Richard W. Hill

Daily torpor in Peromyscus leucopus on an adequate diet.

Abstract 1. 1. Seventeen mice were tested for the occurrence of torpor in the presence of excess food over periods of 6–30 days at ambient temperatures of 13-12°C. 2. 2. Seven animals displayed regularly torpor, and four displayed sporadic episodes of torpor. Body temperatures in mice showing regular daily torpor ranged from 16.8 to 27.7°C, and metabolic rates remained below 2.0 cm3 O2/g per hr for an average of 4.3–12.7 hr/day in various individuals. 3. 3. It is estimated that episodes of torpor in the laboratory environment resulted in energetic savings of 440–1900 cal in animals showing regular daily torpor.

Thermal Physiology and Energetics of Peromyscus; Ontogeny, Body Temperature, Metabolism, Insulation, and Microclimatology

This is one of two concurrent papers reviewing aspects of the thermal and water physiology and energetics of the genus Peromyscus . In this review paper, initial emphasis is given to developing a thermal life history of young mice during the preweaning and immediate post-weaning periods. Subsequent sections discuss the body temperatures, metabolic rates, body insulation, thermoregulatory mechanisms, and microclimates of adults. A comparative approach is taken throughout, and emphasis is given to acclimation and acclimatization. Major goals are to review the extant literature comprehensively and thereby help to identify directions for future research.

Body Surface Temperatures and Thermoregulation in the Black-Capped Chickadee (Parus atricapillus)

Surface temperature (Ts) on most parts of the body of the black-capped chickadee is linearly related to ambient temperature (Ta) between 27 and -22 C. The slope and intercept of regressions of Ts on Ta are generally related as predicted by a model developed previously. The head typically has the highest Ts of all body parts and accordingly is expected to exhibit the highest rate of heat loss per unit area by convection and radiation at given Ta. The breast is warmer than the side of the torso, the beak is kept at relatively high Ts, and Ts on the feet and legs is strongly dependent on whether the appendages have recently been ensconced in the ventral plumage. Differences in Ts are remarkably small between the chickadee and raven, which represent virtual extremes of body size within the Passeriformes. Metabolic rates of chickadees can be calculated from Ts with reasonable success given inadequacies in present knowledge of some relevant parameters. Chickadees show large increases in ptiloerection as Ta is lowered in the range of Ta well below thermoneutrality; significant consequent changes in plumage conductance, body convection coefficient, and operative body surface area are possible and require appraisal in regard to heattransfer analysis. Subcutaneous temperature may fall significantly with Ta on the back and rump but is consistently high on the breast. On the breast the plumage presents most of the resistance to heat flow from bird to environment, and the resistance posed by the living tissues between body core and skin is minor. Plumage and tissue conductances are quantitatively estimated using a new approach based on core temperature, subcutaneous temperature, and Ts; these estimates are extensively compared with others derived from the literature. Apparently, increases in ptiloerection are accompanied by decreases in plumage conductance but increases in plumage conductivity. The first spectral emittance data to appear in the journal literature for plumage of a bird species at wavelengths longer than 2.5 μm are presented.

Growth and development of temperature regulation in nestling cattle egrets

Abstract 1. 1. The growth of cattle egrets is typical of altricial birds of comparable size and appears best described by the logistic equation. 2. 2. The telemetered body temperatures of six nestlings measured in the field over extended periods ranged between 38 and 40°C. 3. 3. Resistance of nestlings to hypothermia develops gradually after hatching as a more intense standard metabolism and capacities for augmenting muscular thermogenesis in the cold are established. 4. 4. Chicks increase their breathing rate and initiate gular flutter in response to heat loads. At ambient temperatures of 44/2–45°C, they evaporatively dissipated heat at rates up to 2/2–5 times heat production. Heat defense is well developed at hatching in cattle egrets.

Inertial Thermostability and Thermoregulation in Broods of Redwing Blackbirds

Metabolic rate and body temperature (Tb) were measured during 2 h of exposure to ambient temperatures (Ta) of 5-32 C in (a) broods of three or four redwing blackbirds (Agelaius phoeniceus) in a nest and (b) single redwings of comparable ages, isolated from the nest. Between 2 and 6 days of age, broods maintained markedly higher Tbs than individuals; for instance, 6-day-old broods usually kept Tb above 35 C even at 5 CTa, whereas the Tb of 6-day-old single animals usually fell to approach Ta at 15 CTa and fell below 35 C even at 25 C Ta. Single 8-day-olds thermoregulated at 15 C and sometimes at 5 C but did so at a higher mass-specific metabolic cost than broods. Thermogenesis is not brought under thermoregulatory control until 4-5 days of age in redwings, although broods can modulate their insulation homeostatically at least as early as 3 days. Two phases are recognized in the life of broods of altricial nestlings. Phase 1 (inertial phase): although thermogenesis is not under thermoregulatory control, Tbs of broods in the nest can remain well above Ta during long parental absences by virtue of thermal inertia; metabolic rates, and probably growth rates, are correspondingly kept from falling. Phase 2 (regulatory phase): broods thermoregulate physiologically, resulting in more effective stabilization of Tb and higher metabolic costs than in phase 1. In redwings and three other passerine species, at least 53%-72% of the increase in body energy content resulting from growth between hatching and fledging occurs during phase 2. Thermoregulatory altriciality has been claimed to promote efficiency of growth by precluding use of energy for thermoregulation. Study of the thermal and metabolic status of broods reveals that although the claim may be valid early in nestling life (phase 1), it can apply only during completion of less than half of nestling growth.

Determination of betaine metabolites and dimethylsulfoniopropionate in coral tissues using liquid chromatography-time-of-flight mass spectrometry and stable isotope-labeled internal standards

A convenient procedure for determination of seven betaine analogs and dimethylsulfoniopropionate (DMSP) in extracts of coral tissues using LC-MS stable isotope dilution is described. Extraction procedures were optimized for selective extraction of polar metabolites from coral tissues. The LC-MS protocol employed a pentafluorophenylpropyl (PFPP) column for HPLC separation, with chromatographic resolution of isobaric and isomeric zwitterionic metabolites optimized by adjusting the acidity of the mobile phase. A ternary gradient was used to exploit the unusual retention characteristics of cationic metabolites on the PFPP column, with incorporation of ammonium acetate in a later gradient stage promoting elution of more hydrophobic betaines which are retained at high organic content in the absence of ammonium acetate. We demonstrate that the new LC-MS based method provides accurate measurements from nanomolar to high micromolar concentrations, and can be applied for profiling of betaine metabolites and DMSP in corals or other aquatic organisms.

Dimethylsulfoniopropionate in giant clams (Tridacnidae).

The tridacnid clams maintain symbiotic associations with certain dinoflagellates (termed zooxanthellae). Tridacnids are thus candidates to have high tissue concentrations of dimethylsulfoniopropionate (DMSP), a tertiary sulfonium compound that is not synthesized by animals but is commonly produced by dinoflagellates. This study establishes that DMSP is about an order of magnitude more concentrated in the light-exposed and shaded mantle and gills of Tridacna maxima and T. squamosa than in any other known animal tissues. The DMSP concentration in the light-exposed, siphonal mantle--the location of most zooxanthellae--is an inverse function of body size, paralleling an inverse relation between apparent density of zooxanthellae (measured as pheophytin concentration) and body size. The shaded mantle and gills are high in DMSP despite having low densities of zooxanthellae, indicating that high DMSP concentrations occur in molluscan tissue, not just in algal cells. DMSP is almost an order of magnitude less concentrated in the adductor muscle than in other tissues. The high DMSP concentrations found in tridacnids, by providing abundant substrate for formation of volatile dimethylsulfide, probably explain the peculiar tendency of tridacnids to rapidly develop offensive odors and tastes after death: a serious problem for their exploitation as food. Tridacnids are the one group of animals in which DMSP concentrations are high enough in some tissues to be in the range capable of perturbing enzyme function at high physiological temperatures. Thus, tridacnids may require enzyme forms adapted to DMSP.

Pinna Temperature in Exercising Jackrabbits, Lepus californicus

Pinna surface temperatures of Lepus californicus were examined radiographically before and after forced exercise (e.g., running at about 6 km/h for 6 min) in an outdoor enclosure. Air temperatures were from −1.6 to +19.4°C, and radiant sky temperatures were from —27 to +22°C. In resting animals, average pinna surface temperature was only 0.3 to 2.5°C above air temperature, and pinna arteries were not evident radiographically. Immediately after exercise, average pinna temperature was often near 30°C and pinna arteries were evident, indicating vasodilation. Cooling of the pinnae to resting temperatures after exercise generally took 15 to 25 min. Calculations indicate that the pinnae can dissipate most of the excess metabolic heat generated during the exercise examined, and it is suggested that the role of the pinnae as dissipators of exercise-induced heat loads should be considered as a factor in the evolution of pinna size.

Aggression and Food Resource Competition between Sympatric Hermit Crab Species

The vertical zonation patterns of intertidal organisms have been topics of interest to marine ecologists for many years, with interspecific food competition being implicated as a contributing factor to intertidal community organization. In this study, we used behavioral bioassays to examine the potential roles that interspecific aggression and food competition have on the structuring of intertidal hermit crab assemblages. We studied two ecologically similar, sympatric hermit crab species, Clibanarius digueti [1] and Paguristes perrieri [2], which occupy adjacent zones within the intertidal region of the Gulf of California. During the search phase of foraging, C. digueti showed higher frequencies of aggressive behaviors than P. perrieri. In competition assays, C. digueti gained increased access to food resources compared to P. perrieri. The results suggest that food competition may play an important role in structuring intertidal hermit crab assemblages, and that the zonation patterns of Gulf of California hermit crab species may be the result of geographical displacement by the dominant food competitor (C. digueti).

Metabolism, thermal conductance, and body temperature in one of the largest species of Peromyscus, P. Pirrensis

Abstract 1. 1.|Body temperature ranged from 36·9 to 38·6°C in quiet animal at ambient temperatures between 5 and 35°C. At lower and higher test temperatures, some animals displayed lower and higher body temperatures, respectively. 2. 2.|Basal metabolic rates of six animals ranged from 0·81 to 0·98 ml O 2 /g,hr. These values are 7–19% lower than those predicted from the Brody equation according to body weight. 3. 3.|Average thermal conductance in seven animals at ambient temperatures below 22°C ranged from 0·078 to 0·094 ml O 2 /g,hr,°C. These values are close to those expected according to body weight.