Animal models are a key component of translational medicine, helping transfer scientific findings into practical applications for human health. A fundamental principle of research ethics involves weighing the benefits of the research to society against the burden imposed on the animals used for scientific purposes. The utilisation of wild animals for research requires evaluation of the effects of capture and invasive sampling. Determining the severity and duration of these interventions on the animal’s physiology and behaviour allows for refining study methodology and for excluding or accounting for biased data. In this study, 39 Scandinavian brown bears (Ursus arctos) captured either while hibernating in winter or via helicopter in summer and that underwent surgery as part of a human health project had their movement, body temperature and timing of onset of hibernation compared with those of 14 control bears that had not been captured during the same period. Bears captured in winter and summer showed decreased movement from den exit until late summer, compared to those in the control group. Bears captured in summer showed reduced movement and body temperature for at least, respectively, 14 and 3 days, with an 11% decrease in hourly distance, compared to pre-capture levels, but did not differ in the timing of hibernation onset. We reveal that brown bear behaviour and physiology can be altered in response to capture and surgery for days to months, post-capture. This has broad implications for the conclusions of wildlife studies that rely upon invasive sampling.

Hibernation is a biological status during which hibernating animals acclimatize themselves to reduced energy consumption through extreme but governed decline in self-metabolism. The role of mitochondria (Mt) in metabolic suppression during hibernation has already been elaborated in different organs and species. Nonetheless, the concretely changing process of mitochondrial architecture and the mechanism underlying this transformation during hibernation remains unclear. Herein, the present study was aimed at clarifying the detailed alteration of mitochondrial morphology and its potential role in the Chinese soft-shelled turtle (Pelodiscus sinensis) during different stages of hibernation. Compared with the nonhibernation period, the mitochondrial architecture was changing from round to crescent, and lipid droplet (LD)/Mt interaction was enhanced during hibernation, as observed by transmission electron microscopy (TEM). Further ultrastructural analysis uncovered that mitochondrial fusion was promptly accelerated in the early stage of hibernation, followed by mitochondrial fission in the middle stage, and mitophagy was boosted in the late stage. Moreover, gene and protein expression related to mitochondrial fusion, fission, and mitophagy accorded closely with the mitochondrial ultrastructural changes in different stages of hibernation. Taken together, our results clarified that the transformation of mitochondrial architecture and mitochondrial dynamics are of vital importance in maintaining internal environment homeostasis of Pelodiscus sinensis.

Determination of critical threshold for induction and termination of diapause (hibernation) are important for better understanding the bio-ecology and population dynamics of Chilo partellus (Swinhoe) under varying climatic conditions. We studied initiation and termination of hibernation under five temperature and photoperiod regimes viz., 27°C + 12L:12D, 22°C + 11.5L:12.5D, 18°C + 11L:13D, 14°C + 10.5L:13.5D and 10°C + 10L:14D under fixed and ramping treatments, and the observations were recorded on various phenological and developmental characteristics at weekly intervals. Present studies revealed that the induction of hibernation in C. partellus larvae takes from 46 to 56 days depending upon temperature and photoperiod conditions. Induction of hibernation varied from 7.9 to 18.3% across treatment conditions, indicating that not all C. partellus larvae undergo diapause under prevailing environmental conditions. Weight, length and head capsule width of diapausing larvae were found significantly lower than the non-diapausing larvae. The non-diapausing C. partellus larvae required a thermal threshold of 1068 degree-days under ambient conditions, while in case of hibernating larvae it varied significantly across treatment conditions. Diapausing larvae underwent up to five supernumerary moults, wherein highest percentage of diapausing larvae (35.7%) exhibited two supernumerary moults. The developmental time of diapausing larvae varied from 94.9 to 160.4 days across treatments. A population loss of 17.2–28.3% was recorded in C. partellus due to hibernation, which has implications for population buildup of post-hibernation first brood and management strategies.

During late autumn insectivorous bats must deposit a fat store to cover their energy demands throughout the period of hibernation, yet the density of aerial insects by this time has already declined from its peak in midsummer. Krzanowski (1961) suggested that bats are able to deposit a fat store by manipulating their energy expenditure; specifically by selecting cold roosting locations rather than warm roosts, and depressing their body temperatures during the day roosting period. It was hypothesized that these behavioural changes result in very low daily energy demands, and despite reduced food intake the animals are still able to gain body fat. We made several tests of this hypodiesis. First, we explored the thermo-selection behaviour of long-eared bats (Plecotus auritus) in the summer and in the pre-hibernal period. We found that in summer bats preferred temperatures of about 32–35° (about thermoneutral), but in the pre-hibernal period they preferred much colder temperatures of about 10°. Second, using open-flow respirometry we found that in the cold pre-hibernal bats entered torpor for an average of 14 h each day. Compared with bats held at 30° (that did not go torpid), the bats at 7° expended less energy. The extent of saving was sufficient to positively affect their mass balance, despite the fact that bats at lower temperature also had reduced digestive efficiencies. Our findings support the hypothesis that during the pre-hibernal period insectivorous bats manipulate their mass balance primarily by alterations in their energy expenditure, specifically utilizing energy-sparing mechanisms such as torpor.

Microbes, particularly Archaea, are well-known for their superb adaptation to extreme environments. However, amazing adaptations to extreme stresses do not only occur in microbes, but also in many multicellular organisms. Examples include tardigrades and their capability to survive freezing to near absolute zero, the Pompeii worm withstanding temperatures of up to 105°C, the Crucian carp remaining active in anoxic conditions for several months, and resurrection plants, which can survive near-complete desiccation. Here, we review some of the cryptobiotic strategies and adaptations exhibited in multicellular organisms, and point out their relevance to astrobiology.

Polistes dominulus are social wasps which are the host of the strepsipteran endoparasite Xenos vesparum. In the hibernating phase, unparasitized and parasitized wasps leave natal nests and aggregate together in sheltered quarters. In aggregations, wasps are socially active, and some individuals perform helping behaviour. Here we investigated if castrated parasitized wasps perform worker tasks in mixed aggregations. Moreover, by gas chromatography and mass spectrometry, we examined the cuticular hydrocarbons of unparasitized and parasitized wasps to evaluate if the infection alters the composition of cuticular waxes that are recognition cues in social insects. In clusters, infected females do not perform helping behaviour and they are less active than unparasitized wasps. Cuticular hydrocarbons are slightly differentiated between unparasitized and parasitized wasps but, generally, unparasitized wasps are more similar to wasps infected by Xenos females compared to wasps infected by Xenos males. Wasps infected by Xenos males do not usually survive the winter. This chemical similarity is probably a consequence of the similar physiological condition of unparasitized and female-affected Polistes wasps. At this stage, it is difficult to affirm whether these modifications are a true parasite manipulation or a consequence of infection.

The seasonal activity of the common dormouse Muscardinus avellanarius was studied in three different habitat types of central Italy: a deciduous beech wood dominated by Fagus sylvatica (Cimini Mountains), and a deciduous oak woodland with Quercus cerris and Q. pubescens and an evergreen wood dominated by holm oak Q. ilex, both along the central Tyrrhenic coast. In each site, 50 nest-boxes were fixed to trees and were monitored monthly for 2 years (May 1998–April 2000). In the beech wood site, the species showed an annual biological cycle similar to that described for populations of central and northern Europe: dormancy in winter, from the first 10 days of November to the end of December; end of hibernation in the first half of April; reproduction between May and July. On the contrary, in the two coastal sites, nest-boxes were occupied from October to June, and the breeding period was in autumn, showing that a winter dormancy phase is absent, probably owing to the mild winter. On the other hand, no dormice or new nests were observed in nest-boxes in summer suggesting that a dormancy phase occurred in summer, probably owing to dry climatic conditions. Two patterns of biological cycle therefore emerged from the results: a temperate pattern in beech forest with winter dormancy and spring reproduction, and a Mediterranean pattern in coastal habitats with autumnal reproduction, winter activity and summer dormancy.

The purpose of this study was to determine whether hibernating European hamsters Cricetus cricetus, L., 1758 stay in their burrows all winter or if they occasionally spent time above ground. If ‘time (spent) above ground’ (TAG) occurred regularly throughout hibernation, the second objective of this work was to categorize and quantify the patterns of TAG during winter. For this purpose, 11 European hamsters were individually housed in wire mesh cages that were buried in the ground of an outdoor enclosure. Each cage was filled with soil up to ground level allowing the animals to construct their own burrows within the cages. Antennae in the bottom and top of the cage were calibrated to receive signals only when the hamsters were in their burrows or above the ground, respectively. This method enabled continuous recordings of the animal's TAG and provided ecologically meaningful results as the animals were housed in a way that closely resembled their natural habitat. About half of the hamsters stayed continuously below ground. Of these hamsters, almost all showed a dense pattern of episodes of reduced body temperature separated by only brief periods of normothermia. In contrast, the other half of the animals moved either episodically or even regularly above ground. For all of these hamsters, TAG was significantly reduced as compared to normothermic values. One hamster did not show any hibernation but did have a significantly reduced normothermic body temperature and did not leave its burrow for periods of up to 3 weeks.

Metabolic rate depression is an important survival strategy for many animal species and a common element of hibernation, torpor, aestivation, anaerobiosis, diapause, and anhydrobiosis. Studies of the biochemical mechanisms that regulate reversible transitions to and from hypometabolic states are identifying principles of regulatory control that are conserved across phylogenetic lines and that are broadly applied to the control of multiple cell functions. One such mechanism is reversible protein phosphorylation which is now known to contribute to the regulation of fuel metabolism, to ion channel arrest, and to the suppression of protein synthesis during hypometabolism. The present review focuses on two new areas of research in hypometabolism: (1) the role of differential gene expression in supplying protein products that adjust metabolism or protect cell functions for long-term survival, and (2) the mechanisms of protein life extension in hypometabolism involving inhibitory controls of transcription, translation and protein degradation. Control of translation examines reversible phosphorylation regulation of ribosomal initiation and elongation factors, the dissociation of polysomes and storage of mRNA transcripts during hypometabolism, and control over the translation of different mRNA types by differential sequestering of mRNA into polysome versus monosome fractions. The analysis draws primarily from current research on two animal models, hibernating mammals and anoxia-tolerant molluscs, with selected examples from multiple other sources.

Annual local survival of the garden dormouse Elyomis quercinus, a small, hibernating rodent, was studied by Cormack–Jolly–Seber models. The survival rates differed significantly between the 4 years of the study; the average rate was 0.38 (95% confidence interval: 0.25–0.52). Survival rates were not significantly different between sexes. Because all garden dormice were captured after weaning, pre-weaning survival could not be estimated. After weaning, the annual survival rates did not differ between age cohorts. In order to find out which phases within the annual cycle were more prone to mortality, survival was studied on a bimonthly scale as well. Survival during hibernation was estimated to be close to unity, while survival during the active phase of life in summer was considerably lower. The winter temperatures of the study years were similar to the long-year average; thus garden dormice were well adapted to these average conditions. Although hibernation is energetically challenging, it is not necessarily accompanied by increased mortality, as found in other studies focusing on survival during hibernation.

Activity patterns of greater horseshoe bats Rhinolophus ferrumequinum were investigated at caves in Cheddar (south-west England) during the hibernation season. An ultrasound detector and datalogger were used to monitor and record the number of echolocation calls in a single cave. Activity of R. ferrumequinum remained largely nocturnal throughout winter, and the mean time of activity over 24 h was 88 to 369 min after sunset. There was an increase in diurnal activity from late May to early June, probably because bats remained active after foraging at dawn towards the end of the hibernation season. Visits to the cave did not increase bat activity. Cave air temperature reflected external climatic temperature, although there was variation in cave temperature and its range within and among caves. Individual R. ferrumequinum are usually dispersed in caves in regions where temperature fluctuations correlate with climatic variations in temperature. There was a positive correlation between the number of daily bat passes monitored by the bat detector and datalogger (= daily activity) and cave temperature. Nocturnal activity may be sometimes associated with winter feeding. Neither date nor barometric pressure had a significant effect on daily activity. Activity patterns largely reflected the findings from individual R. ferrumequinum studied by telemetry (Park, 1998), in that bat activity increased with cave and climatic temperatures, and the temporal pattern of activity remained consistently nocturnal throughout winter, starting at dusk.