Thermoregulation in the primitively eusocial paper wasp, Polistes dominulus

Regulation of wing muscle temperature is important for sustaining flight in many insects, and has been well studied in honeybees. It has been much less well studied in wasps and has never been demonstrated in Polistes paper wasps. We measured thorax, head, and abdomen temperatures of inactive Polistes dominulus workers as they warmed after transfer from 8 to ~25°C ambient temperature, after removal from hibernacula, and after periods of flight in a variable temperature room. Thorax temperature (T _th) of non-flying live wasps increased more rapidly than that of dead wasps, and T _th of some live wasps reached more than 2°C above ambient temperature (T _a), indicating endothermy. Wasps removed from hibernacula had body region temperatures significantly above ambient. The T _th of flying wasps was 2.5°C above ambient at T _a = 21°C, and at or even below ambient at T _a = 40°C. At 40°C head and abdomen temperatures were both more than 2°C below T _a, indicating evaporative cooling. We conclude that P. dominulus individuals demonstrate clear, albeit limited, thermoregulatory capacity.     

Contrasting foraging related behaviours in two sympatric wasps (Vespula maculifrons and V. germanica)

ABSTRACT.

• 1 Using pinned freshly killed wasps (yellowjackets) to simulate feeding animals, it was found that V. germanica was socially facilitated, and concentrated its foraging activity on those feeders with the most pinned wasps (twenty). V. maculifrons foragers responded inversely, preferentially foraging at feeders with few or no pinned wasps.
• 2 Using hand-painted drawing pins (thumb tacks) as wasp models, similar results were found, indicating that visual, rather than olfactory, cues were responsible for the observed distribution.
• 3 Vespula maculifrons and V. germanica exhibit aggression while foraging at honey-baited feeders. Both species attack conspecifics at frequencies lower than would be expected under random encounter.

     

Foraging and spatial dispersion in protein-scavenging workers ofVespula germanica andV. maculifrons (Hymenoptera: Vespidae)

A series of experiments on the discovery of meat bait by scavenging workers ofV. germanica andV. maculifrons showed that workers oriented to meats by visual cues and olfactory cues. Scavening workers ofV. germanica andV. maculifrons responded positively to the sight of conspecifics at meat baits; i.e., meat with (confined) wasps received more visits than meat without wasps. This attraction to conspecific workers on meat baits provides evidence of local enhancement, in that the presence of conspecifics at meat bait directs other wasps to a particular spatial locality. Local enhancement by yellowjackets foraging for meat may contribute to the clumped distribution of worker populations noted in studies of workers captured in meat-baited traps. We hypothesize that local enhancement of foraging is a ubiquitous behavior in species of theV. vulgaris species group and may be one attribute explaining their ecological success.     

Thermoregulation of water foraging wasps (Vespula vulgaris and Polistes dominulus)

A comparison of the thermoregulation of water foraging wasps (Vespula vulgaris, Polistes dominulus) under special consideration of ambient temperature and solar radiation was conducted. The body surface temperature of living and dead wasps was measured by infrared thermography under natural conditions in their environment without disturbing the insects’ behaviour. The body temperature of both of them was positively correlated with T_a and solar radiation. At moderate T_a (22–28 °C) the regression lines revealed mean thorax temperatures (T_th) of 35.5–37.5 °C in Vespula, and of 28.6–33.7 °C in Polistes. At high T_a (30–39 °C) T_th was 37.2–40.6 °C in Vespula and 37.0–40.8 °C in Polistes. The thorax temperature excess (T_th–T_a) increased at moderate T_a by 1.9 °C (Vespula) and 4.4 °C (Polistes) per kW⁻¹ m⁻². At high T_a it increased by 4.0 °C per kW⁻¹ m⁻² in both wasps. A comparison of the living water foraging Vespula and Polistes with dead wasps revealed a great difference in their thermoregulatory behaviour. At moderate T_a (22–28 °C) Vespula exhibited distinct endothermy in contrast to Polistes, which showed only a weak endothermic activity. At high T_a (30–39 °C) Vespula reduced their active heat production, and Polistes were always ectothermic. Both species exhibited an increasing cooling effort with increasing insolation and ambient temperature.     

Resource choice of social wasps: influence of presence, size and species of resident wasps

Summary: The role of visual cues provided by resident wasps on resource choice by yellowjacket and paper wasp foragers was investigated. Large spring queen yellowjackets and small early season yellowjacket foragers (Vespula germanica, Vespula maculifrons, and Vespula vidua) were extracted in hexane to remove odors and posed as though feeding at petri dish feeders bearing daisy-like flower models, equipped with microcapillary feeding tubes, and containing 1:3 honey:water solution. An array of five feeders was presented to foragers at a suburban and a woodland site in Saratoga Springs, New York. The visual cues provided by resident wasps influenced resource choice by approaching social wasp foragers. Vespula germanica, an introduced yellowjacket species that tends to dominate at rich resources, was the only wasp visiting the suburban feeders. Foragers of this species preferentially fed on feeders and flowers with posed wasps and fed most often next to large wasps. Polistes fuscatus foragers at the woodland site similarly preferred to feed on occupied feeders and flowers. Vespula maculifrons and V. consobrina preferentially visited unoccupied feeders. Individual V. maculifrons, V. consobrina and V. vidua foragers that landed on occupied feeders all preferentially visited unoccupied flowers on those feeders. Vespula vidua and V. flavopilosa foragers did not demonstrate a feeder preference based on the presence/absence of posed wasps. Vespula consobrina foragers that visited occupied feeders preferred those occupied by extracted V. maculifrons queens and workers; no other wasps showed species based landing preferences.     

Thermoregulation of water foraging honeybees—Balancing of endothermic activity with radiative heat gain and functional requirements

Foraging honeybees are subjected to considerable variations of microclimatic conditions challenging their thermoregulatory ability. Solar heat is a gain in the cold but may be a burden in the heat. We investigated the balancing of endothermic activity with radiative heat gain and physiological functions of water foraging Apis mellifera carnica honeybees in the whole range of ambient temperatures (T_a) and solar radiation they are likely to be exposed in their natural environment in Middle Europe.The mean thorax temperature (T_th) during foraging stays was regulated at a constantly high level (37.0-38.5 °C) in a broad range of T_a (3-30 °C). At warmer conditions (T_a = 30-39 °C) T_th increased to a maximal level of 45.3 °C. The endothermic temperature excess (difference of T_body − T_a of living and dead bees) was used to assess the endogenously generated temperature elevation as a correlate of energy turnover. Up to a T_a of ∼30 °C bees used solar heat gain for a double purpose: to reduce energetic expenditure and to increase T_th by about 1-3 °C to improve force production of flight muscles. At higher T_a they exhibited cooling efforts to get rid of excess heat. A high T_th also allowed regulation of the head temperature high enough to guarantee proper function of the bees’ suction pump even at low T_a. This shortened the foraging stays and this way reduced energetic costs. With decreasing T_a bees also reduced arrival body weight and crop loading to do both minimize costs and optimize flight performance.     

Effects of flight behaviour on body temperature and kinematics during inter-male mate competition in the solitary desert bee Centris pallida

Abstract. Body temperatures and kinematics are measured for male Centris pallida bees engaged in a variety of flight behaviours (hovering, patrolling, pursuit) at a nest aggregation site in the Sonoran Desert. The aim of the study is to test for evidence of thermoregulatory variation in convective heat loss and metabolic heat production and to assess the mechanisms of acceleration and forward flight in field conditions. Patrolling males have slightly (1–3 °C) cooler body temperatures than hoverers, despite similar wingbeat frequencies and larger body masses, suggesting that convective heat loss is likely to be greater during patrolling flight than during hovering. Comparisons of thorax and head temperature as a function of air temperature (T_a) indicate that C. pallida males are thermoregulating the head by increasing heat transfer from the thorax to the head at cool T_a. During patrolling flight and hovering, wingbeat frequency significantly decreases as T_a increases, indicating that variation in metabolic heat production contributes to thermal stability during these behaviours, as has been previously demonstrated for this species during flight in a metabolic chamber. However, wingbeat frequency during brief (1–2 s) pursuits is significantly higher than during other flight behaviours and independent of T_a. Unlike most other hovering insects, C. pallida males hover with extremely inclined stroke plane angles and nearly horizontal body angles, suggesting that its ability to vary flight speed depends on changes in wingbeat frequency and other kinematic mechanisms that are not yet described.     

A hot lunch for herbivores: physiological effects of elevated temperatures on mammalian feeding ecology

Mammals maintain specific body temperatures (T_b) across a broad range of ambient temperatures. The energy required for thermoregulation ultimately comes from the diet, and so what animals eat is inextricably linked to thermoregulation. Endothermic herbivores must balance energy requirements and expenditure with complicated thermoregulatory challenges from changing thermal, nutritional and toxicological environments. In this review we provide evidence that plant‐based diets can influence thermoregulation beyond the control of herbivores, and that this can render them susceptible to heat stress. Notably, herbivorous diets often require specialised digestive systems, are imbalanced, and contain plant secondary metabolites (PSMs). PSMs in particular are able to interfere with the physiological processes responsible for thermoregulation, for example by uncoupling mitochondrial oxidative phosphorylation, binding to thermoreceptors, or because the pathways required to detoxify PSMs are thermogenic. It is likely, therefore, that increased ambient temperatures due to climate change may have greater and more‐specific impacts on herbivores than on other mammals, and that managing internal and external heat loads under these conditions could drive changes in feeding ecology.     

Energetics and thermoregulation during digging in the rodent tuco-tuco (Ctenomys talarum)

For subterranean rodents, searching for food by extension of the tunnel system and maintenance of body temperature are two of the most important factors affecting their life underground. In this study we assess the effect of ambient temperature on energetics and thermoregulation during digging in Ctenomys talarum. We measured V˙o₂ during digging and resting at ambient temperature (T_a) below, within, and above thermoneutrality. Digging metabolic rate was lowest at T_a within the thermoneutral zone and increased at both lower and higher temperatures, but body temperature (T_b) remained constant at all T_as. Below thermoneutrality, the cost of digging and thermoregulation are additive. Heat production for thermoregulation would be compensated by heat produced as a by-product of muscular activity during digging. Above thermoneutrality, conduction would be an important mechanism to maintain a constant T_b during digging.     

Variation in colour markings of German wasps Vespula germanica (F.) and common wasps Vespula vulgaris (L.) (Hymenoptera: Vespidae) in New Zealand

Abstract

German wasps (Vespula germanica F.) and common wasps (V. vulgaris L.) both show variations in colour markings in New Zealand. Overlap in the ranges of markings of the head and thorax is limited enough for ready distinction of queens and workers of the two species. Abdominal markings overlap considerably between the species. Colour markings of males were too similar to identify the species, which were completely separated by the shape of their genitalia. The frequency of occurrence of “intermediate” markings in V. germanica populations did not increase in areas where the two species overlap. This suggests there is little or no genetic exchange between the two species.     

Thermal stimulation of exposed skin area influences behavioral thermoregulation in pigeons

Summary Pigeons were trained to work instrumentally for thermal reinforcement under ambient heat and cold loads. Facial or breast skin temperature was selectively altered by means of air-perfused thermodes. Facial stimulation with temperatures in the normally occurring range resulted in changes of instrumental response rate, accompanied by stimulus opposing deviations of core temperature (Fig. 5). Breast skin stimulations with the same stimulation amplitudes also affected behavioral thermoregulation, but without changing core temperature. Small temperature changes, as naturally occur at feathered breast skin, had no effect on response rate. Behavioral adjustments occurring within 15 s in response to altering either ambient load temperature or facial temperature locally (Fig. 6), support the hypothesis that the face represents a site driving short term behavioral adjustments to ambient disturbances.Abbreviations RF reinforcement(s) - T _a temporal mean of ambient temperature - T _load load temperature - T _c (colonic) core temperature - T _s skin temperature - T _s(v) ventral skin temperature - T _s(d) dorsal skin temperature - T _ax axilla temperature     

Seasonal variations in the behavioural thermoregulation of roosting Humboldt penguins ( Spheniscus humboldti) in north-central Chile

We examined the thermoregulatory behaviour (TRB) of roosting Humboldt penguins (Spheniscus humboldti) in north central Chile during summer and winter, when ambient temperatures (T_a) are most extreme. Each body posture was considered to represent a particular TRB, which was ranked in a sequence that reflected different degrees of thermal load and was assigned an arbitrary thermoregulatory score. During summer, birds exhibited eight different TRBs, mainly oriented to heat dissipation, and experienced a wide range of T_a (from 14 to 31°C), occasionally above their thermoneutral zone (TNZ, from 2 to 30°C), this being evident by observations of extreme thermoregulatory responses such as panting. In winter, birds exhibited only three TRBs, mainly oriented to heat retention, and experienced a smaller range of T_a (from 11 to 18°C), always within the TNZ, even at night. The components of behavioural responses increased directly with the heat load which explains the broader behavioural repertoire observed in summer. Since penguins are primarily adapted in morphology and physiology to cope with low water temperatures, our results suggest that behavioural thermoregulation may be important in the maintenance of the thermal balance in Humboldt penguins while on land.     

Thermal clamping of temperature-regulating flowers reveals the precision and limits of the biochemical regulatory mechanism

The flowers of several families of seed plants warm themselves when they bloom. In some species, thermogenesis is regulated, increasing the rate of respiration at lower ambient temperature (T _a) to maintain a somewhat stable floral temperature (T _f). The precision of this regulation is usually measured by plotting T _f over T _a. However, such measurements are influenced by environmental conditions, including wind speed, humidity, radiation, etc. This study eliminates environmental effects by experimentally ‘clamping’ T _f at constant, selected levels and then measuring stabilized respiration rate. Regulating flowers show decreasing respiration with rising T _f (Q ₁₀ < 1). Q ₁₀ therefore becomes a measure of the biochemical ‘precision’ of temperature regulation: lower Q ₁₀ values indicate greater sensitivity of respiration to T _f and a narrower range of regulated temperatures. At the lower end of the regulated range, respiration is maximal, and further decreases in floral temperature cause heat production to diminish. Below a certain tissue temperature (‘switching temperature’), heat loss always exceeds heat production, so thermoregulation becomes impossible. This study compared three species of thermoregulatory flowers with distinct values of precision and switching temperature. Precision was highest in Nelumbo nucifera (Q ₁₀ = 0.16) moderate in Symplocarpus renifolius (Q ₁₀ = 0.48) and low in Dracunculus vulgaris (Q ₁₀ = 0.74). Switching temperatures were approximately 30, 15 and 20°C, respectively. There were no relationships between precision, switching temperature or maximum respiration rate. High precision reveals a powerful inhibitory mechanism that overwhelms the tendency of temperature to increase respiration. Variability in the shape and position of the respiration–temperature curves must be accounted for in any explanation of the control of respiration in thermoregulatory flowers.     

Thermoregulatory strategies in two closely related sympatric Scarabaeus species (Coleoptera: Scarabaeinae)

Abstract. The thermoregulation strategies of Scarabaeus sacer L. and Scarabaeus cicatricosus Lucas were studied in the Doñana National Park, Spain. In this area, both species coexist, showing the same habitat and food preferences. However, S. cicatricosus is active during warmer parts of the day compared to S. sacer. Both species thermoregulate their thoracic temperature but, whereas the abdomen of S. sacer is a passive thermal window, S. cicatricosus actively thermoregulates abdominal temperature by increasing heat transfer from the thorax to the abdomen at high T_a values. In the case of S. sacer, their endothermy indicates an adaptive capacity to thorax heat retention, as occurs mainly in winter‐flying insects. This mechanism, possibly related to the aerodynamic flight posture in Scarabaeinae, could be an effective barrier to retard the rate of abdominal heat loss during flight. This endothermic strategy makes flight difficult at higher temperatures, although it allows flight during cooler periods of the day. On the other hand, S. cicatricosus showed a different adaptive behaviour to S. sacer. In this case, a significant decrease in abdominal heat loss at higher ambient temperatures would indicate a decrease in heat transfer from the thorax to the abdomen, as occurs in some desert and semiarid insects. This ‘heat exchanger’ mechanism observed in S. cicatricosus could be due to the irregular posture adopted during flight, with the posterior legs clearly extended and separate from the body. This behaviour increases turbulence and convective cooling, favouring exposure of the soft abdominal tergal cuticle and, subsequently, water loss. Thus, for S. cicatricosus, the well‐adapted ‘heat exchanger’ permits flight during periods of the day when temperatures would possibly be lethal for those species with high endothermy. From an adaptive viewpoint, these mechanisms of thermoregulation may explain how both closely‐related sympatric species respond in different ways to environmental temperature, favouring their coexistence.     

Thermoregulatory responses to variations of photoperiod and ambient temperature in the male lesser mouse lemur: a primitive or an advanced adaptive character?

The lesser mouse lemur, a small Malagasy primate, is exposed to strong seasonal variations in ambient temperature and food availability in its natural habitat. To face these environmental constraints, this nocturnal primate exhibits biological seasonal rhythms that are photoperiodically driven. To determine the role of daylength on thermoregulatory responses to changes in ambient temperature, evaporative water loss (EWL), body temperature (T _b) and oxygen consumption, measured as resting metabolic rate (RMR), were measured in response to ambient temperatures ranging from 5 °C to 35 °C, in eight males exposed to either short (10L:14D) or long (14L:10D) daylengths in controlled captive conditions. In both photoperiods, EWL, T _b and RMR were significantly modified by ambient temperatures. Exposure to ambient temperatures below 25 °C was associated with a decrease in T _b and an increase in RMR, whereas EWL remained constant. Heat exposure caused an increase in T _b and heat loss through evaporative pathways. Thermoregulatory responses to changes in ambient temperature significantly differed according to daylength. Daily variations in T _b and EWL were characterized by high values during the night. During the diurnal rest, lower values were found and a phase of heterothermia occurred in the early morning followed by a spontaneous rewarming. The amplitude of T _b decrease with or without the occurrence of torpor (T _b < 33 °C) was dependent on both ambient temperature and photoperiod. This would support the hypothesis of advanced thermoregulatory processes in mouse lemurs in response to selective environmental pressure, the major external cue being photoperiodic variations. Accepted: 4 August 1998     

Thermoregulatory physiology of the carpenter bee,Xylocopa varipuncta

Summary The carpenter beesXylocopa varipuncta maintain thoracic temperatures of 33.0°C to 46.5°C during continuous free flight from 12°C to 40°C. Since the thoracic temperature excess is not constant (decreasing from 24°C at low air temperatures to 6°C at high) the bees are thermoregulating. We document physiological transfer of relatively large amounts of heat to the abdomen and to the head during pre-flight warm-up and during artificial thoracic heating. Most of the temperature increase of the head is due to passive conduction, while that of the abdomen is due to active physiological heat transfer despite a series of convolutions of the aorta in the petiole that anatomically conform to a counter-current heat exchanger. Although the thermoregulatory mechanisms during flight are far from clarified, our data suggest that thermoregulation involves a strong reliance on active convective cooling through increased flight speed.     

Thermoregulatory responses to thermal stimulation of the preoptic anterior hypothalamus in the red fox (Vulpes vulpes)

The preoptic anterior hypothalamus (POAH) thermoregulatory controller can be characterized by two types of control, an adjustable setpoint temperature and changing POAH thermal sensitivity. Setpoint temperatures for shivering (T_shiver) and panting (T_pant) both increased with decreasing ambient temperature (T_a), and decreased with increasing T_a. The POAH controller is twice as sensitive to heating as to cooling. Metabolic rate (MR) increased during both heating and cooling of the POAH. Resting temperature of the POAH was lower than internal body temperature (T_b) at all temperatures. This indicates the presence of some form of brain cooling mechanism. Decreased T_b during POAH heating was a result of increased heat dissipation, while higher T_b during POAH cooling was a result of increased heat production and reduced heat dissipation. The surface temperature responses indicated that foxes can actively control heat flow from body surface. Such control can be achieved by increased peripheral blood flow and vasodilation during POAH heating, and reduced peripheral blood flow and vasoconstriction during POAH cooling. The observed surface temperature changes indicated that the thermoregulatory vasomotor responses can occur within l min following POAH heating or cooling. Such a degree of regulation can be achieved only by central neural control. Only surface regions covered with relatively short fur are used for heat dissipation. These thermoregulatory effective surface areas account for approximately 33% of the total body surface area, and include the area of the face, dorsal head, nose, pinna, lower legs, and paws.     

Changes in ambient temperature at the onset of thermoregulatory responses in exercise-trained rats

Spontaneous running in a wheel has emerged as a useful method of exercise in rodents. We investigated how exercise training with a running wheel affects ambient temperatures (T _a) at the onset of thermoregulatory responses in rats. Female rats were allowed to run freely in the wheel for 6 months. Sedentary control rats did not exercise during the same period. After the exercise training period, they were loosely restrained and T _a values at the onset of tail skin vasodilation and cold- induced thermogenesis were determined by raising or lowering T _a. Resting levels of core temperature and heat production of the exercise-trained rats were significantly higher than those of the controls. T _a values at the onset of tail skin vasodilation and cold-induced thermogenesis of the exercise-trained rats were higher than those of the controls. The results suggest that, in rats, exercise training with a running wheel elevates ambient temperatures for heat loss and heat production, which may then contribute to maintaining the core temperature at a high level. Received: 20 August 1999 / Revised: 22 November 1999 / Accepted: 24 November 1999     

Metabolism and thermoregulation in the eastern hedgehogErinaceus concolor

Body temperature and oxygen consumption were measured in the eastern hedgehog,Erinaceus concolor Martin 1838, during summer at ambient temperatures (T _a) between-6.0 and 35.6°C.E. concolor has a relatively low basal metabolic rate (0.422 ml O₂·g^-1·h^-1), amounting to 80% of that predicted from its body mass (822.7 g). Between 26.5 and 1.2°C, the resting metabolic rate increases with decreasing ambient temperature according to the equation: RMR=1.980-0.057T _a. The minimal heat transfer coefficient (0.057 ml O₂·g^-1·h^-1·°C^-1) is higher than expected in other eutherian mammals, which may result from partial conversion of hair into spines. At lower ambient temperature (from-4.6 to-6.0° C) there is a drop in body temperature (from 35.2 to 31.4° C) and a decrease in oxygen consumption (1.530 ml O₂·g^-1·h^-1) even though the potential thermoregulation capabilities of this species are significantly higher. This is evidenced by the high maximum noradrenaline-induced non-shivering thermogenesis (2.370 ml O₂·g^-1·h^-1), amounting to 124% of the value predicted. The active metabolic rate at ambient temperatures between 31.0 and 14.5° C averages 1.064 ml O₂·g^-1·h^-1; at ambient temperatures between 14.5 and 2.0° C AMR=3.228-0.140T _a.Abbreviations AMR active metabolic rate - bm body mass - BMR basal metabolic rate - h heat transfer coefficient - NA noradrenaline - NST non-shivering thermogenesis - NST_max maximum rate of NA-induced non-shivering thermogenesis - RMR resting metabolic rate - RQ respiratory quotient - STPD standard temperature and pressure (25°C, 1 ATM) - T _a ambient temperature - T _b body temperature     

Thermoregulation of foraging honeybees on flowering plants: seasonal variability and influence of radiative heat gain

1. During nectar and pollen foraging in a temperate climate, honeybees are exposed to a broad range of ambient temperatures, challenging their thermoregulatory ability. The body temperature that the bees exhibit results from endothermic heat production, exogenous heat gain from solar radiation, and heat loss. In addition to profitability of foraging, season was suggested to have a considerable influence on thermoregulation. To assess the relative importance of these factors, the thermoregulatory behaviour of foragers on 33 flowering plants in dependence on season and environmental factors was investigated.2. The bees (Apis mellifera carnica Pollman) were always endothermic. On average, the thorax surface temperature (T(th)) was regulated at a high and rather constant level over a broad range of ambient temperatures (T(th) = 33.7-35.7°C, T(a) = 10-27°C). However, at a certain T(a), T(th) showed a strong variation, depending on the plants from which the bees were foraging. At warmer conditions (T(a) = 27-32°C) the T(th) increased nearly linearly with T(a) to a maximal average level of 42.6 °C. The thorax temperature excess decreased strongly with increasing T(a) (T(th)-T(a) = 21.6 - 3.6°C).3. The bees used the heat gain from solar radiation to elevate the temperature excess of thorax, head, and abdomen. Seasonal dependance was reflected in a 2.7 °C higher mean T(th) in the spring than in the summer. An anova revealed that season had the greatest effect on T(th), followed by T(a) and radiation.4. It was presumed the foragers' motivational status to be the main factor responsible for the variation of T(th) between seasons and different plants.