Effect of delivery temperature on endocrine stimulation of thermoregulation in lambs born by cesarean section.

We examined the hypothesis that exogenous stimulation with physiological doses of 3,5,3'-triiodothyronine (T(3)) and/or norepinephrine at birth can improve thermoregulation in near-term lambs delivered by cesarean section. This was achieved by investigating the effect of delivery temperature [i.e., warm (30( degrees )C) vs. cool (15( degrees )C) ambient temperatures] on hormonal stimulation on uncoupling protein-1 (UCP1) abundance in brown adipose tissue. In vivo measurements of temperature control (i. e., colonic temperature, oxygen consumption, and incidence of shivering) were made over the first 2.5 h after birth. Each lamb was injected with saline with or without T(3), norepinephrine, or T(3) plus norepinephrine. Irrespective of delivery temperature, abundance of UCP1 increased and incidence of shivering decreased by all hormonal treatments, but this only reduced the rate of decline in colonic temperature of cool-delivered lambs. Oxygen consumption was higher in cool-delivered lambs that were able to fully restore body temperature, an adaptation not observed in controls or any warm-delivered groups. Exogenous administration of endocrine stimulatory factors can enhance the abundance of UCP1 in cesarean-section-delivered lambs with the magnitude of thermoregulatory response being greater at cool than warm delivery temperatures.     

Behavioral and Physiological Thermoregulation of Crocodilians

Crocodilians, like other reptiles, regulate their body temperaturesby a combination of behavioral and physiological mechanisms.Behaviorally, they seek warm surface water or bask when cooland avoid overheating by the evaporation of water from theirdorsum, evaporation of water by gaping or by retreating to deep,cool water. Physiologically, crocodilians increase cutaneousthermal conductance by increasing blood flow to the skin (andsubdermal musculature) during warming. This hastens the warmingprocess. Cutaneous blood flow is reduced during general coolingand locally if the body temperature exceeds skin temperature.This enables crocodilians to increase body temperature significantlywhile basking in cool shallow water. Large crocodilians appearto be able to alter their rates of heat exchange to a largerextent than small ones and they can do so with less cardiovascularinvolvement. Large crocodilians, with their lower surface/volumeratio, are capable of producing sufficient metabolic heat toelevate their body temperature above water temperature.     

Body Site Variation of Cool Perception Thresholds,with Observations on Paradoxical Heat

Thresholds for the perception of coolness and heat pain were determined in sessions that randomly intermixed temperature increases and decreases. Four body sites were tested bilaterally: thenar eminence of the hand, plantar surface of the foot, dorsolateral forearm, and lateral calf. Coolness thresholds were lowest for the hand, intermediate for the forearm, and highest for the leg and foot. Laterality differences were not statistically significant.

In 34% of the sessions, subjects did not consistently report cool or cold sensations with detectable temperatue decreases. When they did not report cool or cold, they most often reported heat or pain, thus exhibiting the phenomenon of “paradoxical heat”. There were significantly more paradoxical heat responses when cooling stimuli were intermixed with painfully hot stimuli than when they were intermixed with only warm stimuli.

There was no significant correlation observed between thresholds for coolness and heat pain, either across body sites or across subjects at any single body site. This result implies that the various factors relevant to thermal sensitivity (i.e., thermal properties of the epidermis, innervation density) are differentially important for cool versus heat pain perception.     

Tactile stimulation and teat-seeking behaviour in newly born lambs

Behavioural effects of tactile stimulation were investigated in newly-born lambs, which had, or had not, been suckled. A smooth or woolly, warm or cold stimulus which covered one side of the face elicited in unsuckled lambs a forceful response resembling its teat-seeking approach to the dam: vigorous forward and upward head movements, munching and sucking. Smaller amounts of tactile stimulation applied at discrete facial sites showed that most head movements occurred in response to touch on the upper surfaces of the face and most oral activity in response to touch on the muzzle. The response to touch was less in lambs which had been suckled, even when age was kept constant. Results are discussed in terms of the natural situation and of the response to touch in the 40–80 day foetus.     

Thermotactile thresholds at the fingertip: Effect of contact area and contact location

Thresholds for the detection of changes in temperature are used to indicate neuropathy, but a variety of different contact areas and contact locations are used. This study was designed to determine the effects of variations in contact area and contact location on both warm and cool thresholds at the fingertip. With 20 healthy subjects (10 females and 10 males aged 20–30 years), warm thresholds and cool thresholds were determined in two separate sessions using the method of limits. In the first part of each session, thresholds were determined around the centre of the whorl using circular contactors with five different diameters (3, 6, 9, 12, and 55 mm). In the second part of each session, thresholds were determined using two contactors (6- and 12-mm diameter) at three locations along the fingertip: (i) distal (5 mm from the nail), (ii) middle (centre of whorl), and (iii) proximal (3 mm from the distal interphalangeal joint). With increasing contact area, the warm thresholds decreased, the cool thresholds increased, and the inter-subject variability in both warm and cool thresholds decreased. Using the 6-mm diameter contactor, warm thresholds were independent of location but cool thresholds increased from distal to proximal locations. It is concluded that temperature sensitivity at the fingertip increases with increasing area of contact, with the variability in thresholds consistent with the existence of warm and cool “insensitive fields”. The findings show that the influence of contact area and contact location should be considered when assessing thermotactile thresholds at the fingertip.     

Diel and seasonal variations in the thermal biology of San Cristobal Lava Lizards (Microlophus bivittatus)

Thermal biology, and therefore energy acquisition and survival, of ectotherms can be affected by diel and seasonal patterns of environmental temperatures. Galápagos Lava Lizards live in seasonal environments that are characterized by a warm and wet period when reproductive activity is maximal, and cooler and drier period. With the use of radiotelemetric techniques to record lizard surface temperatures (T_s), we studied the thermal ecology of the San Cristóbal Lava Lizard (Microlophus bivittatus) during both the warm and cool seasons over two years. During the diel activity period and when operative temperatures exceeded T_set-min, at least on rock faces without canopy, 52% or less of the T_s observations fell within the laboratory-determined T_set range (36–40 °C). Therefore, lizards may have avoided very warm midday temperatures in shaded microhabitats and the lag times in changes in T_s values occurred as operative temperatures rose rapidly during late morning warming phase. Lizards effectively thermoregulated during a year with moderate warm season temperatures and during a cool season that was unseasonably warm. In contrast, lizards less effectively thermoregulated during the warmest and coolest years of the study. We did not detect intersexual differences in thermoregulation although males may thermoregulate less effectively than do females during the cool season although we were unable to detect significant differences using our nonparametric statistical techniques.     

PHOTOSYNTHETIC SENSITIVITY TO TEMPERATURE IN POPULATIONS OF TWO C4 BOUTELOUA (POACEAE) SPECIES NATIVE TO DIFFERENT ALTITUDES

The relationships between photosynthesis, flowering, and growth temperatures were examined experimentally in four populations of the C₄ grass genus Bouteloua. Field-collected plants were grown under two temperature regimes, cool (20 C day/6 C night) and warm (30/16), representative of the extreme populations. Populations collected from the warm climates had significantly lower photosynthetic capacity when grown in the cool chamber relative to the warm chamber, while photosynthetic capacity in the cool climate populations did not differ between the growth conditions. Additionally, exposure to a 2-day cold temperature treatment (10/-2), representative of late-season frosts in high altitude sites, resulted in further reductions in photosynthesis in the warm climate plants, but not in the cool climate plants. This effect was greater for plants grown in the cool growth chamber. Flowering was reduced by 70% in the warm climate plants grown in the cool chamber, and was correlated with photosynthetic inhibition following the short-term cold temperature treatment. These results indicate that genetic differentiation for photosynthetic temperature sensitivity has occurred in the cool climate populations, and that long-term exposure to cool temperatures coupled with short-term relatively extreme low temperatures results in greater photosynthetic inhibition in nontolerant populations.     

Seasonal shifts along the oviparity–viviparity continuum in a cold‐climate lizard population

Squamate embryos require weeks of high temperature to complete development, with the result that cool climatic areas are dominated by viviparous taxa (in which gravid females can sun‐bask to keep embryos warm) rather than oviparous taxa (which rely on warm soil to incubate their eggs). How, then, can some oviparous taxa reproduce successfully in cool climates – especially late in summer, when soil temperatures are falling? Near the northern limit of their distribution (in Sweden), sand lizards (Lacerta agilis) shift tactics seasonally, such that the eggs in late clutches complete development more quickly (when incubated at a standard temperature) than do those of early clutches. That acceleration is achieved by a reduction in egg size and by an increase in the duration of uterine retention of eggs (especially, after cool weather). Our results clarify the ability of oviparous reptiles to reproduce successfully in cool climates and suggest a novel advantage to reptilian viviparity in such conditions: by maintaining high body temperatures, viviparous females may escape the need to reduce offspring size in late‐season litters.     

The effect of weather on the life cycle of the speckled wood butterfly Pararge aegeria

ABSTRACT.

• 1 Pararge aegeria (L.) is a very unusual butterfly of Britain, having a long period of adult activity, from April to October, without discrete flight periods. In central Britain it overwinters in two stages: pupae and third instar larvae, both being the progeny of late summer adults. Other larval stages die at the onset of cold winter weather. The overwintering stages give rise to the first adult generation in spring, split into two parts.
• 2 Different temperature regimes affect development rates in larvae and pupae differently. Late larval development is more rapid than that of pupae at low temperatures, thus in cool spring weather the overlap of the two parts of the first generation is greater than in warm spring weather.
• 3 Adults emerge continuously throughout the summer because larval development rates are variable. When summer is warm there is a partial third generation but when cool only two.
• 4 The timing of the end of the flight period is consistent with the hypothesis that both temperature and photoperiod are important in determining whether individuals enter diapause or develop directly. In warm summers larvae develop beyond a sensitive stage before critical daylength is reached and develop directly, but in cool summers individuals enter diapause because they are at the sensitive stage when critical daylength is reached.
• 5 It is suggested that variable development rates can facilitate parasite escape in autumn and increase the probability of adult success when weather is unpredictable, and this strategy is maintained because these benefits are greater than the cost of winter mortality of larvae.

     

Influence of skin temperature distribution on thermal sensation in a cool environment

Thermal sensation and distribution of skin temperatures in persons exercising at 36.5 W on a bicycle ergometer and resting in a cool environment (10 degrees C) in two different clothings, one with the insulation mainly over the trunk (1.22 clo), and one with well insulated limbs (1.67 clo), were studied. Their general thermal sensations varied from slightly warm to slightly cool. The placing of the insulation had a decisive influence on skin temperature distribution, so that skin temperature was always high in well-insulated areas. When the insulation was placed over the limbs, a greater amount of heat was lost than if a similar insulation was placed on the trunk. Neither Tsk nor skin temperature distribution correlated with general thermal sensation. Instead, mean body temperature seemed to be the determinant of general thermal sensation in these conditions. The best prediction of general thermal sensation was obtained by adding Tre with a weighting factor of 0.8-0.9 and Tsk with a weighting factor of 0.1-0.2.     

Seasonal intake responses in the nectar-feeding bat Glossophaga soricina

Food intake in nectar-feeding animals is affected by food quality, their energetic demands, and the environmental conditions they face. These animals increase their food intake in response to a decrease in food quality, a behavior named “intake response”. However, their capacity to achieve compensatory feeding, in which they maintain a constant flux of energy, could be constrained by physiological processes. Here we evaluated how both a seasonal change in environmental conditions and physiological constraints affected the food ingestion in the bat Glossophaga soricina. We measured food intake rate during both the wet/warm and dry/cool seasons at sucrose solutions ranging from 146 to 1,022 mmol L⁻¹. We expected that food intake and metabolic demands would be greater during the dry/cool season. Bats ingested ~20% more food in the dry/cool than in the wet/warm season. Regardless of season, bats were unable to achieve a constant flux of energy when facing the different sugar concentrations that we used in our experiments. This suggests that the rate of food intake is physiologically constrained in G. soricina. Using the digestive capacity of bats we modeled their food intake. The analytic model we used predicts that digestive limitations to ingest energy should have an important effect on the ecology of this species.     

Effects of powdery mildew on grain filling in spring barley in contrasting environments

Circumstantial evidence from field experiments at Rothamsted suggested that effects of powdery mildew on grain filling in spring barley may be determined partly by temperature during the grain-filling period. An experiment was, therefore, done which compared the effects of fungicides applied to control powdery mildew on grain filling in early- and late-sown spring barley plants kept either out-of-doors throughout their growth (‘cool’ environment) or under the same conditions until the start of grain filling and then transferred to a heated glasshouse (‘warm’ environment) until harvested. Fungicides that controlled mildew increased the total grain yield of the late-sown barley more than that of the early-sown and much more in the warm environment than in the cool. On average, the effect of the fungicides in the cool environment was to increase grain yield by 17·7%. Small increases in numbers of grains/ear (+ 3·4%) and thousand-grain weight (TGW) (+ 2·3%) contributed to this increase but it could be attributed principally to an average increase in numbers of ears/plant of 12·4%. Contrastingly, fungicides increased average grain yield in the warm environment by 58·2%. Effects of the fungicides on numbers of ears/plant (+ 27·8%) and on numbers of grains/ear (+ 4·5%) were not significantly different to those in the cool environment, and the much greater responses in the warm than in the cool environment could be attributed mostly to much larger effects on grain size (+ 19·2%) The greater benefits of the fungicides and, by implication, the greater damage done by powdery mildew in the warm than in the cool environment cannot, unequivocally, be attributed to differences in temperature during grain-filling because the two environments clearly differed in other ways and especially in light intensity. Nevertheless, the results obtained do illustrate the potential risks involved in using data obtained under one set of circumstances to predict what will happen in another, especially when environments differ as greatly as glasshouses and fields.     

The growth of largemouth bass, Micropterus salmoides (Lacepede), under constant and fluctuating temperatures

Growth of largemouth bass, Micropterus salmoides , was tested under constant (15° C, 29° C) and cyclic (18 h at 15°C, 6 h at 29° C) temperature conditions. Six groups of 10 fish each were tested; one group under each constant condition, and four groups in the thermocycles. The four latter groups differed in the timing of their feeding; one group each was fed at the start and middle of the warm and cool periods, respectively. All groups were fed to near-satiation. The fish fed at the start of the warm cycle and start cool group grew most rapidly, followed by the constant warm, mid warm, mid cool, and constant cool groups. These data were evaluated in relation to vertical migrations of fish to test the physiological enhancements that may be important to vertical migrations. Apparently thermocycles allow more rapid consumption of food than constant cool conditions and lower metabolic rates than constant warm conditions, which allows some fish to grow more rapidly under thermocycles than under constant conditions at either extreme of the cycle. However, the timing of feeding in relation to temperature in the thermocycle is important in the degree of growth enhancement.     

Development of the cellulolytic microflora in the rumen of lambs transferred into sterile isolators a few days after birth

Seven lambs, separated from their dam 24 h after birth, were kept in a conventional environment until transferred to sterile isolators between 1 and 9 days of age: two on day 1 (IA and IB), two on day 4 (IVA and IVB), one on day 8 (VIIIA), and two on day 9 (IXA and IXB). The lambs were reared in these isolators until 120 days of age. Lambs IA, IB, IXA, and IXB were free of cellulolytic bacteria when they were placed in the isolators. They were then inoculated with Bacteroides succinogenes S85 which became established in the four lambs. Until the age of 2 months, the population of this strain fluctuated and then stabilized at a high level (10(8)-10(9) cells/mL). Cellulolytic bacteria were present in the rumen of lambs IVA, IVB, and VIIIA when they were transferred to the isolators. In IVA, and IVB, the cellulolytic population slowly increased with the animal age. In contrast, in VIIIA, the cellulolytic bacteria disappeared within a few days. Bacteroides succinogenes S85 inoculated thereafter became established rapidly and reached a level comparable to that observed in lambs IA and IB. The total number of viable rumen bacteria in the isolated lambs was similar to that observed in conventionally raised animals, but differences were observed in the selective enumeration of bacteria utilizing specific energy sources.     

Disappearance of opioidergic tone on LH secretion in underfed prepubertal sheep

A study was conducted to determine whether an opioid tonus inhibitory of LH secretion is present in underfed prepubertal sheep. Ten Suffolk ewe lambs were subjected to food restriction during 60 days. During this period they were allowed to pasture only 2 hours per day while control ewe lambs were allowed for 10 hours. Body weight and plasma blood levels of glucose, urea and total proteins were measured weekly. At the end of this period, an intravenous injection of Naloxone (NAL, 1.5 mg/kg BW) was given to control and underfed animals followed 60 min later by an intravenous injection of LHRH to test the pituitary responsiveness. Underfed animals did not show an increase in plasma LH while control animals presented a rise from 0.28 +/- 0.08 to 2.02 +/- 0.6 ng/ml after the NAL stimulus (P less than 0.05). The response to LHRH was similar in both group of animals. Basal plasma levels of insulin were lower in underfed ewe lambs than in control animals (P less than 0.05). Underfed animals were placed on plain feeding with a schedule similar to control lambs for 30 days and the same experiment was repeated. During this occasion, NAL increased plasma LH concentration in both group of lambs. Levels of plasma insulin were not different in both groups. The lack of effect of NAL on LH secretion in food restricted ewe lambs suggests that the opioid modulation of LH secretion is absent by underfeeding in female prepubertal sheep.(ABSTRACT TRUNCATED AT 250 WORDS)     

Time course of photosynthetic temperature acclimation in Carex eleocharis Bailey

Abstract Photosynthetic temperature acclimation in Carex eleocharis has been demonstrated in a previous study in which warm grown (35/15°C) plants were shown to have photosynthetic temperature optima approximately 14°C higher than cool grown (20/15°C) plants (Monson, Littlejohn & Williams, 1983). The current study examined the time course of this acclimation by determining photo-synthetic temperature optima as a function of time, of cool grown plants moved to warm growing conditions. Leaves which had developed under cool conditions were capable of an upward adjustment of 6–8°C of their optimum photosynthetic temperature within a time span of 6–14 d. For greatest photosynthetic temperature acclimation it was necessary for leaves to form and develop entirely under warm conditions. These leaves exhibited a 14–15°C upward adjustment of their optimum temperature for photosynthesis within 20–31 d since moving plants from cool to warm growing conditions. Thus, the time course of this acclimation is of short enough duration to be significant during the growing season and presumably contributes toward the ability of this species to maintain active growth during the cool and warm portions of the growing season. It is also noted that the plant with its capacity to form new leaves, has a much wider acclimation capacity than any single leaf.     

Seasonal variation of thermoregulatory behaviour in the Hippopotamus (Hippopotamus amphibius)

The hippopotamus (Hippopotamus amphibius) spends more than 12 h a day in the water. Hippos are often submitted to water temperatures that vary with the seasons. We hypothesize that this difference between cool and warm water temperatures leads to variations in behavioural thermoregulation. We recorded the exposure of hippos to sunshine at the beginning and at the end of the dry season. Our results show that (1) sunshine exposure lasted much longer in cool water and (2) sun-bathing occurred during the hottest hours. It is therefore likely that in cool water hippos were cold and expressed an original behaviour of search for heat.     

Pre- and post-harvest influences on seed dormancy status of an Australian Goodeniaceae species, Goodenia fascicularis

Background and Aims

The period during which seeds develop on the parent plant has been found to affect many seed characteristics, including dormancy, through interactions with the environment. Goodenia fascicularis (Goodeniaceae) seeds were used to investigate whether seeds of an Australian native forb, harvested from different environments and produced at different stages of the reproductive period, differ in dormancy status.

Methods

During the reproductive phase, plants were grown ex situ in warm (39/21 °C) or cool (26/13 °C) conditions, with adequate or limited water availability. The physiological dormancy of resulting seeds was measured in terms of the germination response to warm stratification (34/20 °C, 100 % RH, darkness).

Key Results

Plants in the cool environment were tall and had high above-ground biomass, yet yielded fewer seeds over a shorter, later harvest period when compared with plants in the warm environment. Seeds from the cool environment also had higher viability and greater mass, despite a significant proportion (7 % from the cool-wet environment) containing no obvious embryo. In the warm environment, the reproductive phase was accelerated and plants produced more seeds despite being shorter and having lower above-ground biomass than those in the cool environment. Ten weeks of warm stratification alleviated physiological dormancy in seeds from all treatments resulting in 80–100 % germination. Seeds that developed at warm temperatures were less dormant (i.e. germination percentages were higher) than seeds from the cool environment. Water availability had less effect on plant and seed traits than air temperature, although plants with reduced soil moisture were shorter, had lower biomass and produced fewer, less dormant seeds than plants watered regularly.

Conclusions

Goodenia fascicularis seeds are likely to exhibit physiological dormancy regardless of the maternal environment. However, seeds collected from warm, dry environments are likely to be more responsive to warm stratification than seeds from cooler, wetter environments.Key words: Goodenia fascicularis, Goodeniaceae, Australia, physiological dormancy, seeds, temperature, soil moisture, maternal influence, climate     

Selection for cold tolerance in Phaseolus vulgaris— yields of selected lines grown in warm and cool environments

Forty-eight F₄ families of a cross between two cultivars of Phaseolus vulgaris were grown in ‘warm’ and ‘cool’ environments in the field. The F₂ and F₃ generations had been assessed for cold tolerance using the test described by Hardwick & Andrews (1980). The mean seed yields of the F₄'s were 333 and 167 g m^-2 in the ‘warm’ environment (blackened soil surface, clear polyethylene mulch, windbreaks) and ‘cool’ environment (whitened soil surface, no mulch or windbreaks) respectively. The ratio of yields in the two environments was larger in families selected for cold sensitivity than in those selected for cold tolerance (values of ratio 2.28 to 1 and 1.76 to 1 respectively). The ‘warm’ treatment decreased the number of days between sowing and emergence from 15.6 to 8.6, increased the estimated weight per seedling axis at emergence from 544 to 904 mg/plant, and increased the weight/plant at flowering from 3.75 to 4.7 g. Plants from the ‘warm’ treatment had bigger leaf weights, smaller stem weights, more branches and bigger specific leaf areas than plants of the same weight from the ‘cool’ treatment. Differences in yield were due mainly to differences in the number of seeds produced/plant. Eleven F, families were grown in a simple yield trial the following year. The season was cooler and yields were reduced. The reduction in yield was greater in the cold sensitive than in the cold tolerant families.