Thermoregulatory responses to manipulations of photoperiod in wood mice Apodemus sylvaticus from high latitudes (57°N)

1. 1. The thermoregulatory responses to manipulations of photoperiod in wood mice (Apodemus sylvaticus), which were drawn from a population living at a high latitude (57°N) were studied.

2. 2. Mice captured in spring were acclimated to two different photoperiod regimes 16L:8D and 8L:16D at a constant ambient temperature of 24°C, for 3 weeks.

3. 3. Daily rhythms of body temperature, oxygen consumption and body temperature at various ambient temperatures, nonshivering thermogenesis (the response to a noradrenaline injection) and body mass were measured. Minimal overall thermal conductance was calculated for both groups.

4. 4. Acclimation to long photophase increased the thermoregulatory abilities at relatively high ambient temperatures while that of long-scotophase increased thermoregulatory abilities at low ambient temperatures.

5. 5. Changes in photoperiod may therefore be used as cues for seasonal acclimatization of thermoregulatory mechanisms in this population of wood mice.

     

Humidity selection by thermoregulating grasshoppers

1. 1.|To make the most effective use of evaporative cooling, an insect must be in an environment of the lowest humidity.

2. 2.|To test the hypothesis that, at temperatures requiring evaporative cooling, grasshoppers were able to select such a favourable environment, we observed the selection of, and time spent in dry (RH 5%) or humid (RH 97%) alternative chambers of a shuttle box at a range of temperatures from 28 to 50°C, in two species, Schistocerca americana and Romalea microptera.

3. 3.|Below 45°C, both species tended to remain in the chamber in which they began the trial; above 48°C, they all selected the arid chamber.

4. 4.|These findings suggest that grasshoppers can select the environment best for maintaining their body temperature below lethal levels but do not necessarily mean that they can actually sense relative humidity.

The importance of microhabitat in thermoregulation and thermal conductance in two namib rodents—a crevice dweller, Aethomys namaquensis, and a burrow dweller, Gerbillurus paeba

1. 1.|Thermoregulatory measurements of two Nambi rodents; Gerbillurus paeba, a burrow dweller, and Aethomys namaquensis, a crevice dweller were compared. Both were similar to other small arid-adapted rodents in that basal metabolic rates were reduced, thermoneutral zones narrow and evaporative water losses low. Rates of conductance and thermal lability, however, at ambient temperatures (T_a) below thermoneutral zone, were significantly different (P 0.01).

2. 2.|The rock rat A. namaquensis, living in a microclimate characterized by a large diel range and low humidities, compensates for a reduced basal metabolic rate by having a low rate of conductance. In this way it maintains precise thermoregulatory control. G. paeba, on the other hand, living in a thermally-stable milieu, does not control body temperature precisely. This animal instead utilizes a high rate of conductance to remove metabolic heat produced within the body. This would be advantageous to an animal living in a plugged burrow where the high humidities encountered impede the rate of evaporative cooling.

3. 3.|The energetic responses of both species, above the thermoneutral zone, appear to reflect very closely the environmental conditions which occur in the microhabitat that they rest in during the day. G. paeba shows less tolerance to temperature fluctuations than A. namaquensis, but shows more marked increases in short-term cooling mechanisms at high T_as.

4. 4.|Despite the increased use of evaporative cooling through salivation and panting in addition to pulmocutaneous evaporation, exposure to T_as above 38°C is rapidly lethal to G. paeba.

Convective and evaporative cooling in sawfly larvae

Responses to radiant and convective heat input were analysed in the gregarious larvae of Perga dorsalis (0·5-2·5 g body weight). Aggregating diminishes convective heat loss from each individual and augments the body temperature of larvae in the sun. Voluntary raising of the abdomen, occurring at body temperatures above about 30·4°C, increases convective heat loss. At body temperatures above about 37°C, a filtrate from the semiliquid midgut contents is excreted from the anus and spread over the body. This increases evaporative heat loss and maintains the body temperature below the critical thermal maximum (42°C) even when ambient temperature rises to 48°C. Based on the tolerance to water loss (17 per cent of the body weight) and the rates of evaporation, it is evident that evaporative cooling may be employed successfully throughout the hottest hours of the day.     

Effect of nifedipine on core cooling in rats during tail cold water immersion

Male rats (450 g, n=11/group) were heated at an ambient temperature of 42°C until a rectal temperature of 42.8°C was attained. Rats, then received either saline (30°C)+tail ice water immersion (F+I) or saline (30°C)+tail ice water immersion+Nifedipine, a peripheral vasodilator, (F+I+N) to determine cooling rate effectiveness and survivability. The time to reach a rectal temperature of 42.8°C averaged 172 min in both groups resulting in similar heating rates (0.029°C/min). The cooling rates in group F+I and F+I+N were not significantly different from each other. We conclude that since Nifedipine did not improve cooling rates when combined with fluid+tail ice water immersion, its use as a cooling adjunct does not seem warranted.     

The combined effects of ambient temperature and enforced sustained swimming activity on body temperatures of arctic charr (Salvelinus alpinus L.)

1. 1.|The difference between tissue temperatures and ambient water temperatures (ΔT) of the ectothermic Arctic charr (Salvelinus alpinus L.) ranged between 0.2 and 0.6°C.

2. 2.|For fish held at 5.7°C there were no significant differences in ΔT of exercising fish and those of controls.

3. 3.|By contrast, for fish held at 1.7°C sustained exercise led to a significant increase in ΔT of all body compartments compared with fish held in standing water (controls).

4. 4.|It is suggested that Arctic charr are capable of a limited control of metabolic heat exchange between body compartments and surrounding water when subjected to sustained exercise and ambient temperatures <2°C.

The thermal biology of three southern African elephant-shrews

1. 1. The thermal characteristics of Petrodromus tetradactylus, Elephantulus intufi and E. brachyrhynchus were investigated and compared with other elephant-shrews that occur in the southern African subregion.

2. 2. E. intufi and E. brachyrhynchus appear to have lower than expected basal metabolic rates (1.1185 ± 0.1623 and 0.9649 ± 0.1638 ml O₂ g⁻¹ h⁻¹, respectively) and high, narrow thermoneutral zones, similar to other elephant-shrews investigated previously. In contrast P. tetradactylus has a basal metabolic rate (0.871 ± 0.027 ml O₂ g⁻¹ h⁻¹) close to expected for body mass, and a broad, low thermoneutral zone.

3. 3. The thermal biology of macroscelids is discussed in terms of their distribution, microhabitat and body size.

     

Exhalant air temperatures in the Virginia opossum

1. 1.Nasal exhalant air temperature in the adult Virginia opossum averages 20.9°C at ambient temperatures near 20.8°C (relative humidity: 47%) and 15.1°C at ambient temperatures near 9.2°C (RH: 78%). Exhalant air temperature is well below deep body temperature (34.5–35.6°C), indicating counterecurrent cooling of the exhalant air in the nasal passages.

2. 2.The extent of cooling of exhalant air is similar in juvenile (15-week-old) and adult opossums.

3. 3.As judged from exhalant air temperature, the effectiveness of countercurrent cooling is similar in the opossum to that seen in small and medium-sized placental mammals. The question is discussed of whether cooling of the exhalant air in these animals represents an adaptation or a physically inevitable, fortuitous effect.

Evaporative water loss and intertidal vertical distribution in relation to body size and morphology of stichaeoid fishes from California

Five species of amphibious stichaeoid fishes (four stichaeids, one pholidid) with distinct but overlapping distribution patterns in the rocky intertidal zone of central California were studied in the laboratory with respect to body size and shape, survival out of water, evaporative water loss and water resorption upon re-immersion. Members of all species survived periods of emersion of at least 6 h, but maximum survival times varied with species and body size. Surface area to weight ratios in relation to body length were highest in Xiphister atropurpureus (Kittlitz) and X. mucosus (Girard), lowest in Cebidichthys violaceus (Girard) and Anoplarchus purpurescens Gill and most variable in Xererpes fucorum (Jordan & Gilbert) (the pholidid). Weight-specific water loss (mg · g⁻¹ · h⁻¹) was highest in the two species of Xiphister followed in order by Xererpes fucorum, Cebidichthys violaceus and Anoplarchus purpurescens.

In general, adaptive relationships were found between body size, surface area, tolerance of water loss and intertidal distribution patterns. Among juvenile stichaeoids, for which problems of emersion are most critical, those of Cebidichthys violaceus possess the combination of attributes, including small surface area to weight ratio, high water content and long tolerance of emersion, that should give them an adaptive edge in occupying the upper levels of the shore. In accordance with these characteristics, C. violaceus has the highest, most exposed vertical distribution of the five study species.     

Morphology and germination characteristics of the cysts of Chattonella ovata (Raphidophyceae), a novel red tide flagellate in the Seto Inland Sea, Japan

To elucidate the mechanism of bloom outbreaks of Chattonella ovata (Raphidophyceae), we investigated the cysts of C. ovata and succeeded in finding them from the bottom sediments of Hiroshima Bay. The morphology of the cysts was mostly hemispherical in shape, with a diameter of ca. 30 μm and height of ca. 20 μm. The cysts were usually adhering to solid materials, such as diatom frustules, yellow-greenish in color and had several dark brown grains. The cyst wall was smooth and had no ornamentation. Because the morphological characteristic of the cysts was in general agreement with those of Chattonella antiqua and Chattonella marina, it was difficult to differentiate the cysts of these three species. Germination of the cysts of C. ovata was observed at temperatures from 17.5 to 30 °C, but not at 15 °C or below. The number of the germinated cysts increased with increasing temperature and the optimum temperature for germination was 30 °C. Although cysts of C. antiqua and C. marina germinated at temperatures from 15 to 30 °C, optimum temperature of germination was 22.5 °C. The lower limit and optimum temperatures for germination of C. ovata cysts was higher than for C. antiqua and C. marina. The role of cysts in the population dynamics of C. ovata is discussed.     

Development of thermoregulation in Hawaiian brown noddies (Anous stolidus pileatus)

1. 1.|Oxygen consumption ( ) and body temperture (T_b) of Hawaiian brown noddies (Anous stolidus pileatus [Aves: Laridae]) during late incubation and in the first 24 h after hatching were measured at ambient temperatures (T_a) between 28 and 38°C and between 15 and 43°C, respectively. Evaporative cooling by hatchings at T_a of 36–43°C was also measured.

2. 2.|Throughout the late incubation stages studied, and T_b both varied directly with T_a in an ectothermic pattern.

3. 3.|The hatchlings successfully regulated T_b at T_a between ca. 29 and 43°C.

4. 4.|The functional basis of the abrupt increase in thermoregulatory capacity with hatching is discussed.

Behavioral thermoregulation of Bulla gouldiana (Gastropoda: Opisthobranchia: Cephalaspidea)

1. 1. The preferred temperature of Bulla gouldiana is 26.7–28.7°C.

2. 2. In constant scotophase, photophase, and light and dark photoperiod the organisms do not have a diel cycle of thermoregulation.

3. 3. It takes the animal 6–16 h to reach the preferred temperature.

4. 4. The lowest and highest temperatures visited were 11 and 33°C.

5. 5. Spawning of the species occurred in the thermal gradient between 27 and 28.5°C.

     

Respiratory heat loss and core temperatures during submaximal exercise

1. 1. This study examined the effect of inhaling air supersaturated with water on changes of core temperatures in submaximally exercising males.

2. 2. During exercise with inhalation of supersaturated relative to low-air-humidity air, a significant elevation in tympanic temperature (P = 0.009) and a significant decrease in esophageal temperature (P = 0.004) were observed.

3. 3. Forehead skin temperatures significantly decreased during humidified air inhalation (P = 0.02) supporting that this treatment induced greater thermolytic responses that cooled the skin.

4. 4. The results are consistent with the conclusion that heat loss from the upper airways directly influenced human cerebral temperatures as indexed by tympanic temperatures.

     

Seasonal acclimatization in the migratory hamster Cricetulus migratorius—the role of photoperiod

1. 1.|The migratroy hamster Cricetulus migratorius, a small nocturnal rodent, inhabits ecosystems characterized by dramatic seasonal fluctuations of ambient temperatures. The aim of this study was to assess seasonal acclimatization of its thermoregulatory system.

2. 2.|Heat production by means of oxygen consumption and body temperature in various ambient temperatures as well as non-shivering thermogenesis were measured in C. migratorius. The hamsters were acclimated to two different photoperiod regimes (16L:8D and 8L:16D) at a constant ambient temprature of 24°C. Overall thermal conductance was calculated for such hamsters.

3. 3.|The results of this study indicate that photoperiod manipulations adjust the thermoregulatory system of the migratory hamster mainly by affecting overall thermal conductance.

Critical thermal maximum and body water loss in first instar larvae of three Cetoniidae species (Coleoptera)

Critical thermal maximum (CT_max) and body water losses were measured in first instar larvae of Gnorimus nobilis, Osmoderma eremita (Trichiinae) and Cetonischema aeruginosa (Cetoniinae) when air temperature was increased gradually (0.5 °C/min) from 20 °C to the critical thermal maximum (CT_max), in dry air (near 0% R.H.).

The CT_max was significantly lower in O. eremita (45.6±0.7 °C) than in G. nobilis (48.5±0.6) and C. aeruginosa (51.4±0.9 °C).

An increase of 10 °C (30–40 °C) induced a 2-fold increase of the water loss in C. aeruginosa and O. eremita (Q₁₀=2.10±0.12 and 2.13±0.20, respectively). In the range from 40 to 45 °C to CT_max a strong increase of the water loss was observed in O. eremita and C. aeruginosa, respectively. Body water losses were significantly lower in C. aeruginosa than in O. eremita and G. nobilis over the range 20 °C—CT_max; no significant difference occurred between G. nobilis and O. eremita.     

A test of the accuracy of operative temperature thermometers for studies of small ectotherms

1. 1. Various devices have been used to estimate the equilibrium body temperature of ectotherms occupying natural environments. We tested the accuracy of such devices under a range of conditions.

2. 2. We measured body temperatures of lizards (Sceloporus magister) exposed to short-wave radiation under varying convective conditions and compared these to temperatures of hollow metal casts duplicating the animal's shape and reflectivity, as well as to the temperatures of cylinders similar to those used by other workers.

3. 3. Casts equilibrated within 2–3°C of live animals, yielding errors of 14–37% of the radiation-produced elevation of body temperature.

4. 4. Various cylinders differed from animal body temperature more than lizard casts did, producing errors equally 33–53% of the radiation-produced elevation.

5. 5. It is imperative that workers using operative-temperature thermometers experimentally confirm the adequacy of the devices they use for the range of conditions encountered within a specific analysis.

     

Comparative aspects of the thermal biology of the short-tailed gerbil, Desmodillus auricularis, and the bushveld gerbil, Tatera leucogaster

1. 1. The response of oxygen consumption (VO₂), thermal conductance (C_d and C_min, body temperature (T_b), and evaporative water loss (EWL) of Tatera leucogaster and Desmodillus auricularis were measured over the range of ambient temperatures (T_a) from 5–35°C.

2. 2. Basal metabolic rate (BMR) of T. leucogaster was 0.841 ± 0.049 ml O₂ g⁻¹ h⁻¹ and lower than predicted, while that of D. auricularis was similar to the expected value (1.220 ± 0.058 ml O₂ g⁻¹ h⁻¹). D. auricularis had a high, narrow thermoneutral zone (TNZ) typical of nocturnal, xerophilic, burrowing rodents.

3. 3. D. auricularis and T. leucogaster regulated T_b over the range T_a = 5–35°C and kept EWL and dry thermal conductance at a minimum below the TNZ. However, the EWL of T. leucogaster increased rapidly above T_a = 30°C.

4. 4. After comparison with data from other species, it was concluded that there is an optimum size for xeric, nocturnal, burrowing rodents.

The effect of acclimation temperature on energy metabolism as a function of body weight in rats

1. 1|Energy metabolism of 38 rats acclimated to 10, 20 and 30°C was measured at these ambient temperatures and the regression equations over body weight were calculated.

2. 2|Expressing metabolic rate as M = kWⁿ, the results showed that the value of n is apparently variable according to the acclimation and measurement temperatures.

3. 3|It was also shown that the 2/3 power of body weight is a suitable parameter to express metabolic rate, regardless of acclimation or environmental temperatures.

Response of brown mussel, Perna indica, to elevated temperatures in relation to power plant biofouling control

1. 1. Results of a study on lethal and sublethal responses of different size groups of the tropical brown mussel, Perna indica, when exposed to different temperatures are presented.

2. 2. Exposure to a temperature of 38°C showed 100% mortality of 9 mm size group mussels in 120 min.

3. 3. Mortality was dependent on age (size) of the mussels, young ones being more susceptible than older ones.

4. 4. All size groups showed a progressive reduction in physiological activities such as filtration rate, foot activity and byssus thread production when temperature was increased from 30°C.

5. 5. This study suggests that heat treatment is an attractive alternative to chlorination for mussel fouling control in tropical power stations.

     

Direct heat injury of roots of woody swamp species

1. 1.Three month-old seedlings of Taxodium distichum, Nyssa aquatica, Cephalanthus occidentalis and cuttings of Salix nigra were acclimated to simulated natural swamp conditions (ambient temperature, saturated soil) and then used to assess direct high temperature injury of root tissue.

2. 2.Electrolyte leakage from excised root tissue exposed for 30 min to temperatures ranging from 30 to 66°C was used to assess cellular injury.

3. 3.The relationship between leakage and temperature was sigmoidal for each species.

4. 4.Inflection point temperatures on the response curves, ranged from 45.4 to 51.0°C, were species-specific, and indicated differences in thermal tolerance of root membranes.

5. 5.Root of C. occidentalis and N. aquatica were more heat tolerant than roots of T. distichum and S. nigra.