Temperature regulation and metabolic rhythms in populations of the house sparrow Passer domesticus
Kimzey, Stephen Lee
Hudson, Jack W.
Master of Arts
This study was an attempt to correlate the influences of the environmental stresses of high ambient temperatures and high humidities on selected physiological properties related to temperature regula-tion in the house sparrow, Passer domesticus. Measurements were made of metabolism, evaporative water loss, and body temperatures at various ambient temperatures. These physiological properties were compared among four populations of house sparrows from Boulder, Colorado; Syracuse, New York; Ann Arbor, Michigan; and Houston, Texas. It was found that both the diurnal and nocturnal levels of metabolism of the Houston population were significantly lower than any of the other populations at all temperatures tested. Evaporative water loss did not differ significantly among the populations in the absolute amount lost at various ambient temperatures. However, by virtue of its reduced level of endogenous heat production, the Houston population was able to dissipate a greater percentage of its heat load. There was no significant difference in the body temperatures of the four populations within the range of ambient temperatures measured. The Houston population was able to tolerate a higher ambient temperature than any of the other populations, though the mechanism of this response is not clear. This study suggests that there has been evolutionary alteration of some of the metabolic processes of house sparrows since their introduction into the United States about the middle of the nineteenth century. It is evident from this study that metabolism does not possess the adaptive "rigidity" ascribed to it by many earlier workers, and that under certain conditions of environmental stress, metabolism may exhibit adaptive alteration. Because this change in metabolic rate persists for long periods of time in absence of environmental stresses, it is suggested that this is genotypic alteration. This would be indicative of evolutionary rates much faster than previously ascribed to for higher organisms.