Metabolism, mass and allometric transitions

Prokaryotes, like these Escherichia coli, have an allometric exponent for mass specific metabolism around 0.84 (Delong et al., 2010). This is close to 5/6; a predicted value when body masses are selected from the primary selection of mass specific metabolism (Witting, 2016). Photo: (c) iStockPhoto.com

In a new release on bioRxiv (Witting, 2016) I take the original “allometries are selected by the selection of mass”-hypothesis (Witting, 1995, 1997) and integrate primary selection on mass specific metabolism into the selection of mass. This shows how a change in the importance of mass specific metabolism for the selection of mass is explaining allometric transitions from prokaryotes over larger unicells to multicellular animals.

The study finds that mass specific metabolism is selected as the pace (speed) of the resource handling that generates net energy for self-replication, with mass being selected as a function of the average net energy in the population. The evolved mass is then a joint function of the mass specific metabolism and resource handling that generates net energy for self-replication, with the exponent of the inter-specific allometry for mass specific metabolism increasing with the importance of mass specific metabolism for the generation of the essential variation in net energy.

This mechanism explains the range of exponents that are observed from prokaryotes to mammals. A positive 5/6 exponent is predicted for prokaryotes with three dimensional ecology given body mass variation that evolves from primary variation in mass specific metabolism. A negative 1/4 exponent is predicted for multicellular animals with two dimensional ecology given body mass variation that evolves from adaptations to ecological niches. And an observed decline in the exponent (from 0.61 over 0 to -0.20) with an increase in the mass of protozoa, is predicted from a gradual decline in the importance of mass specific metabolism for the selection of mass.

The conclusion is that the primary selection of metabolism and mass is the only thing that we need to explain the broad-scale evolution of body mass allometries from prokaryotes over larger unicells to multicellular animals.

References

• DeLong, J.P., J.G. Okie, M.E. Moses, R.M. Sibly and J.H. Brown 2010. Shifts in metabolic scaling, production, and efficiency across major evolutionary transitions of life. Proceedings of the National Academy of Sciences 107:12941--12945.
• Witting, L. 1995. The body mass allometries as evolutionarily determined by the foraging of mobile organisms. Journal of Theoretical Biology 177:129--137, https://doi.org/10.1006/jtbi.1995.0231.
• Witting, L. 1997. A general theory of evolution. By means of selection by density dependent competitive interactions. Peregrine Publisher, Århus, 330 pp, URL https://mrLife.org.
• Witting, L. 2016. The natural selection of metabolism and mass selects allometric transitions from prokaryotes to mammals. Preprint at bioRxiv https://dx.doi.org/10.1101/084624.