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Biological size as a predictor of physiological performance and evolution: Evidence from lungless salamanders

Johnson, Benjamin1

Published Dec 02, 2022 on Dryad. https://doi.org/10.5061/dryad.r2280gbh6

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Dec 02, 2022 version files 3.10 MB

Abstract

Gross physiological performance in multicellular organisms coordinates processes operating from the cellular to whole-organism level, and thus may be influenced by physical constraints imposed by both cell size and body size. A useful measure of joint cell and body size variation is biological size, defined here as the ratio of body volume to mean cell volume. We surveyed literature data across four vertebrate clades and documented wide variation in two proxies for biological size, even between species of equivalent body size. We evaluated these proxies in a sample of lungless salamanders (Urodela: Plethodontidae) and used linear and evolutionary regressions to compare their power to predict variation in metabolic and water loss physiology to that of body size alone. One proxy (the ratio of body length to the square root of genome size) consistently outperformed mass in predicting water loss rates, and residual variation from evolutionary trends in the other proxy (the ratio of mass to genome size) consistently explained the most variance across all physiological responses. These results suggest that for some traits in some taxa, biological size may be a more functionally relevant predictor of performance than body size alone. Physiological ecology is replete with studies characterizing the effects of body size. We suggest that future studies of size effects additionally consider the role of cell size variation (and genome size variation as one of its determinants) to improve our understanding of when and how biological size influences organismal form and function.