Body Temperature in Wisconsin Peromyscus leucopus: A Reexamination

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Abstract
Body temperatures ( ) of 87 Peromyscus leucopus from Wisconsin, acclimated to 20-23 C, were monitored while the animals were exposed for 4 h in confining 5.1-cmdiameter chambers to ambient temperatures ( ) of 0-2 C and 10-12 C. Each animal was tested at both after having had free access to food up to the start of the test (unfasted tests) and after having been denied food for about 12.5 h (fasted tests). Measurements of after 1 h in the unfasted tests provided a direct replication of experiments by Morrison and Ryser (1959). After 1 h and 4 h at either in the unfasted tests, averaged 36.0-36.9 C and exhibited a standard deviation of 1.7-2.2 C. The especial lability of reported by Morrison and Ryser was not observed, a result that agrees with several other studies and indicates that thermoregulation in unfasted P. leucopus during short-term cold exposure is probably not distinctive within the genus Peromyscus. Some individuals were prone to enter torpor during a night of fasting, but those that started fasted tests in hypothermia characteristically aroused over the first hour of the tests. After 1 h at 0-2 C and 10-12 C in fasted tests, mean was 35.7-35.8 C; and variation in , though greater than in unfasted tests, was unremarkable (SD: 2.3-2.5 C). After 4 h at 0-2 C and 10-12 C when fasted, many individuals continued to maintain above 37 C, but others allowed to fall below 30 C; mean fell (34.8 C at 10-12 C , 30.8 C at 0-2 C ), and standard deviation increased (4.2 C at 10-12 C , 8.2 C at 0-2 C ). There was no tendency for torporprone individuals to be those that became hypothermic during fasted tests. Individuals tended to rank similarly in under conditions that did not elicit hypothermia in appreciable numbers (all 1-h measurements on fasted and unfasted mice, 4-h measurements on unfasted mice). However, the tendency toward consistent ranking broke down in fasted animals after 4 h at either . Development of hypothermia in fasted animals at 0-2 C was independent of that at 10-12 C , and individuals becoming hypothermic under these conditions did not tend significantly to be those occupying the lower end of the distribution under more moderate conditions.

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