Jack W. Hudson

Temperature regulation in normothermic and hibernating eastern chipmunk, Tamias striatus

Abstract 1. 1. In normothermia, body temperature (Tb) of T. striatus was 36 to 40·3°C at an ambient temperature (Ta) range of −7 and 32°C. Minimum oxygen consumption was 1·03 cm3O2/g per hr between Ta = 28·5 and 32°C. Minimum thermal conductance was 0·120 cm3O2/g per hr per °C. Minimum heart rate at a Ta of 30–31°C was 165 beats/min and irregular. Atropinization abolished irregular T-P intervals of electrocardiograms observed at Ta of 3–34°C. 2. 2. During entry into torpor, skipping of heart beats, successive declines of oxygen consumption and episodes of intermittent shivering were typical. 3. 3. During torpor, minimum heart rate and oxygen were 8·3–23% and 1·6–33% of normothermic values for comparable Ta. The Tb-Ta gradient of torpid animals increased from 2·8 to 13·4°C when the Ta decreased from 25·8 to 2°C. Body temperature in deafened animals was 2·4°C lower than that of undeafened animals. The lowest Tb at which arousal occurred was 5°C. 4. 4. During arousal, heart rate increased 10–23 times, oxygen consumption 7–28 times the torpid value. The fastest increase in Tb was associated with the strongest shivering episodes. The maximum cheek pouch-rectal temperature difference was 6·6°C and both temperatures increased in parallel. The maximum arousal rate was 0·72°C/min.

Metabolism and Thermoregulation in Hatchling Ring-Billed Gulls

The extensive efforts to analyze the size dependence of various parameters of thermoregulation in birds (King and Farner 1961, Lasiewski and Dawson 1967, Lasiewski et al. 1967, Herreid and Kessel 1967, Crawford and Lasiewski 1968, Aschoff and Pohl 1970) have been useful in defining certain physiological characteristics of these animals. However, the analyses have tended to obscure the fact that variation beyond that associated with general allometric relations can occur in these parameters within particular taxa. For example, House Sparrows (Passer domesticus) show geographic variation in heat resistance, thermal conductance, and metabolic responses to cold (Hudson and Kimzey 1966, Blem 1973, 1974, Kendeigh and Blem 1974). Horned Larks (Eremophila alpestris) in deserts surpass their counterparts from more mesic situations in thermoregulation in hot environments (Trost 1972). Basal metabolic rate of certain pigeons is inversely correlated with the degree of aridity of their respective environments (Dawson and Bennett 1973). Variation in thermoregulatory parameters is also evident among young of closely related species, judging by the results of Koskimies and Lahti (1964). These authors demonstrated that hatchling ducks of species breeding exclusively at arctic and subarctic latitudes tended to have better control of body temperature at cool ambient temperatures than those of species with wider and more southerly distributions. We feel that variation of this type within taxa may well reflect functionally significant adjustments. To evaluate the physiological role of these adjustments more precisely, we have studied the metabolism and thermoregulatory capacities of hatchling gulls in the genus Larus. This group is a particularly useful one for considerations of physiological variation, for it is represented by more than 30 species over a latitudinal span extending from the arctic to the sub-antarctic. Our initial study in this series (Dawson et al. 1972) concerned the Laughing Gull (Larus atricilla). We now report results obtained on the Ring-billed Gull (Larus delawarensis). This species nests predominantly on lakes at midlatitude in northern United States and southern Canada. It also breeds in maritime situations in Quebec and Newfoundland (A.O.U. Check-list 1957).

Growth and development of temperature regulation in nestling cattle egrets

Abstract 1. 1. The growth of cattle egrets is typical of altricial birds of comparable size and appears best described by the logistic equation. 2. 2. The telemetered body temperatures of six nestlings measured in the field over extended periods ranged between 38 and 40°C. 3. 3. Resistance of nestlings to hypothermia develops gradually after hatching as a more intense standard metabolism and capacities for augmenting muscular thermogenesis in the cold are established. 4. 4. Chicks increase their breathing rate and initiate gular flutter in response to heat loads. At ambient temperatures of 44/2–45°C, they evaporatively dissipated heat at rates up to 2/2–5 times heat production. Heat defense is well developed at hatching in cattle egrets.

Metabolism, pulmocutaneous water loss and respiration of eight species of ground squirrels from different environments

Abstract 1. 1. The night time metabolism of eight species of ground squirrels ( Spermophilus spp.) is described by the allometric relationship: metabolism ( ml/hr ) = 3·2G 0·66 ± 0·1176 (2 S.E.)—60 per cent of the metabolism for other mammals of comparable size. 2. 2. The circadian cycle of T b has an amplitude of 1·9°C, with a nocturnal T b of 35·7 ± 0·2 (2 S.E. ) . 3. 3. The Q 10 of metabolism vs. T b between 1·96 and 5·4. 4. 4. The dry conductance of six species decreased at T a of 35°C and above. 5. 5. Breathing rate was 2·25−2·75 times minimal values resulting in 100 per cent dissipation of metabolic heat at T a between 38·7 and 42°C, inclusive. 6. 6. There were distinct differences between species in their tolerance to high T a .

Temperature regulation in the tree shrew Tupaia glis

Abstract 1. 1. The mean day-night difference of body temperature in Tupaia glisis 5-1°C. 2. 2. The nocturnal standard metabolic rate is 0.76 ml O 2 /g per hr ± 0.07 (2 S.E.) at a mean body temperature of 37.0°C. 3. 3. The thermal neutral zone extends from near 30 to above 37°C. 4. 4. The marked decline in body temperature at lower ambient temperatures is interpreted to reflect the tropical habitation of this species.

Thermal sensitivity of isolated-perfused hearts from the ground squirrels, citellus tereticaudus and Citellus tridecemlineatus

SummaryPerfused hearts of C. tereticaudus cease to beat at an average TA slightly below 5.7±0.7° C, whereas perfused hearts of C. tridecemlineatus stop at a TA slightly below −0.7±0.9° C. Although both species are approximately the same size and both can hibernate, the desert inhabiting C. tereticaudus has a smaller heart which beats slower, consistent with its lower metabolism, than the plains inhabiting C. tridecemlineatus. It is suggested that ecological factors were more important than taxonomic characteristics in the development of these specific features of hibernators adaptive for different habitats.

The estrous cycle, reproduction, growth, and development of temperature regulation in the pygmy mouse, Baiomys taylori.

The estrous cycle of Baiomys taylori averages 4.9 days. The gesta-tion period is estimated to be 22 to 23 days. A postpartum estrus is frequent. Puberty occurs as early as 28 days of age. Seven of 10 females between 25 and 29 days of age conceived within a week after pairing. The average weight of 47 individuals at birth was 1.20 ± 0.08 (SD) grams. The adult level of body temperature could be maintained at ages between 10 and 15 or 15 and 20 days for neonates exposed to 30 and 28°C, respectively, for a period of 2 hours. Growth during the first 20 to 35 days occurred in two phases with the first phase exhibiting an instantaneous growth rate of 7.50 ± 0.32 and 7.29 ± 0.42 per cent of body weight per day for experimentals (those young used for metabolic as well as body temperature and body weight measurements) and controls (those young used only for body weight measurements), respectively. The second growth phase commenced at 11.3 days for the experimentals and 17.0 days for the controls. The second growth phase averaged only. 4.01 ± 0.26 and 3.30 °: 0.52 per cent of body weight per day for the experimentals and controls, respectively, and coincided with the full development of homeothermy. At a body temperature of 36 to 37°C and a body weight of 2.0 to 2.5 grams—the lower size limit for homeothermy—the oxygen consumption was 3.6 ° 0.40 (2 SE) cc O2/g/hr if the ambient temperature was 30°C. The oxygen consumption for neonates averaging 22.5 ± 0.7 days of age was 4.31 ± 0.16 cc O2/g/hr at an ambient temperature of 30°C. This relatively high level of oxygen consumption indicated that 30°C was below thermal neutrality, the ambient temperatures at which the oxygen consumption of adults is 1.95 ± 0.25 (2 SE).

42K efflux, EKG and tension in isolated perfused hearts of white-footed mice

Abstract 1. 1. The EKG and systolic tension of isolated, perfused hearts from Peromyscus leucopus is a function of the perfusion temperature. 2. 2. The marked loss of 42 K during perfusion at lower temperatures indicates a loss of intracellular potassium and suggests a breakdown in the ability to maintain electrolyte balance. 3. 3. The decline in EKG potential and tension as well as the increased 42 K efflux which occur at perfusion temperatures similar to the lower range of body temperature during torpidity of the intact animal indicate that cardiac performance may limit the depth and length of torpor in P. leucopus .

Running performance of the thirteen-lined ground squirrel, the eastern chipmunk and the albino Norway rat

Abstract 1. 1. The procedure used to compare the forced running performance of three rodent species was the number of electrical stimuli required each minute to keep the animals running. 2. 2. During running trials, ground squirrels, Spermophilus tridecemlineatus, required fewer stimuli than white rats. Squirrels ran 12.4 ± 6.9 (2 SE) min before requiring stimulation vs 3.1 ± 1.4 min for rats. 3. 3. Total oxygen consumption during the running period was significantly higher for ground squirrels than white rats, 4.70 ± 0.36 and 4.18 ± 0.38ml O2/g/hr, respectively. 4. 4. Heart weight/body weight ratios were significantly higher for the ground squirrels than the white rats. 5. 5. No differences were noted between ground squirrels and chipmunks other than those which could be accounted for by body weight differences.