Infradian cycles in dormice (Glis glis)

Summary Infradian cycles of body weight occur in captive dormice,Glis glis. The period of these cycles is often about 2 months but is highly variable both between and within individuals. These cycles can persist for at least 3 years. This paper describes a number of variables that change on an infradian basis along with body weight. These include: food and water intake, weight of the liver, adrenal and salivary gland weight, testes weight and spermatogenic condition, body temperature and wheel-running activity. Both the amount of running and its distribution over a 24 h period change. However, infradian cycles do not appear to be generated by the circadian system because they persist even in continuous bright light sufficiently intense to disrupt circadian organization. They also persist in LD 186, LD 1212, LD 618 and in naturally changing photoperiods. No evidence of photoperiodic effects on cycles was detected except that animals in long days have slightly higher moulting scores than those in short days. Moulting is more marked when body weight stays relatively stable. In dormice remaining stable in weight for several months testes have sperm present. The period of infradian cycles is temperature dependent: in a cool room animals that hibernate have longer cycles with periods varying from a few months to about a year. In a number of respects at least, infradian cycles appear to be accelerated circannual cycles. The adaptive value of a system that gives rise to infradian cycles probably relates to opportunism in an unpredictable environment. Infradian cycles in dormice may be a useful preparation for obtaining data on spontaneous physiological and behavioural changes in hibernators in less than a year.This work was supported by the Natural Sciences and Engineering Research Council of Canada and by an Ontario Graduate Scholarship to R.M. Many people have helped us in these experiments. We thank: Suzanne Hoy, Jenny Martin, Janice Farintosh, John Glover, Alex Joyner, Michael Juergensen, Harry Meyer, Yasmin Shah, Sara Shettleworth, Wendy Stewart, Vern Thiel, Patricia Williams, and Rae Weaver.     

Energetic constraints on sexual activity in the male edible dormouse (Glis glis)

The aim of this study was to examine to what extent reproductive activity in male edible dormice (Glis glis) might be energetically constrained. Demographic data, morphometric data, and oral body temperature (T _or) measurements were collected in two study areas between 1993 and 2002 in southwest Germany and combined with subcutaneous body temperature (T _sc) registrations of captive dormice. T _sc measurements were collected directly after emergence from hibernation (June) until the end of the mating season (July). Wild edible dormice showed strong fluctuations in their reproductive output between years. Not all males were sexually active each year and the number of litters born was positively correlated with the number of sexually active males, which suggests that sexual activity in males is constrained and in turn limits reproductive success. A comparison of the T _or of sexually quiescent and active males revealed that sexually quiescent males had significantly lower T _or (median: 28.8°C; 25/75% quartiles: 16.4/31.0; n=31) than sexually active males (median: 34.2°C; 25/75% quartiles: 32.0/35.6; n=156). Body condition of sexually active and quiescent males was not different after emergence from hibernation. However, sexually active males showed a significant reduction in their body condition between June and July, the time of mating, while body condition of sexually quiescent males remained constant. Continuous T _sc registrations in captive sexually active male dormice showed strong circadian T _sc fluctuations. Even though daily torpor bouts with T _sc below 20°C occurred in these males, most of the time T _sc fluctuated above 30°C, which is known as the critical body temperature threshold above which testes maturation can take place in this species. These results demonstrate that male dormice incur high costs due to sexual activity and that thermoregulation is determined by a trade-off between energetic savings and reproductive activity.     

Seasonal changes in thyroid-gonadal interactions in the edible dormouse,Glis glis

Summary This study was conducted to determine changes in thyroid-gonadal interaction in the edible dormouse during the phase of the annual cycle that corresponds to the end of the breeding season (from June to September). We evaluated intra-hypothalamic luteinizing hormone-releasing hormone (LHRH) content, and plasma concentrations of luteinizing hormone (LH), testosterone, thyroid-stimulating hormone (TSH) and thyroxine (T4) in three groups of dormice: (1) controls; (2) dormice receiving sufficient T4 supplementation to maintain June levels in control animals until September, thus counteracting the seasonal reduction of T4 that normally begins in July; and (3) thyroidectomized dormice. The effect of thyroidectomy was only detectable in June, when plasma T4 concentration in the control group was maximal, and consisted of a significant decrease in plasma testosterone levels. This provides strong support for the hypothesis that thyroid function positively influences gonadal function during the breeding season. The T4 supplementation resulted in a decrease in hypothalamic LHRH concentration, suggesting that an increased LHRH release led to the observed stimulated hypophyseal secretion of LH in June and September and the increased circulating testosterone levels in September. There was no detectable effect in July and August. These results show that thyroid axis activation of the hypothalamic-pituitary-gonadal system is only possible during certain phases of the annual cycle, particularly evidenced here during the breeding season. They also reinforce our conclusions drawn from the thyroidectomy results. Conversely, the summer testicular regression which normally occurs after the breeding season is no longer controlled by plasma T4 levels. Even though the sensitivity of the gonadal axis to the thyroid axis appears to reappear at the end of the summer, results of previous studies indicate that this resumption is only temporary.Abbreviations LH luteinizing hormone - LHRH luteinizing hormone-releasing hormone - RIA radioimmunoassay - T4 thyroxine - TSH thyroid-stimulating hormone     

Glucagon secretion in the hibernating edible dormouse (Glis glis)

Plasma glucose and glucagon concentrations were measured in edible dormice during the bout of hibernation, arousal and active periods. During lethargy, plasma glucose and glucagon were low, compared to active values and did not fluctuate throughout the phase. During rewarming, plasma glucose regularly increased from 17 degrees to 37 degrees C while plasma glucagon rose after the 17 degrees C stage and reached the higher values at 26 degrees C, then slightly decreased at 37 degrees C. During arousal, plasma levels of free amino acids progressively increased. The effect of temperature and secretagogue (glucose and arginine) on glucagon secretion was studied using perfused pancreas from hibernating edible dormouse. In vitro rewarming of pancreas induced an increase in glucagon secretion. Glucagon secretion was regulated by glucose (inhibitory effect) and by arginine (stimulating effect) up to 25 degrees C. The effect of temperature and glucagon on oxygen uptake of hibernating edible dormouse brown fat was studied using an in vitro technique. Rewarming strongly increased oxygen consumption from 10 to 37 degrees C. Glucagon enhanced oxygen consumption up to 20 degrees C.     

Age-related reproductive success in solitarily and communally nesting female dormice (Glis glis)

The factors underlying the occurrence of communal nesting in a natural population of fat dormouse ( Glis glis ) breeding in nest-boxes have been analysed on the assumption that such behaviour is adaptive. Since co-nesting females were previously shown to be close kin (prevalently mother-daughter pairs), they were expected to obtain kin-selected benefits not enjoyed by solitary breeders. The only advantage so far detected accrues to the younger partner, which gives birth, on average, several days earlier than it would as a solitary breeder and thus allows its progeny to attain a heavier weight by the time of hibernation. On the other hand, pup predation in the nest, presumably caused by the older female towards the younger's litter, was occasionally recorded. On the whole, it is perhaps more plausible that communal nesting results from delayed dispersal of yearling females when a high population density limits breeding space, as proposed for other small rodents.     

Comparative morphology of incisor enamel and dentin in humans and fat dormice (Glis glis)

The structure of teeth in all living beings is genetically predetermined, although it can change under external physiological and pathological factors. The author's hypothesis was to indicate evolutional shifts resulting from genetic, functional and other differences. A comparative study about certain characteristics of incisors in humans and myomorpha, the fat dormouse (Glis glis) being their representative as well, comprised measurements of enamel and dentin thickness in individual incisor segments, evaluation of external enamel index, and also assessment of histological structure of enamel and dentin. The study results involving dormice showed the enamel to be thicker in lower than in the upper teeth, quite contrary to enamel thickness in humans. In the upper incisors in dormice the enamel is the thickest in the medial layer of the crown, and in the cervical portion of the crown in the lower incisors. The thickness of dentin in dormice is greater in the oral than in the vestibular side. These findings significantly differ from those reported in reference literature, but they are based on the function of teeth in dormice. Histological characteristics of hard dental tissues in dormice are similar to those in humans, with exception of uniserial structure of enamel and appearance of dentinoenamel junction.     

New polymorphic microsatellite loci developed and characterized from edible dormouse (Glis glis)

Eight new polymorphic microsatellite loci were isolated and characterized from the edible dormouse (Glis glis). All loci were polymorphic in the 70 individuals tested. The number of alleles per locus ranged from 2 to 6, with a mean of 4. Observed and expected heterozygosities ranged from 0.10 to 0.71 and 0.15 to 0.67, respectively. No evidence of linkage disequilibrium between loci has been found. These eight new loci, plus previously characterized markers, now make it possible to undertake more detailed population genetic studies of G. glis, which is relevant to the preservation of this species.     

Seasonal variations in plasma glucose and insulin concentrations after glucose loading in the edible dormouse (Glis glis L.).

Glucose tolerance tests made in the Edible dormouse showed annual variations in B cell secretory capacity, associated with glucose tolerance changes. 1. During autumn and winter, the B cell is sensitive to glucose, and insulin regulates the high peripheral consumption of this hexose. 2. At the beginning of spring, insulin secretion decreases and glucose tolerance is impaired. In June, the B cell response si low or absent and a poor tolerance to glucose still persists. 3. The variations in B cell activity can be related to changing energy requirements during the year.     

Spontaneous and experimental variations in body weight, food intake and metabolic rate in captive dormice (Glis glis)

Captive dormice (Glis glis) showed spontaneous cyclical fluctuations in body weight that were not synchronous between animals and not directly related to season. Presenting the animals with a varied and palatable (cafeteria) diet for short periods caused marked increases in energy intake and body weight, and higher levels of oxygen consumption (V02). The level of hyperphagia was fairly constant, but the rise in V02 during cafeteria feeding varied (20-80%) according to season, being greatest in the winter (Nov.-Jan.). Removal of the cafeteria foods caused weight loss, hypophagia and a fall in V02 to levels below that seen in either normally-fed or fasted dormice. This hypometabolism was associated with increased periods of sleep and torpor, and it is suggested that the excess fat deposition resulting from cafeteria feeding may have induced a transient "hibernation-like" state.     

Insulin secretion in the hibernating edible dormouse (Glis glis): in vivo and in vitro studies

Plasma glucose and insulin have been studied during lethargy and spontaneous arousal of hibernating edible dormouse. During lethargy blood glucose was low while plasma insulin remained at the same level as in other seasons. Plasma glucose and insulin did not fluctuate along the phase of lethargy. During spontaneous arousal plasma insulin rose strongly from the 17 degrees C stage, reaching the higher values at 26 degrees C while blood glucose was only 85 mg/100 ml, then decreased at 37 degrees C. The effect of glucose and temperature on insulin secretion was studied using perfused pancreas preparation from hibernating edible dormice. During the rewarming of the edible dormouse pancreas the insulin release did not occur in response to the absolute extracellular glucose level but occurred in response to a B cell membrane phenomenon which was dependent on the changing rate of glucose level. The effect of glucose and temperature on insulin secretion from perfused pancreas was compared between edible dormouse and homeotherm permanent, the rat. The B cell response to glucose of the dormouse pancreas increased up to 15 degrees C whereas that of the rat only from 25 degrees C. The dormouse insulin secretion reached a peak value at the 30 degrees C of temperature, whereas that of the rat progressively increased until 37 degrees C. These results showed that some biochemical adjustment or process of acclimatization took place in the B cells of the hibernators.     

External factors controlling annual testosterone and thyroxine cycles in the edible dormouse Glis glis

Annual patterns of hibernation, body weight, plasma testosterone and thyroxine were measured in two groups of edible dormice exposed to a constant photoperiod and to either environmental temperature (I), the four functions displayed annual cycles and the two hormonal cycles were parallel and restricted to the aroused state, while in group II only irregular infradian fluctuations were observed. However, a body temperature of 30 degrees C remained the critical lower limit enabling the start of the testosterone cycles for the two groups. Respective roles of endogenous and synchronizing mechanisms in controlling biological rhythms are discussed.     

Seasonal fluctuations of food intake and bodyweight in the dormouse Glis glis (author's transl)]

Cycles of body weight lasting a few weeks occurred in dormice fed ad libitum, throughout the year with the same food. The pattern of the fluctuations suggests an oscillation between an upper and a lower limit. When the lower limit is reached, compensatory mechanisms acting on the food intake are induced which cause an increase in body weight to the upper one; when this upper limit is reached, other mechanisms cause the body weight to decrease to the lower one. Thus, body weight and variations in food intake may well be controlled by the difference between the body weight and the limit it will reach. In a warm environment (23-25 degrees C) these fluctuations are smaller than in the cold (5-6 degrees C). They are also smaller during summer than during winter in animals placed in natural climatic conditions. In summer, the body weight stays near the upper limit; in this season, as in the warm environment, the lower limit approaches the upper one. Thus, the main circannual variation of body weight regulation in dormice may be the elevation during summer of the lower body weight limit.     

Morphometric and genetic structure of the edible dormouse (Glis glis): a consequence of forest fragmentation in Turkey

Past climatic fluctuations influenced forest habitats and impacted heavily the distribution of forest species, such as the edible dormouse, by changing the distribution and composition of forests themselves. Such effects may be valid for ongoing climate change as well. To improve our understanding of the edible dormouse's history and how it responded to changes in its environment, we investigated its variation across the understudied zone of Northern Turkey using two complementary markers of differentiation: the mitochondrial cytochrome b gene for genetics, and size and shape of the first upper molar for phenotypic differences. Genetic and morphometric results were strongly discrepant. Genetic analyses evidenced an amazing homogeneity throughout the Eurasian range of the edible dormouse, whereas morphometrics pointed to a complex, step‐wise differentiation along the Black Sea coast, the main signal being an opposition between Easternmost and Westernmost Turkish dormice. The genetic homogeneity suggests that this phenotypic differentiation is not the inheritance of glacial refuges, but the consequence of a more recent post‐glacial isolation. The transition between the European and Asian groups is located eastwards from the Marmara straits, undermining its claimed role as an efficient barrier but stressing the importance of climatic and vegetational factors. A secondary differentiation between populations from the Central Black Sea coast and Easternmost regions was evidenced, attributed to a complex interplay of climatic, topographic, anthropogenic, and ecological factors. Turkey, at the crossroad of European and Asian species, heavily impacted by the current global change including climatic and anthropogenic factors, appears of importance for understanding the historical dynamics of differentiation and exchanges between populations that shaped the current distribution of Eurasian species and their future survival. © 2012 The Linnean Society of London, Biological Journal of the Linnean Society, 2012, 107 , 611–623.     

Seasonal Prevalence of Lyme Disease Spirochetes in a Heterothermic Mammal,the Edible Dormouse (Glis glis)

In Europe, dormice serve as competent reservoir hosts for particular genospecies of the tick-borne agent of Lyme disease (LD) and seem to support them more efficiently than do mice or voles. The longevity of edible dormice (Glis glis) and their attractiveness for ticks may result in a predominance of LD spirochetes in ticks questing in dormouse habitats. To investigate the role of edible dormice in the transmission cycle of LD spirochetes, we sampled skin tissue from the ear pinnae of dormice inhabiting five different study sites in south western Germany. Of 501 edible dormice, 12.6% harbored DNA of LD spirochetes. Edible dormice were infected most frequently with the pathogenic LD spirochete Borrelia afzelii. The DNA of B. garinii and B. bavariensis was detected in ca. 0.5% of the examined individuals. No spirochetal DNA was detectable in the skin of edible dormice until July, 6 weeks after they generally start to emerge from their obligate hibernation. Thereafter, the prevalence of spirochetal DNA in edible dormice increased during the remaining period of their 4 to 5 months of activity, reaching nearly 40% in September. Males were more than four times more likely to harbor LD spirochetes than females, and yearlings were almost twice more likely to be infected than adults. The seasonality of the prevalence of LD spirochetes in edible dormice was pronounced and may affect their role as a reservoir host in respect to other hosts.     

Comparison of hibernation, estivation and daily torpor in the edible dormouse, Glis glis

Three major forms of dormancy in mammals have been classified: hibernation in endotherms is characterised by reduced metabolic rate (MR) and body temperature (T _b) near ambient temperature (T _a) over prolonged times in the winter. Estivation is a similar form of dormancy in a dry and hot environment during summertime. Daily torpor is defined as reduced MR and T _b lower than 32 °C, limited to a duration of less than 24 h. The edible dormouse (Glis glis) is capable for all three distinct forms of dormancy. During periods of food restriction and/or low T _a, daily torpor is displayed throughout the year, alternating with hibernation and estivation in winter and summer respectively. We recorded T _b, O₂-consumption and CO₂-production in unrestrained dormice at different T _a's for periods of up to several months. Cooling rate and rate of metabolic depression during entrance into the torpid state was identical in all three forms of dormancy. The same was true for thermal conductance, maximum heat production, duration of arousal and cost of an arousal. The only difference between hibernation and daily torpor was found in the bout duration. A daily torpor bout lasted 3–21 h, a hibernation bout 39–768 h. As a consequence of prolonged duration, MR, T _b and also the T _b − T _a gradient decreased to lower values during hibernation bouts when compared to daily torpor bouts. Our findings suggest that all three forms of dormancy are based on the same physiological mechanism of thermal and metabolic regulation. Accepted: 27 June 2000     

Glucose oxidation by adipose tissue of the edible dormouse (Glis glis) during hibernation and arousal: effect of insulin

1. The effect of insulin on U-14C-glucose oxidation by adipose tissue isolated from hibernating or arousing edible dormouse has been studied. 2. CO2 production derived from radioglucose was analysed point by point during in vitro rewarming (from 6 to 37 degrees C). 3. The rate of temperature increase was 2 degrees/5 min in order to mimic the rate of rewarming during the spontaneous arousal of the dormouse. 4. Insulin did not increase the glucose oxidation by the adipose tissue from hibernating dormouse whereas adipocytes from active animal present high insulin sensitivity. 5. These results suggest that insulin resistance occurs during hibernation.     

Age determination and age structure in the edible dormouse Glis glis based on incremental bone lines

1. Absolute age was estimated from incremental bone layers of the mandible in 109 edible dormice Glis glis collected between May and September 1997 in mixed beech and fir forests of central Slovenia. 2. Mandible cross-sections of juveniles obtained in September showed a great number of vascular canals and no resting lines. In the remaining animals (n = 81), the number of resting lines varied between one and seven, with two or three lines being the most common condition (62% of specimens). Among these adult animals, which hibernated at least once, females attained higher mean (3.3 years) and maximum age (7 years) than males (mean = 2.2, maximum = 6 years). 3. The frequency distribution of age classes suggested unequal reproductive success between years but there was no indication of any lack of litters in years of low mast production.     

Isolation, characterization and PCR multiplexing of polymorphic microsatellite markers in the edible dormouse, Glis glis

We isolated and characterized 10 dinucleotide microsatellite loci in the edible dormouse, Glis glis (Linnaeus). Four multiplex panels were developed. Loci were amplified in samples from two geographically distant populations (Torgny in Belgium and Montseny in Spain). All loci were polymorphic in Spain but four were monomorphic in Belgium. Individuals from Belgium and Spain exhibited an average allelic diversity of 1.9 and 3.3 and an observed heterozygosity ranging from 0.08 to 0.47 and from 0.04 to 0.72, respectively.