The insensitive dormouse: reproduction skipping is not caused by chronic stress in Glis glis.

Entire populations of edible dormice (Glis glis) can skip reproduction in years without mast seeding of deciduous trees (particularly beech or oak seed), because juveniles require high-calorie seeds for growth and fattening prior to hibernation. We hypothesized that, in mast failure years, female dormice may be forced to spend larger amounts of time foraging for low-quality food, which would increase their exposure to predators, mainly owls. This may lead to chronic stress, i.e. long-term increased secretion of glucocorticoids (GC), which can have inhibitory effects on reproductive function in both female and male mammals. We monitored reproduction in free-living female dormice over 3 years with varying levels of food availability, and performed a supplemental feeding experiment. To measure stress hormone levels, we determined fecal GC metabolite (GCM) concentrations collected during the day, which reflect hormone secretion rates in the previous nocturnal activity phase. We found that year-to-year differences in beech mast significantly affected fecal GCM levels and reproduction. However, contrary to our hypothesis, GCM levels were lowest in a non-mast year without reproduction, and significantly elevated in full-mast and intermediate years, as well as under supplemental feeding. Variation in owl density in our study area had no influence on GCM levels. Consequently, we conclude that down-regulation of gonads and reproduction skipping in mast failure years in this species is not caused by chronic stress. Thus, in edible dormice, delayed reproduction apparently is profitable in response to the absence of energy-rich food in non-mast years, but not in response to chronic stress.

Edible dormice (Glis glis) avoid areas with a high density of their preferred food plant - the European beech.

BACKGROUND: Numerous species, especially among rodents, are strongly affected by the availability of pulsed resources. The intermittent production of large seed crops in northern hemisphere tree species (e.g., beech Fagus spec.,oak Quercus spec., pine trees Pinus spec.) are prime examples of these resource pulses. Adult edible dormice are highly dependent on high energy seeds to maximize their reproductive output. For juvenile dormice the energy rich food is important to grow and fatten in a very short time period prior to hibernation. While these erratic, often large-scale synchronized mast events provide overabundant seed availability, a total lack of seed production can be observed in so-called mast failure years. We hypothesized that dormice either switch territories between mast and non-mast years, to maximize energy availability or select habitats in which alternative food sources are also available (e.g., fleshy fruits, cones). To analyze the habitat preferences of edible dormice we performed environmental niche factor analyses (ENFA) for 9 years of capture-recapture data. RESULTS: As expected, the animals mainly used areas with high canopy closure and vertical stratification, probably to avoid predation. Surprisingly, we found that dormice avoided areas with high beech tree density, but in contrast preferred areas with a relatively high proportion of coniferous trees. Conifer cones and leaves can be an alternative food source for edible dormice and are less variable in availability. CONCLUSION: Therefore, we conclude that edible dormice try to avoid areas with large fluctuations in food availability to be able to survive years without mast in their territory.

Telomere dynamics in free-living edible dormice (Glis glis): the impact of hibernation and food supply.

We studied the impact of hibernation and food supply on relative telomere length (RTL), an indicator for aging and somatic maintenance, in free-living edible dormice. Small hibernators such as dormice have ∼50% higher maximum longevity than non-hibernators. Increased longevity could theoretically be due to prolonged torpor directly slowing cellular damage and RTL shortening. However, although mitosis is arrested in mammals at low body temperatures, recent evidence points to accelerated RTL shortening during periodic re-warming (arousal) from torpor. Therefore, we hypothesized that these arousals during hibernation should have a negative effect on RTL. Here, we show that RTL was shortened in all animals over the course of ∼1 year, during which dormice hibernated for 7.5-11.4 months. The rate of periodic arousals, rather than the time spent euthermic during the hibernation season, was the best predictor of RTL shortening. This finding points to negative effects on RTL of the transition from low torpor to high euthermic body temperature and metabolic rate during arousals, possibly because of increased oxidative stress. The animals were, however, able to elongate their telomeres during the active season, when food availability was increased by supplemental feeding in a year of low natural food abundance. We conclude that in addition to their energetic costs, periodic arousals also lead to accelerated cellular damage in terms of RTL shortening. Although dormice are able to counteract and even over-compensate for the negative effects of hibernation, restoration of RTL appears to be energetically costly.

Seasonal variation in telomerase activity and telomere dynamics in a hibernating rodent, the garden dormouse (Eliomys quercinus).

Telomere dynamics in hibernating species are known to reflect seasonal changes in somatic maintenance. Throughout hibernation, the periodic states of rewarming, known as inter-bout euthermia or arousals, are associated with high metabolic costs including shortening of telomeres. In the active season, if high energetic resources are available, telomere length can be restored in preparation for the upcoming winter. The mechanism for telomere elongation has not been clearly demonstrated, although the action of the ribonucleoprotein complex, telomerase, has been implicated in many species. Here we tested for levels of telomerase activity in the garden dormouse (Eliomys quercinus) at different seasonal time points throughout the year and across ages from liver tissues of male juveniles to adults. We found that telomerase is active at high levels across seasons (during torpor and inter-bout euthermia, plus in the active season) but that there was a substantial decrease in activity in the month prior to hibernation. Telomerase levels were consistent across age groups and were independent of feeding regime and time of birth (early or late born). The changes in activity levels that we detected were broadly associated with changes in telomere lengths measured in the same tissues. We hypothesise that i) telomerase is the mechanism used by garden dormice for maintenance of telomeres and that ii) activity is kept at high levels throughout the year until pre-hibernation when resources are diverted to increasing fat reserves for overwintering. We found no evidence for a decrease in telomerase activity with age or a final increase in telomere length which has been detected in other hibernating rodents.

The costs of locomotor activity? Maximum body temperatures and the use of torpor during the active season in edible dormice.

Measuring T b during the active season can provide information about the timing of reproduction and the use of short bouts of torpor and may be used as a proxy for the locomotor activity of animals (i.e., maximum T b). This kind of information is especially important to understand life-history strategies and energetic costs and demands in hibernating mammals. We investigated T b throughout the active season in edible dormice (Glis glis), since they (i) have an expensive arboreal life-style, (ii) are known to show short bouts of torpor, and (iii) are adapted to pulsed resources (mast of beech trees). We show here for the first time that maximum T b's in free-living active dormice (during the night) increase regularly and for up to 8 h above 40 °C, which corresponds to slight hyperthermia, probably due to locomotor activity. The highest weekly mean maximum T b was recorded 1 week prior to hibernation (40.45 ± 0.07 °C). At the beginning of the active season and immediately prior to hibernation, the mean maximum T b's were lower. The time dormice spent at T b above 40 °C varied between sexes, depending on mast conditions. The date of parturition could be determined by a sudden increase in mean T b (plus 0.49 ± 0.04 °C). The occurrence of short torpor bouts (<24 h) was strongly affected by the mast situation with much higher torpor frequencies in mast-failure years. Our data suggest that locomotor activity is strongly affected by environmental conditions, and that sexes respond differently to these changes.

Telomeres are elongated in older individuals in a hibernating rodent, the edible dormouse (Glis glis).

Telomere shortening is thought to be an important biomarker for life history traits such as lifespan and aging, and can be indicative of genome integrity, survival probability and the risk of cancer development. In humans and other animals, telomeres almost always shorten with age, with more rapid telomere attrition in short-lived species. Here, we show that in the edible dormouse (Glis glis) telomere length significantly increases from an age of 6 to an age of 9 years. While this finding could be due to higher survival of individuals with longer telomeres, we also found, using longitudinal measurements, a positive effect of age on the rate of telomere elongation within older individuals. To our knowledge, no previous study has reported such an effect of age on telomere lengthening. We attribute this exceptional pattern to the peculiar life-history of this species, which skips reproduction in years with low food availability. Further, we show that this "sit tight" strategy in the timing of reproduction is associated with an increasing likelihood for an individual to reproduce as it ages. As reproduction could facilitate telomere attrition, this life-history strategy may have led to the evolution of increased somatic maintenance and telomere elongation with increasing age.

How to spend the summer? Free-living dormice (Glis glis) can hibernate for 11 months in non-reproductive years.

Edible dormice are arboreal rodents adapted to yearly fluctuations in seed production of European beech, a major food source for this species. In years of low beech seed abundance, dormice skip reproduction and non-reproductive dormice fed ad libitum in captivity can display summer dormancy in addition to winter hibernation. To test whether summer dormancy, that is, a very early onset of hibernation, actually occurs in free-living dormice, we monitored core body temperature (Tb) over ~12 months in 17 animals during a year of beech seeding failure in the Vienna Woods. We found that 8 out of 17 dormice indeed re-entered hibernation as early as in June/July, with five of them having extreme hibernation durations of 11 months or more (total range: 7.8-11.4 months). Thus, we show for the first time that a free-living mammal relying on natural food resources can continuously hibernate for >11 months. Early onset of hibernation was associated with high body mass in the spring, but the distribution of hibernation onset was bimodal with prolonged hibernation starting either early (prior to July 28) or late (after August 30). This could not be explained by differences in body mass alone. Animals with a late hibernation onset continued to maintain high nocturnal Tb's throughout summer but used short, shallow torpor bouts (mean duration 7.44 ± 0.9 h), as well as occasional multiday torpor for up to 161 h.