Stam M. Zervanos

Adaptational Biology and Energy Relationships of the Collared Peccary (Tayassu Tajacu)

Field and laboratory investigations were conducted to determine the major seasonal adaptations exhibited by the collared peccary (Tayassu tajacu) in the desert. Emphasis was placed on the animals thermoregulation, water relations, and energy requirements under changing environmental conditions. Body core temperatures were labile and ranged from 37.5 degrees C to approximately 40.9 degrees C during both winter and summer seasons. Skin temperatures were always above ambient and reached a high of 49.2 degrees C during summer. Heat loss across the skin of summer animals averaged 0.041 cal/cm2 min during the day and 0.038 cal/cm2 min at night. Winter animals by basking exhibited a slight heat gain during the day (0.033 cal/cm2 min) but lost heat at a rate of 0.223 cal/cm2 min at night. The pelage of the peccary had a poor insulative value; thermal conductance equaled 0.291 cal/cm2 hr degrees C. Summer animals became lighter in color over certain parts of their body and also decreased density of bristles over most of their body. Total water requirement for summer peccaries was 66.5 ml/kg day and for winter peccaries 38.6 ml/kg day. Respiratory evaporation was the major avenue of water loss and accounted for 6.1% of body wt/day for summer dehydrated pecaries. during dehydration peccaries were able to reduce evaporative water loss by as much as 68% and urinary water loss by 93%, but were unable to produce dry feces. Their maximum osmolar urine/plasm ration was 4.0. Total daily energy requirement for an 18.2 kg peccary was 794.05 Kcal/day in summer and 916.96 Kcal/day in winter. The annual energy requirement was estimated at 17,166 Kcal/kg year. On the basis of these calculations, a herd of 25 individuals occupying a home range of 388 ha at the Three—Bar wildlife Area would require approximately 20% of the annual production of prickly pear cactus (7,985.0 kg/year or 20,130.9 Kcal/ha year).

Latitudinal differences in the hibernation characteristics of woodchucks (Marmota monax).

There is little information on the phenotypic flexibility of hibernation characteristics within species. To address this issue, we observed differences in hibernation characteristics of three free‐ranging populations of woodchucks (Marmota monax) distributed along a latitudinal gradient from Maine to South Carolina. Data from free‐ranging animals exhibited a direct relationship between latitude and length of the hibernation season. As expected, woodchucks in the northern latitudes hibernated longer than those in the southern latitudes. Also, the length of interbout arousals decreased with increase in latitude, whereas the length of torpor bouts and the number of arousals increased. Thus, we observed phenotypic plasticity in hibernation characteristics based primarily on latitudinal temperature differences in each population. Further analysis revealed a direct relationship between latitude and total time spent in torpor. Maine animals spent 68% more time in torpor than South Carolina animals. However, total time spent euthermic did not differ among the three populations. The “cost‐benefit” hypothesis of hibernation may help to explain these results. It assumes that hibernators avoid the physiological stress of torpor by staying euthermic as much as possible. Woodchucks in each population maximized time spent euthermic, utilizing torpor only at the level needed to survive winter hibernation and to commence reproduction in the spring.

SEASONAL BODY TEMPERATURE FLUCTUATIONS AND ENERGETIC STRATEGIES IN FREE-RANGING EASTERN WOODCHUCKS (MARMOTA MONAX)

Abstract During a 2-year period, radiotelemetry was used to continuously monitor body temperature (Tb) of free-ranging woodchucks (Marmota monax) in southeastern Pennsylvania. Hibernation was preceded by daily Tb fluctuations (“test drops”) of 2–4°C. During hibernation, woodchucks exhibited the characteristic pattern of torpor bouts. Time of arousals occurred randomly, but onset of torpor occurred predominantly between 1800 and 0000 h. Males had shorter hibernation periods (mean of 104.8 days) than did females (121.8 days). Males had shorter torpor bouts, but euthermic bouts were the same length as in females. Males also maintained higher Tb during torpor. Overall, the cost of hibernation was greater for males than for females: males spent 38% more energy than did females. The primary energetic expense for both sexes was the periodic maintenance of euthermy throughout hibernation, which accounted for 75.2% of the energy budget for males and 66.8% for females. Compared with the 1999–2000 hibernation seasons, woodchucks during the 1998–1999 season had longer euthermic bouts, fewer torpor bouts (11.8 compared with 13.1), and spent less time in torpor (68% compared with 75%). These differences conserved more energy during the 1999–2000 hibernation season and may have been the result of severe drought conditions during summer 1999. After emergence from hibernation, woodchucks generally maintained a constant state of euthermy throughout the active season, with Tb fluctuating daily by 1–2°C. However, during the summer drought of 1999, daily Tb fluctuated 8–17°C in 5 of 8 woodchucks, presumably to conserve energy and water.

Effect of body mass on hibernation strategies of woodchucks (Marmota monax).

The benefits of mammalian hibernation have been well documented. However, the physiological and ecological costs of torpor have been emphasized only recently as part of a hibernation-optimization hypothesis. This hypothesis predicts that hibernators with greater availability of energy minimize costs of torpor by less frequent utilization of torpor and by maintaining higher body temperatures (T(b)) during torpor. In order to further examine the relationship between body mass and other parameters of hibernation, we present data, collected over a 12-year period, on the hibernation patterns of free-living woodchucks (Marmota monax) in southeastern Pennsylvania. Body mass was positively correlated with T(b) and negatively correlated with percentage of the heterothermic period spent in torpor. Thus, woodchucks with greater mass exhibited less time in torpor as a proportion of their heterothermic period and at higher T(b) than those with lesser mass. This strategy potentially enhances the physiological and physical ability of woodchucks to defend territories, avoid predation, find mates, and complete the reproductive cycle upon emergence from hibernation. Our results further support the hibernation-optimization hypothesis by demonstrating the relationship between body mass and characteristics of torpor and contributing toward a fuller understanding of this concept.

Seasonal effects of temperature on the respiratory metabolism of the collared peccary (Tayassu tajacu)

Abstract 1. 1. Information on metabolism, heat flux, evaporation, heart rate and respiration for winter- and summer-acclimatized collared peccaries (Tayassu tajacu) was obtained using an open-flow respiratory chamber. 2. 2. Peccaries exhibited a narrow thermal neutral zone with a lower critical temperature of 25°C in winter or 28°C in summer and an upper critical temperature of 30 or 35°C, respectively. 3. 3. To compensate for poor insulation, winter animals exhibited an increased basal metabolic rate. 4. 4. Body core temperatures were labile and ranged from 37·5 to 40·9°C for both groups. Both body core temperatures and skin temperatures remained above ambient over the entire temperature range employed (10–40°C). This facilitated heat loss to the environment under warm conditions, but hampered heat balance during cold temperatures. 5. 5. Winter animals appeared to be more severely heat stressed by high temperature due to their higher metabolic rate and poorer heat-dissipating mechanism.

Energetic relationships between field and laboratory woodchucks (Marmota monax) along a latitudinal gradient

Hibernation is a strategy for energy conservation during periods of low food availability, but has energetic costs associated with arousal and maintenance of core body temperature above ambient temperature. Animals hibernating at low ambient temperatures generally exhibit low metabolic rates and reduced body mass loss, but little is known how these energetic costs differ in a single species in varying environments and temperatures. Also, it is unknown how populations along an extreme latitudinal gradient may alter energetic costs in a common environment. We investigated three free-living populations of woodchucks (Marmota monax) along a latitudinal gradient in the United States. In addition, animals obtained from the same three field populations were studied in the laboratory under a “common garden experimental design” to determine whether trends in energetic costs would be maintained. Based on calculated metabolic rates and body mass loss, animals from the northern most latitude exhibited a significantly higher total energetic cost (mlO2/g) over the hibernation season, but a significantly lower cost per day, compared with animals from more southern latitudes. Results from laboratory animals showed similar trends to those found in the field. However, the calculated energetic costs of hibernation in the laboratory were less than the freeliving populations. Energetic cost was compared among the laboratory populations during a period when food was removed and ambient temperature was 5 °C. The southern latitude population was torpid the least amount of time and incurred the highest energetic cost. We conclude that latitude has a significant effect on the energetic costs of hibernation.