Accumulate Fat Reserves Research Articles

Seasonal changes in blood rheology in little ground squirrels.

The annual cycle of small ground squirrels (Spermophilus pygmaeus) consists of 2 periods: wakefulness (spring-autumn) and hibernation (winter). During the active period, ground squirrels breed (spring), accumulate fat reserves (summer) and prepare for hibernation (autumn). We suppose that the rheological properties of blood and the deformability of erythrocytes can change in different seasons of the animal's wakefulness period to adequately provide tissues with oxygen. The aim of this study was to identify possible adaptive changes in erythrocyte deformability and erythrocyte indices in ground squirrels during their active period. The deformability of erythrocytes was studied by ektacytometry in an osmotic gradient. It was found that in spring, after the arousal of ground squirrels, erythrocytes have the highest deformability (El_max), hydration (O_hyper), water permeability (El_min) and osmotic stability (∆O). In summer, compared with spring, the deformability of erythrocytes decreases, and the average volume of erythrocytes (MCV) also decreases. In autumn, before hibernation, the integral deformability of erythrocytes, their hydration, as well as the range of osmotic stability of erythrocytes increases relative to the summer period. In summer and autumn, in contrast to spring, the average concentration of hemoglobin in the erythrocyte (MCHC) increases. At low shear stress (1 Pa) in summer and autumn, osmoscan becomes a pronounced polymodal form, indicating a change in the viscoelastic properties of ground squirrel erythrocyte membranes. Thus, for the first time, we discovered seasonal variability in the deformability of ground squirrel erythrocytes, which is consistent with the spring-summer activity of animals and preparation for hibernation.

Depleted lean body mass after crossing an ecological barrier differentially affects stopover duration and refuelling rate among species of long‐distance migratory birds

Abstract During the long‐distance migratory flights of birds, lean mass breakdown occurs in concert with fat catabolism and is expected to have repercussions on total stopover duration because birds require time to rebuild lean tissue before accumulating fat reserves. Despite this, little is known about the role of in‐flight lean mass breakdown on stopover duration because direct measurements are restricted by the destructive nature of traditional body composition analysis and the technological limitations of tracking small birds over large expanses. We used non‐lethal, non‐invasive Quantitative Magnetic Resonance technology and plasma metabolite profiling to measure the body composition and physiological state of free‐living birds captured at a migratory stopover site after flight across the Gulf of Mexico, and an automated radiotelemetry array covering ~5000 km2 to track stopover duration and regional movements. We tested whether stopover duration is prolonged in individuals arriving with lower lean mass and investigated how lean mass affects regional movements. Stopover duration decreased by 22% for each additional gram of lean mass in Northern Waterthrush (Parkesia noveboracensis), but this relationship was not apparent in Swainson's Thrush (Catharus ustulatus), Grey‐cheeked Thrush (Catharus minimus) or Yellow‐billed Cuckoo (Coccyzus americanus), even though these species also arrived with depleted lean mass. Stopover duration increased for Swainson's Thrush with higher plasma uric acid, a marker of protein catabolism. Northern Waterthrush with higher plasma triglycerides had longer stopover duration. Our findings suggest that migratory birds may compensate for substantial lean mass losses by increasing refuelling rate or moving to a different stopover site, and highlights species‐level differences in lean mass breakdown and the associated impacts on physiological function. Our results highlight the strategies used by different species to recover from a trans‐Gulf of Mexico flight and resume migration, which improves our understanding of the annual cycle of migratory birds. Read the free Plain Language Summary for this article on the Journal blog.

Resource pulses and human–wildlife conflicts: linking satellite indicators and ground data on forest productivity to predict brown bear damages

AbstractPulsed resources have prominent effects on community and ecosystem dynamics; however, there is little research on how resource pulses affect human–wildlife interactions. Tree masting is a common type of pulsed resource that represents a crucial food for many species and has important bottom‐up effects in food webs. In anthropogenic landscapes, years of food shortage after mast years can have negative outcomes for both people and wildlife, for instance when an increased use of anthropogenic foods by animals exacerbates human–wildlife conflicts. Here, we used novel remote sensing indicators of forest productivity and phenology, together with weather cues and ground measures of mast production, to assess whether years of masting and crop failures lead to changes in human–wildlife conflict occurrence. We used a unique 14‐year dataset including the production of European beech Fagus sylvatica seeds and brown bear Ursus arctos damage in the northeastern Carpathians as our model system. Linking these data in a panel regression framework, we found that temporal fluctuations in damage occurrence were sensitive to the year‐to‐year variation in beechnut production. Specifically, the number of damages during bear hyperphagia (i.e., September to December, when bears need to accumulate fat reserves prior to hibernation) was significantly higher in years with low beechnut production than in normal or mast years. Furthermore, we provide evidence that beech masting and failure can be predicted through a combination of remote‐sensing, weather, and field indicators of forest productivity and phenology. We demonstrate how pulsed resources, such as tree masting, can percolate through food webs to amplify human–wildlife conflict in human‐dominated landscapes. Given the recent range expansion of large carnivores and herbivores in many regions, including Europe, predicting years of natural food shortage can provide a pathway to proactive damage prevention, and thus to foster coexistence between wildlife and people.

Pre-spawning fat and trace metals in Diplodus sargus (Pisces, Sparidae) and possible relationship with the abnormally tough syndrome (ATS)

This research aimed to explore the variability in the distribution of muscle, perivisceral, and retroperitoneal fat in Diplodus sargus during the pre-spawning period (the period of maximum accumulation of fat reserves) and its possible relationship with the abnormally tough specimen syndrome (ATS) affecting this species. Since pollutants accumulate in adipose tissue, trace metal load in the fattest specimens were also analyzed. Muscle fat content and abdominal fat were highly correlated, and larger individuals had more abundant abdominal fat. However, given its great variability (26% of the specimens had no abdominal fat at all), abdominal fat is likely a transitional fat to be quickly transferred to other tissues. The liver appeared to have a minor role as a fat deposit in D. sargus since HSI varied relatively little. None of the fishes without lipidic reserves were ATS individuals; by contrast, the only ATS individual found, a 28 cm male, showed a muscle fat content above the observed average and one of the highest amounts of perivisceral and retroperitoneal fat. Therefore, we conclude that flesh hardness is not directly related to the low lipid reserves. However, this ATS individual showed a very high liver copper concentration, suggesting a potential link between fat content, copper concentration, and ATS syndrome that should be explored in the future.

Modelling and mapping how common guillemots balance their energy budgets over a full annual cycle

Abstract The ability of individual animals to balance their energy budgets throughout the annual cycle is important for their survival, reproduction and population dynamics. However, the annual cycles of many wild, mobile animals are difficult to observe and our understanding of how individuals balance their energy budgets throughout the year therefore remains poor. We developed a hierarchical Bayesian state‐space model to investigate how key components of animal energy budgets (namely individual energy gain and storage) varied in space and time. Our model used biologger‐derived estimates of time‐activity budgets, locations and energy expenditure to infer year‐round time series of energy income and reserves. The model accounted for seasonality in environmental drivers such as sea surface temperature and daylength, allowing us to identify times and locations of high energy gain. Our study system was a population of common guillemots Uria aalge breeding at a western North Sea colony. These seabirds manage their energy budgets by adjusting their behaviour and accumulating fat reserves. However, typically during severe weather conditions, birds can experience an energy deficit over a sustained period, leading to starvation and large‐scale mortality events. We show that guillemot energy gain varied in both time and space. Estimates of guillemot body mass varied throughout the annual cycle and birds periodically experienced losses in mass. Mass losses were likely to have either been adaptive, or due to energetic bottlenecks, the latter leading to increased susceptibility to mortality. Guillemots tended to be lighter towards the edge of their spatial distribution. We describe a framework that combines biologging data, time‐activity budget analysis and Bayesian state‐space modelling to identify times and locations of high energetic reward or potential energetic bottlenecks in a wild animal population. Our approach can be extended to address ecological and conservation‐driven questions that were previously unanswerable due to logistical complexities in collecting data on wild, mobile animals across full annual cycles. Read the free Plain Language Summary for this article on the Journal blog.

The use of radiography for measurements of the medullary cavity in the metacarpal bone in the European roe deer Capreolus capreolus for assessment of ontogenetic quality – preliminary study

<b>The objective was to verify the research hypothesis concerning a correlation between the surface area of the medullary bone and other fat indices and carcass weight. This study was also focused on identification of potential differences in the mean values of the fat parameters and carcass weight between the forest and field ecotypes of roe deer. The medullary cavity area was measured using the DIRA 200 program. Metacarpal bone III and the phalanges of the 2nd and 3rd fingers were measured as well. The investigations involved 38 females of the European roe deer Capreolus capreolus aged 3-5 years.The investigations revealed a negative statistically significant correlation between the surface area of the medullary cavity in metacarpal bone III and the kidney fat index KFI (rs = -0.483; p<0.05) and the weight of the perirenal adipose tissue (rs = -0.362; p<0.05). No correlation was shown between the area of the medullary cavity of metacarpal bone III and the doe carcass weight (rs = 0.093; ns). The size of the medullary cavity is an anatomical parameter that is not susceptible to cyclical changes in environmental conditions. As shown in this study, it is independent of the body weight and determines the amount of bone marrow and, hence, the amount of accumulated fat reserves. We believe that, besides biometric measurements, the surface area of the medullary cavity can be a good parameter for assessment of the ontogenetic quality of roe deer and for comparison of populations.

Flight Performance of Migrating Juvenile Barn Swallows Hirundo rustica in Relation to Fat Load and Wing Morphology

Migratory birds have evolved the ability to accumulate fat reserves to fuel their migratory journeys. However, increased fuel load leads to an increased body mass, which is expected to impair flight performance and increase predation risk. Results of previous research are contradictory, with some studies reporting detrimental effects of fat load on flight performance, while others showing no such influences. Furthermore, no studies have investigated the relationship between fat load and flight performance in obligate aerial insectivores, which are known to accumulate only moderate fat loads while migrating overland and not crossing wide ecological barriers such as oceans or deserts. In this study we investigated the inter-individual variation in short-term flight performance (flight manoeuvrability, velocity and acceleration) in juvenile Barn Swallows Hirundo rustica in relation to fat load in Poland (central Europe), during the initial stages of autumn southward migration. We evaluated individual swallow fat loads by means of a Total Body Electrical Conductivity (TOBEC) scanner. In order to evaluate short-term flight performance in a standardised manner we used flight tunnels. We controlled statistically for the independent effect of wing morphology, which can be expected to influence flight performance. Juvenile fat loads were on average 7.5% (range 0.2–20.5) of lean body mass, but we found no negative effect of the fat mass on short-term flight performance traits. Individuals with larger fat mass reached higher velocity compared to leaner ones, which is in line with theoretical expectations. However, fat mass did not significantly predict flight manoeuvrability or acceleration. The results indicate that relatively small fat loads accumulated by juvenile Barn Swallows during overland migration do not impair short-term flight performance.

Losing seasonal patterns in a hibernating omnivore? Diet quality proxies and faecal cortisol metabolites in brown bears in areas with and without artificial feeding.

Bears are omnivores particularly well-adapted to variations in the nutritional composition, quality and availability of food resources. Artificial feeding practices have been shown to strongly influence diet composition and seasonality, as well as to cause alterations in wintering and movement in brown bears (Ursus arctos). In this study, we investigated seasonal differences (hypophagia vs hyperphagia) in food quality of two brown bear subpopulations in the Polish Carpathians using faecal nitrogen (FN) and carbon (FC) estimates. The subpopulations inhabit areas that differ in artificial feeding practices: no artificial feeding occurs in the western subpopulation (Tatra Mountains), while artificial food targeted to ungulates is provided and used year-round in the eastern subpopulation (Bieszczady Mountains). We also compared these results with faecal cortisol metabolites (FCM) to explore how FN and FC correlate with the hypothalamic-pituitary-adrenal axis activity and if the seasonal patterns are apparent. We found that in Tatra Mts bears fed on significantly higher quality diet, as shown by FN and FC values, and had significantly higher FC levels in hyperphagia, when they accumulate fat reserves for wintering. The pattern in FCM levels for Tatra subpopulation followed the changes in energy intake during the seasons of hypo- and hyperphagia, while in Bieszczady Mts, the area with intensive feeding, no seasonal patterns could be observed. Artificial feeding practices may disrupt nutrient phenology and seasonality, relative to subpopulations with natural diets. We showed that the availability of human-provided foods may alter not only the overall dietary quality, but also hormonal patterns linked to seasonal nutritional requirements. Combining FN, FC and FCM proved to be a useful tool for reconstructing diet quality and related physiological patterns.

Cold and hungry: combined effects of low temperature and resource scarcity on an edge‐of‐range temperate primate, the golden snub‐nose monkey

Both biotic and abiotic factors play important roles in influencing ecological distributions and niche limits. Where biotic and abiotic stressors co‐occur in space and time, homeostatic systems face a scenario in which stressors can compound to impose a challenge that is greater than the sum of the separate factors. We studied the homeostatic strategies of the golden snub‐nosed monkey Rhinopithecus roxellana, a species living in temperate deciduous forests at the edge of the global distribution range for folivorous primates, to cope with the co‐occurrence of cold temperatures and resource scarcity during winter. We discovered that in winter the monkeys experience a dietary energy deficit of 101 kJ mbm−1 d−1 compared with calculated needs, despite increased feeding. This is partly offset by behavioral changes (reduced locomotion and increased resting) and reducing skin temperature by an average of 3.2°C through a cutaneous vasoconstriction to decrease heat loss. However, their major strategy is ingesting surplus energy and accumulating fat reserves when food was not limiting during summer and autumn. Their 14% of body mass lost over the winter represented an energy yield of 102 kJ mbm−1 d−1, which closely matched the calculated winter energy deficit of 101 kJ mbm−1 d−1. However, the latter value assumes that all the 75.41 kJ mbm−1 d−1 of protein ingested in winter was available for energy metabolism. This is almost certainly an over‐estimate, suggesting that the study population was in negative energy balance over the study period. Our study therefore suggests that despite its suit of integrated homeostatic responses, the confluence of low temperatures and resource limitation during winter places this edge‐of‐range primate close the threshold of what is energetically viable. It also provides a framework for quantitative models predicting the vulnerability of temperate primates to global change.

Fatty acids and stable isotopes (δ13C, δ15N) in southern right whale Eubalaena australis calves in relation to age and mortality at Península Valdés, Argentina

Baleen whales accumulate fat reserves during the summer to sustain reproduction while fasting in the winter. The southern right whaleEubalaena australispopulation that calves off Península Valdés, Argentina, experienced high calf mortality events from 2003 to 2013 and poor nutritional states of mothers could be a contributing cause. Previous studies found that the population’s reproductive success is influenced by prey availability. Mothers unable to build sufficient fat reserves or feeding on prey with different nutritional value may fail to meet the demands of lactation. Milk is the only source of nutrients and energy for calves at Valdés, so their fatty acids (FAs) and stable isotopes should reflect their mother’s diet and feeding-ground locations. Here, we compared FA profiles and C and N stable isotopes of dead calves with those of living calves to evaluate the potential impact of maternal nutrition on calf survival. We found no differences in the FA composition of blubber in dead and living calves, indicating similar maternal diets. Likewise, the isotopic values of living and dead calves imply that their mothers had similar foraging ranges. However, FA composition was greatly affected by calf length, indicating effects of calf age and duration of nursing. These findings suggest that mothers of dead calves did not feed on different diets or feeding grounds compared to mothers of living calves. Future research should further assess the overall health and body condition of the Valdés southern right whale calves.

Denning in brown bears.

Hibernation represents an adaptation for coping with unfavorable environmental conditions. For brown bears Ursus arctos, hibernation is a critical period as pronounced temporal reductions in several physiological functions occur.Here, we review the three main aspects of brown bear denning: (1) den chronology, (2) den characteristics, and (3) hibernation physiology in order to identify (a) proximate and ultimate factors of hibernation as well as (b) research gaps and conservation priorities.Den chronology, which varies by sex and reproductive status, depends on environmental factors, such as snow, temperature, food availability, and den altitude. Significant variation in hibernation across latitudes occurs for both den entry and exit.The choice of a den and its surroundings may affect individual fitness, for example, loss of offspring and excessive energy consumption. Den selection is the result of broad‐ and fine‐scale habitat selection, mainly linked to den insulation, remoteness, and availability of food in the surroundings of the den location.Hibernation is a metabolic challenge for the brown bears, in which a series of physiological adaptations in tissues and organs enable survival under nutritional deprivation, maintain high levels of lipids, preserve muscle, and bone and prevent cardiovascular pathologies such as atherosclerosis. It is important to understand: (a) proximate and ultimate factors in denning behavior and the difference between actual drivers of hibernation (i.e., factors to which bears directly respond) and their correlates; (b) how changes in climatic factors might affect the ability of bears to face global climate change and the human‐mediated changes in food availability; (c) hyperphagia (period in which brown bears accumulate fat reserves), predenning and denning periods, including for those populations in which bears do not hibernate every year; and (d) how to approach the study of bear denning merging insights from different perspectives, that is, physiology, ecology, and behavior.

Circadian transcription factors differentially regulate features of the adult overwintering diapause in the Northern house mosquito, Culex pipiens

The short days of late summer and early fall are the environmental cues that most temperate insects and other animals use to predict winter's arrival. Although it is still unclear precisely how insects measure daylength, there is mounting evidence that the circadian clock regulates seasonal responses including photoperiodic diapause. Females of the Northern house mosquito, Culex pipiens, enter an adult reproductive diapause in response to short daylengths. While in this state, females divert their resources from reproduction to survival, arresting egg follicle development and increasing fat content. Here, we characterized the expression profile of two circadian transcription factors, vrille (vri) and Par domain protein 1 (Pdp1), as well as genes downstream of the clock, takeout (to) and Nocturnin (Noc) and under different seasonal conditions. We saw that while vri mRNA oscillated under both long day and short day conditions, Pdp1 expression oscillated only under long day conditions and was constitutively upregulated in diapausing females. We saw similar expression profiles for to and Noc, suggesting that PDP1 might regulate their expression or that Pdp1, to and Noc might be regulated by the same transcription factor. We suppressed vri and Pdp1 using RNA interference. dsRNA against vri provided inconsistent results, sometimes stimulating autogenous egg follicle development in both long and short day-reared females, and other times had no effect. In contrast, knocking down Pdp1 prevented short day-reared females from accumulating fat reserves, but increased expression of to and Noc. Taken together, these data suggest that the circadian transcription factors Vri and Pdp1 may independently regulate signaling pathways underlying arrested egg follicle development and fat accumulation in diapausing females of Cx. pipiens.

Phenotypic plasticity under desert environment constraints: mandible variation in the dwarf fat-tailed jerboa, Pygeretmus pumilio (Rodentia: Dipodidae)

Arid areas have a comparatively narrow range of habitat types, with restricted variation in environmental parameters, leaving narrow boundaries for phenotypic variation to correlate with ecological variables. To test this presumption, we explored variation in size and shape of the mandible in the dwarf fat-tailed jerboa (Pygeretmus pumilio (Kerr, 1792)) under the constraints of a rigorous desert environment. Size varied significantly and predictably with geographic position and demonstrated a strong, nonlinear longitudinal pattern. Moreover, size was associated with several other climatic variables but not with soil properties or with proxies for primary productivity. Our results suggest that for rodents exposed to rapid and extreme changes, larger size may have multiple advantages, notably in maintaining euthermia during cold nights and efficient water metabolism under aridity stress, in accumulating fat reserves for hibernation, and in digging deeper burrows, better protected from surface extremes. Shape varied clinally along the longitudinal transect, and the pattern was affected more by temperature than by precipitation. We conclude that the success of dwarf fat-tailed jerboa in occupying an extensive geographic range relies on their ability to meet environmental heterogeneity through cohesive and diverse responses, including physiology, behaviour, life-history traits, and morphological plasticity.

Developmental plasticity in metabolism but not in energy reserve accumulation in a seasonally polyphenic butterfly.

The evolution of seasonal polyphenisms (discrete phenotypes in different annual generations) associated with alternative developmental pathways of diapause (overwintering) and direct development is favoured in temperate insects. Seasonal life history polyphenisms are common and include faster growth and development under direct development than in diapause. However, the physiological underpinnings of this difference remain poorly known despite its significance for understanding the evolution of polyphenisms. We measured respiration and metabolic rates through the penultimate and final larval instars in the butterfly Pieris napi and show that directly developing larvae grew and developed faster and had a higher metabolic rate than larvae entering pupal diapause. The metabolic divergence appeared only in the final instar, that is, after induction of the developmental pathway that takes place in the penultimate instar in P. napi. The accumulation of fat reserves during the final larval instar was similar under diapause and direct development, which was unexpected as diapause is predicted to select for exaggerated reserve accumulation. This suggests that overwinter survival in diapause does not require larger energy reserves than direct development, likely because of metabolic suppression in diapause pupae. The results, nevertheless, demonstrate that physiological changes coincide with the divergence of life histories between the alternative developmental pathways, thus elucidating the proximate basis of seasonal life history polyphenisms.

Genetic features of hormonal regulation of energy metabolism (literature review)

Summary: Many chronic diseases are associated with impaired human energy metabolism and its hormonal regulation. According to the WHO, there are more than 300 million people with obesity in the world, 24.1% of the population are suffering from obesity in Ukraine. Being overweight is one of the main factors in the development of type 2 diabetes, cardiovascular and oncological diseases, pathology of the musculoskeletal and digestive systems, as well as reproductive dysfunction. Obesity is a multifactorial disease. According to the results presented in the literature, the accumulation of fat in the subcutaneous and visceral region will lead to a change in the expression of genes encoding proteins that regulate energy metabolism. Leptin belongs to the group of adipocyte hormones of subcutaneous fat. The expression of leptin is regulated by several hormones, including insulin and glucocorticoids, and starvation also leads to a decrease of leptin concentration in plasma. Leptin reduces hunger, activates the use of fats in energy metabolism and inhibits the excessive accumulation of fat reserves. Leptin resistance may occur due to the presence of a mutation or polymorphic variation in its receptor gene. One of the most studied and clinically significant polymorphic variants of the leptin receptor gene (LEPR) is the replacement of glutamine amino acid with arginine at 223 positions (Q223R), which leads to a decrease in the sensitivity of receptors to leptin. Mutations in POMC lead to obesity, which is accompanied by atrophy of the adrenal cortex and multiple disorders. Mutations in MC4R lead to obesity in patients but ensure normal sexual development and adequate functioning of the endocrine glands. Now scientists on the whole world are actively developing methods to fight obesity, based on stimulating the functioning of cascades of leptin-dependent signaling.

Fatty acid synthase 2 contributes to diapause preparation in a beetle by regulating lipid accumulation and stress tolerance genes expression

Diapause, also known as dormancy, is a state of arrested development that allows insects to survive unfavorable environmental conditions. Diapause-destined insects store large amounts of fat when preparing for diapause. However, the extent to which these accumulated fat reserves influence diapause remains unclear. To address this question, we investigated the function of fatty acid synthase (FAS), which plays a central role in lipid synthesis, in stress tolerance, the duration of diapause preparation, and whether insects enter diapause or not. In diapause-destined adult female cabbage beetles, Colaphellus bowringi, FAS2 was more highly expressed than FAS1 at the peak stage of diapause preparation. FAS2 knockdown suppressed lipid accumulation and subsequently affected stress tolerance genes expression and water content. However, silencing FAS2 had no significant effects on the duration of diapause preparation or the incidence of diapause. FAS2 transcription was suppressed by juvenile hormone (JH) and the JH receptor methoprene-tolerant (Met). These results suggest that the absence of JH-Met induces FAS2 expression, thereby promoting lipid storage in diapause-destined female beetles. These results demonstrate that fat reserves regulate stress tolerance genes expression and water content, but have no significant effect on the duration of diapause preparation or the incidence of diapause.

Plumage quality mediates a life-history trade-off in a migratory bird

BackgroundMoult is one of the most costly activities in the annual cycle of birds and most avian species separate moult from other energy-demanding activities, such as migration. To this end, young birds tend to undergo the first post-juvenile moult before the onset of migration, but in some species the time window for the pre-migratory feather replacement is too narrow. We hypothesized that in such species an increased investment in the structural quality of juvenile feathers may allow to retain juvenile plumage throughout the entire migratory period and delay moult until arriving at wintering grounds, thus avoiding a moult-migration overlap.MethodsThe effect of juvenile plumage quality on the occurrence of moult-migration overlap was studied in a migratory shorebird, the common snipe Gallinago gallinago. Ca. 400 of first-year common snipe were captured during their final stage of autumn migration through Central Europe. The quality of juvenile feathers was assessed as the mass-length residuals of retained juvenile rectrices. Condition of migrating birds was assessed with the mass of accumulated fat reserves and whole-blood hemoglobin concentration. Path analysis was used to disentangle complex interrelationships between plumage quality, moult and body condition.ResultsSnipe which grew higher-quality feathers in the pre-fledging period were less likely to initiate moult during migration. Individuals moulting during migration had lower fat loads and hemoglobin concentrations compared to non-moulting birds, suggesting a trade-off in resource allocation, where energetic costs of moult reduced both energy reserves available for migration and resources available for maintenance of high oxygen capacity of blood.ConclusionsThe results of this study indicate that a major life-history trade-off in a migratory bird may be mediated by the quality of juvenile plumage. This is consistent with a silver spoon effect, where early-life investment in feather quality affects future performance of birds during migration period. Our results strongly suggest that the juvenile plumage, although retained for a relatively short period of time, may have profound consequences for individuals’ fitness.Electronic supplementary materialThe online version of this article (doi:10.1186/s12983-016-0179-4) contains supplementary material, which is available to authorized users.

Variation of parasitism patterns in bats during hibernation: the effect of host species, resources, health status, and hibernation period.

During critical periods of food shortage or variable climatic conditions, the choice of an appropriate host can increase the survival and reproductive performance of parasites. In turn, one of the unique adaptations to periodical food shortages is hibernation, which is often found among insectivorous bat species in the temperate zone. While hibernating, bats are completely defenseless against both predators and ectoparasites, their immune and endocrine systems are diminished, and survival is dependent on the accumulated fat reserves. Differences in the health status or in the rate of consumption of the resources might also explain species-specific differences in ectoparasite abundance, especially between closely related host species, such as the greater mouse-eared bat (Myotis myotis) and the lesser mouse-eared bat (M. blythii) during hibernation. In the present study, the abundance of two ecologically distinct (summer and winter) types of ectoparasites was examined in terms of its influence on the body condition and hemoglobin content of the two host species. The effects of demographic factors, such as host sex and age, were also investigated. Despite a similar pattern of deteriorating body condition and hemoglobin concentration, M. myotis was more parasitized than was M. blythii. The marked decrease in hemoglobin content in first-year females of both host species correlated with the highest parasite load and indicated a risk of anemia. At the intraspecific level, ectoparasite abundance was not correlated with body condition (resources), but it negatively affected hemoglobin content; however, this mostly concerned M. blythii, which had a lower parasite load. Therefore, it can be concluded that interspecific differences in ectoparasite abundance may result from parasites selecting the host species that is less sensitive to their activity. In turn, in summer ectoparasites, the preference for female hosts is probably attributable to the likelihood of reinfection rather than to an effect of host resources or health status. The absence of sex-based preferences in winter ectoparasites could be explained by equal host availability.

Feeding in an unpredictable environment: yearly variations in the diet of the hazel dormouse Muscardinus avellanarius

Yearly variations in the diet composition of the hazel dormouse Muscardinus avellanarius were studied in typical dormouse habitat in Lithuania over 5 years (2010–2014) with different feeding conditions. A high proportion of birch seeds in the dormouse diet in two out of 5 years was a very much unexpected result. Dormice consumed them from mid-June until late October even when the most preferable food—hazel nuts—was abundant. In autumn when accumulating fat reserves for hibernation, hazel dormice fed on four main food sources—fruits of glossy buckthorn, oak acorns, hazel nuts and birch seeds. The consumption of these food sources was directly related to their availability. During the study period, only one, two or three of these food sources were abundant in any particular year, while others were absent or scarce. In total, the fruits of glossy buckthorn and oak acorns accounted for the major portion of dormouse diet in autumn. Dormice living in habitat with irregular fruiting of the main food plants are adapted to feed on varying food sources and can switch from one food source to another in different years.

Physiological leptin resistance

Leptin is an adipose tissue-derived hormone whose circulating levels correlate with the amount of body fat stores. The main function of this adipokine is to regulate energy metabolism. By modulating the expression of orexigenic and anorexigenic neuropeptides in the hypothalamus, leptin reduces appetite. It also increases energy expenditure, contributing to the decrease of body fat and body weight. Mutations in the leptin receptor gene or prolonged consumption of a high-fat diet may impair leptin action, leading to leptin resistance. Resistance to leptin can also be an adaptive response that occurs in seasonal animals and in pregnant mammals. Reversible insensitivity to the satiety signal of leptin promotes hyperphagia, which is essential for animals living in dynamic environments and experiencing seasonal variation in food availability, since it allows them to forage intensely when food is abundant and accumulate fat reserves necessary to survive periods when food is scarce. Moreover, leptin resistance and subsequent hyperphagia develop during pregnancy in order to meet the energy needs of the growing fetus. Physiological leptin resistance may be due to impaired transport of leptin across the blood-brain barrier and/or to decreased sensitivity of the hypothalamus to this hormone resulting from an inhibition of leptin signalling in hypothalamic neurons. In pregnancy, an increased resistance to leptin action is also mediated by the binding of this adipokine to its placenta-derived soluble receptor. Reduced entry of leptin into the brain as well as alterations in the leptin signalling pathway in the hypothalamus leads to a transient decrease in sensitivity to this hormone preventing appetite suppression.