From single celled bacteria to complex multicelled vertebrates, intraspecific variation in metabolism commonly scales allometrically, but with considerable variation. Here, I investigate if and how scaling relationships in colonies vary with the degree of integration. Clones can live in different states: a loosely associated group, a highly integrated colony, and eventually transition into a fully integrated individual. I hypothesized that highly integrated colonies are more likely to exhibit standard metabolic scaling (allometric, with exponent = 3/4), as is observed in fully integrated individuals. Furthermore, loosely associated groups of clones are more likely to scale isometrically (exponent=1) because the addition of new clones should not affect the metabolism of the other group members.
Results/Conclusions
The effect of colonial state on metabolic scaling was tested using ~100 taxa, including Arthropods (24), Bacteria (7), Bryozoans (8), Chordates (9), Cnidarians (37), Plants (4), and Protozoa (5). While colonial state and phyla are poor predictors of the scaling exponent, the scaling exponent generally decreases with integration, from 0.97 +/- 0.08 in loosely associated groups, to 0.90 +/- 0.07 in highly integrated colonies, and to 0.85+/-0.06 in fully integrated individuals. Thus, increases in integration are associated with a shift from isometry to allometry. In theory, an increase in integration indicates an evolutionary transition in individuality, but integration is difficult to quantify. Thus, metabolic scaling exponents can represent a continuous measure of a transition in individuality.