Effects of lipopolysaccharide and acclimation temperature on induced behavioral fever in juvenile Iguana iguana

We examined the effects of acclimation temperature and two doses (2.5 and 2 5 mg kg(-1)) of a pyrogen (lipopolysaccharide, LPS) on behavioral thermoreg ulation in juvenile green iguanas. Overall means of body temperatures for t he three-day trial periods were compared among three groups of animals accl imated at 15, 25, and 34 degreesC. The responses of each group of animals t o the two dosages of LPS and a control saline injection were examined. With in each treatment block, animals either chose high body temperatures charac teristic of a fever response or chose low body temperatures characteristic of a hypothermic response. Thermoregulation was influenced by interaction e ffects between and among, and independent effects of, acclimation temperatu re, dose of LPS, and day. In some treatment blocks, individual lizard mass positively correlated with mean individual body temperature. Mean mass of l izards that chose higher body temperatures within a treatment block was hig her than the mean mass of lizards that chose lower body temperatures. From these results, we concluded that LPS may induce two different behavioral th ermoregulatory responses: fever or hypothermia. The actual amplitude and di rection of body temperature change appears to be affected by acclimation te mperature and possibly by mass or energy reserves of the animal. If the ene rgy reserves an not sufficient to sustain the higher rate of metabolism ass ociated with the higher body temperatures of a hyperthermic or feverish sta te, the animal may resort to hypothermia. (C) 2001 Elsevier Science Ltd. Al l rights reserved.