Search

Energy management models provide theories and predictions for how animals manage their energy budgets within their energetic constraints, in terms of their resting metabolic rate (RMR) and daily energy expenditure (DEE). Thus, uncovering what associations exist between DEE and RMR is key to testing these models. Accordingly, there is considerable interest in the relationship between DEE and RMR at both inter- and intraspecific levels. Interpretation of the evidence for particular energy management models is enhanced by also considering the energy spent specifically on costly activities (activity energy expenditure [AEE] = DEE - RMR). However, to date there have been few intraspecific studies investigating such patterns. Our aim was to determine whether there is a generality of intraspecific relationships among RMR, DEE, and AEE using long-term data sets for bird and mammal species. For mammals, we use minimum heart rate (fH), mean fH, and activity fH as qualitative proxies for RMR, DEE, and AEE, respectively. For the birds, we take advantage of calibration equations to convert fH into rate of oxygen consumption in order to provide quantitative proxies for RMR, DEE, and AEE. For all 11 species, the DEE proxy was significantly positively correlated with the RMR proxy. There was also evidence of a significant positive correlation between AEE and RMR in all four mammal species but only in some of the bird species. Our results indicate there is no universal rule for birds and mammals governing the relationships among RMR, AEE, and DEE. Furthermore, they suggest that birds tend to have a different strategy for managing their energy budgets from those of mammals and that there are also differences in strategy between bird species. Future work in laboratory settings or highly controlled field settings can tease out the environmental and physiological processes contributing to variation in energy management strategies exhibited by different species.

Fish have a central respiratory pattern generator (CRPG) in the brain stem that initiates activity in a series of cranial nerves innervating respiratory muscles. These nerves burst sequentially in the order of their rostrocaudal distribution in the central nervous system. When respiratory drive is high, this activity spreads caudally to occipital and anterior spinal neurons that project via the hypobranchial nerves to stimulate hypaxial muscles, causing active jaw abduction. The CRPG may also recruit the heart. Fish, like mammals, show respiratory components in the intrinsic variability of heart rate (HRV). Cardiorespiratory synchrony in the dogfish is driven by bursting activity in the cardiac branches of the vagus nerve, which emanates from preganglionic neurons in the dorsal vagal motor nucleus. A respiratory component in HRV is difficult to discriminate in other species, requiring the use of power spectral analysis and the subsequent elimination of aliased components.

Several previous reports, often from studies utilising heavily instrumented animals, have indicated that for teleosts, the increase in cardiac output (Vb) during exercise is mainly the result of an increase in cardiac stroke volume (V(S)) rather than in heart rate (fH). More recently, this contention has been questioned following studies on animals carrying less instrumentation, though the debate continues. In an attempt to shed more light on the situation, we examined the heart rates and oxygen consumption rates (Mo2; normalised to a mass of 1 kg, given as Mo2kg) of six Murray cod (Maccullochella peelii peelii; mean mass+/-SE = 1.81+/-0.14 kg) equipped with implanted fH and body temperature data loggers. Data were determined during exposure to varying temperatures and swimming speeds to encompass the majority of the biological scope of this species. An increase in body temperature (Tb) from 14 degrees C to 29 degrees C resulted in linear increases in Mo2kg (26.67-41.78 micromol min(-1) kg(-1)) and fH (22.3-60.8 beats min(-1)) during routine exercise but a decrease in the oxygen pulse (the amount of oxygen extracted per heartbeat; 1.28-0.74 micromol beat(-1) kg(-1)). During maximum exercise, the factorial increase in Mo2kg was calculated to be 3.7 at all temperatures and was the result of temperature-independent 2.2- and 1.7-fold increases in fH and oxygen pulse, respectively. The constant factorial increases in fH and oxygen pulse suggest that the cardiovascular variables of the Murray cod have temperature-independent maximum gains that contribute to maximal oxygen transport during exercise. At the expense of a larger factorial aerobic scope at an optimal temperature, as has been reported for species of salmon and trout, it is possible that the Murray cod has evolved a lower, but temperature-independent, factorial aerobic scope as an adaptation to the largely fluctuating and unpredictable thermal climate of southeastern Australia.

While optimal diving models focus on the diver's oxygen (O(2)) stores as the predominant factor influencing diving behaviour, many vertebrate species surface from a dive before these stores are exhausted and may commence another dive well after their O(2) stores have been resaturated. This study investigates the influence of hypoxia and also hypercapnia on the dive cycle of tufted ducks, Aythya fuligula, in terms of surface duration and dive duration. The birds were trained to surface into a respirometer box after each dive to a feeding tray so that rates of O(2) uptake (VO2) and carbon dioxide output (VCO2) at the surface could be measured. Although Vco2 initially lagged behind Vo2, both respiratory gas stores were close to full adjustment after the average surface duration, indicating that they probably had a similar degree of influence on surface duration. Chemoreceptors, which are known to influence diving behaviour, detect changes in O(2) and CO(2) partial pressures in the arterial blood. Thus, the need to restore blood gas levels appears to be a strong stimulus to continue ventilation. Mean surface duration coincided with peak instantaneous respiratory exchange ratio due to predive anticipatory hyperventilation causing hypocapnia. For comparison, the relationship between surface duration and O(2) uptake in reanalysed data for two grey seals indicated that one animal tended to dive well after fully restocking its O(2) stores, while the other dived at the point of full restocking. More CO(2) is exchanged than O(2) in tufted ducks during the last few breaths before the first dive of a bout, serving to reduce CO(2) stores and suggesting that hypercapnia rather than hypoxia is more often the limiting factor on asphyxia tolerance during dives. Indeed, according to calculations of O(2) stores and O(2) consumption rates over modal diving durations, a lack of O(2) does not seem to be associated with the termination of a dive in tufted ducks. However, factors other than CO(2) are also likely to be important, and perhaps more so, such as food density and rate of food ingestion. Because some predictive success has been demonstrated for optimal diving models, they should continue to incorporate O(2) stores as a variable, but their validity is likely to be improved by also focusing on CO(2) stores.

The impact of relatively small externally attached time series recorders on some foraging parameters of seabirds was investigated during the austral summer of 1995 by monitoring the diving behaviour of 10 free-ranging king penguins (Aptenodytes patagonicus) over one foraging trip. Time-depth recorders were implanted in the abdominal cavities of the birds, and half of the animals also had dummy loggers attached on their backs. Although most of the diving behaviour was not significantly affected by the external loggers (P0.05), the birds with externally attached loggers performed almost twice as many shallow dives, between 0 and 10 m depth, as the birds without external loggers. These shallow dives interrupted more frequently the deep-diving sequences in the case of birds with external loggers (percentage of deep dives followed by deep dives: 46% for birds with implants only vs. 26% for birds with an external attachment). Finally, the distribution pattern of the postdive durations plotted against the hour of the day was more heterogeneous for the birds with an external package. In addition, these penguins had extended surfacing times between two deep dives compared to birds without external attachments (P0.0001). These results suggest the existence of an extra energy cost induced by externally attached loggers.

Heart rate () and oxygen consumption () were recorded from gentoo penguins walking on a variable-speed treadmill. After an initial increase, and increased linearly with walking speed. A curvilinear regression equation best described the relationship between and . Over a 3-d period, and were recorded continuously from six gentoo penguins that had been injected with doubly labeled water (DLW). When was used to predict over the 3 d, the estimate uwas not significantly different from the measured with an error (-1.0%) that was less than that produced by the DLW method (+ 1.6%). The estimate produced by the technique was also accurate when applied both to shorter periods (30 min) and to periods of activity and inactivity. Seven gentoo penguins were also swum in a water channel, and and were again recorded. The relationship between and determined from the birds in the water channel was not significantly different from that obtained from the walking birds. It is seems reasonable that, since the relationship of most behaviors of the penguin have been determined while the animal is walking and swimming, can be used to predict the metabolic rate of free-ranging animals.

We investigated whether daily O2, consumption (Vo2) could be predicted from heart rate (f(H)) in five exercising barnacle geese (Branta leucopsis) and compared the accuracy of this method with that of the doubly labeled water (DLW) method. The regressions of Vo2 on f(H), based on incremental speed tests, differed among individual birds. The O2 pulse (i. e., Vo2/f(H)) progressively increased with exercise level from 0.22 mL O2 heartbeat-1 during resting to an estimated 0.47 mL O2 heartbeat-1 during flight. Daily Vo2 was generally underestimated (-3.9%) by (individual) resting O2 pulses but overestimated (+8.4%) by linear regressions of Vo2 on f(H). However, it was well predicted (+0.8%) by the O2 pulses appropriate for each exercise level. When using relationships derived from the group of birds, the estimations were generally improved (-3.3% for resting O2 pulse, -0.03% for appropriate O2 pulse) but poorer (+13.6%) for the group linear regression. Some of these predictions were better than the estimation of daily CO2 production (Vco2) by the two-compartment model of the DLW method (average algebraic error of +0.9%). We conclude that f(H) can be used to estimate daily energy expenditure in birds accurately provided that (1) its application is limited to the range of exercise levels in which f(H) has been calibrated against Vo2 and (2a) Vo2-f(H) relationships are determined for each individual bird or (2b) the f(H) measurements of several free-ranging birds are averaged. Heart rate can also be used to indicate within-day variation in energy expenditure.

Miniature pulsed Doppler flow probes were implanted on the left pulmonary artery and left aorta of juvenile green turtles (Chelonia mydas) to measure the cardiovascular changes associated with intermittent ventilation at rest and its conversion to a continuous pattern during swimming at 0.4 m·s⁻¹. In resting turtles, respiratory frequency, tidal volume, and oxygen uptake were also measured and convection requirements and the oxygen-content difference across the lungs calculated. Respiration-related increases in heart rate and blood flow were most pronounced in resting turtles in which bursts of breaths, rather than single breaths, occurred in ventilatoryperiods. Hypoxia (10% O₂) produced continuous ventilation in resting turtles, and pulmonary blood flow was maintained at a high, steady level Increases in heart rate and both left pulmonary and left aortic blood flow were associated with the sevenfold increase in ventilation frequency observed during swimming. Most of the increase in left pulmonary flow du...