Hibernation Strategy Research Articles

Energy availability influences microclimate selection of hibernating bats

Many species hibernate to conserve energy during periods of low food and water availability. It has long been assumed that the optimal hibernation strategy involves long, deep bouts of torpor that minimize energy expenditure. However, hibernation has ecological (e.g. decreased predator avoidance) and physiological (e.g. sleep deprivation) costs that must be balanced with energy savings; therefore, individuals possessing sufficient energy reserves may reduce their use of deep torpor. We tested the hypothesis that energy (fat) availability influences temperature selection of two fat-storing bat species during hibernation. We predicted that individuals with small energy reserves would select colder temperatures for hibernation in order to minimize energy expenditure, while individuals with larger energy reserves would choose warmer temperatures to minimize the costs of hibernation. Results from our field experiment indicate that little brown myotis (Myotis lucifugus) hibernating in warm microclimates were significantly heavier than individuals hibernating in cooler microclimates. To determine if energy availability was mediating this relationship, we limited fatty acid availability with mercaptoacetate (MA) and quantified its effect on torpid metabolic rate (TMR) and thermal preference of big brown bats (Eptesicus fuscus). Administration of MA caused a 43% drop in TMR at 10 degrees C and caused bats to choose significantly colder temperatures for hibernation. Our results suggest that fat-storing bats minimize torpor expression using both physiological and behavioral mechanisms.

Use of an impedance threshold valve for cardiac arrest during cardiopulmonary resuscitation:a new cardiopulmonary resuscitation method

心肺复苏(cardiopulmonary resuscitation, CPR)成功率和存活率仍然很低,主要原因是CPR期间回心血量少,心脏和脑灌注不足.增加胸内负压的措施和器材明显提高心肺复苏的效果[1～4].近来,Lurie等[5～10]又研制出在胸壁放松时增加胸内负压的阻力单向活瓣(inspiratory impedance threshold valve(device),ITV or ITD),使心肺复苏的效果进一步提高。

An alternative hibernation strategy involving sun‐exposed ‘hotspots’, dispersal by flight, and host plant finding by olfaction in an alpine leaf beetle

Abstract Oreina cacaliae (Schrank) (Coleoptera: Chrysomelidae) has a 2‐year life cycle that it has to complete within the short warm seasons of the harsh alpine environment. Three years of field observations and experiments revealed that not all beetles overwintered in the soil next to their principal host Adenostyles alliariae (Asteraceae), as was previously assumed, but that many O. cacaliae left their host in autumn and flew to overwintering sites that were extensively sun‐exposed. In spring, these individuals became active 2 months earlier than their conspecifics that had remained in the soil close to the host plant. These early beetles flew from their hibernation sites against the direction of the prevailing wind. After a random landing in snow, they walked to the spring host Petasites paradoxus (Asteraceae) and fed on its floral stalks, the only plant parts present at that time. A few weeks later, they took flight again to locate newly emerging A. alliariae on which they would feed and deposit larvae as did individuals that had overwintered close to A. alliariae. Leaves of A. alliariae contain pyrrolizidine alkaloids (PAs), which the beetles sequester for their own defence. The dominating PA (seneciphylline) was also found to be present in the floral stalks of P. paradoxus. With additional behavioural assays in the field and laboratory, we demonstrated the importance of plant odours in the short‐range host location process. This study reveals a unique hibernation behaviour in which part of the beetle population uses exceptionally warm locations from which they emerge in spring, long before all the snow has melted. This early, but risky emergence allows them to exploit a second, highly suitable host plant, which they locate first by wind‐guided flight and then by odour‐guided walking. The well‐fed beetles then use odour again to move to their principal host plant, on which they reproduce.

Density, home range, seasonal movements and habitat use of the mountain pygmy‐possumBurramys parvus(Marsupialia: Burramyidae) at Mount Blue Cow, Kosciuszko National Park

AbstractA population of mountain pygmy‐possumsBurramys parvuswas studied at the Mount Blue Cow ski resort in Kosciuszko National Park between 1986 and 1989. Forty‐eight individuals were radiotracked during the snow‐free months and 21 individuals were tracked during winter over the 3 years of study. Trapping and radiotracking showed that the density, population structure, movements and home range sizes ofB. parvuson Mount Blue Cow were strongly correlated with elevation and changed with the season. Female densities were greatest in habitats characterized by deep boulderfields, at high elevations with an abundance of Bogong moths. Males visited the areas where females were located to breed in November–December and then by February, the majority migrated to lower elevations or north and westerly aspects. Females that nested at lower elevations also visited high‐elevation habitats to access the high concentrations of Bogong moths, which were the main food source in summer. A high proportion of the juvenile males and some juvenile females dispersed to lower elevations in March and April. The resulting sexual segregation during autumn and winter may be a result of female aggression or scramble competition, but is also explainable by differences in energy requirements, seed availability and hibernation strategies between the sexes. The extraordinarily large nightly and seasonal movements between habitat patches of up to 2 km for females and 3 km for males, sexual segregation and the use of different hibernation sites have important implications for the management of this species. These include the need for movement and dispersal corridors and the conservation of boulder‐heath habitats outside the main boulderfields.

Ecology of natural hibernation in the marsupial mountain pygmy-possum (Burramys parvus).

The hibernating marsupial mountain pygmy-possum (Burramys parvus, 40 g) has to raise its slow-growing offspring during a short alpine summer. Only females provide parental care, while after mating males emigrate to marginal habitats often at lower altitudes which can sustain only low possum densities. We predicted that the hibernation strategies in mountain pygmy-possums are distinct from those of similar-sized placental hibernators, because of the developmental constraints in marsupials and because hibernation differs between the sexes. Using temperature-sensitive radio transmitters, we studied the hibernation patterns of free-living male and female mountain pygmy-possums living in a north- and a south-facing boulder field (Kosciusko National Park) for two consecutive winters. Individual possums commenced hibernation several months before the snow season. As in other hibernators, torpor in the mountain pygmy-possum was interrupted by periodic arousals which occurred most often during the late afternoon. Torpor bouts initially lasted a few days when the hibernacula temperature (T hib) ranged from 4 to 7°C. As the hibernation season progressed, torpor bouts became longer and possum body temperatures (T b) approached 2°C. The T bs of females were significantly lower and torpor bouts were longer in the second half of the hibernation season than in males. Between torpor bouts, both sexes were often active and left hibernacula for periods of up to 5 days. Especially during the first months of the hibernation season, possums also frequently changed hibernacula sites probably in an attempt to select a site with a more suitable microclimate. Emergence from hibernation was closely coupled with the disappearance of snow from the possum habitat (September 1995, October 1996) and the limited fat stores probably dictate an opportunistic spring emergence. However, in 1995, spring was early and males emerged significantly earlier than females. In 1996, when snow melt was delayed, this difference vanished. Testes are regressed in males during hibernation and the time needed for testes growth and spermatogenesis favours an earlier emergence for males which was probably achieved by their preference for the more sun exposed north-facing boulder field. A sexual dimorphism in hibernation strategies and spring emergence therefore enables mountain pygmy-possums to cope with their harsh alpine environment.

Freezing survival of the garter snake Thamnophis sirtalis parietalis

Cold hardiness was evaluated for the red-sided garter snake, Thamnophis sirtalis parietalis. Snakes collected in the autumn near communal den sites showed an ability to supercool (Supercooling point, SCP = −5.5 °C). However, by midwinter, supercooling capacity was reduced and snakes cooled only to −0.8 to −1.2 °C before freezing. Survival of freezing and body ice contents were determined over a time course of freezing exposure at −2.5 °C. Snakes recovered fully after freezing exposures of 3 h or less that produced ice contents of up to 40% of total body water. After longer periods and with ice contents of over 50%, survival was reduced. Only 50% of snakes survived 10 h of freezing and no snakes recovered after 24 or 48 h with a maximal ice content of 70% of body water. Putative cryoprotectants were assessed in seven organs (liver, kidney, muscle, intestine, brain, lung, heart) as well as the eggs after 5 h of freezing at −2.5 °C. Glucose content increased 4-fold in liver, and lactate rose by 50% in heart, but levels of these and other possible cryoprotectants did not increase in other organs during freezing. However, a high free amino acid pool, including 14–24 μmol/g wet weight taurine, was present in the organs. The data suggest that long-term freezing survival is not part of the winter hibernation strategy of this species, but tolerance of brief freezing exposures may be adaptive in dealing with overnight frosts when the animals are active above ground.

Behavioral Factors in the Altitudinal Zonation of Chipmunks (Eutamias)

Behavioral factors important in the determination of the lines of contact between 3 altitudinally zone chipmunks, Eutamias minimus, Eutamias amoenus, and Eutamias speciosus, were investigated at a field site in the Sierra Nevada, California. These species are contiguously allopatric and restricted to particular vegetational communities. Extensive mark—release—recapture studies and a removal experiment suggested that the E. minimus—E. amoenus border results from a physiological limitation of E. amoenus and competitive exclusion of E. minimus from E. amoenus habitat. In areas where E. amoenus were removed, E. minimus captures increased; the converse did not occur. Behavioral observations coupled to vegetation surveys showed that E. amoenus had a much stronger preference for the vicinity of trees than the other species. Eutamias minimus, because it is physiologically more capable of handling dry heat loads than E. amoenus, showed a weaker orientation to trees. Eutamias speciosus shows even less orientation to trees, even though it is the most vulnerable of the 3 to heat stress. Field observations of interactions revealed that all 3 species are highly aggressive intraspecifically, and that a clear—cut interspecific dominance hierarchy exists: E. speciosus dominates both E. amoenus and E. minimus, and E. amoenus in turn dominates E. minimus. The evolution of aggressiveness is explained in terms of the hibernation strategy of the animals and the concomitant need to storage large quantities of food for the winter. Interspecific aggression is not selected against because of large overlaps in food utilization among the species. It is concluded that physiological and behavioral factors interact to produce the contiguously allopatric distribution of these chipmunks: E. speciosus aggressively excludes other species from its forest habitat, to which it is restricted by physiological considerations and habitat selection; E. amoenus tolerates the more severe conditions in arid woodlands, from which it excludes E. minimus; E. minimus has extensive thermoregulatory adaptations enabling it to inhabit the extremely hot, dry sagebrush, which is intolerable for the more aggressively dominant species.