RIVERSIDE, Calif. Life scientists have long maintained that, based on body size, small organisms are more metabolically active than large organisms. But a new study led by Bai-Lian Li, professor of ecology at UC Riverside, shows that this is true only for organisms that are closely related evolutionarily and have body masses differing by no more than 6-7 orders of magnitude about the difference in body mass between an elephant and a shrew.

For a pair of organisms that don't meet these conditions, that is, organisms that are not closely related evolutionarily and whose body mass difference exceeds the 6-7 orders of magnitude range, the researchers find that the small organism consumes about the same amount of energy per unit mass as the large organism: 1-10 watts per kilogram of body mass in the resting state of the organisms.

In other words, while metabolic activity per unit body mass varies within a group of organisms, such as mammals, it tends not to vary much when two diverse groups of organisms that differ greatly from each other in size are compared such as bacteria and mammals.

"Our findings indicate there is a universal rate of energy supply per unit mass which can maintain life in organisms regardless of size," Li said. "Living matter appears to be able to function at its own optimum rhythm, overriding various limitations imposed by the evolutionary increase in body size."

Results from the study appear in the Oct. 22 issue of the Proceedings of the Royal Society: Biological Sciences.

The study is the first to compare bacterial metabolism with that of larger organisms, and the first to cover very diverse groups of organisms from unicellular and multicellular organisms to plant leaves, insects and mammals.

Li explained that all living organisms have to transport energy obtained from food they eat to support the working of their inte
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Contact: Iqbal Pittalwala
iqbal@ucr.edu
951-827-6050
University of California - Riverside
19-Oct-2005

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