Prehibernation Period Research Articles

Seasonal Variation in TLR4 Expression in The Testis and Epididymis of Anatolian Ground Squirrels (Spermophilus xanthoprymnus): Insights from Non-Breeding Period of Pre-Hibernation and Hibernation

This study investigates the modulation of Toll-like receptor 4 (TLR4) expression within the testis and epididymis of Anatolian ground squirrels (Spermophilus xanthoprymnus) during the non-breeding period of pre-hibernation and hibernation. Immunohistochemical investigation showed that TLR4 was not detected in germ cells, Leydig cells, or Sertoli cells in the testicular tissue during the pre-hibernation period. Nevertheless, there was a presence of TLR4 in the vessels walls and certain interstitial cells within the intertubular regions. Epithelial cells in the caput, corpus, and cauda regions of the epididymis showed no TLR4 expression. However, it was observed in the vessel walls, smooth muscle layers, and some interstitial cells. TLR4 expression was seen in spermatogonia and primary spermatocytes during hibernation, with strong labeling observed in the vessel walls of the intertubular area. In contrast, TLR4 was detected in the epididymal epithelium, as well as in the smooth muscle layers and vessel walls throughout all segments. A notable upregulation in the expression of TLR4 in the testis was identified through quantitative image analysis during hibernation as compared to pre-hibernation. During pre-hibernation, the cauda segment of the epididymis exhibited the highest expression of TLR4, whereas during hibernation, the corpus segment demonstrated the highest expression. These findings suggest a dynamic modulation of TLR4 in response to hibernation, highlighting its potential role in reproductive function and immune adaptation.

Supersize me: hypotheses on torpor-assisted prehibernation fattening in a boreal bat.

Hibernators face an energetic dilemma in the autumn at northern latitudes; while temperatures and food availability decrease, hibernating species need to build fat deposits to survive the winter. During this critical fattening phase, insectivorous boreal bats use torpor to build and conserve their reserves. However, we still know little about temporal variability in torpor use employed by bats during the prehibernation fattening period and how decreasing temperatures and food availability in combination with increasing individual body mass impact this. Here, we present two general hypotheses for explaining temporal torpor patterns observed in a boreal bat (Eptesicus nilssonii), in which torpor use (i) facilitates rapid mass gain or (ii) conserves stored body mass. Although temporally separated in our dataset, data on temperature, insect abundance and body mass throughout the prehibernation period indicate that E. nilssonii reaches the majority of its overwintering mass before the onset of increasing daytime and night-time torpor use. In combination with low food availability by this point in time, these observations suggest torpor expression may be intended to conserve gained reserves rather than facilitate mass gain. Our study is intended as a first proof of concept for disentangling temporal drivers of torpor in bats during the prehibernation fattening phase.

IGF-1 and myostatin-mediated co-regulation in skeletal muscle and bone of Daurian ground squirrels (Spermophilus dauricus) during different hibernation stages

Muscle and bone are cooperatively preserved in Daurian ground squirrels (Spermophilus dauricus) during hibernation. As such, we hypothesized that IGF-1 and myostatin may contribute to musculoskeletal maintenance during this period. Thus, we systematically assessed changes in the protein expression levels of IGF-1 and myostatin, as well as their corresponding downstream targets, in the vastus medialis (VM) muscle and femur in Daurian ground squirrels during different stages. Group differences were determined using one-way analysis of variance (ANOVA). Results indicated that the co-localization levels of IGF-1 and its receptor (IGF-1R) increased by 50% during the pre-hibernation period (PRE) and by 35% during re-entry into torpor (RET) compared to the summer active period (SA). The phosphorylation level of FOXO1 in the VM muscle increased by 50% in the torpor (TOR) group and by 82% in the inter-bout arousal (IBA) group compared to the PRE group. The phosphorylation level of SGK-1 increased by 54% in the IBA group and by 62% in the RET group compared to the SA group. In contrast, the protein expression of IGF-1 and phosphorylation levels of PI3K, Akt, mTOR, and GSK3β in the VM muscle showed no obvious differences among the different groups. β-catenin protein expression was up-regulated by 84% in the RET group compared to the SA group, while the content of IGF-1 protein, correlation coefficients of IGF-1 and IGF-1R, and phosphorylation levels of PI3K, Akt, and GSK3β in the femur showed no significant differences among groups. Regarding myostatin and its downstream targets, myostatin protein expression decreased by 70% in the RET group compared to the SA group, whereas ActRIIB protein expression and Smad2/3 phosphorylation in the VM muscle showed no obvious differences among groups. Furthermore, Smad2/3 phosphorylation decreased by 58% in the TOR group and 53% in the RET group compared to the SA group, whereas ActRIIB protein expression in the femur showed no obvious differences among groups. Overall, the observed changes in IGF-1 and myostatin expression and their downstream targets may be involved in musculoskeletal preservation during hibernation in Daurian ground squirrels.

Seasonal roost characteristics and fall behavior of coastal populations of Northern Myotis (Myotis septentrionalis)

Abstract Temperate bats exhibit seasonal and sex differences in resource selection and activity patterns that are influenced by ambient conditions. During fall, individuals face energetic trade-offs as they make choices relating to migration, mating, and hibernation that may diverge for populations throughout their range. However, research has largely focused on the summer maternity and winter hibernation seasons, whereas the prehibernation period remains comparatively understudied. Northern Myotis (Myotis septentrionalis) have experienced precipitous population declines from white-nose syndrome (WNS), leading to their protected status in the United States and Canada. Therefore, understanding their ecology throughout the year is paramount to inform conservation. We compared seasonal roosts and documented fall behaviors between study sites and sexes on 3 islands: Long Island (New York), Martha’s Vineyard, and Nantucket Island (Massachusetts). Between 2017 and 2020, we radio-tracked 54 individuals to analyze activity patterns and characterize fall roosts to compare with previously known summer roosts. Summer tree roosts were of smaller diameter, later stages of decay, and lower canopy closure than those used in fall. Both sexes selected trees of similar diameter and decay stage during fall. Anthropogenic roost use was documented in both seasons but use of anthropogenic structures was greater during fall and increased as the season progressed. Bats made short inter-roost movements with males traveling greater distances than females on average. Activity occurred until late November, with males exhibiting a longer active period than females. We tracked 23% of tagged bats to local hibernacula in subterranean anthropogenic structures, the majority of which were crawlspaces underneath houses. Use of anthropogenic structures for roosts and hibernacula may facilitate survival of this species in coastal regions despite the presence of WNS infections. Timing of restrictions on forest management activities for bat conservation may be mismatched based on prehibernation activity observed in these coastal populations, and the conservation of habitat surrounding anthropogenic roosts or hibernacula may be warranted if the structures themselves cannot be protected.

Peculiarities of adaptational changes in leukocytes and platelets of yakutian ground squirrels during the pre-hibernation period in autumn

Earlier, it was shown that a series of physiological and biochemical changes in Yakutian long-tailed ground squirrels start to happen during autumn (the pre-hibernation period): in the brain, heart, skeletal muscles, etc. This study was conducted to analyze the composition of peripheral blood cells obtained from Yakutian ground squirrels in autumn, and for the first time an increase in the total number of leukocytes, particularly granulocytes, and a decrease in the number of lymphocytes were observed when compared with those obtained in summer; a shift of the leukogram from the lymphocytic fraction to the granulocytic fraction was revealed. Significant increase in a platelet count and thrombocrit with preservation of the percentage ratio of mature and young cell fractions was shown. Still, information on the cellular components of blood during the autumn season when hibernators prepare for winter months of hibernation remains scarce. Nonetheless, the results of our study indicate that there are very significant adaptive changes that occur in leukocytes and platelets of ground squirrels in this period. Possible causes of these changes are discussed.

Patterns of Adaptational Changes in Leukocytes and Platelets of Yakutian Ground Squirrels during the Pre-Hibernation Period in Autumn

Patterns of Adaptational Changes in Leukocytes and Platelets of Yakutian Ground Squirrels during the Pre-Hibernation Period in Autumn

Lean Mass Dynamics in Hibernating Bats and Implications for Energy and Water Budgets.

AbstractHibernation requires balancing energy and water demands over several months. Many studies have noted the importance of fat for hibernation energy budgets, but protein catabolism in hibernation has received less attention, and whole-animal changes in lean mass have not previously been considered. We used quantitative magnetic resonance body composition analysis to measure deposition of fat and lean mass of cave myotis (Myotis velifer) during the prehibernation period and decreases in fat and lean mass of Townsend's big-eared bats (Corynorhinus townsendii) during hibernation. For cave myotis, lean mass represented 25% and 38% (female and male, respectively) of prehibernation mass gain. In hibernating Townsend's big-eared bats, lean mass decrease was similar for females and males. We used values for Townsend's big-eared bats to explore the functional implications of lean mass change for water and energy budgets. Lean mass accounted for a substantial proportion of mass change during hibernation (female: 18%, male: 35%), and although not accounting for a large proportion of the energy budget (female: 3%, male: 7%), lean mass catabolism represented an important contribution to water production (female: 14%, male: 29%). Although most mammals cannot rely on protein catabolism for metabolic water production because of the water cost of excreting urea, we propose a variation of the protein-for-water strategy whereby hibernators could temporally compartmentalize the benefits of protein catabolism to periods of torpor and the water cost to periodic arousals when free drinking water is typically available. Combined, our analyses demonstrate the importance of considering changes in lean mass during hibernation.

Energetski metabolizam u pankreasu tekunica (Spermophilus citellus) tokom produženog izlaganja hladnoći i u hibernaciji

Mammalian hibernators undergo a host of biochemical adaptations that allow them to survive the harsh cold environment and food restriction. Since the energy metabolism of the pancreas during hibernation remains unknown, we investigated the molecular basis of mitochondrial energy-producing pathways in line with their regulating mechanisms, as well as the (re)organization of antioxidative defence in the pancreas during the prehibernation period and in the hibernating state. To this end, male ground squirrels (Spermophilus citellus) were divided into two groups, the control group kept at room temperature (22±1 °C) and the group exposed to low temperature (4±1 °C). Active animals from the cold exposed group were sacrificed after 1, 3, 7, 12, and 21 days; animals that entered hibernation were sacrificed after 2-5 days of torpor. Our results showed that the protein levels of respiratory complexes I, II, IV and cytochrome c were increased in response to prolonged cold exposure (from day 12) and that such expression profiles were maintained during hibernation. In parallel, AMP-activated protein kinase a (AMPKa) and nuclear respiratory factor 1 (NRF-1) were shown to be upregulated. Moreover, prolonged cold exposure and hibernation induced an increase in the protein expression of antioxidative defence enzymes copper-zinc superoxide dismutase (CuZnSOD) and glutathione peroxidase (GSH-Px). In conclusion, these results point to a controlled metabolic remodeling in the pancreas of ground squirrels during prolonged cold exposure and in hibernation, which includes an improvement of mitochondrial oxidative capacity along with a proportional upregulation of antioxidative defence.

Patterns of resource use by Asiatic black bear Ursus thibetanus during pre-hibernation in Kashmir Himalaya, India

ABSTRACT Resource use is the way in which an animal (or population) utilises the available resources, and is known to occur in a hierarchical fashion. The Asiatic black bear Ursus thibetanus is an opportunistic omnivore whose diet and intensity of habitat use fluctuates with season and availability of resources in the environment. In this study, we assessed the habitat use and food habits of black bears during the autumn season (pre-hibernation) in Dachigam National Park, Kashmir Himalaya, to understand the reasons behind recurrent bear–human conflict in the area. We walked 14 natural trails covering different habitats of the study area. At each bear sign location, we recorded habitat variables in plots of 10 m radius. Black bear diet was assessed from 192 scats using a standard protocol. Black bear scat encounter rate varied significantly between habitats and was highest in forest scrub. Bear habitat use exhibited a significant association with medium canopy cover represented by the forest scrub and riverine habitat, and a negative association with the distance from human habitation, indicating use of forest patches close to nearby villages. Scat analysis revealed the occurrence of 17 plant species, mainly dominated by hard mast fruit species (88.54%) including Celtis australis (55.21%), Quercus robur (39.06%), and Pyrus malus (13.54%), with no evidence of animal food. Overall resource use by black bears showed a strong association with hard mast and fruit-producing trees adjacent to human habitations (i.e. orchard plantations close to forest scrub and riverine habitats), thereby increasing the risk of bear–human conflict. By elucidating the factors affecting bear occurrence and resource use during the autumn season, this study is expected to assist in resolving issues related to bear–human conflict management in the Dachigam landscape, particularly during their pre-hibernation period.

Retreat Sites Shared by Two Liolaemus Lizard Species: Exploring the Potential Role of Scents

Some lizard species modulate the use of a retreat site based on the presence of scents from other individuals, behavior that requires scent recognition. Here, we investigated if two congeneric and syntopic lizards (adults of Liolaemus coeruleus and juveniles of L. ceii, which can be found sharing retreat sites in the wild) discriminate scents from each other during the pre-hibernation period. If the presence of heterospecific scents modulates sharing retreat sites, species would discriminate each other's scents. Lizards were individually exposed to four treatments, which were enclosures with scents of (1) from the focal individual (own); (2) a conspecific of the same sex as the focal lizard; (3) a heterospecific of the same sex as the focal lizard; and (4) a control (i.e., enclosure with a clean substrate). Our results suggest that there is no heterospecific recognition. This finding was not due to an inability to chemo-assess scents, since both species exhibited self-recognition (recognition of their own scents) and juveniles of L. ceii also showed conspecific recognition. Although it might be advantageous for species to share retreat sites, chemical recognition of heterospecific scents does not modulate this behavior in these syntopic species.

Environmental variables do not explain the high size fluctuations in Rhinolophus euryale pre-hibernating aggregation

The Mediterranean horseshoe bat, Rhinolophus euryale, creates in the pre-hibernation period an aggregation in the Domica cave (Slovakia) and despite the harsh winter conditions displays a certain amount of flying activity. The goal of the study was to find out whether some environmental factors influence these conspicuous aggregation dynamics. We used image and statistical analysis of pictures of the aggregation taken automatically in the cave along with atmospheric pressure, humidity, outside and inside cave temperature and oxygen and carbon dioxide contents in the cave. These environmental variables were assumed to explain the observed activity. We hypothesised that the number of bats in particular time periods would correlate with some of these variables, but this was not confirmed. The only significant relations confirmed were those between bat numbers and humidity and carbon dioxide values in the cave. No trend in the spatial positioning of the bats was observed, and no environmental factors influenced the numbers, movements or groupings of bats. On the contrary, bats by their presence (breathing), activity and production of excrements may significantly influence the microclimate of the cave environment.

Active Turnover of Heme in Hibernation Period in Mammals.

Heme oxygenase (HO)-1 plays an important role during hibernation by catalyzing the degradation of heme to biliverdin/bilirubin, ferrous iron, and carbon monoxide, which activates the protective mechanisms against stress. In this context, it was important to analyze the metabolic processes of heme. Nevertheless, to date, no study has approached on biosynthesis of heme. Therefore, our study aims to understand the process of heme biosynthesis, which regulates cell survival in conditions of hypothermia and calorie restriction (CR). During hibernation, the mRNA levels of enzymes responsible for de novo heme biosynthesis were increased in the liver tissue of a Syrian hamster model of hibernation. Moreover, heme trafficking and iron metabolism were found to be more active, as assessed based on the changes in the levels of heme transporter and ferroportin mRNA. The levels of HO-1, a powerful antioxidant, were also upregulated during hibernation. Additionally, increased levels of Sirt-1 mRNA were also observed. These enzymes are known to act as cellular metabolic sensors that activate the cytoprotective mechanisms. These results indicate that HO-1 induction, brought about by the upregulation of heme during the pre-hibernation period, may protect against external stress. Here, we describe heme catabolism during hibernation by analyzing the regulation of the key molecular players involved in heme metabolism. Therefore, this study offers a new strategy for the better regulation of intracellular heme concentrations during hypothermia and other stresses.

Expressions of TLR4, MyD88 and IRAK4 in the Skin of Chinese Brown Frog (Rana Dybowskii) During the Breeding and Pre-Hibernation Periods

Toll-Like Receptors (TLRs) are membrane-bound proteins that recognize invading organisms with Pathogen-Associated Molecular Patterns (PAMPs) and Damage-Related Molecular Patterns (DAMPs)...

Expression patterns of natriuretic peptides in pre-hibernating and hibernating Anatolian ground squirrel (Spermophilus xanthoprymnus) kidney.

Hibernation is characterized by marked suppression of renal function. Natriuretic peptides (NPs) are involved in the regulation of renal function. However, the role ofNPs in the renal function during hibernation remains unclear. We aimed to investigate the distribution patterns of atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP) in Anatolian ground squirrel (Spermophilus xanthoprymnus) kidneys during pre-hibernation and hibernation periods. Cortical proximal tubules showed weak ANP immunoreactivity, with moderate staining on the brush border during the pre-hibernation period. In the hibernation period, moderate ANP immunoreactivity was seen in cortical proximal tubules, with very weak reaction in hibernating cortical distal tubules, medullary proximal and collecting tubules. Cortical proximal and distal tubules of both periods had strong and weak BNP immunoreactivity, respectively. Medullary proximal, distal and Henle's loop segments showed very weak BNP immunoreactivity during pre-hibernation. Medullary distal, proximal and collecting tubules and Henle's loop segments had moderate staining during hibernation. In both periods, cortical proximal tubules displayed strong immunoreactivity to CNP. Distal tubules had moderate CNP staining during pre-hibernation, albeit weak staining during hibernation. Medullary proximal tubules exhibited moderate to strong immunoreactivity during pre-hibernation. Medullary distal and proximal tubules had weak and moderate CNP staining, respectively, during pre-hibernation. In both periods, Henle's loop segments displayed moderate CNP immunoreactivity. Glomeruli had similar weak ANP, BNP and CNP staining in both periods. These results suggest that heterothermic conditions differently affected the expression of NPs in the squirrel kidney. This different expression of NPs may contribute to the renal adaptation during hibernation.

Localization profiles of natriuretic peptides in hearts of pre-hibernating and hibernating Anatolian ground squirrels (Spermophilus xanthoprymnus).

The Anatolian ground squirrel (Spermophilus xanthoprymnus) is a typical example of true mammalian hibernators. In order to adapt to extreme external and internal environments during hibernation, they lower their body temperatures, heart rates and oxygen consumption; however, pathological events such as ischemia and ventricular fibrillation do not occur in their cardiovascular systems. During the hibernation, maintenance of cardiac function is very important for survival of ground squirrels. Natriuretic peptides (NPs) are key factors in the regulation of cardiovascular hemostasis. Since NPs' role on the protection of heart during hibernation are less clear, the aim of this study was to investigate dynamic changes in NPs content in the cardiac chambers and to reveal the possible role of NPs on establishing cardiac function in ground squirrel during hibernation using immunohistochemistry. The immunohistochemical results indicate that cardiac NP expressions in atrial and ventricular cardiomyocytes were different from each other and were sex-independent. ANP and BNP were expressed in a chamber-dependent manner in female and male squirrel hearts. Furthermore, cardiac NPs expression levels in hibernation period were lower than those at the pre-hibernation period. During prehibernation period, ANP, BNP and CNP were expressed in the white and beige adipocytes of epicardial adipose tissue (EAT); while during hibernation period, the brown adipocytes of EAT were positive for BNP and CNP. These data suggest that the hibernation-dependent reduction in levels of NPs, particularly ANP, in cardiac chambers and EAT may be associated with low heart rate and oxygen consumption during hibernation. However, further studies are needed to better delineate the roles of NPs during the hibernation.

Molecular Basis of White Adipose Tissue Remodeling That Precedes and Coincides With Hibernation in the Syrian Hamster, a Food-Storing Hibernator.

Mammalian hibernators store fat extensively in white adipose tissues (WATs) during pre-hibernation period (Pre-HIB) to prepare for hibernation. However, the molecular mechanisms underlying the pre-hibernation remodeling of WAT have not been fully elucidated. Syrian hamsters, a food-storing hibernator, can hibernate when exposed to a winter-like short day photoperiod and cold ambient temperature (SD-Cold). Animals subjected to prolonged SD-Cold had smaller white adipocytes and beige-like cells within subcutaneous inguinal WAT (iWAT). Time-course analysis of gene expression with RNA-sequencing and quantitative PCR demonstrated that the mRNA expression of not only genes involved in lipid catabolism (lipolysis and beta-oxidation) but also lipid anabolism (lipogenesis and lipid desaturation) was simultaneously up-regulated prior to hibernation onset in the animals. The enhanced capacity of both lipid catabolism and lipid anabolism during hibernation period (HIB) is striking contrast to previous observations in fat-storing hibernators that only enhance catabolism during HIB. The mRNA expression of mTORC1 and PPAR signaling molecules increased, and pharmacological activation of PPARs indeed up-regulated lipid metabolism genes in iWAT explants from Syrian hamsters. These results suggest that the Syrian hamster rewires lipid metabolisms while preparing for hibernation to effectively utilize body fat and synthesize it from food intake during HIB.

Understanding patterns of distribution and space-use by Ursus thibetanus in Khangchendzonga, India: Initiative towards conservation

Increasing rate of bear-human conflict and declining black bear population remains a conservation paradox throughout its distributional range. Sound information on the patterns and dynamics of bear occurrence seems prerequisite towards addressing this issue, particularly in sub-tropical and temperate ecosystems. We aimed to understand the patterns of space-use and distribution of Asiatic black bears Ursus thibetanus in the Khangchendzonga Biosphere Reserve (BR) of Eastern Himalaya, and the factors influencing the same. We also modelled the distribution and extent of suitable habitats for bears in the Khangchendzonga landscape. We used sign surveys, trail monitorings, camera trapping, occupancy based space-use modelling and presence-only habitat suitability modelling using Ecological Niche Factor Analysis (ENFA). Almost all the black bear evidences (98%) were recorded from temperate and subalpine habitats. Broadleaved and coniferous forests were the best predictors for bear occurrence, and the percentage of acorn producing trees in temperate zone was the most important factor positively influencing the proportion of site utilization by bears during pre-hibernation periods. ENFA results indicate black bear as a ‘habitat specialist species’ and delineated only a small portion of the Biosphere Reserve (5.35%) as highly suitable for its occurrence. These highly suitable patches mostly occurred in the buffer zone outside the National Park boundary and were therefore, found as more susceptible to conflicts. Such patterns in habitat preference highlight the importance of local landscapes and demand for site specific conservation and management strategies for black bears in Khangchendzonga.

Documentation of Overwintering Bat Species Presence and Hibernacula Use In the Badlands of North Dakota

Little work has focused on species presence, distributions, and habitat use of bats in the Great Plains of North America. In particular, no previous study has attempted to determine if bats are utilizing hibernacula during the winter months in North Dakota. The current lack of information regarding bat species presence during the winter months in North Dakota can have great conservation implications. Pseudogymnoascus destructans, the fungal pathogen responsible for white-nose syndrome (WNS) in bats across the United States and Canada, has led to great concern for wildlife managers. For many of the areas where WNS is present, information about the presence and location of hibernacula are known, allowing for close monitoring of the spread of the disease. However, some locations within the predicted path of WNS still lack information as to bat species presence during the winter months. Due to mortality rates sometimes reaching upwards of 100% as a result of WNS infection, filling in these information gaps is critical for conservation research. The purpose of this study was to determine if the badlands region of North Dakota supports over-wintering bat communities, document both utilized and potential hibernacula, and develop a Geographic Information Systems model in the program MaxEnt to be used for future studies and wildlife managers. Six species were positively identified in the badlands region of North Dakota during the pre-hibernation and winter hibernation periods: Big Brown Bat (Eptesicus fuscus), Silver-haired Bat (Lasionycteris noctivagans), Little Brown Bat (Myotis lucifugus), Long-eared Myotis (Myotis evotis), Townsend's Big-eared Bat (Corynorhinus townsendii), and Western Small-footed Myotis (Myotis ciliolabrum). Habitat suitability modeling was employed to model potential hibernacula in the study area. Knowledge of these potential hibernacula could be of great importance to wildlife managers, and results from this study may be used by regional wildlife managers to develop strategies for curtailing the spread of this disease into North Dakota.

No evidence of hyperphagia during prehibernation in a northern population of little brown bats (Myotis lucifugus)

During autumn, temperate bats must deposit fat stores for hibernation. Populations at high latitudes face four challenges: a shorter active season and shorter nights during the active season (less time to accumulate fat), a longer hibernation period (larger fat store needed), and colder nights (reduced prey availability). Mating also occurs during the prehibernation period, placing time constraints for mating and fattening on northern populations. We tested the hypothesis that these factors constrain prehibernation foraging in northern populations of little brown bats (Myotis lucifugus (Le Conte, 1831)). We measured plasma triglyceride concentration to study prehibernation fueling rates of a population near the northern range limit of the species and compared our results with previously published results from a more southern population. In contrast to bats at the lower latitude, we found consistently low concentrations of plasma triglycerides, indicating a low fuelling rate throughout the prehibernation period. However, despite an apparently low fuelling rate, bats achieved a substantially greater body mass. The discrepancy between populations suggests that environmental constraints lead northern populations to employ different behavioural or physiological strategies to prepare for hibernation.

Proliferation and apoptosis processes in the seasonal testicular development of the wild Daurian ground squirrel (Citellus dauricus Brandt, 1844).

The aim of the present study was to elucidate the regulatory role of cell proliferation and apoptosis in testicular development of wild Daurian ground squirrels during the breeding season (April), the non-breeding season (June) and before hibernation (September). Gross mass and hormonal analysis showed that the testis:body mass ratio and plasma testosterone concentration fluctuated seasonally, with a peak in April and lowest values in June. Similarly, spermatogenesis was fully developed in April but suppressed in June and September. Testicular decellularisation and vacuolisation was seen during the transition from the breeding to the non-breeding season. Furthermore, testicular levels of proliferating cell nuclear antigen, cyclin D2 and caspase-3 protein were significantly increased in June and September. Intriguingly, positive terminal deoxyribonucleotidyl transferase-mediated dUTP-digoxigenin nick end-labelling staining and nuclear translocation of caspase-3 in testicular germ cells appeared only during the prehibernation period, whereas accumulation of cyclin D2 in spermatocyte nuclei occurred in September. These findings demonstrate, for the first time, that both cell proliferation and apoptosis are stimulated during the prehibernation period, indicating that a hormonal-regulated balance of testicular germ cell proliferation and apoptosis may play a pivotal role in preparing for testicular recrudescence of wild Daurian ground squirrels.