Fever response in laboratory-maintained and free-ranging chuckwallas (Sauromalus obesus).

The fever response was studied in laboratory-maintained and free-ranging chuckwallas. Five animals were used in a self-pairing laboratory experiment in which each animal was first injected with a sterile, pyrogen-free saline solution. Approximately 7 days later, each individual was injected with a solution of 4.75 x 10(9) Aeromonas sobria (formerly A. hydrophila). Saline-injected individuals had a mean preferred body temperature (MPBT) of 36.8 +/- 0.4 (SE) degrees C, whereas bacteria-injected animals had a MPBT of 39.1 +/- 0.6 (SE) degrees C (an increase of 2.3 degrees C). The within-animal variance associated with MPBT was significantly decreased in bacteria-injected animals. In the natural environment, 10 chuckwallas were divided into five pairs, so that both animals of a pair could be monitored simultaneously. One animal in a pair was given an injection of sterile, pyrogen-free saline, whereas the other animal received an injection of 4.75 x 10(9) A. sobria. On day 2, both the MPBT and the rate of heating were greater in bacteria-injected animals. The between-animal variation in fever MPBT was greater than the mean increase in MPBT of fever animals. Also, the absolute level of the MPBT during the fever response was related to time of the year, with spring-active animals having the highest fever MPBTs.