The research described in this proposal aims to increase our knowledge concerning the fever response in animals other than humans; specifically relating to the occurrence of the fever response in one species of amphibian and two species of mammals living in their natural environment, the generality of the fever response in reptiles, and the energetic cost of the fever response in a free-living reptile. All of the studies concerning the fever response has never been demonstrated or investigated under natural field conditions where the greater heterogeneity of biotic and abiotic factors may lead to a more complex response. Also, although the fever response has been demonstrated in a number of ectothermic vertebrates under laboratory conditions, no systematic study of the fever response has been undertaken with any specific taxonomic group of ectothermic vertebrates to demonstrate the generality of the response and its relationship to life history characteristic of a species. Data on the fever response of the bullfrog, the California Ground squirrel, and the desert cottontail rabbit will first be gathered in the laboratory and than the laboratory baseline data will be applied to experiments on free-living animals. Body temperatures will be determined with the use of temperature sensitive radio transmitters. In the survey of the Class Reptilia for the fever response, II species representing 7 different Families will be given injections of heat-killed Aeromonas hydrophila, a gram negative bacterium known to be pathogenic to reptiles. The reptilian species to be used represent animals from different habitats (aquatic, mesic, desert), with different food habits (herbivorous, insectivorous, carnivorous), and with different activity patterns (diurnal, nocturnal). In the section that pertains to the energetic cost of the fever response, time budget analysis and oxygen consumption measurements will be combined to yield an estimate of the energetic cost of the fever response in a free-living reptile; the chuckwalla.