Effects of meal size, clutch, and metabolism on the energy efficiencies of juvenile Burmese pythons, Python molurus

We explored meal size and clutch (i.e., genetic) effects on the relative proportion of ingested energy that is absorbed by the gut (apparent digestive efficiency), becomes available for metabolism and growth (apparent assimilation efficiency), and is used for growth (production efficiency) for juvenile Burmese pythons (Python molurus). Sibling pythons were fed rodent meals equaling 15%, 25%, and 35% of their body mass and individuals from five different clutches were fed rodent meals equaling 25% of their body mass. For each of 11–12 consecutive feeding trials, python body mass was recorded and feces and urate of each snake was collected, dried, and weighed. Energy contents of meals (mice and rats), feces, urate, and pythons were determined using bomb calorimetry. For siblings fed three different meal sizes, growth rate increased with larger meals, but there was no significant variation among the meal sizes for any of the calculated energy efficiencies. Among the three meal sizes, apparent digestive efficiency, apparent assimilation efficiency, and production efficiency averaged 91.0%, 84.7%, and 40.7%, respectively. In contrast, each of these energy efficiencies varied significantly among the five different clutches. Among these clutches production efficiency was negatively correlated with standard metabolic rate (SMR). Clutches containing individuals with low SMR were therefore able to allocate more of ingested energy into growth.     

Food,feeding rates and assimilation in woodland snails

Summary Analyses of the faeces of seven species of woodland, litterdwelling snails (Marpessa laminata, Clausilia bidentata, Oxychilus cellarius, O. alliarius, Discus rotundatus, Arianta arbustorum and Hygromia striolata), showed that all feed predominently on higher plant material, be it living or dead. H. striolata and A. arbustorum took more chlorophyll-containing plant material than the other species, D. rotundatus had a significant amount of fungus in its faeces, while the faeces of O. cellarius and O. alliarius contained significant amounts of animal material.The consumption and assimilation of a variety of foods by molluscs was studied in the laboratory using an ash-ratio technique, which had been shown to give similar results to those obtained by the standard gravimetric technique. The assimilation efficiency of the molluscs was found to be temperature independent, but ingestion rates and absolute assimilation rates were temperature dependent. The assimilation efficiency of D. rotundatus on living plant material (three field layer species) was 44.8±4.43% that of H. striolata (Urtica dioica) was 52.4±8.78% while O. cellarius and H. aspersa (on Lactuca sativa) had assimilation efficiencies of 70.2±4.40% and 53.50±6.04% respectively. The results fall within the range shown by other invertebrate groups. The assimilation efficiency of D. rotundatus on leaf litter (a mean of 49.1±1.88% on five litter types) was higher than that shown by other invertebrates, probably due to the presence of gut polysaccharidases. The assimilation on dead earthworm as animal material (86.9±2.53% with O. alliarius and 78.6±6.73% with D. rotundatus) was in the range of true carnivores. Consumption rates were more variable; Urtica dioica, amongst living material, was eaten in greatest quantity; Acer pseudoplatanus, Castanea sativa and Quercus robur litter were eaten in greater quantity than Fagus sylvatica and Carpinus betulus. Consumption was examined in terms of percentage body weight.     

Consequences of dam‐altered thermal regimes for a riverine herbivore's digestive efficiency,growth and vulnerability to predation

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Adaptations for avian frugivory: assimilation efficiency and gut transit time of Manacus vitellinus and Pipra mentalis

Summary I examined the digestive physiology of two avian frugivores, the golden-collared manakin, Manacus vitellinus, and the red-capped manakin, Pipra mentalis, to discover how these birds extract energy from fruit. Using 14 species of fruit in the natural diet of manakins, I examined the assimilation of nutrients from fruit pulp, fruit passage rates, seed passage rates, and gut morphology. Fruits in the manakins' diets had high water content (average, 84%) and low nutrient concentrations (3 kJ/g wet pulp; 17 kJ/g dry pulp; 1% nitrogen/g dry pulp). Manacus and Pipra did not differ in the average assimilation of energy in fruit pulp (63%), although it varied from 37 to 84% depending on fruit species. Assimilation of total nonstructural carbohydrates in the fruit pulp was very high (86–98%) in both species. Gut evacuation was rapid; maximum transit time of a labeled fruit was 30 min. Seeds passed through the gut faster (Manacus: 15 min; Pipra: 12 min) than the accompanying fruit epidermis (both spp: 22 min). Manakins regurgitated large seeds (>5 mm diameter) in 7 to 9 min. Rapid gut passage time, high assimilation of nonstructural carbohydrates, and the selective regurgitation and rapid elimination of bulky seeds enable manakins to process a large volume of food per day. By increasing rates of fruit intake and gut passage, manakins can effectively increase total nutrient uptake. These adaptations of manakins are requisite for harvesting sufficient nutrients from fruit, due to its low nutrient density, high water content, and bulky seeds.     

Digestive performance in five Mediterranean lizard species: effects of temperature and insularity

Temperature sensitivity of digestive processes has important ramifications for digestive performance in ectothermic vertebrates. We conducted a comparative analysis of temperature effects on digestive processes [gut passage times (GPTs) and apparent digestive efficiencies (ADEs)] in five lacertid lizards occurring in insular (Podarcis erhardii, P. gaigeae), and mainland (P. muralis, P. peloponnesiaca, Lacerta graeca) Mediterranean environments. GPTs were negatively correlated to temperature with mainland taxa having 10–20% longer GPTs than island taxa. In contrast to previous studies that estimate ADEs using bomb calorimetry, we compare ADEs by analyzing discrete efficiencies for lipids, sugars and proteins at three temperature regimes (20, 25, and 30°C); each of these categories produces different results. ADEs for lipids and sugars showed a monotonic increase with temperature whereas ADEs for proteins decreased with temperature. Island taxa had consistently higher ADEs than their mainland counterparts for lipids and for proteins but not for sugars. They are characterized by superior energy acquisition abilities despite significantly shorter GPTs. Their increased digestive performance relative to the mainland species appears to allow them to maximize energy acquisition in unproductive island environments where food availability is spatially and seasonally clustered.     

Thermophilic response post feeding in Pleurodema nebulosum (Anura: Leptodactylidae) from Monte desert,Argentina.

We studied the thermophilic response to feeding of a typical desert adapted anuran from the Monte Desert. Our aim was to evaluate thermal changes in the selected body temperature of adult frogs of Pleurodema nebulosum, and measure the intestinal passage time, and food digestion. Our results show that after feeding, they selected higher micro-environmental temperatures ~ + 2 °C than frogs that remained starved. Pleurodema nebulosum would present a postprandial thermophilic response. The time of retention of food in the digestive tract was thermo-dependent, being lower in those individuals who were incubated at high temperatures (25 °C) compared to those subjected to lower temperatures (20 °C). Although we did not detect effects of temperature on digestive efficiency, the mass of faecal material indicates an increase at temperatures closer to the selected ones, suggesting that the defecation rate is influenced by temperature. Laiuoperinae frogs are characterized by explosive breeding behavior and fast growing rate. The digestive efficiency is essential for acquiring energy necessary for growth, reproduction and refuge-seeking, among others. In this framework, the differential selection of temperatures between moments of fasting and feeding allows the frogs to maintain a high digestive efficiency, maximizing the absorption of nutrients.     

Effects of meal size, clutch, and metabolism on the energy efficiencies of juvenile Burmese pythons, Python molurus.

We explored meal size and clutch (i.e., genetic) effects on the relative proportion of ingested energy that is absorbed by the gut (apparent digestive efficiency), becomes available for metabolism and growth (apparent assimilation efficiency), and is used for growth (production efficiency) for juvenile Burmese pythons (Python molurus). Sibling pythons were fed rodent meals equaling 15%, 25%, and 35% of their body mass and individuals from five different clutches were fed rodent meals equaling 25% of their body mass. For each of 11-12 consecutive feeding trials, python body mass was recorded and feces and urate of each snake was collected, dried, and weighed. Energy contents of meals (mice and rats), feces, urate, and pythons were determined using bomb calorimetry. For siblings fed three different meal sizes, growth rate increased with larger meals, but there was no significant variation among the meal sizes for any of the calculated energy efficiencies. Among the three meal sizes, apparent digestive efficiency, apparent assimilation efficiency, and production efficiency averaged 91.0%, 84.7%, and 40.7%, respectively. In contrast, each of these energy efficiencies varied significantly among the five different clutches. Among these clutches production efficiency was negatively correlated with standard metabolic rate (SMR). Clutches containing individuals with low SMR were therefore able to allocate more of ingested energy into growth.     

The diet and digestive energetics of an Australian short-necked turtle, Emydura macquarii

We described the diet of Emydura macquarii, an omnivorous turtle from south-eastern Australia, compared its digestive performance on diets of fish or plants at two temperatures, and related how both diet and temperature affect its food selection in nature. Filamentous algae constituted 61% of the stomach content of E. macquarii. The turtles rarely fed on motile prey, but selected carrion from the lagoon bottom and terrestrial insects (Diptera, Hymenoptera and Coleoptera) trapped on the surface of the water. Digestive efficiency of E. macquarii was affected little by body temperature, in contrast to consumption rates and rates of passage which were strongly influenced by both temperature and diet. In combination, these responses resulted in a slower rate of digestion at 20°C than at 30°C. Digestive efficiency of E. macquarii on a herbivorous diet at 30°C (49%) was about half that of turtles on a carnivorous diet (91%), but they had longer transit times (118 h on the plant diet versus 70 h). Lower consumption rates and longer mean retention times in turtles fed plants compared those fed fish relate to slower digestive processing of the plant. Rapid processing and higher consumption rates of fish by E. macquarii resulted in higher energy gains compared to turtles consuming plants (almost 100 times more energy at 30°C). The laboratory results suggest that fish carrion and aquatic and terrestrial invertebrates are probably essential dietary items of E. macquarii in the wild, because its metabolic requirements cannot be met from aquatic macrophytes alone.     

Effects of acclimation and acute temperature change on specific dynamic action and gastric processing in the green shore crab, Carcinus maenas

The effects of temperature acclimation and acute temperature change were investigated in postprandial green shore crabs, Carcinus maenas. Oxygen uptake, gut contractions and transit rates and digestive efficiencies were measured for crabs acclimated to either 10 °C or 20 °C and subsequently exposed to treatment temperatures of 5, 15, or 25 °C. Temperature acclimation resulted in a partial metabolic compensation in unfed crabs, with higher oxygen uptake rates measured for the 10 °C acclimated group exposed to acute test temperatures. The Q₁₀ values were higher than normal, probably because the acute temperature change prevented crabs from fully adjusting to the new temperature. Both the acclimation and treatment temperature altered the characteristics of the specific dynamic action (SDA). The duration of the response was longer for 20 °C acclimated crabs and was inversely related to the treatment temperature. The scope (peak oxygen consumption) was also higher for 20 °C acclimated crabs with a trend towards an inverse relationship with treatment temperature. Since the overall SDA (energy expenditure) is a function of both duration and scope, it was also higher for 20 °C acclimated crabs, with the highest value measured at the treatment temperature of 15 °C. The decline in total SDA after acute exposure to 5 and 25 °C suggests that both cold stress and limitations to oxygen supply at the temperature extremes could be affecting the SDA response. The contractions of the pyloric sac of the foregut region function to propel digesta through the gut, and contraction rates increased with increasing treatment temperature. This translated into faster transit rates with increasing treatment temperatures. Although pyloric sac contractions were higher for 20 °C acclimated crabs, temperature acclimation had no effect on transit rates. This suggests that a threshold level in pyloric sac contraction rates needs to be reached before it manifests itself on transit rates. Although there was a correlation between faster transit times and the shorter duration of the SDA response with increasing treatment temperature, transit rates do not make a good proxy for calculating the SDA characteristics. The digestive efficiency showed a trend towards a decreasing efficiency with increasing treatment temperature; the slower transit rates at the lower treatment temperatures allowing for more efficient nutrient absorption. Even though metabolic rates of 10 °C acclimated crabs were higher, there was no effect of acclimation temperature on digestive efficiency. This probably occurred because intracellular enzymes and digestive enzymes are modulated through different control pathways. These results give an insight into the metabolic and digestive physiology of Carcinus maenas as it makes feeding excursions between the subtidal and intertidal zones.     

Effect of chronic low body temperature on feeding and gut passage in a plethodontid salamander

Although feeding in some plethodontid salamander species, such as Dusky Salamanders (Desmognathus, family Plethodontidae), occurs at short-term (acute) low temperature below 5 °C, it is unknown whether feeding, digestion, and gut passage continue to occur during periods of long-term (chronic) low temperature. We performed a controlled laboratory experiment to examine the effect of several chronic low environmental temperatures on both feeding and gut passage in semiaquatic Spotted Dusky Salamanders (D. conanti). We quantified salamander feeding and defecation for different experimental groups maintained for many weeks at a constant temperature of 4, 7, 10, or 13 °C. Although feeding frequency, number of prey items consumed per feeding, and defecation frequency were significantly less for individuals at 4 °C than for individuals at 10 or 13 °C, salamanders continued to feed, defecate, and maintain body mass for 12 weeks at 4 °C. The ratio of the number of fecal pellets produced to the number of prey items consumed each week by individuals did not significantly decrease at 4 °C, which indicates gut passage was sustained at this temperature. Because both time between feeding and time between defecation were similarly affected by prolonged low temperature, the significant decrease in feeding frequency at 4 °C may depend, in part, on a decrease in digestive function and an extended time for gut passage at low temperature. We conclude that most individuals of D. conanti can feed, digest, and maintain body mass for several months at constant low temperature down to 4 °C. Our results support a growing body of data that indicate some plethodontid salamanders may acquire energy at environmental temperatures only a few degrees above freezing.     

华北丽斑麻蜥食物同化和疾跑速的热依赖性

作者研究山西阳泉丽斑麻蜥(Eremias argus)成体的选择体温、热耐受性及食物同化和疾跑速的热依赖性。选择体温、临界低温和临界高温无显著的两性差异,分别为36·0℃、1·0℃和44·9℃。在实验温度范围内,体温显著影响食物通过时间、日摄食量、日粪尿排量、表观消化系数和同化效率。食物通过时间在26 -34℃范围内随体温升高而缩短,在更高的体温下则延长。蜥蜴在30、32、34和36℃体温下明显摄入较多的食物、排出明显较多的粪尿。34℃和36℃下的表观消化系数和同化效率大于其它更低或更高温度下的对应数值,但这两个变量未因体温变化而呈现清晰的规律性变化。疾跑速在18 -36℃范围内随体温升高而加快,在38℃体温下则减缓。36℃或附近体温最适合疾跑速。疾跑速最适体温接近蜥蜴的选择体温,表明蜥蜴疾跑速的最适温度可能与其选择体温密切相关[动物学报52 (2) : 256 -262 , 2006]。     

Prey envenomation does not improve digestive performance in Taiwanese pit vipers (Trimeresurus gracilis and T. stejnegeri stejnegeri)

It has been a common belief that snake venom may help in the digestion of its prey, although direct examples and supporting evidence have not been sufficient. To address this, the present study examined whether pre-injecting natural amounts of pit viper venom into experimental mice may accelerate their digestion by the snakes or gain energy benefit as compared to the control without the envenomation. Live adults of two Asian pit viper species Trimeresurus gracilis and T. stejnegeri stejnegeri, which inhabit the cold and warm environment respectively, were the subjects studied herein. A natural dose of 1.2 mg of each of the pit viper venom in phosphate-buffered saline (PBS) was injected into the mouse (about 10% of the snake mass) before it was being fed to the same species of vipers, while the pit vipers in control group were given mouse injected with sterile PBS. The snakes were kept at 14 °C or 24 °C, and parameters of gut passage time, costs of digestion, and/or digestive efficiency were measured. The results did not support the hypotheses that envenomation facilitates prey digestion. The venom in fact caused longer first defecation time and lower assimilation energy at 14 °C. Besides, the time to reach the oxygen consumption peak, and the first defecation time of T. s. stejnegeri were longer than that of T. gracilis.     

Digestive constraints on an aquatic carnivore: effects of feeding frequency and prey composition on harbor seals

We hypothesized that increased feeding frequency in captive harbor seals would increase nutrient loads and thus reduce retention time and the digestive efficiency of natural prey. We measured daily feed intake and excretion during 6 feeding trials and fed herring (49% lipid), pollock (22% lipid) or an equal mix of each diet over 24 months. Animals were accustomed to feeding at either high or low frequency. Body mass and intake did not vary with season. Although mean retention times were similar between diets and feeding frequencies, solute and particulate digesta markers separated at high feeding frequency. Consistent dry matter digestibility resulted in greater gut fill from pollock than from herring. Digestible energy intakes from pollock were approximately 25% greater than from either herring or the mixed diet. Lipid digestibility of herring declined from 90% to 50% when lipid intake exceeded 60 g kg^–0.75 day^–1. Our hypothesis of a trade-off between intake and digestion was not supported for protein but was supported for lipid. Results of this study imply that a flexible digestive system for harbor seals can compensate for ingesting prey of lower energy density by increasing gut fill and enhancing protein and lipid assimilation, to sustain digestible energy intake.Abbreviations DM dry matter - DEI digestible energy intake - DIT diet-induced thermogenesis - FF feeding frequency - MRT mean retention time Communicated by: G. Heldmaier     

Interactive effects of season and temperature on enzyme activities,tissue and whole animal respiration in roach,Rutilus rutilus

Synopsis This paper reviews investigations on the ecophysiology of a population of roach, Rutilus rutilus, from a subalpine oligotrophic lake in the Austrian Tirol. Metabolic responses to season and temperature were studied in whole animals, tissues and selected enzymes. The exponent of the relationship between body mass and three levels of the metabolic rate of acclimated fish was 0.82 ± 0.02, 0.60 ± 0.15, and 0.75 ± 0.01 at 4, 12, and 20° C respectively. Various combinations of long-term acclimation to constant or seasonally fluctuating temperatures and long-term (up to 14 days) monitoring of O₂ at the acclimation temperature led to the conclusion that the aerobic power of fish swimming in the routine mode does not show any sign of being temperature compensated. On the other hand, there are several indications that the energy expenditure of spontaneously swimming fish is adjusted to the seasonal pattern of environmental change and that these responses of metabolism and behaviour are controlled by both endogenous and exogenous factors. The rate of oxygen consumption of gill and muscle tissue brei from fish caught during a seasonal cycle and measured at 15° C appears to follow closely the reproductive and gonadal cycle of the living fish. The same holds for the activities of phosphofructokinase, acetoacetyl-CoA thiolase, and cytochrome oxidase. On the other hand, the Na⁺, K⁺-ATPase of the kidney shows near perfect temperature compensation when fish acclimated to 5 and 25° C are compared, whereas an equally pronounced case of inverse temperature acclimation has been reported for the activity of digestive enzymes in the gut. Summarizing these data it is pointed out that the temperature relationship of a poikilothermic organism is the sum of often very diverse temperature relationships of specific metabolic and behavioural functions. In the case of the roach, strong effects of acclimation temperature on the molecular level, sometimes in the opposite direction, combine with seasonal effects on enzyme activities and tissue respiration. However, on the whole animal level the fish behave as strictly non-compensating poikilotherms, the reproductive cycle being the only detectable influence capable of modulating the basic temperature relationship of energy expenditure.     

Effects of temperature on food ingestion rate and absorption,retention, and equilibrium burden of phosphorus in an aquatic snail,Goniobasis clavaeformis Lea *

The effects of sublethal temperatures on feeding rates and phosphorus dynamics of a freshwater snail, Goniobasis clavaeformis Lea, were determined and feeding rates were measured at four temperatures. The food source was aufwuchs labelled with radioactive phosphorus. A model was developed to elucidate the results of this type of study. Food ingestion rate increased with increasing temperature up to 14°C and then decreased at temperatures above 14°C. The elimination rate of absorbed phosphorus increased with increasing temperature throughout the entire range of experimental temperatures, 10-19.3°C. Mean retention times of absorbed phosphorus i n Goniobasis were estimated to be 34, 24, 10, and 6 days at 10, 13.8, 15, and 193°C, respectively. Mean retention time of unabsorbed ³²P in the gut of this species as a function of temperature followed the same temperature relationship as that of ingestion rate. The absorption efficiency of phosphorus was estimated to be constant at about 39% for ail experimental temperatures, although the data suggest that the absorption ePRciency may have been related inversely to the rate of gut clearance or directly to the residence time of food in the gut. The equilibrium body load of phosphorus at each experimental temperature was estimated based on concentrations of stable phosphorus in the food source and the kinetics of ³²P in Goniobasis. The equilibrium body burden of phosphorus in Goniobasis increased with increasing temperatures up to a maximum at 11–12°C and then decreased at temperatures above 12°C.     

Effect of ambient temperature and energy demands on digestive functions in leaf-eared mice (Phyllotis darwini) from central Chile

 The leaf-eared mouse, Phyllotis darwini, is a nocturnal rodent inhabiting the semiarid and Mediterranean habitats of northern and central Chile. Previous observations suggested that in the field, individuals may change food intake according to seasonal changes in ambient temperature. We therefore anticipated that P. darwini should increase food intake in response to lower ambient temperature. As predicted, results of food trials and digestive measurements demonstrated that P. darwini increases food intake and assimilation at lower ambient temperatures but does not increase food mean retention time. At lower ambient temperatures, individuals increase digestive tract size thus improving body mass maintenance and perhaps survival during winter. Received 17 June 1996 / Revised: 25 February 1997 / Accepted: 13 March 1997     

Effects of water temperature and initial weight on growth,digestion and energy budget of yellow catfish Pelteobagrus fulvidraco (Richardson, 1846)

The effects of water temperature and body weight on feeding, growth, and energy budget were inevitable in the yellow catfish Pelteobagrus fulvidraco (Richardson, 1846), an important fish cultivated in China. This study explores the interaction of water temperature and body weight on both energy utilization strategy and energy conversion efficiency to promote further healthy culture of yellow catfish. Fish with body weights of 6 g (Group S), 16 g (Group M) and 35 g (Group B) were reared in 15 circular glass steel cylinders 80 cm in diameter × 70 cm in height (180 L) at water temperatures of 21, 24, 27, 30 and 33°C (3 replicates for each temperature) for 42 days to investigate effects of water temperature and body weight on the feeding, growth, digestion and energy budget in yellow catfish. Results showed that the levels of dry matter, protein and energy in the body were significantly affected by water temperature (p < .05). Feeding, growth, feed conversion efficiency, digestion and energy allocation parameters were significantly related to both water temperature and body weight (p < .05). Yellow catfish had higher maximal food consumption (C_max), food intake rate, specific growth rate, food conversion efficiency, appear digestibility coefficient, and growth energy allocation (G) at 24–30°C, and optimal growth at a water temperature of 27°C. Two‐factor analysis of variance revealed that there was reciprocation of both water temperature and body weight on the above parameters. At the optimal temperature of 27°C, the value of energy for growth (G) was the highest, and the value of energy for feces (F) produced was the lowest. Yellow catfish with various body weights had energy budget equations of 100 A = 63.70 R + 36.30 G in Group S, 100 A = 62.54 R + 37.46 G in Group M, and 100 A = 67.47 R + 32.53 G in Group B if the equations were described as percentage of the proportion of the assimilation energy. Therefore, the optimal temperature was 27°C according to its feeding, growth and digestion.     

Rate of digesta passage in the Philippine flying lemur,Cynocephalus volans

The rate of digesta passage was measured in five captive Philippine flying lemurs (Cynocephalus volans). These animals were force fed capsules containing known quantities of either particulate or soluble markers. The volumes of the gastrointestinal tracts of three flying lemurs were determined based on the wet weight of the contents of each section of the gut. The mean rate of digesta passage was 14.37±3.31 h when determined using the particulate marker and 21.9±0.03 h when determined using the soluble marker. The values based on the particulate marker are between 2% and 10% of similar values for other arboreal folivores. The morphology of the gastrointestinal system of the Philippine flying lemur is similar to that of other hindgut fermenters. Flying lemurs have a simple stomach and a large caecum. The total gut capacity of the Philippine flying lemur is similar to that of other herbivores, but is slightly smaller than that of either the koala (Phascolarctos cinereus), a hindgut fermenter, or the three-toed sloth (Bradypus variegatus), a foregut fermenter. These data suggest that flying lemurs deal with the problems of a folivorous diet very differently than some other arboreal mammals. Phascolarctos cinereus and Bradypus variegatus may represent one extreme with Cynocephalus volans representing the other extreme along a continuum of foraging strategies that are compatible with the arboreal folivore lifestyle.Abbreviations bw body weight - EDTA ethylenediaminetetraaceticacid - MR metabolic rate - i mean rate of passage - t _exp expected time to appearance - t _o time to first appearance     

Milk intake,growth and energy consumption in pups of ice-breeding grey seals (Halichoerus grypus) from the Gulf of St. Lawrence,Canada

In this study we document growth, milk intake and energy consumption in nursing pups of icebreeding grey seals (Halichoerus grypus). Change in body composition of the pups, change in milk composition as lactation progresses, and mass transfer efficiency between nursing mothers and pups are also measured. Mass transfer efficiency between mother-pup pairs (n=8) was 42.5±8.4%. Pups were gaining a daily average of 2.0±0.7 kg (n=12), of which 75% was fat, 3% protein and 22% water. The total water influx was measured to be 43.23±8.07 ml·kg^-1·day^-1. Average CO₂ production was 0.85±0.20 ml·g^-1·h^-1, which corresponds to a field metabolic rate of 0.55±0.13 MJ·kg^-1·day^-1, or 4.5±0.9 times the predicted basal metabolic rate based on body size (Kleiber 1975). Water and fat content in the milk changed dramatically as lacation progressed. At day 2 of nursing, fat and water content were 39.5±1.9% and 47.3±1.5%, respectively, while the corresponding figures for day 15 were 59.6±3.6% fat and 28.4±2.6% water. Protein content of the milk remained relatively stable during the lactation period with a value of 11.0±0.8% at day 2 and 10.4±0.3% at day 15. Pups drank an average of 3.5±0.9 kg of milk daily, corresponding to a milk intake of 1.75 kg per kg body mass gained. The average daily energy intake of pups was 82.58±19.80 MJ, while the energy built up daily in the tissue averaged 61.72±22.22 MJ. Thus, pups assimilated 74.7% of the energy they received via milk into body tissue. The lactation energetics of ice-breeding grey seals is very similar to that of their land-breeding counterparts.Abbreviations bm body mass - BMR basal metabolic rate - FMR field metabolic rate - IU international unit - RQ respiration quotient - HTO tritiated water - HT¹⁸O doubly labeled water - TBW total body water - VHF very high frequency     

The effect of temperature on the pattern of torpor in a marsupial hibernator

Physiological variables of torpor are strongly temperature dependent in placental hibernators. This study investigated how changes in air temperature affect the duration of torpor bouts, metabolic rate, body temperature and weight loss of the marsupial hibernator Burramys parvus (50 g) in comparison to a control group held at a constant air temperature of 2°C. The duration of torpor bouts was longest (14.0±1.0 days) and metabolic rate was lowest (0.033±0.001 ml O₂·g^-1·h^-1) at2°C. At higher air temperatures torpor bouts were significantly shorter and the metabolic rate was higher. When air temperature was reduced to 0°C, torpor bouts also shortened to 6.4±2.9 days, metabolic rate increased to about eight-fold the values at 2°C, and body temperature was maintained at the regulated minimum of 2.1±0.2°C. Because air temperature had such a strong effect on hibernation, and in particular energy expenditure, a change in climate would most likely increase winter mortality of this endangered species.Abbreviationst STP standard temperature and pressure - T _a air temperature - T _b body temperature - VO₂ rate of oxygen consumption