Mass-specific Oxygen Consumption Rate Research Articles

Energetics of Surface Swimming in Brandt’s Cormorants (Phalacrocorax Penicillatus Brandt)

The energy requirements of Brandt's cormorants (Phalacrocorax penicillatus) during surface swimming were measured in birds swimming under a metabolic chamber in a water flume. From the oxygen consumption recordings, we extrapolated the metabolic rate and cost of transport at water speeds ranging from 0 to 1.3 m s(-)(1). In still water, the birds' mean mass-specific rate of oxygen consumption ( V(O2)) while floating at the surface was 20.2 ml O(2 )min(-)(1 )kg(-)(1), 2.1 times the predicted resting metabolic rate. During steady-state voluntary swimming against a flow, their V(O2) increased with water speed, reaching 74 ml O(2 )min(-)(1 )kg(-)(1) at 1.3 m s(-)(1), which corresponded to an increase in metabolic rate from 11 to 25 W kg(-)(1). The cost of transport decreased with swimming velocity, approaching a minimum of 19 J kg(-)(1 )m(-)(1) for a swimming speed of 1.3 m s(-)(1). Surface swimming in the cormorant costs approximately 18 % less than sub-surface swimming. This confirms similar findings in tufted ducks (Aythya fuligula) and supports the hypothesis that increased energy requirements are necessary in these birds during diving to overcome buoyancy and heat loss during submergence.

Leptocephalus energetics: metabolism and excretion.

Leptocephali are the unusual transparent larvae that are typical of eels, bonefish, tarpon and ladyfish. Unlike the larvae of all other fishes, leptocephali may remain in the plankton as larvae for several months before metamorphosing into the juvenile form. During their planktonic phase, leptocephali accumulate energy reserves in the form of glycosaminoglycans, which are then expended to fuel metamorphosis. The leptocephalus developmental strategy is thus fundamentally different from that exhibited in all other fishes in two respects: it is far longer in duration and energy reserves are accumulated. It was anticipated that the unusual character of leptocephalus development would be reflected in the energy budget of the larva. This study describes the allocation of energy to metabolism and excretion, two important elements of the energy budget. Metabolic rates were measured directly in four species of leptocephali, Paraconger caudilimbatus, Ariosoma balearicum, Gymnothorax saxicola and Ophichthus gomesii, using sealed-jar respirometry at sea. Direct measurements of metabolic rates were corroborated by measuring activities of lactate dehydrogenase and citrate synthase, two key enzymes of intermediary metabolism, in addition to that of Na(+)/K(+)-ATPase, a ubiquitous ion pump important in osmotic regulation. Excretion rates were determined by subsampling the sea water used in the respiratory incubations. The entire premetamorphic size range for each species was used in all assays. Mass-specific oxygen consumption rate, excretion rate and all enzyme activities (y) declined precipitously with increasing mass (M) according to the equation y=aM(b), where a is a species-specific constant and -1.74<b<-0.44. In leptocephali, the highly negative slope of the familiar allometric equation describing the relationship between mass-specific metabolic rate and mass, normally between -0.33 and 0, showed that a massive decline in metabolic rate occurs with increasing size. The result suggests that the proportion of actively metabolizing tissue also declines with size, being replaced in large measure by the metabolically inert energy depot, the glycosaminoglycans. Leptocephali can thus grow to a large size with minimal metabolic penalty, which is an unusual and successful developmental strategy.

Capacity for red blood cell aggregation is higher in athletic mammalian species than in sedentary species

The purpose of this study was to show that two rheological parameters, red blood cell (RBC) sedimentation rate and apparent blood viscosity at low shear rate, characterizing the degree of RBC aggregation, correlate significantly with the maximal mass-specific rate of oxygen consumption or aerobic capacity (VO2max). Comparisons were made within two groups of similarly sized athletic and sedentary species: group 1, pronghorn antelope, dog, goat, and sheep; and group 2, horse and cow. The pronghorn antelope (Antilocapra americana) is one of the most athletic mammals, and we have obtained data on the rheological properties of blood from this species for the first time. The values of apparent viscosity at hematocrit = 40% and shear rate = 0.277 s-1 measured in a rotational viscometer were 59.5, 42.6, and 9.1 cP for antelope, dog, and sheep blood, respectively, and 55.3 and 11.5 cP for horse and cow blood, respectively. The viscosity values for antelope, dog, and sheep blood can be correlated with aerobic capacity: ln viscosity = 4.48-106.3 VO2(-1)max (r2 = 0.998; P < 0.05). The values of RBC sedimentation rate at hematocrit = 40% were 12.8, 7.0, and 0 mm/h for antelope, dog, and sheep blood, respectively, and 45.3 and 0.1 mm/h for horse and cow blood, respectively. Therefore, the data showed that the athletic species exhibit a consistently higher degree of RBC aggregation than do the corresponding nonathletic species.

Oxygen consumption rates of adults and chicks during brooding in king quail (Coturnix chinensis)

Oxygen consumption rates were measured in chicks (0-17 days of age), and in non-brooding and brooding adults. Brooded chicks maintained a constant oxygen consumption rate at a chamber ambient temperature of 10-35 degrees C (0-5 days of age: 2.95 ml O2.g-1.h-1 and 6-17 days of age: 5.80 ml O2.g-1.h-1) while unbrooded chicks increased oxygen consumption rate at ambient temperature below 30 degrees C to double the brooded oxygen consumption rate at 25 and 15 degrees C for chicks < 5 days of age and > 5 days of age, respectively. The mass-specific oxygen consumption rate of breeding male and females (non-brooding) were significantly elevated within the thermoneutral zone thermal neutral zone (28-35 degrees C) in comparison to non-breeding adults. Below the thermal neutral zone, oxygen consumption rate was not significantly different. The elevation in oxygen consumption rate of breeding quail was not correlated with the presence of broodpatches, which developed only in females, but is a seasonal adjustment in metabolism. Male and females that actively brooded one to five chicks had significantly higher oxygen consumption rate than nonbrooding quil at ambient temperature below 30 degrees C. Brooding oxygen consumption rate was constant during day and night, indicating a temporary suppression of the circadian rhythm of metabolism. Brooding oxygen consumption rate increased significantly with brood number, but neither adult body mass nor adult sex were significant factors in the relationship between brooding oxygen consumption rate and ambient temperature. The proportion of daylight hours that chicks were brooded by parents was negatively correlated with ambient temperature. After chicks were 5 days old brooding time was reduced but brooding oxygen consumption rate was unchanged. Heat from the brooding parent appeared to originate mainly from the apteria under the wings and legs rather than the broodpatch. The parental heat contribution to chick temperature regulation below the chicks' thermal neutral zone is achieved by increasing parental thermal conductance by a feedback control similar to that suggested for the control of egg temperature via the broodpatch. It is concluded that the brooding period is an energetic burden to parent quail, and the magnitude of the cost increases directly with brood number and inversely with ambient temperature during this period.(ABSTRACT TRUNCATED AT 400 WORDS)

Seasonal Changes in Body Mass and Use of Torpor in a Migratory Hummingbird

-In a study designed to determine seasonal patterns of body mass and torpor in Rufous Hummingbirds (Selasphorus rufus), birds were maintained for 12 months in the laboratory on a photoregime approximating that experienced by free-living birds. Ambient temperature cycled from 20?C during the day to 5?C at night. Body mass, torpor, and rates of nighttime oxygen consumption were measured under conditions of ad libitum feeding in LD 12:12 in autumn (when free-living birds are normally migrating south), LD 12:12 in spring (during molt), and LD 16:8 in summer. Both body mass and use of torpor were highest in autumn, suggesting that torpor is not reserved for immediate crises at this time, but may be important in maximizing savings and thus minimizing the time required for premigratory fattening. In spring, body mass was lowest; use of torpor, however, was significantly lower than in autumn, suggesting that torpor is used primarily for energy emergencies at this time of year. In summer, body mass was intermediate and use of torpor was also significantly lower than in autumn. Mass-specific rates of oxygen consumption during both normothermia and torpor were inversely related to body mass when data from all seasons were combined; large fat stores may contribute to lower metabolic rates by providing additional insulation, as well as by decreasing the proportion of highly metabolically active tissue in the body. Low fat stores also coincide with the molt, which itself may result in higher metabolic rates. Although the propensity for using torpor has a strong seasonal component that appears to reflect different energetic circumstances during such activities as migration and molt, Rufous Hummingbirds retain the ability to enter nocturnal torpor at all times of year, thus improving their chances of survival year-round. Submitted 14 May 1992, accepted 12 November 1992. MIGRATORY HUMMINGBIRDS living in cool climates face potentially extreme threats to balance. Like other small homeotherms, they have high thermoregulatory costs resulting from high surface-to-volume ratios that increase rates of heat loss to the environment. Like other hummingbirds, they incur the additional cost of hovering, the most energetically demanding mode of flight. Unlike the many species of hummingbirds that are year-round residents in lowlatitude habitats, however, the relatively few migratory species have an additional energetic requirement-they need to accumulate large fat stores to fuel long-distance flight. Nocturnal torpor, during which expenditure is greatly reduced, is an important means by which hummingbirds offset large daytime expenditures and maintain balance. All species of hummingbirds that have been studied show this physiological ad' Present address: Department of Biology, Swarthmore College, Swarthmore, Pennsylvania 19081, USA. aptation. Most studies, however, have focused on instantaneous features of torpor (e.g. comparisons between rates of metabolism during steady-state torpor and steady-state normothermia), or on the effects of torpor on total nighttime balance (Hiebert 1990). Little consideration has been given to the fact that hummingbirds, particularly species residing at least part of the year in temperate zones, engage in activities that place very different energetic demands on the animal at different times of year. Therefore, one might expect there to be corresponding seasonal changes in the use of torpor. Yet, with the exception of Carpenter's (1974) study of the Andean Hillstar (Oreotrochilus estella), there have been no systematic comparisons of seasonal changes in the use of torpor. The seasonality of torpor has never been studied in a migratory species. The Rufous Hummingbird (Selasphorus rufus) is one of the most highly migratory species of hummingbirds. It breeds at high latitudes, as far north as Alaska, but winters in Mexico. Yearly round-trip migratory flights may exceed 6,000 km (Phillips 1975, Calder 1987). Because of their

Energetic Costs of Lactation with and without Simultaneous Pregnancy in the White-Toothed Shrew Crocidura russula monacha

Milk composition, gas exchange, and energy intake in food were measured in whitetoothed shrews, Crocidura russula monacha, in lactating females (LF) and in simultaneously lactating and pregnant females (LPF). Milk contained 51.2% ± 11.3 SD solids and 9.4% ± 1.0 SDproteins. Milk fat increased from 28.5% ± 0. 46 SD on day 2 of lactation to 42.6% ± 3.5 SD on day 20. Lactose decreasedfrom 3%-8% during the first week of lactation to 2%-4% at the end. Energy content of milk paralleled fat concentration, increasing from 14.86 kJ. g⁻¹ + 0. 4 SD to 17.92 kJ. g⁻¹ ± 1.04 SD. Mass-specific oxygen consumption rate (Mspo₂) of the LF reached apeak value of 3. 68 mL. (g . h)⁻¹ ± 0.58 SD on days 6-8 of lactation, then declined to the nonreproductive value on day 16 (2. 48 mL. [g . h]⁻¹). The Mspo₂ of the LPF remained unchanged throughout lactation at 2. 75 mL. (g . h)⁻¹ ± 0.47 SD. Energy intake in food in both LF and LPF increased daily depending on litter size. In a onepup litter it increased from 31.4 kJ. d⁻¹ ± 4.4 SD to 62.3 kJ. d⁻¹ ± 11.2 SD on day 10, whereas in a four-pup litter it increased from 53.0 kJ. d⁻¹ ± 7.5 SD to 119.3 kJ . d⁻¹ ± 19.2 SD on day 10. The milk with moderate protein and high fat content suits the fast growth rate and heat loss of the pups. Although lactation imposes a severe energy load on the LF, this burden is mainly expressed by the up to fivefold increase in energy intake in food where Mspo₂ increases only up to 1.5 times the normal value. The energy requirements of simultaneous lactation and pregnancy are not simple additives. They seem to overlap partially and thus are energetically less demanding

Effects of Hypoxia on Oxygen consumption by two species of Freshwater Mussel (Unionacea: Hyriidae) from the River Murray

The mussel Alathyria jacksoni typically occurs in the main rivers of the Murray-Darling Basin and not in slow-flowing or standing waters. Conversely, Velesunio ambiguus is typical of billabongs and creeks and rarely occurs in big rivers except in the vicinity of impoundments. The exclusion of V. ambiguus from the main rivers probably reflects its weak anchorage, whereas the exclusion of A. jacksoni from billabongs may reflect its inability to withstand low levels of oxygen (hypoxia). At normal oxygen levels the mean rates of oxygen consumption for A. jacksoni and V. ambiguus are 21.5 (s.d. = 6.43, n = 17) and 13.5 (s.d. = 5.85, n = 10) �mol g-0.75 (dry tissue) h-1, respectively (a body-mass exponent of 0.75 was included in calculations of the mass-specific oxygen consumption rate). When exposed to declining oxygen, A. jacksoni shows little or no regulatory ability, whereas V. ambiguus maintains a steady rate of oxygen consumption down to 65 torr. Under extreme hypoxia, A. jacksoni loses muscular tone but V. ambiguus closes its values and remains inactive. On removal from water A. jacksoni incurs a significant oxygen debt after 10 days, but V. ambiguus shows no oxygen debt after 15 days. In general, animals adapted to lotic environments may need more oxygen, and may be more susceptible to hypoxia, than those adapted to lentic environments.

Seasonality of torpor and thermoregulation in three dasyurid marsupials

Seasonal variation in the pattern of torpor and temperature regulation was investigated in the closely related arid zone dasyurid marsupialsSminthopsis crassicaudata (17 g),S. macroura (24 g), andDasyuroides byrnei (120 g). The tendency to enter torpor was greater, torpor commenced earlier, torpor duration was longer, and body temperatures (Tb) were lower inSminthopsis spp. than inD. byrnei. The minimum mass-specific rate of oxygen consumption (\(\dot V_{O_2 } \)) of torpid animals was similar among the three species despite the differences in minimumTb. The mass-specific oxygen consumption of normothermic animals was reduced during winter when compared with the summer values in all species, but there was no seasonal variation in normothermicTb in any species. The tendency to enter torpor was incrased during winter. TorpidSminthopsis spp. had lower values ofTb and\(\dot V_{O_2 } \) during winter than during summer;D. byrnei did not show seasonal changes in these variables. These results suggest that seasonal changes in the pattern of thermoregulation and torpor in small dasyurids may be more distinct than in larger species.