tested the relationships between the two thermal variables and several leaf functional traits. Even under laboratory‐controlled conditions, leaf temperatures varied by over 8.5°C among species. Maximum leaf temperature was positively correlated with leaf area, and rate of leaf warming was negatively correlated with water content per leaf area. This suggests that some species may be able to offset rising air temperatures through acclimation or adaptation of these leaf properties. Next, we tested the relationships between the species’ leaf thermal properties and their climatic niches/distributions, but we found no significant associations. These results call into question the use of regional air temperatures to model plant physiological and demographic performance.Abstract in Spanish is available with online material.

Field-based body temperatures reveal behavioral thermoregulation strategies of the Atlantic marsh fiddler crab Minuca pugnax.

Behavioral thermoregulation is an important defense against the negative impacts of climate change for ectotherms. In this study we examined the use of burrows by a common intertidal crab, Minuca pugnax, to control body temperature. To understand how body temperatures respond to changes in the surface temperature and explore how efficiently crabs exploit the cooling potential of burrows to thermoregulate, we measured body, surface, and burrow temperatures during low tide on Sapelo Island, GA in March, May, August, and September of 2019. We found that an increase in 1°C in the surface temperature led to a 0.70-0.71°C increase in body temperature for females and an increase in 0.75-0.77°C in body temperature for males. Body temperatures of small females were 0.3°C warmer than large females for the same surface temperature. Female crabs used burrows more efficiently for thermoregulation compared to the males. Specifically, an increase of 1°C in the cooling capacity (the difference between the burrow temperature and the surface temperature) led to an increase of 0.42-0.50°C for females and 0.34-0.35°C for males in the thermoregulation capacity (the difference between body temperature and surface temperature). The body temperature that crabs began to use burrows to thermoregulate was estimated to be around 24°C, which is far below the critical body temperatures that could lead to death. Many crabs experience body temperatures of 24°C early in the reproductive season, several months before the hottest days of the year. Because the use of burrows involves fitness trade-offs, these results suggest that warming temperatures could begin to impact crabs far earlier in the year than expected.

Do dominant monkeys gain more warmth? Number of physical contacts and spatial positions in huddles for male Japanese macaques in relation to dominance rank

Animals show various forms of behavioral thermoregulation to minimize cold stress. Given that higher dominance rank is often associated with increased fitness in group-living animals, higher-ranking individuals may also benefit from better access to thermally optimal spatial positions within huddles. This study examined the association between dominance rank and the potential thermoregulatory benefits of huddling behavior in Japanese macaques (Macaca fuscata) inhabiting Shodoshima Island, which form exceptionally large huddles. I photographed monkey huddles, and analyzed the number of individuals that males were in contact with and males’ spatial positons in huddles. Higher-ranking males were significantly more likely to be in contact with larger numbers of individuals in huddles. Higher-ranking males occupied non-peripheral positions in huddles more often than lower-ranking males, which put them in contact with larger numbers of individuals. These results suggest that high dominance rank may confer potential thermal advantages on male Japanese macaques. The mechanism for this is likely that the highest-ranking male often intrude in already-formed huddles, although such behaviors of males were not quantitatively assessed. This study contributes to a better understanding of the mechanisms of cold adaptation in relation to dominance rank in group-living animals.

An mPOA-ARC <sup>AgRP</sup> Pathway Modulates Cold-Evoked Eating Behavior

Behavioral thermoregulation involves enhanced appetite under decreased temperature. The neural circuitry mediating the crosstalk between behavioral thermoregulation and energy homeostasis remains to be elucidated. We find that the hypothalamic orexigenic agouti-related neuropeptide (AgRP) neurons in the arcuate nucleus (ARC) are profoundly activated by cold exposure. Inhibition of AgRP neurons attenuates the cold-evoked eating behavior. The calcium signals in AgRP neurons display an immediate-response pattern in response to cold stimulation. We find that the upstream cold-responsive neurons in the medial preoptic area (mPOA) make excitatory synaptic connections onto AgRP neurons. These findings reveal an mPOA-ARC neural pathway that modulates the cold-evoked eating behavior.

Thermal robustness of biomechanical processes

Temperature influences many physiological processes that govern life as a result of the thermal sensitivity of chemical reactions. The repeated evolution of endothermy and widespread behavioral thermoregulation in animals highlight the importance of elevating tissue temperature to increase the rate of chemical processes. Yet, movement performance that is robust to changes in body temperature has been observed in numerous species. This thermally robust performance appears exceptional in light of the well-documented effects of temperature on muscle contractile properties, including shortening velocity, force, power and work. Here, we propose that the thermal robustness of movements in which mechanical processes replace or augment chemical processes is a general feature of any organismal system, spanning kingdoms. The use of recoiling elastic structures to power movement in place of direct muscle shortening is one of the most thoroughly studied mechanical processes; using these studies as a basis, we outline an analytical framework for detecting thermal robustness, relying on the comparison of temperature coefficients (Q 10 values) between chemical and mechanical processes. We then highlight other biomechanical systems in which thermally robust performance that arises from mechanical processes may be identified using this framework. Studying diverse movements in the context of temperature will both reveal mechanisms underlying performance and allow the prediction of changes in performance in response to a changing thermal environment, thus deepening our understanding of the thermal ecology of many organisms.

Water temperature is a key driver of horizontal and vertical movements of an ocean giant, the whale shark Rhincodon typus

Integrated analysis of the vertical and horizontal movements of epipelagic fishes requires high-resolution data from tags that have been attached to animals for long periods. The recovery of a SPLASH tag deployed on a whale sharkRhincodon typusfor 3 mo enabled access to archival data of horizontal and vertical movements of the shark that travelled 5380 km from Christmas Island to the Banda Sea. We examined water temperature and bathymetry to compare movements of the shark with key oceanographic features. Over 89 d, we identified 1931 dives and grouped these into 5 broad categories depending on dive shape. To investigate the potential for these dives to reflect behavioural thermoregulation, we used boosted regression trees to model the relationship between pre- and post-dive surface durations and dive characteristics. The movements of the shark were correlated with water temperatures, with the animal following frontal systems while remaining in a sea surface temperature (SST) range of 24-29°C. Across the continental shelf off north-western Australia, the shark mostly remained near the seafloor, likely avoiding very warm SSTs and strong currents at the surface. U- (foraging) and V- (searching) shaped dives accounted for ~78% of dives. Foraging dives during the day descended to 200-500 m and were preceded and followed by extended periods at the surface, whereas at night, the shark rarely dived below 200 m, likely foraging near the thermocline. Our results show how water temperatures influence the movement of this whale shark, with ‘basking’ at the surface during the day likely to gather environmental heat for thermoregulation, aiding to maintain body temperatures.

Behavioral thermoregulation in the fasted C57BL/6 mouse.

Under relatively cool ambient temperatures and a caloric deficit, mice will undergo daily torpor - a short-term regulated reduction in metabolic rate with a concomitant drop in body temperature. Mice can alternatively achieve metabolic savings by utilizing behavioral changes, such as seeking a warmer environment. However, there is a lack of knowledge about the behavioral interaction between torpor utilization and thermotaxis. That is, if a fasted mouse is faced with a choice between a warm environment not conducive for torpor, and a cool environment that will induce torpor, which scenario will the fasting mouse choose? Here, the temperature preferences of fasted mice were studied using a temperature gradient device that allows a mouse to freely move along a gradient of temperatures. C57BL/6 mice were implanted with temperature telemeters that recorded location, core temperature (Tb), and activity concurrently over a 23-h period in the thermal gradient. When the gradient was on, mice preferred the warm end of the gradient when fed (71±4% of the time) and even more so when fasted (84±2%). When the gradient was on, the fasted minimum Tb was significantly higher (34.4±0.3°C) than when the gradient was off (27.7±1.6°C). Further, fasted mice lost significantly more weight when the gradient was off despite maintenance of a metabolically favorable lower minimum Tb in this condition. These results indicate that fasted mice not only prefer warm ambient temperatures when given the choice, but that it is also the pathway with more favorable metabolic outcomes in a period of reduced caloric intake.

Regulate or tolerate: Thermal strategy of a coral reef flat resident, the epaulette shark, Hemiscyllium ocellatum.

Highly variable thermal environments, such as coral reef flats, are challenging for marine ectotherms and are thought to invoke the use of behavioural strategies to avoid extreme temperatures and seek out thermal environments close to their preferred temperatures. Common to coral reef flats, the epaulette shark (Hemiscyllium ocellatum) possesses physiological adaptations to hypoxic and hypercapnic conditions, such as those experienced on reef flats, but little is known regarding the thermal strategies used by these sharks. We investigated whether H. ocellatum uses behavioural thermoregulation (i.e., movement to occupy thermally favourable microhabitats) or tolerates the broad range of temperatures experienced on the reef flat. Using an automated shuttlebox system, we determined the preferred temperature of H. ocellatum under controlled laboratory conditions and then compared this preferred temperature to 6 months of in situ environmental and body temperatures of individual H. ocellatum across the Heron Island reef flat. The preferred temperature of H. ocellatum under controlled conditions was 20.7 ± 1.5°C, but the body temperatures of individual H. ocellatum on the Heron Island reef flat mirrored environmental temperatures regardless of season or month. Despite substantial temporal variation in temperature on the Heron Island reef flat (15-34°C during 2017), there was a lack of spatial variation in temperature across the reef flat between sites or microhabitats. This limited spatial variation in temperature creates a low-quality thermal habitat limiting the ability of H. ocellatum to behaviourally thermoregulate. Behavioural thermoregulation is assumed in many shark species, but it appears that H. ocellatum may utilize other physiological strategies to cope with extreme temperature fluctuations on coral reef flats. While H. ocellatum appears to be able to tolerate acute exposure to temperatures well outside of their preferred temperature, it is unclear how this, and other, species will cope as temperatures continue to rise and approach their critical thermal limits. Understanding how species will respond to continued warming and the strategies they may use will be key to predicting future populations and assemblages.

Assessing contributions of cold-water refuges to reproductive migration corridor conditions for adult salmon and steelhead trout in the Columbia River, USA

Diadromous fish populations face multiple challenges along their migratory routes. These challenges include suboptimal water quality, harvest, and barriers to longitudinal and lateral connectivity. Interactions among factors influencing migration success make it challenging to assess management options for improving migratory fish conditions along riverine migration corridors. We describe a spatially explicit simulation model that integrates complex individual behaviors of fall-run Chinook Salmon (Oncorhynchus tshawytscha) and summer-run steelhead trout (O. mykiss) during migration, responds to variable habitat conditions over a large extent of the Columbia River, and links migration corridor conditions to fish condition outcomes. The model is built around a mechanistic behavioral decision tree that drives individual interactions of fish within their simulated environments. By simulating several thermalscapes with alternative scenarios of thermal refuge availability, we examined how behavioral thermoregulation in cold-water refuges influenced migrating fish conditions. Outcomes of the migration corridor simulation model show that cold-water refuges can provide relief from exposure to high water temperatures, but do not substantially contribute to energy conservation by migrating adults. Simulated cooling of the Columbia River decreased reliance on cold-water refuges and there were slight reductions in migratory energy expenditure. This modeling of simulated thermalscapes provides a framework for assessing the contribution of cold-water refuges to the success of migrating fishes, but any final determination will depend on analyzing fish survival and health for their entire migration, water temperature management goals and species recovery targets.

Modelling the joint effects of body size and microclimate on heat budgets and foraging opportunities of ectotherms

Abstract Body size affects the body temperature of an ectotherm by altering both heating rates and the microclimate experienced. These joint effects are rarely considered in the analyses of climatic constraints on ectotherms but nonetheless influence body temperatures and thus activity periods and foraging opportunities. Here we develop and test transient heat‐budget models that use height‐specific microclimatic forcing to compute the dynamics of size‐dependent body temperatures of ectotherms in sun and in shade. We incorporate a model of behavioural thermoregulation and use it to compute potential body temperatures and then to map these to ecologically relevant indices, including foraging opportunities and thermal constraints. To illustrate potential applications, we combine a microclimate model driven by a global climate database with the transient behavioural algorithm developed for lizards to explore how body size (10 and 1,000 g) and size‐specific microclimate (at natural heights of 1 and 7.5 cm, respectively) interactively influence body temperatures and ecological indices at a warm, arid location in Australia in both spring and summer. To explore microclimatic effects, we contrast temperatures and indices for animals positioned at their natural versus reciprocal heights above the ground. Our simulations show that the behavioural and ecological consequences of size can be strongly biased when joint effects of body size and size‐imposed microclimate are ignored. For example, the two body sizes did not differ in total foraging time when compared at their natural heights, but did differ if compared at the same height, the direction of this difference reversing with the height at which they were compared. We show how computed foraging times can be translated to potential foraging radii from a central place (burrow or shade‐providing bush), thereby illustrating how body size can be physiologically translated into habitat connectivity as a function of different shade configurations, for example, as modified by fire regimes or shrub dieback. All functions are now integrated into the biophysical modelling r package NicheMapR and as a Shiny app, which should provide new insights and avenues for investigation into functional interactions between body size and habitat structure for ectotherms.

Effects of simazine and food deprivation chronic stress on energy allocation among the costly physiological processes of male lizards (Eremias argus).

The residue of simazine herbicide in the environment is known as one of pollutant stress for lizards by crippling its fitness on direct toxic effects and indirect food shortage via the food chain effects. Both stressors were considered in our experiment in the simazine exposure and food availability to lizards (Eremias argus). The results revealed that starvation significantly reduced the lizard's energy reserve and native immune function, while the accumulation of simazine in the liver was significantly increased. Simazine caused oxidative stress in the liver of lizards, but oxidative damage only occurred in the starved lizards. Simazine also changed the energy reserves, native immune function and detoxification of well-fed lizards, while the starved lizards showed different sensitivity to simazine. Simazine or starvation treatment independently activated the lizard HPA axis, but co-treatment caused the HPA axis inhibition. Besides, according to the variations on amino acid neurotransmitters, corticosterone hormone and thermoregulatory behavior, we inferred that lizards in threatens take the appropriate strategy on energy investment and allocation through neural, endocrine and behavioral pathways to maximize benefits in dilemma. Energy allocation was necessary, while suppression on any physiological process comes at a cost that is detrimental to long-term individual fitness.

Short-term captivity does not affect immediate voluntary thermal maximum of a neotropical pitviper: Implications for behavioral thermoregulation.

Ectotherms depend on temperature to maintain their physiological functions and through behavioral changes, they can avoid overheating in their habitats. The voluntary thermal maximum (VTMax ) represents the maximum temperature tolerated by individuals before actively moving to a colder place. However, if and how VTMax might change after capture and in captivity remains understudied. We investigate if measurements taken in captivity are a good proxy for thermal tolerance of wild individuals. Asthermal history has been shown to affect behavioral response and physiological parameters, herein we hypothesized that VTMax of the neotropical viper Bothrops pauloensis varies throughout the captivity period. We measured the VTMax of individuals immediately after capture and in three trials during a short-term period in captivity. Measurements were done by recording their body temperature at which they exited a heating box experimental setup. In contrastto our hypothesis, the VTMax was not significantly affected by time in captivity but there was interindividual variation. There were also no significant differences between field and captivity measurements, in spite of the small effect size. Our results indicate that the VTMax of this snake population is not affected by a short-term captivity period. Furthermore, an invariant VTMax might indicate low phenotypic plasticity, as individuals do not appear to adjust their tolerance to short-term exposure to higher temperaturesand potential vulnerability to threats such as global warming. We expect that our results can contribute to understanding the effect of captivity on thermal tolerance in neotropical squamates, allowing for insights into their thermal physiology and ecology.

The effects of simulated transportation conditions on the core body and extremity temperature, blood physiology, and behavior of white-strain layer pullets

Transportation of poultry is stressful. The transportation of broilers has been well studied, while the transportation of layer pullets from rearing to laying facilities has not been thoroughly evaluated. This experiment aimed to establish the effects of temperature (T)/RH combinations and duration (D) of transport, via a 5 × 2 factorial arrangement of simulated transport conditions using 5 T/RH combinations (21°C with 30% RH [21/30], 21°C with 80% RH [21/80], 30°C with 30% RH [30/30], 30°C with 80% RH [30/80], and −15°C with uncontrolled RH [−15]), and 2 exposure D (4 or 8 h). Pullets (18–19 wk; n = 240) were obtained from 3 commercial farms (N = 3 farms). Pretreatment, birds were orally administered a miniature data logger to record core body temperature (CBT), an initial blood sample was taken (5 birds/replicate), and initial foot T was recorded. Behavior during exposure was video recorded. Following exposure, a final blood sample was taken (analyzed for heterophil to lymphocyte ratio, partial pressure of CO2, total CO2, bicarbonate, and glucose), birds were slaughtered, and data loggers were retrieved. Data were analyzed as a randomized complete block design via Proc Mixed (SAS 9.4) and significance was declared at P ≤ 0.05. There were no interactions observed for the T/RH and D combinations throughout the study. The CBT and foot T were lowest in pullets exposed to −15 compared with all other treatments. Foot T was also highest in pullets exposed to 30/80 compared with −15, 21/30, and 21/80. There was no impact of T/RH on pullet blood physiology. Activity and thermoregulatory behaviors were impacted by the T/RH combinations. Pullets exposed to 30/30 and 30/80 spent the most time panting. Pullets exposed to 30/80 also spent the least amount of time motionless. Duration had minor impacts on pullet CBT, blood physiology, and behavior. These data indicate that as a response to thermal stress, layer pullets were successful at implementing mechanisms to maintain homeostasis.

Hot and bothered: The role of behaviour and microclimates in buffering species from rising temperatures.

In Focus: Bladon, A. J., Lewis, M., Bladon, E. K., Buckton, S. J., Corbett, S., Ewing, S. R., … Turner, E. C. (2020). How butterflies keep their cool: Physical and ecological traits influence thermoregulatory ability and population trends. Journal of Animal Ecology. https://doi.org/10.1111/1365-2656.13319 Threatened with rising average temperatures and the new normal of climate extremes, species that cannot keep pace with climate change must adapt where they are, or face extinction. The ranges of many British butterflies have indeed extended northwards as the climate has warmed, but this option is increasingly restricted by the expansion and intensification of urban and agricultural lands. On a day-to-day basis, butterflies can thermoregulate using behaviours such as adjusting their wing positioning or moving into suitable microclimates. The extent to which these two options buffer individuals from free-air temperature, however, is not well known. Nor is the extent to which the different mechanisms are exploited by different species, and whether that has had any bearing on species' population trends over the time-scale of recent climate change. Using a simple and easily replicated approach, Bladon etal.(2020) were able to quantify intra- and interspecific variation in buffering ability, and species' relative reliance on the two thermoregulatory mechanisms of wing adjustment versus microclimate selection. The authors report marked variation in buffering capacity, correlated with wing size, wing colouration and taxonomic family. Species also differed in their thermoregulatory behaviours, with some - such as the Ringlet Aphantopus hyperantus and Large Skipper Ochlodes sylvanus-achieving impressive buffering through wing positioning. Others, like the Brown Argus Aricia agestis and Small Heath Coenonympha pamphilus, were more reliant on microclimate selection, and these were the species most likely to have shown declining population trends over the past 40years. The study underscores the importance of individual thermoregulatory behaviours for understanding species' vulnerability to climate change. In combination with much improved methods for measuring and modelling climate at biologically relevant scales, the approach of Bladon etal.(2020) can and should be extended to identify the places and species most at risk, and the steps that conservation practitioners can take to maximise resilience to climate change. Much attention has been given to improving habitat connectivity to facilitate range shifts, but we should also consider how microclimate availability can be enhanced to allow species to manage when they cannot move.

Thermal adaptations to extreme freeze–thaw cycles in the high tropical Andes

AbstractTemperature plays a key role in the biology of ectotherms, including anurans, which are found at higher elevations in the tropics than anywhere in the temperate zone. High elevation tropical environments are characterized by extreme daily thermal fluctuation including high daily maxima and nightly freezing. Our study investigated the contrasting operative temperatures of the anurans Telmatobius marmoratus and Pleurodema marmoratum in different environmental contexts at the same elevation and biome above 5,200 m. Telmatobius marmoratus avoids extremes of daily temperature fluctuation by utilizing thermally buffered aquatic habitat at all life stages, with minimal operative temperature variation (range: 4.6–8.0°C). Pleurodema marmoratum, in contrast, experienced operative temperatures from −3.5 to 44°C and has one of the widest thermal breadths reported for any tropical frog, from >32°C (critical thermal maximum) to surviving freezing periods of 1 and 6 hr down to −3.0°C. Our findings expand experimental evidence of frost tolerance in amphibians to the widespread Neotropical family Leptodactylidae, the first such evidence of frost tolerance in a tropical amphibian. Our study identifies three strategies (wide thermal tolerance breadth, use of buffered microhabitats, and behavioral thermoregulation), which allow these tropical frogs to withstand the current wide daily thermal fluctuation above 5,000 m.a.s.l. and which may help them adapt to future climatic changes.Abstract in Spanish is available with online material