Variation in daily and seasonal foraging routines of non-breeding barnacle geese (Branta leucopsis): working harder does not overcome environmental constraints

This study describes the changes in stored body fat in Svalbard barnacle geese Branta leucopsis over the non-breeding period, and uses behavioural patterns to explain the variation in body fat stores. It was predicted that foraging effort would: (1) increase at low food densities; (2) increase when days were short; (3) decrease in smaller flocks; (4) be bimodally distributed throughout the day for long days, but constant for short days. Time constraints were found to be the major driving force behind foraging decisions during the shortest days of mid-winter, whereas food density was found to drive decisions during longer days. Field observations of fat stores showed that fat was rapidly accumulated at the start and end of the non-breeding period, but that fat stores remained constant during mid-winter. It is suggested that day length prevented a positive fat storage rate in mid-winter through the limitation of foraging time, even though foraging effort was high during this period. During a single day, evidence for a bimodal foraging routine was found, where feeding activity was concentrated in the early morning and late afternoon periods. This pattern was found in the full range of day lengths, which suggests that even for short days, feeding must be interrupted so that other essential activities can be conducted. It is concluded that the behavioural choices of barnacle geese were constrained by environmental conditions, and that these behavioural patterns allow the variation in fat stores to be explained.     

Protein appetite is increased after central leptin-induced fat depletion

Leptin reduces body fat selectively, sparing body protein. Accordingly, during chronic leptin administration, food intake is suppressed, and body weight is reduced until body fat is depleted. Body weight then stabilizes at this fat-depleted nadir, while food intake returns to normal caloric levels, presumably in defense of energy and nutritional homeostasis. This model of leptin treatment offers the opportunity to examine controls of food intake that are independent of leptin's actions, and provides a window for examining the nature of feeding controls in a "fatless" animal. Here we evaluate macronutrient selection during this fat-depleted phase of leptin treatment. Adult, male Sprague-Dawley rats were maintained on standard pelleted rodent chow and given daily lateral ventricular injections of leptin or vehicle solution until body weight reached the nadir point and food intake returned to normal levels. Injections were then continued for 8 days, during which rats self-selected their daily diet from separate sources of carbohydrate, protein, and fat. Macronutrient choice differed profoundly in leptin and control rats. Leptin rats exhibited a dramatic increase in protein intake, whereas controls exhibited a strong carbohydrate preference. Fat intake did not differ between groups at any time during the 8-day test. Despite these dramatic differences in macronutrient selection, total daily caloric intake did not differ between groups except on day 2. Thus controls of food intake related to ongoing metabolic and nutritional requirements may supersede the negative feedback signals related to body fat stores.     

The significance of the moult cycle to cold tolerance in the Antarctic collembolan Cryptopygus antarcticus

Research into the ecophysiology of arthropod cold tolerance has largely focussed on those parts of the year and/or the life cycle in which cold stress is most likely to be experienced, resulting in an emphasis on studies of the preparation for and survival in the overwintering state. However, the non-feeding stage of the moult cycle also gives rise to a period of increased cold hardiness in some microarthropods and, as a consequence, a proportion of the field population is cold tolerant even during the summer active period.In the case of the common Antarctic springtail Cryptopygus antarcticus, the proportion of time spent in this non-feeding stage is extended disproportionately relative to the feeding stage as temperature is reduced. As a result, the proportion of the population in a cold tolerant state, with low supercooling points (SCPs), increases at lower temperatures.We found that, at 5 °C, about 37% of the population are involved in ecdysis and exhibit low SCPs. At 2 °C this figure increased to 50% and, at 0 °C, we estimate that 80% of the population will have increased cold hardiness as a result of a prolonged non-feeding, premoult period. Thus, as part of the suite of life history and ecophysiological features that enable this Antarctic springtail to survive in its hostile environment, it appears that it can take advantage of and extend the use of a pre-existing characteristic inherent within the moulting cycle.     

The fat body of bullfrog (Lithobates catesbeianus) tadpoles during metamorphosis: changes in mass, histology, and melatonin content and effect of food deprivation

The fat body of Lithobates catesbeianus (formerly Rana catesbeiana) tadpoles was studied during metamorphosis and after food deprivation in order to detect changes in its weight, adipocyte size, histology, and melatonin content. Bullfrog tadpoles have large fat bodies throughout their long larval life. Fat bodies increase in absolute weight, and weight relative to body mass, during late stages of prometamorphosis, peaking just before climax, and then decreasing, especially during the latter stages of transformation into the froglet. The climax decrease is accompanied by a reduction in size of adipocytes and a change in histology of the fat body such that interstitial tissue becomes more prominent. Food deprivation for a month during early prometamorphosis significantly decreased fat body weight and adipocyte size but did not affect the rate of development. However, food restriction just before climax retarded development, suggesting that the increased nutrient storage in the fat body before climax is necessary for metamorphic progress. Melatonin, which might be involved in the regulation of seasonal changes in fat stores, stayed approximately at the same level during most of larval life, but increased sharply in the fat body during the late stages of climax. The findings show that the rate of development of these tadpoles is not affected by starvation during larval life as long as they can utilize fat body stores for nourishment. They also suggest that the build up of fat body stores just before climax is necessary for progress during the climax period when feeding stops.     

Energetics of lactation in harp seals (Phoca groenlandica) from the gulf of St. Lawrence,Canada

 This study reports the findings of an integrated, comprehensive analysis of lactation energetics in harp seals conducted using longitudinal measurements of mass, body composition and milk composition from mother-pup pairs in conjunction with water flux measurements in pups. The nursing period of harp seals is a short, intense and relatively efficient period of energy transfer from mothers to pups. The average daily milk intake for pups was 3.65±0.24 kg which is equivalent to 79.5 MJ of energy. Eighty-one per cent of the energy received in the milk was metabolisable and 66% of the energy was stored by the pups as body tissue. The field metabolic rate of pups was 3.9±0.4 time basal metabolic rate. The pups were growing at a rate of 2.2 kg per day during the nursing period. The distribution of this mass gain varied in terms of tissue composition, depending on the age of the pups, but over the whole nursing period approximately half of the tissue was stored as fat. Harp seal mothers lost an average of 3.1 kg per day during lactation which was composed of 37% water, 50% fat, 11% protein and 2% ash. Mothers spent half of their time during the lactation period actively diving and only one-third of their time on the surface of the ice. Milk compositional changes followed the normal phocid pattern with increasing fat content and decreasing water content as lactation progressed. The mean mass transfer efficiency was 73%. However, this value cannot be used without qualification because female harp seals in this study fed to varying degrees, consuming an estimated 0–4.8 kg of fish per day. Feeding does not appear to be required in order to achieve the energy requirements for lactation, given the energy stores possessed by females, and some females do fast through the entire period so feeding may be considered opportunistic in nature. Accepted: 25 April 1996     

Lability of fat stores in peripubertal wild house mice

Summary Traditionally, the adaptive value of mammalian white fat stores is considered in relation to longterm needs such as providing protection against the vagaries of winter or signalling the reproductive system when energy reserves are sufficient to risk pregnancy. As shown here, the fat stores of young house mice could not serve such needs. Despite prolonged acclimation and excess nesting material, food deprivation at 10°C significantly lowered the fat stores of peripubertal female house mice in only 12 h, and would exhaust them in 30 h. Even close to thermoneutrality (24°C) the calculated time to exhaustion was only 70 h. The fat stores of a young house mouse are obviously too meager to offer any meaningful protection over a winter of several months duration, or even over a 5–6-week cycle of pregnancy and lactation. Furthermore, in a wild habitat where food availability and ambient temperature can vary rapidly and greatly, such fat stores would be too labile to effectively coordinate puberty with somatic development.     

Lipid dynamics in the viperine snake, Natrix maura, from the Ebro Delta (NE Spain)

Body reserves play a major role in several aspects of vertebrate biology. Accurate identification and quantification of body reserves constitute a useful contribution to the better understanding of the energetic costs of reproduction and the implication of food availability in life history traits of organisms. In this study, lipid content in fat bodies, liver and muscle of the viperine snake (Natrix maura) were measured along an active season. Samples were collected monthly from a natural population of the Ebro Delta Natural Park (NE Spain). This methodology pointed out that lipids stored in fat bodies were the main energetic source during reproduction. In addition, lipids stored in liver appeared to be critical for vitellogenesis, while lipids stored in muscle turned out to be a supplementary energetic resource to fuel reproductive effort. Relationships between changes in body reserves and prey availability in canals of the Ebro Delta were also considered. In males, lipid reserves presented a positive correlation with food availability. On the contrary, lipid reserves in female viperine snakes decreased during vitellogenesis even though food availability increased in this period, which suggests a quick transfer of body lipids to clutch. In April, when rice fields of the Ebro Delta were dry and aquatic prey was scarce for viperine snakes, males and females presented a lower lipid content in fat bodies, liver and muscle than they did in other months, showing a clear link between prey availability and body reserves during food shortage. Thus, patterns of variation in fat levels indicated that Natrix maura is a capital breeder since it acquires resources in advance and stores them until they are invested during the reproductive period. Nevertheless, the shortage in April forces Natrix maura to turn into a facultative income breeder to fuel vitellogenesis. Finally, fat reserves in body components were compared with an estimate of body condition calculated by the residuals from the regression of body mass on body length. In male viperine snakes, the estimate of body condition was correlated with fat levels, revealing that this index is useful to measure condition in living individuals. On the contrary, body condition in females was not correlated with fat levels, which suggests that it is not appropriate to infer condition in female viperine snakes since it depends on the reproductive status of the individuals.     

Effect of non-feeding period length on the intermittent operation of UASB reactors treating dairy effluents

Recent environmental concerns have prompted a re-evaluation of conventional management strategies and refueled the search of innovative waste management practices. In this sense, the anaerobic digestion of both fat and the remaining complex organic matter present in dairy wastewaters is attractive, although the continuous operation of high rate anaerobic processes treating this type of wastewaters causes the failure of the process. This work accesses the influence of non-feeding period length on the intermittent operation of mesophilic UASB reactors treating dairy wastewater, in order to allow the biological degradation to catch up with adsorption phenomenon. During the experiments, two UASB reactors were subject to three organic loading rates, ranging from 6 to 12 g(COD) x L(-1) x d(-1), with the same daily load applied to both reactors, each one with a different non-feeding period. Both reactors showed good COD removal efficiencies (87-92%). A material balance for COD in the reactors during the feeding and non-feeding periods showed the importance of the feedless period, which allowed the biomass to degrade substrate that was accumulated during the feeding period. The reactor with the longest non-feeding period had a better performance, which resulted in a higher methane production and adsorption capacity for the same organic load applied with a consequent less accumulation of substrate into the biomass. In addition, both reactors had a stable operation for the organic load of 12 g(COD) x L(-1) x d(-1), which is higher than the maximum applicable load reported in literature for continuous systems (3-6 g(COD) x L(-1) x d(-1)).     

Fattening responses to daily intervals of heat exposure in the Syrian hamster

Warm ambient temperature (38 degrees C) provided daily for one hr induced time-dependent changes in body weight and fat stores in the Syrian hamster. In animals held on 10-hr daily photoperiods and room temperature (23 degrees C), daily one-hour thermopulses at 8 and 20 hr after light onset stimulated increases in body weights and indices of body fat storage. Abdominal fat pad weights of these groups were twice those of untreated controls after 17 and 28 days of thermoperiodic treatments. On the other hand, daily thermopulses were completely ineffective at 0 and 16 hr after light onset. These results demonstrate that body fat stores may be influenced by a temporal interaction of environmental stimuli and implicate underlying circadian mechanisms in the regulation of body fat.     

Late‐moulting Black‐necked Grebes Podiceps nigricollis show greater body mass in the face of failing food supply

From August to December, thousands of Black‐necked Grebes Podiceps nigricollis concentrate during the flightless moult period in salt ponds in the Odiel Marshes, southern Spain, where they feed on the brine shrimp Artemia parthenogenetica. We predicted that because Black‐necked Grebes moulted in a food‐rich, predator‐free environment, there would be no net loss of body mass caused by the use of fat stored to meet energy needs during remigial feather replacement (as is the case for some other diving waterbirds). However, because the food resource disappears in winter, we predicted that grebes moulting later in the season would put on more body mass prior to moult because of the increasing risk of an Artemia population crash before the moult period is completed. Body mass determinations of thousands of birds captured during 2000–2010 showed that grebes in active wing‐moult showed greater mass with date of capture. Early‐moulting grebes were significantly lighter at all stages than late‐moulting birds. Grebes captured with new feathers post‐moult were significantly lighter than those in moult. This is the first study to support the hypothesis that individual waterbirds adopt different strategies in body mass accumulation according to timing of moult: early‐season grebes were able to acquire an excess of energy over expenditure and accumulate fat stores while moulting. Delayed moulters acquired greater fat stores in advance of moult to contribute to energy expenditure for feather replacement and retained extra stores later, most likely as a bet hedge against the increasing probability of failing food supply and higher thermoregulatory demands late in the season. An alternative hypothesis, that mass change is affected by a trophically transmitted cestode using brine shrimps as an intermediate host and Black‐necked Grebes as final host, was not supported by the data.     

A cost-benefit analysis of feeding in female tsetse

Abstract. Three models for feeding in female tsetse are considered. Model I: there is a prolonged non-feeding phase after each meal followed by feeding at a constant rate, with a constant probability of dying as a consequence of feeding. Model II: the feeding rate increases linearly after each meal. Model III: the feeding rate increases exponentially after each meal. In Models II and III the feeding hazard is a linear function of the probability of feeding. Production of viable female offspring is estimated under each model, making allowance for losses of adults due to starvation and to background and feeding mortality, losses of pupae due to predation and parasitization, and losses of young flies if their mothers take insufficient blood during pregnancy. Under Model I, if females require three meals to produce viable pupae in 9 days, then for a non-decreasing population with a background mortality of 1%/day, and 25% pupal losses due to predation and parasitism, the feeding risk must be ≤5%/feed. At this maximum level the non-feeding phase should be 2–2.5 days for optimal productivity, with a mean feeding interval of 60–72 h. If the background mortality is 2%/day, feeding losses cannot exceed 1%/feed for a non-decreasing population. If four or five meals are required for the production of fully viable pupae, the optimal values of the non-feeding phase and mean feeding interval tend towards 1 and 2 days respectively. Under Models II and HI the mean feeding interval is 50–60 h for optimal productivity (with variances 3 times as large as for Model I), in good agreement with estimates from recent models for feeding and digestion. Field evidence suggests that feeding tsetse take greater risks as their fat levels dwindle. This should result in feeding (and feeding mortality) rates which increase during the feeding phase - as assumed in Models II and III but not in Model I. These models allow greater flexibility than Model I, because flies can feed early in the hunger cycle, at low probability, as long as the feeding risk is also low.     

The metabolism of glycerol in the locust Schistocerca gregaria during flight

The concentration of glycerol in locust haemolymph increases 10-fold during 1 hr flight but decreases rapidly when flight ceases. [¹⁴C]Glycerol is rapidly metabolized by locusts in vivo. Trehalose and diacyl glycerol are the main products to appear in the haemolymph but the proportion of diacyl glycerol is increased in flown insects or when adipokinetic hormone is injected. Trehalose and diacyl glycerol are also the main products formed when isolated fat body is incubated with [¹⁴C]glycerol. Adipokinetic hormone increases the proportion of diacyl glycerol formed.It is proposed that during flight glycerol is produced by hydrolysis of diacyl glycerol in the flight muscles. It is then transported to fat body for esterification with fatty acid produced during conversion of triacyl glycerol stores to diacyl glycerol.     

Temporal changes in fat and protein levels in the tropical Anabantid Trichogaster pectoralis (Regan)

Samples of a wild population of the Anabantid Trichogaster pectoralis (Regan) were taken during and after one of the two main breeding periods of the year. Carcasses of both sexes and female gonads were analysed for fat, protein and carbohydrate. Carbohydrates were present in insignificant amounts in all tissues. The fat content of the ovary proved to be high (over 30% of wet weight) and, as a result, ovarian energy in a ripe female formed a substantial proportion of the total energy content of the fish. However, it did appear possible for females to develop large ovaries without depleting the carcass fat stores.
Although protein levels in the carcass were significantly higher in 1 month, relative to fat levels, protein levels remained fairly constant during the period of study. Conversely fat levels showed marked fluctuations throughout the breeding period, being high at the start of the breeding period, low towards the end, finally rising again 1 month after most fish had terminated breeding. The range of fat levels appeared to be independent of the gonadal state of the fish at capture and seemed more closely related to month of capture. Two explanations are suggested; (1) changes in food availability over the period in question and/or (2) if repeated spawnings occur this could deplete fat reserves in the carcass.
In this species fat is stored largely in the muscle but some is stored around the coiled intestine. A visual scoring system was used to assess the extent of this fat deposition and it was found that the fat score was correlated with the level of fat in the carcass. Thus the level of fat around the intestine, although insignificant relative to carcass fat, could be used as a method of assessing the fatness of a fish.     

Wing moult and mass change in free‐living mallard Anas platyrhynchos

Captured free‐living male mallard Anas platyrhynchos at Abberton in southern Britain showed peak mass gain immediately prior to simultaneous remex moult. Individuals of both sexes were heavier before shedding wing feathers than when flightless confirming literature accounts that show mallard accumulate fat stores in anticipation of moult to contribute to meeting energy needs during remex re‐growth. Over the course of four seasons, males lost 13 17% of initial body mass on average during re‐growth of flight feathers, females 13 23%. Based on energy expenditure of 1.3 times BMR, male mallard were estimated to be able to fulfil 42 60% and females 41 82% of their energy needs throughout moult from stores. Free‐flying male mallard fed ad libitum in a predator‐free environment did not differ in starting body mass or rate of mass loss during wing moult compared to free‐living Abberton birds, suggesting depletion of fat stores, irrespective of available sources of exogenous energy. Based on this evidence, we reject that the hypotheses that mass loss in moulting mallard is due to 1) simple energy stress and 2) restrictions on feeding and consider that 3) attaining the ability to fly at an earlier stage on incompletely grown flight feathers is not the primary factor shaping this trait. Rather, we consider the accumulation and subsequent depletion of fat stores, together with reductions in energy expenditure, enable mallard to re‐grow feathers as rapidly as possible by exploiting habitats that offer safety from predators, but do not necessarily enable them to balance energy budgets during the flightless period of remex feather re‐growth.     

Crcadian and Seasonal Variations of Lipogenesis in the Gulf Killifish,Fundulus Grandis

Lipogenesis was measured in male Gulf killifish at three seasons under different environmental conditions. Cold temperature is stimulatory for lipogenesis in the fall and spring, but warm temperature is more stimulatory during the summer. The highest rate of lipogenesis occurs during the spring. However, total body fat content is relatively low at that time, which suggests that lipids are being actively mobilized as well. A high rate of lipogenesis also occurs at a cold temperature (20°C) during the fall, and more lipids are stored at that time of year, as evidenced by higher liver and body fat stores. Both lipogenesis and total body fat content are at a minimum during the summer. These results indicate that high levels of lipid synthesis do not necessarily result in higher body fat content, as the latter is the product of both lipid synthesis and lipid mobilization. This study is also in agreement with previous studies which had indicated a changing responsiveness to temperature during the annual cycle of the Gulf killfish.     

Crcadian and Seasonal Variations of Lipogenesis in the Gulf Killifish, Fundulus Grandis

Lipogenesis was measured in male Gulf killifish at three seasons under different environmental conditions. Cold temperature is stimulatory for lipogenesis in the fall and spring, but warm temperature is more stimulatory during the summer. The highest rate of lipogenesis occurs during the spring. However, total body fat content is relatively low at that time, which suggests that lipids are being actively mobilized as well. A high rate of lipogenesis also occurs at a cold temperature (20°C) during the fall, and more lipids are stored at that time of year, as evidenced by higher liver and body fat stores. Both lipogenesis and total body fat content are at a minimum during the summer. These results indicate that high levels of lipid synthesis do not necessarily result in higher body fat content, as the latter is the product of both lipid synthesis and lipid mobilization. This study is also in agreement with previous studies which had indicated a changing responsiveness to temperature during the annual cycle of the Gulf killfish.     

Timing of eclosion affects diapause development, fat body consumption and longevity in Osmia lignaria, a univoltine, adult-wintering solitary bee

Most insects from temperate areas enter diapause ahead of winter. Species diapausing in a feeding stage and accumulating metabolic reserves during permissive pre-wintering conditions are expected to enter diapause shortly before the onset of winter. In contrast, species diapausing in a non-feeding stage are expected to lower their metabolism as soon as possible to avoid excessive consumption of metabolic reserves. The solitary bee Osmia lignaria winters as a non-feeding adult within its cocoon, but previous studies show important weight losses and increased winter mortality in populations pre-wintered for extended periods. We measured respiration rates to assess diapause initiation and maintenance during pre-wintering, and tested whether timing of adult eclosion affected fitness by measuring fat body depletion, winter mortality and post-winter longevity. We worked with different cohorts of a population reared under natural conditions, and manipulated pre-wintering duration in a population reared under artificial conditions. In agreement with our expectation, O. lignaria lower their metabolic rates within a few days of adult eclosion, but nonetheless suffer strong weight loss during pre-wintering. Early developing individuals suffer greater weight loss and fat body depletion, and have short post-winter longevity. Although, we found no differences in winter mortality among treatments, our results indicate that increased mortality may occur in years with late winter arrivals. We discuss fundamental ecophysiological differences between adult and prepupal diapause within the Megachilidae, and hypothesize that species wintering as adults will be more negatively affected by a situation of extended summers under a scenario of global warming.     

Migration and moult in Pallas's Grasshopper Warbler

From 1987 to 1989, 11 passerine species caught during their autumn migration on the Mettnau peninsula at Lake Constance (SW Germany) were examined for weight, visible fat deposition and actual fat load using a Soxhlet extraction. From the amount of fat deposited, mean theoretical flight ranges were calculated. Visible stored fat is only deposited in large quantities towards the end of the migration period. Before migration, the mean fat content stored in relation to fat-free dry weight ranges from 9–12%, whereas during migration it ranges from 13–30%. There is no difference between long- and short-distance migrants. A weight change cannot be accounted for exclusively by fat deposition. The mean weight of first-captures was low in all species. Only 5 of the 11 species studied gained weight more or less extensively during the migration period. All species showed an increase in fat deposition during migration. Since 1972, a marked annual decrease in average body weight during migration was found in the Reed Warbler. On average, water content in relation to fat-free dry weight is between 208 and 254% during migration and between 216 and 270% during the premigration period. For the species studied at Mettnau, mean theoretical flight range is 49 to 85 km during the pre-migration period and 84 to 216 km during migration (n = 211 birds). An average flight range of up to 100 km implies short migrational ‘legs’ from Lake Constance to the nearby Swiss midlands, which is probable if only parts of the small fat reserves are utilized during their flight. Because birds have to increase their initial fat stores considerably to reach and cross the Mediterranean, a low fat deposition rate may lead to problems before they reach their winter quarters. Short flight ranges are discussed in connection with trends of decreasing populations in central Europe.     

Rapid declines in metabolism explain extended coral larval longevity

Lecithotrophic, or non-feeding, marine invertebrate larvae generally have shorter pelagic larval durations (PLDs) than planktotrophic larvae. However, non-feeding larvae of scleractinian corals have PLDs far exceeding those of feeding larvae of other organisms and predictions of PLD based on energy reserves and metabolic rates, raising questions about how such longevity is achieved. Here, we measured temporal changes in metabolic rates and total lipid content of non-feeding larvae of four species of reef corals to determine whether changes in energy utilization through time contribute to extended larval durations. The temporal dynamics of both metabolic rates and lipid content were highly consistent among species. Prior to fertilization, metabolic rates were low (2.73–8.63 nmol O₂ larva^?1 h^?1) before rapidly increasing to a peak during embryogenesis and early development 1–2 days after spawning. Metabolic rates remained high until shortly after larvae first became competent to metamorphose and then declined by up to two orders of magnitude to levels at or below rates seen in unfertilized eggs over the following week. Larvae remained in this state of low metabolic activity for up to 2 months. Consistent with temporal patterns in metabolic rates, depletion of lipids was extremely rapid during early development and then slowed dramatically from 1 week onward. Despite the very low metabolic rates in these species, larvae continued to swim and retained competence for at least 2 months. The capacity of non-feeding coral larvae to enter a state of low metabolism soon after becoming competent to metamorphose significantly extends dispersal potential, thereby accruing advantages typically associated with planktotrophy, notably enhanced population connectivity.