In the complex world of living matter, the scaling law linking the metabolic rate of an organism with its body mass almost seems peerless — both in its simplicity and its longevity. But what drives the scaling? That different species elude quantitative comparison and single species span too narrow a size range has made this a difficult question to answer. Now, Albert Thommen and colleagues have sought help from the remarkable flatworm Schmidtea mediterranea, which grows when fed and shrinks when starved — exhibiting a 40-fold range in body length.
Using microcalorimetry, Thommen and co-workers confirmed the expected scaling, then devised a theoretical framework casting growth and shrinkage as a function of the organism’s metabolic energy budget. Armed with both model and data, they identified an increase in the mass per cell due to size-dependent energy storage as the cause of the scaling in the starving worms. It remains to be seen whether the same mechanism underpins allometric scaling in all animals.
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Klopper, A. The long and short of it. Nature Phys 15, 110 (2019). https://doi.org/10.1038/s41567-019-0429-4
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DOI: https://doi.org/10.1038/s41567-019-0429-4