Henry J. Harlow

Muscle strength in overwintering bears

Unlike humans, bears retain their muscle tone when moribund for long periods.

Winter Resting Site Ecology of Marten in the Central Rocky Mountains

We investigated the resting site ecology of American marten (Martes americana) in the central Rocky Mountains during 2 winters, 1985-86 and 1986-87. We found 8 marten used 57 resting sites on 141 occasions. Marten rested primarily in subnivean sites associated with coarse woody debris, including logs and stumps. Use of spruce (Picea spp.)-fir (Abies lasiocarpa) stands by adults was greater than expected and use of lodgepole pine (Pinus contorta) stands was less than expected on the basis of spatial availability. Juveniles used stand types in proportion to spatial availability. Fidelity to individual resting sites and to subnivean sites associated with coarse woody debris was highest among adults. Type of resting site used depended on air temperature at the time of resting; above-snow sites were used during the warmest weather, and subnivean sites associated with coarse woody debris were used during the coldest weather. Marten rested for longer periods where coarse woody debris formed all or part of the resting site than they did at other sites. Log densities were higher and mean log diameters greater in spruce-fir stands than in lodgepole pine stands. Resting sites associated with coarse woody debris occurred primarily in spruce-fir stands, whereas other resting sites occurred in other stand types. Resting sites were closer to streams and lakes than expected. The importance of resting where coarse woody debris is available to provide thermal cover may explain the apparent dependence of marten on old-growth forest in the central Rocky Mountains in winter. J. WILDL. MANAGE. 53(1):191-196 Resting sites used by American marten have been described for a wide range of geographic locations and include a variety of natural and man-made microhabitats (Campbell 1979, Steventon and Major 1982, Martin and Barrett 1983, Buskirk 1984). Locations of resting sites range from the forest canopy to beneath the soil surface. Winter resting sites are often associated with coarse woody debris (CWD), including logs, stumps, and snags (Steventon and Major 1982, Martin and Barrett 1983, Spencer 1987). In summer, marten generally rest in sites above the ground, often in the canopy layer (Masters 1980, Burnett 1981, Martin and Barrett 1983). Temporal differences in resting site preferences could be explained by thermoregulatory needs of marten, or by other factors such as vulnerability to predation. Marten live where above-snow air temperatures (Ta) in winter are lower than their lower critical temperature (T,c = the temp at which an animal must increase its metabolic rate above resting levels to offset thermal losses [16 C]) (Buskirk et al. 1988) by ?50 C. Thus they would appear to pay high energetic costs to rest at or near To in winter. Marten are associated with late successional stands of conifer-dominated forest over a wide geographic area (Francis and Stephenson 1972, Koehler and Hornocker 1977, Simon 1980, Bateman 1986) and have a close and seemingly obligatory association with old-growth stands in the Rocky Mountains in winter (Campbell 1979). However, a clear understanding of why marten are associated with old-growth is lacking. Patte ns of use of resting sites may provide a better understanding of the apparently obligatory nature of this association. We report on characteristics of resting sites used by marten in the Medicine Bow Mountains, Wyoming during 2 winter field seasons. We identify environmental and behavioral correlates of resting site use and draw inferences about the importance of resting site types for thermoregulation. We also discuss the importance of CWD as a resting site component in understanding the old-growth dependency of marten during winter. L. R. Forrest provided invaluable assistance during the winter field studies. We appreciate the cooperation of R. H. Abell, for allowing use of a portion of his trapline for field work. This research was supported by the Committee for Research and Exploration, National Geographic Society, the U.S. Forest Service (USFS), Rocky Mountain Forest and Range Experiment Station, and the Office of Research, University of Wyoming. We thank the Wyoming Game and

Protein Use and Muscle-Fiber Changes in Free-Ranging, Hibernating Black Bears

Studies of the metabolic and physiological changes that bears undergo during hibernation have, for the most part, supported the paradigm that bears use only fatty tissues as a metabolic substate during hibemation. This study was performed to document the extent of protein loss and alteration of muscle‐fiber characteristics of selected muscles in black bears during winter dormanc. Muscle biopises were removed from the gas‐trocnemius and biceps femoris from seven free‐ranging female black bears on the Uncompahgre Plateau in west‐central Colo‐rado. Six of the seven bears produced cubs during the hibernat‐ing season. Muscle samples were collected from the left hind limb shortly after bears entered their dens (fall), and additional samples were collected from the right hind limb Just prior to bears leaving their dens (spring). Protein concentration, fast‐and slow‐twitch muscle‐fiber rations and muscle‐fiber cross‐sectional areas, and citrate synthase activity were measured in the laboratory. While Protein concentration decreased in both muscles during the hibernation period, it was lower than pre‐dicted for lactating females, In addition, muscle‐fiber number and cross‐sectional area were unchanged in these muscles, sug‐gesting only limited muscle atrophy. In support of these obser‐vations, there were a moderate but significant increase in the proportion of fast‐twitch fibers only in the biceps femoris, with a concomitant decrese in citrate synthase activity, but no alteration of the fiber ratio in the gastrocnemius during hiber‐natio. The findings suggest that hibernating bears, particu

Levels of plasma corticosterone and testosterone in male copperheads (Agkistrodon contortrix) following staged fights.

Fighting behavior between male copperheads (Agkistrodon contortrix) occurs during the two mating periods (late summer/fall and spring) to gain priority of access to females. Fights are characterized by prominent vertical challenge displays, swaying, and a high degree of physical contact that does not involve biting. At the moment of subordination, losers retreat quickly from fights and winners respond by chasing. Subsequently, losers do not participate in further challenge displays or fighting for at least 7 days, and also they show behavioral signs of stress, which includes submissive acts and suppression of sexual behavior. The goal of this study was to determine whether or not losers show elevated levels of plasma corticosterone (B) and depressed levels of plasma testosterone (T) relative to winners and controls. Winners and losers were produced in 13 staged trials. Two different controls (N = 26) were run. Males with no recent agonistic experience were (1) tested in the fighting arena in the absence of a competitive male but paired with a single female (N = 13), and (2) tested alone in their cages (N = 13). All trials, including controls, were conducted in spring and late summer. Mean B in losers at 1-hr postfight was significantly greater than in winners and both control groups in both seasons. Mean T was significantly greater in late summer in all groups, as expected, but in each season was not significantly different between the groups. Levels of B and T were not correlated with SVL, mass, or duration of fighting. This study provides further support for the social insensitivity/challenge hypotheses and is the first to document postfight B and T levels in snakes.

Effect of Melatonin on the Force of Spontaneous Contractions of In Vitro Rat Small and Large Intestine

Segments from various locations of the small and large intestine of the rat were removed, bathed in Tyrodes solution and attached to a force displacement transducer. Melatonin, while not influencing the frequency of contraction, did reduce the force of spontaneous contractions of duodenal and colon segments of rat intestine by 92 and 52%, respectively compared to only 25 and 22% for the ileum and jejunum, respectively. Areas with greatest responsiveness to melatonin were those that previous studies have shown to contain the largest concentrations of endogenous melatonin. Cyclic guanosine monophosphate, when tested in similar preparations, did not produce an inhibitory response characteristic of melatonin. It is hypothesized, therefore, that this hormone has physiological action within the gut, including motility; however, its action may not be directly on smooth muscle contraction but may be through an indirect action inhibiting the contractile response of serotonin, as suggested by other investigators.

Torpor and Other Physiological Adaptations of the Badger (Taxidea-Taxus) to Cold Environments

Oxygen consumption (V̇o2) and heart rate were measured at ambient temperatures between +20 and −40 C. Basal metabolic rate was 0.3 cm³/g·h (65 beats/min), the body temperature was 38 C, the lower critical temperature (Tlc) was 10 C, and conductance was 0.01225 cm³/g·h°C. Fat composition of 79 adult badgers captured during the winter showed maximal fat deposition of 31% body weight in November. Fat stores were reduced 37% between November and March. The burrow temperature remained between 0 and 4 C throughout the winter. Badgers in outdoor enclosures during the winter of 1977–1978 reduced their above-ground exposure by 93% from November through February. Two badgers remained below ground for more than 70 consecutive days during the 1978-1979 winter. While below ground, one telemetered badger entered a state of torpor, on 30 occasions, characterized by a 50% reduction in heart rate (from 55 to 25 beats/min) and a 9 C reduction in body temperature (from 38 to 29 C). The torpor cycle lasted an average of 29 h (entrance-15 h, torpor-8 h, arousal-6 h). Each cycle provided a 27% or 81 kcal/cycle reduction in energy expenditure.

Hibernating Bears Conserve Muscle Strength and Maintain Fatigue Resistance

Black bears spend several months each winter confined to a small space within their den without food or water. In nonhibernating mammals, these conditions typically result in severe muscle atrophy, causing a loss of strength and endurance. However, an initial study indicated that bears appeared to conserve strength while denning. We conducted an in vivo, nonsubjective measurement of strength, resistance to fatigue, and contractile properties on the tibialis anterior muscle of six hibernating bears during both early and late winter using a rigid leg brace and foot force plate. After 110 d of anorexia and confinement, skeletal muscle strength loss in hibernating bears was about one‐half that in humans confined to bed rest. Bears lost 29% of muscle strength over 110 d of denning without food, while humans on a balanced diet but confined to bed for 90 d have been reported to lose 54% of their strength. Additionally, muscle contractile properties, including contraction time, half‐relaxation time, half–maximum value time, peak rate of development and decay, time to peak force development, and time to peak force decay did not change, indicating that no small‐scale alterations in whole‐muscle function occurred over the winter. This study further supports our previous findings that black bears have a high resistance to atrophy despite being subjected to long‐term anorexia and limited mobility.

BODY MASS AND LIPID CHANGES BY HIBERNATING REPRODUCTIVE AND NONREPRODUCTIVE BLACK BEARS (URSUS AMERICANUS)

Abstract This study, conducted on female black bears from 3 study areas in the Rocky Mountains, showed that pregnant females in a state of diapause during early winter had about 89% larger fat depots than did nonreproductive females going into hibernation. Fat provided 92% of the total energy for lactation and gestation. Rates of fat loss (g/day) were 37% greater and protein loss about 2.4 times higher for reproductive females than for nonreproductive females. The cost of winter reproduction, including gestation and lactation, was 1,432 kJ/day to produce 2 young. Although reproduction required elevated protein breakdown, rates of overall protein loss were relatively small, perhaps due to a short period of implantation and an extraordinary ability to hydrolyze urea.

BODY SURFACE TEMPERATURE OF HIBERNATING BLACK BEARS MAY BE RELATED TO PERIODIC MUSCLE ACTIVITY

Abstract Temperature sensors were placed in the abdominal cavity, on the neck, and outside the dens of 5 hibernating black bears (Ursus americanus) during early winter and removed at the end of winter before emergence of bears from their dens. Bears did not arouse from torpor throughout the winter test period. Abdominal temperature remained within a 1.5°C temperature range and did not appear to exhibit circadian rhythmicity. However, neck surface temperature of bears demonstrated elevated spikes from 2 to 30°C about 4 times each day. Adult students wearing the same neck sensors as bears exhibited similar spikes in body surface temperature when vigorously exercising in the cold. We suggest that bears engage in bouts of muscle activity during the winter denning period that may result in the retention of muscle strength without elevating their core body temperature and without arousing from torpor.

Maintenance of slow type I myosin protein and mRNA expression in overwintering prairie dogs (Cynomys leucurus and ludovicianus) and black bears (Ursus americanus).

Hibernating mammals have the remarkable ability to withstand long periods of fasting and reduced activity with dramatic maintenance of skeletal muscle function and protein composition. We investigated several hindlimb muscles of white-tailed prairie dogs (Cynomys leucurus) and black bears (Ursus americanus), two very different hibernators who are dormant and fasting during winter. The black-tailed prairie dog (C.ludovicianus) remains active during winter, but suffers minor skeletal muscle atrophy; nevertheless, they also demonstrate apparent skeletal muscle adaptations. Using SDS-PAGE, we measured myosin protein isoform profiles before and after the hibernation season. All species maintained or increased levels of slow myosin, despite the collective physiological challenges of hypophagia and reduced activity. This contrasts markedly with standard mammalian models of skeletal muscle inactivity and atrophy predicting significant loss of slow myosin. A mechanism for changes in myosin isoforms was investigated using reverse-transcription PCR, following partial sequencing of the adult MHC isoforms in C. leucurus and U. americanus. However, mRNA expression was not well correlated with changes in MHC protein isoforms, and other synthesis and degradation pathways may be involved besides transcriptional control. The muscles of hibernating mammals demonstrate surprising and varied physiological responses to inactivity and atrophy with respect to slow MHC expression.