The Alpine Marmot Project

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Hibernation

The extreme winter weather conditions impose severe constraints on species living in a mountain environment. Faced with these constraints, the alpine marmot has developed an original survival strategy – hibernation. The success of hibernation depends on the balance between energy availability and costs involved. The alpine marmot has developed adaptive strategies to accumulate sufficient energy reserves on the one hand, and to reduce hibernation energy costs on the other.

Acquiring energy reserves

The energy for hibernation is stored as fat predominantly in white adipose tissue. To increase the energy of these reserves (Geiser et al. 1990; Florant 1998), the alpine marmot’s diet, which is primarily herbivorous, is high in foods rich in polyunsaturated fatty acids. The alpine marmot strongly favors certain flowering plants. These represent 70 to 80% of their diet depending on month and site (Bassabo et al. 1996). Among these plants, seven families are favored: Leguminosae, Compositae, Scrophulariacae, Cistaceae, Campanulaceae, Crassulaceae and Caryophillaceae (Bassano et al. 1996). In April the roots are preferred, in May and June roots, stems and young shoots predominate, and in July and August flowers are preferred (Bassano et al. In 1996). At the species level: alpine milkvetch (Astralagus alpinus), Locoweed (Oxytropis spp.), Yarrow (Achillea spp.), and Silver Thistle (Carlina acaulis) are mainly consumed. Among the monocots, the predominate families are the grasses (Graminae) and Sedges (Cyperaceae) and the most favored specie is Sheeps Fescue (Festuca ovina).

flower

Ces réserves atteignent un tiers de la masse corporelle d’un individu à son entrée en hibernation (Körtner et Heldmaier 1995).

A costly strategy

The hibernation phase lasts about 200 days from the beginning of October and ends in early April. The exact time may vary from one year to another and from one site to another depending on snow conditions (Arnold 1990) and can vary from one individual to another. Adult males emerge earlier than females and juveniles (Arnold 1988, Arnold 1993).

hypothermia

Hypothermia phase

euthermia

Euthermia phase

Hibernation is characterized by long phases of hypothermia (or sleep phase) interspersed with short phases of euthermie (or recovery phase). During periods of activity the mean body temperature is 38° C to 40° C (100° F to 104° F)and during phases of hypothermia the mean body temperature can be reduced to a minimum of 5° C (41° F) (Arnold 1988; Cochet 1996). Heart rate during the period of activity is from 180 to 200 beats per minute and only 28 to 38 beats per minute during hibernation and the respiratory rate decreases from 60 breaths per minute to 1-2 breaths per minute (Weaver 1963). Their metabolism is extremely low and is limited mainly to thermogenesis, the process of resuming thermoregulation when body temperature drops below 5° C (41° F) (Arnold 1988). During the phases of euthermie, the animals return to biological rhythms comparable to the period of activity. Although occurring less than 10% of the time during hibernation, euthermie phases are responsible for 85-95% of the animal’s energy expenditure. In the laboratory, the duration and number of euthermie phases observed for a period ranging from 24 to 50 hours varied considerably: from 9 to 15 awakenings were observed (Arnold 1988).

activité

Cardiac rythm (I) and respiratory rythm (II) during euthermia

hibernation

Cardiac rythm (I) and respiratory rythm (II) during hypothermia

Energy costs of hibernation, therefore, depend on three factors: the duration of hibernation, metabolism during hypothermia, and the frequency and length of euthermie phases.

A cooperative strategy

During hibernation, all members of a family group gather in a burrow chamber lined with hay : the hibernaculum. The number of individuals present in the hibernaculum varies from two individuals (one dominate couple) up to twenty individuals. Only individuals not belonging to a social group hibernate alone. Although several times combinations of two or three marginal individuals were observed hibernating together, but they separate at the end of hibernation.

This phenomenon of social hibernation is interpreted as an adaptation to reduce the energy costs associated with hibernation as it allows for a decrease in energy expenditure. Since the animals are in contact with each other, the thermal inertia is increased and the thermal conductance is decreased.

Regarding the alpine marmot, it was demonstrated that (i) the decrease in ambient temperature in the hibernaculum is inversely correlated with the number of individuals present (Arnold et al. 1991), (ii) that for an identical room temperature , an individual group hibernating body has a temperature lower than that of a single individual hibernating alone (Arnold 1993), (iii) that the frequency of phases in an individual euthermie hibernating group is less than that of an individual hibernating alone, and (iv) finally that the phases of euthermie are synchronized in individuals hibernating in groups (Arnold 1988, Arnold 1993).

Increasing the number of individuals hibernating together thus leads to a reduction in energy costs through an increase in ambient temperature, a decrease in body temperature and the frequency of euthermie phases. The decrease of energy costs translates into a reduction in loss of body mass (Arnold 1993) but also increases the probability of the survival of the pups (Arnold 1990; Allaine et al. 2000; Grimm et al. 2003; Allaine and Theuriau 2004) and adults (Arnold 1990b; Grimm et al. 2003) and thus, indirectly, increases the reproductive success of dominant individuals.

If the relationship between increasing hibernating group size and reducing costs associated with hibernation is clearly established, then the composition of hibernating individuals in terms of age and sex also appears to have a significant impact.

The pups, because of their lesser body mass and lower body fat stores, they have a reduced thermal inertia. In addition, the pups awake for a shorter period of time, and come into euthermie phase last and leave first (Arnold 1988). They passively take advantage of the energy spent by adult individuals, a phenomenon called social thermoregulation. Hibernation for the pups is the most expensive from its point of view, than it is from the perspective of the group. While social hibernation is crucial to the survival of the pups (Arnold 1993; Allaine et al. 2000), the presence of pups represents a significant energy cost for the older individuals who experience greater weight loss (Arnold 1990b, 1993).

On the contrary, the increased number of hibernating adult males seems to benefit the group. Specifically, a positive correlation between number of adult males and the survival of the pups was observed (Arnold 1993; Allaine et al. 2000; Allaine and Theuriau, 2004).

Bibliography

Allainé D, Brondex F, Graziani L, Coulon J, Till Bottraud I (2000) Male-biased sex ratio in litters of alpine marmots supports the helper repayment hypothesis. Behavioral Ecology 11, 507-514.

Allainé D, Theuriau F (2004) Is there an optimal number of helpers in alpine marmot family groups? Behavioral Ecology 15, 916-924.

Arnold W (1988) Social thermoregulation during hibernation in alpine marmots (Marmota marmota). Journal of Comparative Physiology B: Biochemical, Systemic, and Environmental Physiology 158, 151-156.

Arnold W (1990) The evolution of marmot sociality: II. Costs and benefits of joint hibernation. Behavioral Ecology and Sociobiology 27, 239-246.

Arnold W (1993) Social evolution in marmots and the adaptive value of joint hibernation. Verhandlungen der Deutschen Zoologischen Gesellschaft 86, 79-93.

Cochet N (1996) Lipolyse et acides gras dans deux dépots adipeux blancs au cours du cycle saisonnier de la Marmotte Alpine (Marmota marmota). Thèse de doctorat, Université Claude Bernard, Lyon.

Couturier MAJ (1963) Contribution à l’étude du sommeil hibernal chez la marmotte des Alpes, Marmota m. marmota L. 1758. Mammalia 27, 455-482.

Florant GL (1998) Lipid metabolism in hibernators: The importance of essential fatty acids. American Zoologist 38, 331-340.

Geiser F, Hiebert SM, Kenagy GJ (1990) Torpor bout duration during the hibernation season of two sciurid rodents: Interrelations with temperature and metabolism. Physiological Zoology 63, 489-503.

Grimm V, Dorndorf N, Frey-Roos F, Wissel C, Wyszomirski T, Arnold W (2003) Modelling the role of social behavior in the persistence of the Alpine Marmot Marmota marmota. Oikos 102, 124-136.

Körtner G, Heldmaier G (1995) Body-weight cycles and energy-balance in the Alpine Marmot (Marmota marmota). Physiological Zoology 68, 149-163.