Spermophilus Citellus Research Articles

The Physiological Link between Metabolic Rate Depression and Tau Phosphorylation in Mammalian Hibernation

Abnormal phosphorylation and aggregation of tau protein are hallmarks of a variety of neurological disorders, including Alzheimer's disease (AD). Increased tau phosphorylation is assumed to represent an early event in pathogenesis and a pivotal aspect for aggregation and formation of neurofibrillary tangles. However, the regulation of tau phosphorylation in vivo and the causes for its increased stage of phosphorylation in AD are still not well understood, a fact that is primarily based on the lack of adequate animal models. Recently we described the reversible formation of highly phosphorylated tau protein in hibernating European ground squirrels. Hence, mammalian hibernation represents a model system very well suited to study molecular mechanisms of both tau phosphorylation and dephosphorylation under in vivo physiological conditions. Here, we analysed the extent and kinetics of hibernation-state dependent tau phosphorylation in various brain regions of three species of hibernating mammals: arctic ground squirrels, Syrian hamsters and black bears. Overall, tau protein was highly phosphorylated in torpor states and phosphorylation levels decreased after arousal in all species. Differences between brain regions, hibernation-states and phosphosites were observed with respect to degree and kinetics of tau phosphorylation. Furthermore, we tested the phosphate net turnover of tau protein to analyse potential alterations in kinase and/or phosphatase activities during hibernation. Our results demonstrate that the hibernation-state dependent phosphorylation of tau protein is specifically regulated but involves, in addition, passive, temperature driven regulatory mechanisms. By determining the activity-state profile for key enzymes of tau phosphorylation we could identify kinases potentially involved in the differentially regulated, reversible tau phosphorylation that occurs during hibernation. We show that in black bears hibernation is associated with conformational changes of highly phosphorylated tau protein that are typically related to neuropathological alterations. The particular hibernation characteristics of black bears with a continuous torpor period and an only slightly decreased body temperature, therefore, potentially reflects the limitations of this adaptive reaction pattern and, thus, might indicate a transitional state of a physiological process.

ALARM CALLS OF THE EUROPEAN GROUND SQUIRREL SPERMOPHILUS CITELLUS AND THE TAURUS GROUND SQUIRREL S. TAURENSIS ENCODE INFORMATION ABOUT CALLER IDENTITY

ABSTRACT Vocalizations of many mammalian species have been reported to encode information about caller identity. In this study, we analyzed 300 alarm calls from 10 free-living European Ground Squirrels Spermophilus citellus (30 per individual) and 300 alarm calls from 10 free-living Taurus Ground Squirrels S. taurensis (30 per individual), and tested the potential of these calls to encode information about the callers' identities. Discriminant analysis including all 10 European Ground Squirrel individuals correctly classified 98% of calls, and cross-validation reached a classification success of 97%. Correct classification of 98% and cross-validation of 98% was assigned when the analysis included only those individuals producing calls consisting of both elements (eight individuals). For the Taurus Ground Squirrel, correct classification was 95% and cross-validation 94% for all 10 animals. When only those individuals producing calls consisting of both elements were included (eight individuals), discriminant analysis led to 94% correct classification and cross-validation produced a classification success of 93%. These analyses demonstrate that the structure of alarm calls in these two closely related species is highly variable and that it has significant potential to encode information about caller identity.

Nest material selection affects nest insulation quality for the European ground squirrel (Spermophilus citellus)

Natural nests of the European ground squirrel (Spermophilus citellus) are constructed almost exclusively of fresh fescue (Festuca pseudovina: Poaceae). We performed laboratory experiments to understand the functional significance of preference of wild squirrels for nest material. We examined the factors contributing to nest quality by monitoring the construction and analyzing the composition of squirrel nests. As in the wild, squirrels showed strong preference for fescue during the laboratory tests and preferred fresh material to dry material. Because preference for fresh material was not expected, because high water content reduces insulation, we manipulated the moisture content of nests made from either fresh or dry fescue to determine how nest quality and moisture level contribute to insulation. We found that the insulation property of fresh grass nests was superior to nests constructed from dry grass only. Intracellular water in the nest material did not affect thermal conductance and insulation significantly. We concluded that fresh fescue provided a more flexible material that allows squirrels to construct nests with better insulation under both field and laboratory conditions.

Blood cell dynamics during hibernation in the European Ground Squirrel

Hibernation is a unique natural model to study large and specific modulation in numbers of leukocytes and thrombocytes, with potential relevance for medical application. Hibernating animals cycle through cold (torpor) and warm (arousal) phases. Previous research demonstrated clearance of leukocytes and thrombocytes from the circulation during torpor, but did not provide information regarding the timing during torpor or the subtype of leukocytes affected. To study the influence of torpor-bout duration on clearance of circulating cells, we measured blood cell dynamics in the European Ground Squirrel. Numbers of leukocytes and thrombocytes decreased within 24 h of torpor by 90% and remained unchanged during the remainder of the torpor-bout. Differential counts demonstrated that granulocytes, lymphocytes and monocytes are all affected by torpor. Although a decreased production might explain the reduced number of thrombocytes, granulocytes and monocytes, this cannot explain the observed lymphopenia since lymphocytes have a much lower turnover rate than thrombocytes, granulocytes and monocytes. In conclusion, although underlying biochemical signaling pathways need to be unraveled, our data show that the leukocyte count drops dramatically after entrance into torpor and that euthermic cell counts are restored within 1.5 h after onset of arousal, even before body temperature is fully normalized.

Interspecific Aggressive Behaviour of European Ground Squirrel (Spermophilus Citellus L.)

ABSTRACTInterspecific behaviour of European ground squirrel (Spermophilus citellus) is still poorly studied. During behavioural studies of free-ranging European ground squirrels tree kinds of aggression to other vertebrate species: reptile, bird and mammal (Lacerta trilineata, Corvus frugilegus, Mustela nivalis) have been described. To our knowledge, this is the first field study describing interspecies aggressive behaviour in S. citellus. The description of this behaviour may have important implications for interpreting studies on interspecies competition and interactions, behaviour activity, and predation in this rear and threatened semi-fossorial rodent.

Diuretic treatment affects the length of torpor bouts in hibernating European ground squirrels (Spermophilus citellus)

During the hibernation season, hibernating mammals show a sequence of torpor bouts that are interrupted by periodic arousals and brief normothermic periods. The functional significance of periodic arousals is still uncertain. We hypothesized that the imbalances in water economy may play a role in the timing of periodic arousals in hibernating species. We applied furosemide, a diuretic drug, to assess whether hibernating European ground squirrels respond to elevated urine production by shortening their torpor bouts. Urine production in the treated squirrels increased and led to more frequent arousals, presumably to restore water balance by recovery of lost water from blood and tissues. The length of the subsequent normothermic phase was not affected by the diuretic treatment. Body mass change correlated primarily with the amount of voided urine. Although our study did not identify the underlying mechanism, our results support the view that water economy, and water loss may play a role in the timing of periodic arousals.

The morphology of the circulus arteriosus cerebri in the ground squirrel (Spermophilus citellus)

In this study, the circulus arteriosus cerebri of the ground squirrel (<i>Spermophilus citellus</i>) was investigated. Five ground squirrels were used as subjects. Coloured latex was injected from the left ventriculi of the hearts of all the squirrels. When the vertebral arteries of two of the animals were ligatured, it was found that there was no internal carotid artery. After careful dissection, the circulus arteriosus cerebri (the circle of Willis) was investigated. The right and left vertebral arteries gave rise to the caudal cerebellar artery before forming the basilar artery. The basilar artery formed the caudal communicans artery that was the caudal part of the circulus arteriosus cerebri on the pontocrural groove (sulcus pontocruralis). The caudal, medial, rostral cerebellar, the common root formed by the caudal cerebral and choroid arteries, the rostral choroid, the rostral and medial cerebral arteries arose from the vertebral, basilar and caudal communicans arteries and dispersed to the cerebrum and cerebellum from caudal to cranial. The termination and the branches of the rostral cerebral artery in ground squirrels varied. It was observed that the internal carotid artery does not supply the circulus arteriosus cerebri in ground squirrels.

Mitochondrial phylogeography of the European ground squirrel, Spermophilus citellus, yields evidence on refugia for steppic taxa in the southern Balkans

The spatial genetic structure of the European ground squirrel, a species characteristic of the short-grass steppe, was investigated on the basis of a 1140-bp cyt b gene sequence. The phylogeographical architecture of this species is expected to shed light on the putative long-term presence of the steppic ecosystem in south-eastern Europe and the evolutionary consequences of glacial cycles as forcing factors in speciation. Among 31 haplotypes, three highly divergent phylogenetic lineages (Southern, Northern and Jakupica) were recognized. This result suggests the past existence of an allopatric fragmentation event caused by effective biogeographical barriers. The Southern lineage consisted of the southernmost populations, those from Greece, Macedonia and European Turkey, and showed the highest divergence from all other samples. Haplotypes of the Northern lineage showed little geographical structure, with dispersal on both sides of the Danube River and in both of the two main geographical fragments of the species. The Jakupica lineage is a geographical isolate on a high plateau in central Macedonia. The estimated time for divergence of the Southern lineage (ca. 0.58 Mya) suggests the long-term persistence of a short-grass steppic refugium in the southern Balkans. Although the divergence between the Northern and Jakupica lineages occurred more recently (ca. 0.3 Mya), it still putatively predates two glacial cycles. The three phylogeographical lineages of the European ground squirrel should be regarded as independent units for conservation management purposes.

Ambient temperature and annual timing affect torpor bouts and euthermic phases of hibernating European ground squirrels (Spermophilus citellus)

The low body temperature state of hibernating mammals is interrupted regularly by short euthermic phases. The frequency of these euthermic phases changes according to the phase of hibernation. This typical pattern, common among ground squirrels (genus Spermophilus F. Cuvier, 1825), can be regulated by internal factors and affected by outside temperature. To evaluate the effects of internal annual timing and ambient temperature, we monitored nest temperatures of overwintering European ground squirrels ( Spermophilus citellus (L., 1766)) under three temperature conditions during late hibernation (9, 5, 0 °C). Our results showed that in spite of constant thermal conditions, an annual timing effect changed torpor-bout length (TBL) at 9 and 5 °C but not at 0 °C. Ambient temperature had an independent influence on TBL and euthermic phases. The loss in body mass was higher at higher ambient temperatures and was affected by TBL and euthermic phases. Thus, the hibernation pattern of European ground squirrels is regulated by both an annual timing pattern and the ambient temperature in the hibernacula.

Distribution and Current Status of the European Souslik (Spermophilus Citellus L.) in Sofia Valley and the Adjacent Areas

ABSTRACTIn the last decades the situation of the European souslik in Bulgaria is undergoing substantial changes towards reduction of inhabited territories and extinction in a number of formerly inhabited areas, which respectively changed its conservation status. At the same time, there is a definite shortage of detailed data concerning the situation of this species in many regions of the country. The present research determines the species ' situation in the study area—Sofia valley and its adjacent territories. A distribution map of the species is elaborated, and the distribution changes dating from the middle of the past century till present day are analyzed. An assessment of the contemporary population status in the study area is made, based on relative population density and on the sizes of inhabited areas. The data obtained allowed the potential risk factors to be estimated and a number of measures for monitoring and protection of the species to be proposed.

Vaginal oestrus during the reproductive and non-reproductive period in European ground squirrels

Most hibernating animals are thought to be monoestrous because reproductive activity is subject to strong time constraints. In previous studies, female European ground squirrels ( Spermophilus citellus) turned out to have elevated oestradiol levels during late lactation and after weaning, indicating ovarian activity during summer. Therefore, we monitored vaginal cytology, endocrine changes, and vulval development in semi-free-living female European ground squirrels throughout one active season. Vaginal oestrus, defined by the predominance of cornified cells in smear samples, was found during the mating period shortly after vernal emergence. This phase was followed by metoestrus, characterised by the appearance of leukocytes, and a subsequent anoestrous phase. During weaning or postlactation, a second vaginal oestrus was documented in all experimental females, again followed by a metoestrous and an anoestrous phase lasting until hibernation. In line with the second vaginal oestrus, plasma oestradiol concentrations peaked during postlactation. Progesterone levels were elevated from gestation to postlactation, and titres were marginally higher during vaginal oestrus in summer than in spring. Vulval swelling was more pronounced during the first than the second vaginal oestrus. The second oestrous cycle was non-reproductive, as males were sexually inactive with regressed testes during summer. We assume that the second oestrous cycle and the accompanying endocrine changes have beneficial effects on prehibernatory fattening and reproductive performance in the subsequent season. This might allow females to become oestrous immediately after emergence from hibernation in spring.

Follicular development in European ground squirrels (Spermophilus citellus) in different phases of the annual cycle

In seasonally breeding mammals, in particular hibernators, reproduction underlies severe energetic and temporal constraints to enable the allocation of sufficient body fat reserves before winter. Thus, the timing of conception in spring can be crucial in terms of reproductive success. This study investigates follicular development in European ground squirrels (Spermophilus citellus) in three phases of the annual cycle: at vernal emergence, after weaning the offspring and shortly before hibernation. The animals were kept in outdoor enclosures within the natural habitat of the species. They were captured in weekly intervals, weighed and reproductive status was determined. Unilateral ovariectomy was scheduled such that the three periods were sampled. Numbers and diameters of tertiary follicles (TF) and corpora lutea (CL) in each ovary were determined, and plasma oestradiol and progesterone levels were analysed. The highest numbers of TF, including Graafian follicles, were found in ovaries at vernal emergence. During post-lactation, the number of TF was lower and active CL appeared in the investigated ovaries. Shortly before hibernation, active CL were present, but luteolysis had started in some individuals. Both oestradiol and progesterone secretion peaked after the termination of lactation and decreased before hibernation. The results demonstrate a second oestrus cycle in European ground squirrels after weaning, including an active luteal phase. This non-reproductive oestrus cycle with its endocrine output is an intriguing phenomenon. It may positively affect both prehibernatory fattening and reproduction in the subsequent season.

Testis development and testosterone secretion in captive European ground squirrels before, during, and after hibernation

In some hibernating species, an extended euthermic period before spring emergence has been reported during which testicular maturation occurred. In this study, we investigated whether male European ground squirrels Spermophilus citellus (Linnaeus, 1766) develop scrotal testes before or after the termination of hibernation. The course of testis development and testosterone concentrations were examined in young-of-year male ground squirrels (n = 4) before, during, and after their first hibernation. In the environmental chamber, all animals showed regular hibernation patterns with decreasing torpor bout lengths prior to the end of hibernation. Four weeks before hibernation ended, testosterone levels were elevated during spontaneous arousals. Testosterone concentrations peaked during the first 2 months post heterothermy and decreased thereafter. In 2 experimental males, testes descended from the inguinal region into the scrotum shortly before the end of heterothermy. The state of testis development and testosterone secretion corresponded to that found in semi-free-living males at spring emergence. Testis size increased in active animals to maximum widths during weeks 3 and 4 post heterothermy. Scrotal skin pigmentation was absent until heterothermy ended and developed during the first month thereafter. The data suggest that male S. citellus do not need a pre-emergence euthermic period for reproductive development.

A Paksi ürge-mező ürgéi

Density and dispersion of the ground-squirrel (Spermophilus citellus) on the Paks Ürge-mező (part of the Dél-Mezőföld Landscape Area) was studied by squirrel hole counting. In autumn of 2006 the density of squirrels was 8 ind./ha and in spring of 2007 was 28-30 ind./ha.

Sexually mature and immature yearling male European ground squirrels: A comparison of behavioral and physiological parameters

Early puberty may increase lifetime reproductive success, but may also entail diverse costs. In male European ground squirrels ( Spermophilus citellus), age at sexual maturity varies among individuals. We compared sexually active and inactive yearling males under standardized conditions in outdoor enclosures. Non-reproductive yearling males hibernated significantly longer than mature males and emerged when the mating period had already started. Testosterone concentrations peaked in the precocious males during premating and mating, and were depressed in the non-reproductive individuals throughout the study period. Emergence body mass was similar in both groups, although sexually immature males were significantly heavier at the end of the active season. Additionally, non-reproductive yearlings grew faster than precocious individuals. Male–male aggression peaked during mating and the following 4 weeks. Intense aggressive interactions like chases and fights were mostly initiated by reproductive males and were directed towards mature competitors. Aggressive behavior in immature males was mainly expressed as spatial displacements. Non-agonistic interactions with females were only observed in sexually active males. Concentrations of fecal cortisol metabolites did not differ between the two male groups and were elevated in the second half of the active season. Leucocyte numbers were reduced during mating in mature males, whereas in immature animals, cell numbers did not change significantly. Our results indicate that early puberty in European ground squirrels involves lower growth rates, high intrasexual aggression, lower prehibernatory body mass, and probably worse immunological condition during mating.

Population genetic structure of the European ground squirrel in the Czech Republic

The European ground squirrel (Spermophilus citellus) is considered an endangered species with declining numbers throughout Europe, most pronounced at the western margin of its distribution area. Being extinct in Germany and Poland, the western margin of its distribution is in the Czech Republic. Here, landscape fragmentation has restricted the ground squirrels into few and very isolated localities where local extinctions still occur. In the present study we analysed European ground squirrels from six Czech and one Slovak localities using five microsatellite loci as genetic marker. The results show a strong genetic differentiation among the investigated populations (mean value of F ST = 0.16) and high levels of inbreeding (values of F IS ranged from 0.34 to 0.90). High level of inbreeding is generally considered to affect the viability of each population, which could lead to extinction. One of the most important factors is the lack of migration due to the large distances between the populations and the presence of migration barriers. Based on the results obtained we recommend a few suggestions for a conservation management of this species.

Taxonomic status of the genus Spermophilus (Mammalia: Rodentia) in Turkey and Iran with description of a new species

We report a new species of Spermophilus ( Rodentia: Sciuridae), here designated as S. torosensis sp. nov., distributed in the Taurus Mountains in southern Anatolia, Turkey. A total of 161 specimens of the genus Spermophilus from Turkey and Iran were analyzed for their morphological, morphometric, and karyological characteristics. Uni- and multi-variate statistical analyses of morphologic data for 95 adult specimens yielded 4 distinct groups. Taxonomic evaluations classified the specimens into 4 species Spermophilus citellus, S. xanthopymnus, S. fulvus and S. torosensis sp. nov. Morphometrics, coat coloration, a brush-shaped tail, and a NFa value of 72 are diagnostic characters that distinguish S. torosensis sp. nov. from the other species. In Turkey, S. torosensis sp. nov. was found in 6 locations. The karyotype of S. fulvus also is described for the first time as 2n= 36, NFa= 70 and NFa= 66; new karyotypic data is reported for S. xanthoprymnus from Iran and Turkey.

Multigenic and morphometric differentiation of ground squirrels ( Spermophilus, Scuiridae, Rodentia) in Turkey, with a description of a new species

This study reports on the molecular phylogenetics of ground squirrels, genus Spermophilus, in Turkey using cytochrome b (1140 bp), part of the D-loop and flanking tRNAs (572 bp), X chromosome (867–1051 bp) and Y chromosome (983–989 bp) DNA sequences. Individuals also were characterized by karyotype and with geometric morphometric analyses of mandibles and skulls. Two hundred fourteen individuals from 91 localities were studied. All the data support the recognition of a new species in SW Anatolia: the Taurus ground squirrel Spermophilus taurensis sp. nov. The new species has a small distribution in the Taurus Mountains in an area that is a hotspot for biodiversity. Molecular clock analysis suggests that the new species diverged from the European ground squirrel, Spermophilus citellus, about 2.5 million years ago and that the ancestor of these two species diverged from the widespread Anatolian ground squirrel, Spermophilus xanthoprymnus, about 5 million years ago. Morphometric differentiation in skull and mandible shape among the three species is incomplete, but statistically significant. S. xanthoprymnus is subdivided into five cytochrome b phylogroups and we use these data to infer the location of glacial refugia where the species lived during the last glacial maximum. This study illustrates the potential of combined molecular and morphometric studies to uncover new Anatolian species and to reconstruct their phylogeographic history. The new species is important for squirrel taxonomy and for understanding Eurasian mammal evolution.

Dynamics in the ultrastructure of asymmetric axospinous synapses in the frontal cortex of hibernating European ground squirrels (Spermophilus citellus)

Recent theories on the function of arousals from torpor in hibernating mammals focus on the repair of the central nervous system from damage accumulating during prolonged hypothermia. In this framework, we investigated the synaptic ultrastructure in Layer 2 of the frontal cortex from hibernating European ground squirrels (Spermophilus citellus) sacrificed at four different phases in the torpor-arousal cycle. Using electron microscopy, we quantified synapse number and morphometric data on asymmetric axospinous synapses. Length, width, and surface area of postsynaptic densities (PSDs), and the synaptic apposition length of the analyzed synapse were measured. Five groups of animals were compared during entrance into torpor (Torpor Early, TE, n = 6), late torpor (Torpor Late, TL, n = 5), beginning of euthermic arousal episodes (Arousal Early, AE, n = 5), late in the euthermic arousal episode (Arousal Late, AL, n = 5), and during continuous euthermy in spring (EU, n = 6). The results showed that during torpor and at the beginning of arousals the PSD length and synaptic apposition length are significantly increased compared to synapses during late arousal and in spring conditions. In contrast, the width and surface area of the PSDs are decreased in torpor. At the beginning of an arousal the width of the PSD increases and gains maximum value in late arousals (AL), returning to spring (EU) values. No differences were found in total number of synapses during the torpor-arousal cycle. The results indicate reversible changes in ultrastructure of (asymmetric axospinous) synapses in the frontal cortex, which may be critical for the maintenance of cortical neuronal networks and for protection against potential deleterious effects of prolonged hypothermic phases of hibernation.

Activity patterns of European ground squirrels (Spermophilus citellus) in a cultivated field in northern Greece

Activity patterns of European ground squirrels (Spermophilus citellus) in a cultivated field in northern Greece