The extent of variation in reptile field metabolism, and its causal bases, are poorly understood. We studied the energetics of the insectivorous lizard Callisaurus draconoides at a site in the California Desert (Desert Center) and at a site at the southern tip of the Baja Peninsula (Cabo San Lucas; hereafter, Cabo). Reproducing Callisaurus were smaller at Cabo than at Desert Center. The allometry of metabolism with body mass can account for most differences in whole-animal metabolism. There was no significant effect of sex or source population on mass-adjusted metabolic rate in the laboratory (resting metabolism, measured by closed-system respirometry) or in the field (field metabolism, measured with doubly labeled water). The mass-adjusted resting metabolism and field metabolism of gravid females and the field metabolism of juvenile lizards were not significantly different from those of nonreproductive adults. Temperature had a significant effect on resting metabolism (Q(10) = 2.7); fed lizards had resting metabolism that was 22% higher than that of fasted lizards; field metabolism was positively correlated with growth rate in juveniles; and field metabolism of adults increased from spring to late summer at Desert Center by 25%, probably because of longer activity period length and slightly higher activity period body temperature. We calculated from water influx and field metabolism that juveniles allocated 18% of their metabolizable energy intake to growth and that most energy deposited into eggs was transferred from energy stores rather than ingested in the weeks prior to laying.
Metabolic consequences of osmotic stress were investigated in the toad Bufo viridis. Toads were acclimated either to terrestrial conditions in the absence of free water or to being partially immersed in 250 mmol L-1 NaCl, which was achieved by gradually increasing the salinity of the bath. This slow acclimation evoked little metabolic response, whereas the immediate osmotic challenge of water restriction resulted in a significant increase in the concentration of urea in the plasma and in liver glycogen. Urea accumulation, involving a transient increase in its rate of synthesis, allows the toads to lower their body water potential and thereby to absorb soil-bound water. The metabolic cost of this response is reduced by conserving the resulting by-product, glucose, as glycogen stored in the liver for future use.
Many techniques have been employed to measure metabolic and cardiovascular changes in diving marine mammals. Each of these methods has its advantages, but the methods also have drawbacks when applied to phocid seals. The aim of this study was to investigate heart rate and metabolic responses to diving in juvenile northern elephant seals that are not associated with forced changes in exercise state, and, secondarily, to investigate whether heart rate could be used as an indicator of metabolic rate in this species. Six seals were allowed to dive freely in a metabolic chamber while simultaneous measurements of heart rate and oxygen consumption were made. Within each dive cycle (dive and surface interval), the seals spent an average of 74% of the time submerged. Mean dive duration was 6.43 +/- 0.6 (SD) min. Mean oxygen consumption during diving was 3.32 +/- 0.4 mL O-2 min(-1) kg(-1), a decrease of approximately 26% from baseline values. An inverse relationship was observed between oxygen consumption and the percentage of time spent submerged in each dive cycle. The total amount of oxygen consumed during the surface interval increased with increasing dive duration, while the duration of the surface interval itself did not change, indicating that seals alter the rate of O-2 uptake rather than the time spent at the surface. Mean heart rate during diving was 34.5 +/- 6.2 beats min(-1), 36% lower than resting values. Mean diving heart rate was independent of dive duration, percent time submerged, and oxygen consumption. Mean surface interval heart rate was 66.6 +/- 11.1 beats min(-1) and was not correlated with oxygen consumption. Average heart rate over the entire dive cycle increased with increasing oxygen consumption in all of the seals, but there was only a significant relationship in two seals, which casts some doubt on the usefulness of heart rate as an indicator of metabolic rate in this species. While providing important information on the changes in heart rate and oxygen consumption during diving in northern elephant seals, a complete understanding of the diving metabolic rate of these animals will require a combination of approaches that can be used in concert with data on freely living animals.
Two species of herbivorous land crabs from Christmas Island, Cardisoma hirtipes and Gecarcoidea natalis, overlap in both diet and distribution. This study compared the dietary preferences and digestive capabilities of these two species on a diet of leaf litter to establish the digestive strategies each adopts and the likely degree of competition for food. C. hirtipes preferred green to yellow or brown leaves of Ficus macrophylla in short‐term food‐choice experiments. Brown leaves were least favoured. G. natalis showed no preference for the different leaf types and in the field ate chiefly brown and decomposing leaf litter. When fed green leaves, C. hirtipes had a low food intake (4.5 ± 0.36 g kg−1 d−1) and a short retention time for food, and the readily digestible components of the diet constituted greater than 84% of the dry matter assimilated. When fed brown leaves, the intake was increased 3.3 times, but retention time remained short, and assimilation coefficients for all nutrients were low. The readily digestible fraction of the diet made the chief contribution to dry matter assimilation (69%), and hemicellulose (19%) and cellulose (21%) were also significantly used. This pattern of food intake and assimilation contrasts with that for G. natalis, which had a low intake of brown leaves and a longer retention time associated with higher nutrient assimilation, particularly of complex polysaccharides. It is suggested that through their feeding preferences and habits, these two sympat‐ric species use opposite ends of the leaf litter quality spectrum on Christmas Island.
We used nestling house sparrows (Passer domesticus) under laboratory conditions to test for modulation of digestive efficiencies during periods of low and high food intake and tested the hypothesis that nestlings would exhibit compensatory changes in digestive efficiency following a period of food restriction. During the low intake period, nestlings were held at constant body mass for 48 h beginning on either day 3 or day 6 of life by feeding them at 50% of control rations. After 48 h of food restriction, nestlings were fed as much as they could consume, allowing the nestlings restricted at day 6 (early restriction not assessed) to consume 14% more food than control nestlings. For nestlings restricted at day 6 apparent dry mass assimilation of the entire diet was found to be 5% and 8% lower during food restriction and realimentation, respectively, compared with control nestlings that were not under- or overfed. There were no significant differences in radiolabeled starch assimilation efficiencies between control and restricted nestlings. Starch assimilation efficiencies remained constant from 3 d of age onward in control nestlings. Total starch extracted was lower during food restriction but reached a rate similar to that of control nestlings during the realimentation period. Passage times (time of first defecation, mean retention time, and mode passage time) measured with an indigestible marker were longer during food restriction and shorter during realimentation, relative to control nestlings. During realimentation there was no difference in intestinal rates of hydrolysis or mediated uptake of L-leucine compared with control nestlings. The main effect of changing food intake was apparently to alter flow rate, and hence retention time, causing slight changes in digestive efficiency. Thus, nestlings did not exhibit compensatory changes in digestion rates as implied by the hypothesis. Our finding of a lower dry mass assimilation efficiency and similar total starch assimilation during realimentation (relative to controls) helps explain why nestling house sparrows do not display compensatory growth, despite higher food intake. Our results indicate that the gut has little spare capacity to deal with increased food intake during growth following food restriction.
We tested predictions of a chemical reactor model of digestion by manipulating the short-term costs of feeding and then measuring the effect on digestive parameters. We compared residence time of digesta and extraction efficiency of glucose in cold-acclimated waxwings (Bombycilla cedrorum) feeding ad lib, and in birds whose costs of feeding were increased through the addition of intervals of time when they received no food. Such a feeding schedule simulated the ecological situation in which a frugivorous bird like a waxwing encounters food in patches and experiences nonfeeding periods as it searches for new preferred food patches. None of the results were consistent with the predictions of the optimal digestion model: extraction efficiency was independent of costs of feeding, and residence times did not increase as costs of feeding increased. This empirical evidence on the passage of digesta in waxwings suggests that movement of digesta in the guts of birds is much more complex than movement of material in an ideal chemical reactor. Tests of the optimal digestion model have involved manipulating food quality or the costs of feeding, and the conclusions are similar: compensatory modulation of retention time or digesta mixing and not rate of hydrolysis and absorption seem most important in maintaining the remarkably constant digestive efficiency.
The production of milk by lactating females, and energy expenditure and foliage intake of their dependent young, were investigated in free-ranging koalas. Koalas had the lowest mass-specific daily milk-energy production at peak lactation so far recorded in a mammal, but the duration of reproduction was 58% longer than the combined marsupial and eutherian average. As a consequence, the total energy input to reproduction in koalas was similar to that in other mammals. We propose that the prolonged lactation and low daily rate of energy transfer to the young by female koalas is an adaptation to the low energy availability from their diet of Eucalyptus foliage. Energy requirements (field metabolic rates) of young koalas were lower than those expected for typical marsupials (only 60% at permanent pouch exit), which may be a necessary preadaptation that allows the low rate of maternal energy transfer. However, the energy requirements of the adult females were no lower than expected for marsupials. This pattern of energy requirements and age resulted in a linear relationship between field metabolic rate and mass for the koalas in this population. Differences in milk production between the years of the study coincided with fluctuations in the availability of preferred young foliage, which suggests that lactational output by koalas may be flexible and affected by diet quality. Despite the interannual differences in milk production, growth of the young was similar in the two years.
Body temperatures of winter‐resident Korean bats typically range from 10° to 40°C between August and September and from 3° to 15°C between January and April. To learn how behavior and the motor systems of heterothermic bats respond to this body‐temperature variation, we examined whole‐organism performance and the temperature‐dependence of contractile properties of flight muscle in Murina leucogaster ognevi. In winter and midspring, the lowest limits of body temperature were 8°C for biting and crawling, 16°C for visually observable shivering, 22°C for wing flapping (without powered flight), and 28°C for aerial flight. In summer, the lowest temperature limits changed little for biting and wing flapping, but the temperature limits increased about 3°C for crawling, shivering, and flight. Maximum isometric tetanic tension of the isolated biceps brachii muscle was almost insensitive to tissue temperatures between 10° and 40°C, with an average temperature coefficient of 1.02 in summer and of 0.96 in winter. Rate of tetanic tension production between 10° and 40°C and shortening velocity and power between 15° and 25°Cwere temperature sensitive, with average temperature coefficients of 1.3–2.3. Seasonal differences in contractile properties within each temperature were not significant, except for maximum tetanic tension at 30°–40°C. Thus, the motor system of the bats had functional capacity over the range of body temperature experienced in winter to summer. The temperature‐dependence of behavior was consistent with muscle physiology. The defensive behaviors, like biting and crawling, observed at 8°–12°C body temperature could be exerted by using temperature‐independent tetanic tension, whereas activities, such as flight, that require power generation would be restricted to higher body temperatures by temperature‐sensitive rate properties. Some rate processes appeared to be more temperature sensitive in summer than in winter.
This study analyzes the capillarity and fibre-type distribution of six locomotory muscles of gulls. The morphological basis and the oxygen supply characteristics of the skeletal muscle of a species with a marked pattern of gliding flight are established, thus contributing to a better understanding of the physiology of a kind of flight with low energetic requirements. The four wing muscles studied (scapulotriceps, pectoralis, scapulohumeralis, and extensor metacarpi) exhibited higher percentages of fast oxidative glycolytic fibres (>70%) and lower percentages of slow oxidative fibres (<16%) than the muscles involved in nonflight locomotion (gastrocnemius and iliotibialis). Capillary densities ranged from 816 to 1,233 capillaries mm(-2), having the highest value in the pectoralis. In this muscle, the fast oxidative glycolytic fibres had moderate staining for succinate dehydrogenase and relatively large fibre sizes, as deduced from the low fibre densities (589-665 fibres mm(-2)). All these findings are seen as an adaptive response for gliding, when the wing is held outstretched by isometric contractions. The leg muscles studied included a considerable population of slow oxidative fibres (>14% in many regions), which suggests that they are adapted to postural activities. Regional variations in the relative distributions of fibre types in muscle gastrocnemius may reflect different functional demands placed on this muscle during terrestrial and aquatic locomotion. The predominance of oxidative fibres and capillary densities under 1,000 capillaries mm(-2) in leg muscles is probably a consequence of an adaptation for slow swimming and maintenance of the posture on land rather than for other locomotory capabilities, such as endurance or sprint activities.
Nectarivore sugar preferences and nectar composition in the Cape Floristic Kingdom (southern Africa) differ from trends reported for analogous systems in America and Europe in that sugarbirds and sunbirds show no aversion to sucrose, which is the dominant nectar sugar in many of their food plants. To elucidate the physiological bases (if any) of nectarivore sugar preferences, we determined apparent sugar absorption efficiencies in a passerine endemic to this region, the Cape sugarbird Promerops cafer. Apparent absorption efficiencies for the three major nectar sugars, sucrose, glucose, and fructose, were extremely high (> 99%), as in other specialized avian nectarivores. Xylose, a pentose sugar recently reported in the nectar of some Proteaceae, was absorbed and/or metabolized inefficiently, with a mean of 47.1% of ingested sugar recovered in cloacal fluid. We did not measure the proportions of xylose that were absorbed and/or metabolized. We also compared three methods of estimating absorption efficiency: (1) measurements of total sugar in cloacal fluid with refractometry, without correction for differences between volumes of ingesta and excreta; (2) the same measurements combined with correction for volume differences; and (3) HPLC analyses quantifying individual sugars in cloacal fluid, With correction for volume differences. Refractometry has been frequently used in previous studies. For all sugars except xylose, method 1 yielded results similar to those obtained with method 2, but the convergence was artifactual, and we do not recommend use of this method. Apparent absorption efficiencies calculated with method 2 underestimated true absorption efficiency, because refractometry measures nonsugar solutes, but this error is biologically significant only when efficiencies are low.
Studies of the metabolic and physiological changes that bears undergo during hibernation have, for the most part, supported the paradigm that bears use only fatty tissues as a metabolic substate during hibemation. This study was performed to document the extent of protein loss and alteration of muscle‐fiber characteristics of selected muscles in black bears during winter dormanc. Muscle biopises were removed from the gas‐trocnemius and biceps femoris from seven free‐ranging female black bears on the Uncompahgre Plateau in west‐central Colo‐rado. Six of the seven bears produced cubs during the hibernat‐ing season. Muscle samples were collected from the left hind limb shortly after bears entered their dens (fall), and additional samples were collected from the right hind limb Just prior to bears leaving their dens (spring). Protein concentration, fast‐and slow‐twitch muscle‐fiber rations and muscle‐fiber cross‐sectional areas, and citrate synthase activity were measured in the laboratory. While Protein concentration decreased in both muscles during the hibernation period, it was lower than pre‐dicted for lactating females, In addition, muscle‐fiber number and cross‐sectional area were unchanged in these muscles, sug‐gesting only limited muscle atrophy. In support of these obser‐vations, there were a moderate but significant increase in the proportion of fast‐twitch fibers only in the biceps femoris, with a concomitant decrese in citrate synthase activity, but no alteration of the fiber ratio in the gastrocnemius during hiber‐natio. The findings suggest that hibernating bears, particu
We examined the effects of acute low-pH exposure on ion balance (Na+, Cl-, K+) in several species of fish captured from the Rio Negro, a dilute, acidic tributary of the Amazon. At pH 5.5 (untreated Rio Negro water), the four Rio Negro species tested (piranha preta, Serrasalmus rhombeus; piranha branca, Serrasalmus cf. holandi; aracu, Leporinus fasciatus; and pacu, Myleus sp.) were at or near ion balance; upon exposure to pH 3.5, while Na+ and Cl- loss rates became significant, they were relatively mild. In comparison, tambaqui (Colossoma macropomum), which were obtained from aquaculture and held and tested under the same conditions as the other fish, had loss rates seven times higher than all the Rio Negro species. At pH 3.0, rates of Na+ and Cl- loss for the Rio Negro fish increased three- to fivefold but were again much less than those observed in tambaqui. Raising water Ca2+ concentration from 10 micromol L-1 to 100 micromol L-1 during exposure to the same low pH's had no effect on rates of ion loss in the three species tested (piranha preta, piranha branca, aracu), which suggests that either they have such a high branchial affinity for Ca2+ that all sites are saturated at 10 micromol L-1 and additional Ca2+ had no effect, or that Ca2+ may not be involved in regulation of branchial ion permeability. For a final Rio Negro species, the cardinal tetra (Paracheirodon axelrodi), we monitored body Na+ concentration during 5 d of exposure to pH 6.0, 4.0, or 3.5. These pH's had no effect on body Na+ concentration. These data together suggest that exceptional acid tolerance is a general characteristic of fish that inhabit the dilute acidic Rio Negro and raise questions about the role of Ca2+ in regulation of branchial ion permeability in these fish.
Numerous studies have demonstrated how the performance physiology of fish may change when they are acclimated to designated laboratory temperatures, but few researchers have examined naturally occurring seasonal effects on several physiological parameters associated with swimming performance. Using field-acclimatized smallmouth buffalo (Ictiobus bubalus) collected each season, we report significant seasonal effects in the following variables: critical swimming speed (modified), metabolic rate (standard, active, and scope for activity), and swimming efficiency (total and net cost of transport). Underlying seasonal changes in performance was the reproductive cycle of buffalo, particularly the period of fall gonadal recrudescence. Compared with spring, fall buffalo had a significantly lower mean critical swimming speed (72%) and lower active metabolic rate (53%), even when tested at similar temperatures. During spring, buffalo had a high mean critical swimming speed and low net cost of transport in comparison with other seasons. Buffalo are known to participate in a spring migration and spawning that may require the increased performance and efficiency observed during that season. In addition, significant sex effects were detected in winter measurements of standard metabolic rate and net cost of transport, with females the more efficient swimmers.
Previous articleNext article No AccessCorrectionGlyconeogenesis and Urea Synthesis in the Toad Bufo viridis during Acclimation to Water RestrictionJ. Hoffman and U. KatzJ. Hoffman Search for more articles by this author and U. Katz Search for more articles by this author PDFPDF PLUS Add to favoritesDownload CitationTrack CitationsPermissionsReprints Share onFacebookTwitterLinkedInRedditEmail SectionsMoreDetailsFiguresReferencesCited by Volume 71, Number 5September/October 1998 Article DOIhttps://doi.org/10.1086/515945 Journal History This article was published in Physiological Zoology (1928-1998), which is continued by Physiological and Biochemical Zoology (1999-present). PDF download Crossref reports no articles citing this article.
The energy expenditure of breeding male harbour seals Phoca vitulina, on Sable Island, Nova Scotia, was investigated by measuring changes in body mass, body comosition, and water flux using isotope dilution. Seals lost 0.04% ± 0.04% (n = 34) of their initial mass per day during the breeding season (4 wk),and fat, water, and protein accounted for 64.3% ± 4.8%, 27.8% ± 3.3%, and 6.9 ± 1.4% of this was estimated as 33.3 ± 1.9 MJ d‐1, or 3.9 ± 0.2 W kg‐1 (n = 17), similar to rates measured in terrestrially mating pinniped species. However, unlike terrestrially mating pinni‐peds, male harbour seals did not fast during the breeding season, and energy intake from foraging accounted for 61.8% ± 4.0% of the total energy expended. Males derived most of their expended energy from food intake early in the breeding season. However, as oestrus females became increasingly available, reduced rates of food intake in males were coupled with increased rates of total energy expenditure. Larger males expended significantly more energy from body stores and more total energy than smaller males. Male harbour seals appeared to balance the energetic costs of reporduction against the constraints of small body size by foraging during deep‐diving trips before the appearance of oestrus females and by opportunistie feeding throughout the breeding season while at sea. We suggest that size dimorphism may be less pronounced in aquatically mating pinnipeds partly because the temporal and spatial separation of foraging and repro‐duction is less distinct than it is for terrestrially breedings pinnipeds.
Body temperatures of winter-resident Korean bats typically range from 10 degrees to 40 degrees C between August and September and from 3 degrees to 15 degrees C between January and April. To learn how behavior and the motor systems of heterothermic bats respond to this body-temperature variation, we examined whole-organ ism performance and the temperature-dependence of contractile properties of flight muscle in Murina leucogaster ognevi. In winter and midspring, the lowest limits of body temperature were 8 degrees C for biting and crawling, 16 degrees C for visually observable shivering, 22 degrees C for wing flapping (without powered flight), and 28 degrees C for aerial flight. In summer, the lowest temperature limits changed little for biting and wing flapping, but the temperature limits increased about 3 degrees C for crawling, shivering, and flight. Maximum isometric tetanic tension of the isolated biceps brachii muscle was almost insensitive to tissue temperatures between 10 degrees and 40 degrees C, with an average temperature coefficient of 1.02 in summer and of 0.96 in winter. Rate of tetanic tension production between 10 degrees and 40 degrees C and shortening velocity and power between 15 degrees and 25 degrees C were temperature sensitive, with average temperature coefficients of 1.3-2.3. Seasonal differences in contractile properties within each temperature were not significant, except for maximum tetanic tension at 30 degrees-40 degrees C. Thus, the motor system of the bats had functional capacity over the range of body temperature experienced in winter to summer. The temperature-dependence of behavior was consistent with muscle physiology. The defensive behaviors, like biting and crawling, observed at 8 degrees-12 degrees C body temperature could be exerted by using temperature-independent tetanic tension, whereas activities, such as flight, that require power generation would be restricted to higher body temperatures by temperature-sensitive rate properties. Some rate processes appeared to be more temperature sensitive in summer than in winter.
Adams, S. Reid, 350 Species with Low Rates of Energy Use, the Pine Vole (Microtus pinetorum), 611 Adelung, Dieter, 524 Anderson, Roger A., 93 Changes in Lean Mass and in Organs of Nutrient Assimilation in a Long-Distance Passerine Migrant at a Springtime Stopover Andrés, M. Dolores, 285 Andrews, Russel D., 116 Site, 435 Changes in Pattern of Heat Loss at High Ambient Temperature Apneic Oxygen Uptake in the Torpid Pocket Mouse Perognathus parvus, 624 Caused by Water Deprivation in a Large Flightless Bird, the Emu, 712 Apparent Absorption Efficiencies of Nectar Sugars in the Cape Sugarbird, with a Comparison of Methods, 106 Chippindale, Adam K., 584 Cho, Yeonmi, 257 Ar, Amos, 407 Austin, Mitzi W., 611 Choi, In-Ho, 257 Coltman, David W., 387 Comments on a Negative Appraisal of Taxidermic Mounts as Baillieul, Marc, 703 Tools for Studies of Ecological Energetics, 596 Beck, Thomas D. I., 414 Comparative Development in Captive and Migratory Populations Behavior and Muscle Performance in Heterothermic Bats, 257 of the Barnacle Goose, 198 Belan, Ingrid, 303 Comparison of Spectrophotometry and Color Charts for EvaluatBennett, Albert F., 333 ing Total Plasma Carotenoids in Wild Birds, A, 708 Bergman, Harold L., 15, 658 Congdon, Justin D., 27, 633 Bhargava, Valmik, 157 Cork, Steven J., 45 Bishop, Charles M., 198 Correlates of Average Daily Metabolism of Field-Active ZebraBlanco, Guillermo, 708 Tailed Lizards (Callisaurus draconoides), 93 Blázquez, MarıB a C., 708 Costa, Daniel P., 116, 208, 485 Blood Volume and Diving Ability of the New Zealand Sea Lion, Crocker, Daniel E., 208, 485 Phocarctos hookeri, 208 Cullum, Alistair J., 541 Blust, Ronny, 703 Body Condition and the Adrenal Stress Response in Captive American Kestrel Juveniles, 67 Daan, Serge, 245, 693 Body Cooling and Its Energetic Implications for Feeding and DivDaily and Seasonal Rhythms in Selected Body Temperatures in ing of Tufted Ducks, 720 the Australian Lizard Tiliqua rugosa (Scincidae): Field and LaboBoness, Daryl J., 387 ratory Observations, 303 Booth, David T., 23 Daily Energy Budgets of Avian Embryos: The Paradox of the PlaBowen, W. Don, 329, 387 teau Phase in Egg Metabolic Rate, 147 Bozinovic, Francisco, 226 Dalton, Nancy, 157 Bradley, Timothy J., 584 Darken, Rachel S., 400 Bradshaw, S. Donald, 214 Dawson, Terence J., 712 Burness, Gary P., 247 D’Cruz, Leela Marie, 359, 642 Burnett, Lou, 469 deFur, Peter, 469 Butler, Patrick J., 198, 720 de Leeuw, Joep J., 720 Del Rio, Carlos MartıB nez, 226 Derting, Terry L., 611 Capillarity and Fibre Types in Locomotory Muscles of Wild Yellow-Legged Gulls (Larus cachinnans), 425 Development of Thermoregulation and Posthatching Growth in the Altricial Cockatiel Nymphicus hollandicus, 237 Carbon Release from Purified Chemoautotrophic Bacterial Symbionts of the Hydrothermal Vent Tubeworm Riftia pachyptila, de Wachter, Bart, 703 Dietary Flexibility and Intestinal Plasticity in Birds: A Field and 294 Cardiovascular Regulation during Anoxia in the Turtle: An In Laboratory Study, 226 Dietz, Maurine W., 147 Vivo Study, 1 Caviedes-Vidal, Enrique, 561 Digestive Responses during Food Restriction and Realimentation in Nestling House Sparrows (Passer domesticus), 561 Changes in Gut Capacity with Lactation and Cold Exposure in a
Heart rate, swimming speed, and diving behaviour were recorded simultaneously for an adult female southern elephant seal during her postbreeding period at sea with a Wildlife Computers heart‐rate time depth recorder and a velocity time depth recorder. The errors associated with data storage versus real‐time data collection of these data were analysed and indicated that for events of short duration (i.e., less than 10 min or 20 sampling intervals) serious biases occur. A simple model for estimating oxygen consumption based on the estimated oxygen stores of the seal and the assumption that most, if not all, dives were aerobic produced a mean diving metabolic rate of 3.64 mL O2 kg−1, which is only 47% of the field metabolic rate estimated from allometric models. Mechanisms for reducing oxygen consumption while diving include cardiac adjustments, indicated by reductions in heart rate on all dives, and the maintenance of swimming speed at near the minimum cost of transport for most of the submerged time. Heart rate during diving was below the resting heart rate while ashore in all dives, and there was a negative relationship between the duration of a dive and the mean heart rate during that dive for dives longer than 13 min. Mean heart rates declined from 40 beats min−1 for dives of 13 min to 14 beats min−1 for dives of 37 min. Mean swimming speed per dive was 2.1 m s−1, but this also varied with dive duration. There were slight but significant increases in mean swimming speeds with increasing dive depth and duration. Both ascent and descent speeds were also higher on longer dives.
Because of its small body mass, the shrew Crocidura russula monacha has a relatively high surface area to volume ratio, thin skin, and high thermal conductance compared with larger mammals. This study was aimed at examining the possibility that such a mammal may exhibit a significant skin gas exchange. Gas composition was measured in subcutaneous gas pockets. CO2 and O2 exchange through skin were measured both in vitro and in vivo. In 7-wk-old gas pockets, the steady-state PO2 and PCO2 values were 50 Torr (where 1 Torr = 133.322 Pa) and 35 Torr, respectively, compared with PO2 and Pco2 values of 73 Torr and 33 Torr, respectively, in 1-wk-old gas pockets. These changes are attributed to an increased capillary density and a decreased skin thickness after 7 wk. There was no significant gas exchange through skin during in vitro measurements. In vivo measurements indicated that O2 uptake was 0.5% and CO2 loss was 0.9% of total body metabolism at 20 degrees C. At 35 degrees C, skin O2 uptake and CO2 loss increased to 1.3% and 2.9%, respectively. These values are only part of the expected skin metabolism; thus, the rest must come from blood. Because gas exchange through the skin of this shrew is within the range of other mammals, the relatively low PCO2 and high PO2 in the gas pockets is better explained by the relative hyperventilation state exhibited by this shrew.
We investigated the relationship between maintenance costs (standard metabolic rates, measured as O2 consumption at rest) in tadpoles of the bullfrog, Rana catesbeiana, and exposure to contaminants in a coal ash-polluted habitat (characterized by a variety of trace elements). We compared metabolic rates of tadpoles collected from the polluted site with those from an unpolluted reference pond. Tadpoles collected in the polluted site had 40%-97% higher standard metabolic rates than those collected from the reference pond. We also reciprocally transplanted eggs of the bullfrog between the polluted site and another reference pond and compared standard metabolic rates of tadpoles at 25 and 80 d posthatching. Metabolic rates of tadpoles raised in the polluted site were from 39% to 175% higher than those raised in a reference pond, depending on tadpole age and temperature at which metabolic rates were measured. There were no effects of site of origin of the eggs (polluted or unpolluted) on metabolic rates. Survival to hatching did not differ between sites, although survival to the end of the experiment (80 d posthatching) was lower in the polluted area than in the reference site. Surviving tadpoles were larger in wet body mass in the polluted site than in the reference pond, possibly due to lower survival in the former, but there was no relationship between survival and metabolic rate. It is clear that some feature of the polluted habitat was responsible for causing substantial elevation of standard metabolic rates of tadpoles. We hypothesize that the mixture of trace elements present in sediment and water in the polluted site was responsible for the observed physiological differences.
