This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: The energy required for brains of different sizes to function could play a role in how different species evolved over time. While the energetic costs of brains have long been deemed important in evolution, direct measurements of the rate at which the brains of different species consume energy, also known as brain metabolic rates (MRs), remain scarce.
Researchers at Arizona State University and Boston University recently studied a group of ant species called harvester ants, looking at the proportion of resting energy they devote to their brains. Their observations, presented in a paper published in Proceedings of the Royal Society B: Biological Sciences, suggest that species with smaller worker ants allocate more of their resting energy budget to their brains than those with larger workers. The researchers set out to test three main experimental hypotheses.
They first tried to determine whether more socially complex ant species exhibit higher brain MRs, or in other words, whether their brains use more energy per unit of time than those of less socially complex species. In addition, they wanted to test whether species with smaller bodies use more energy per unit of brain tissue. Finally, they investigated the possibility that the brains of species with evolutionary lineages that branched out more recently use less energy per unit of tissue, which may suggest that they evolved to be more metabolically "frugal." To test these hypotheses, the authors measured the mass of the brains and bodies of worker ants of different species.
They also examined brains dissected from the ants, specifically looking at indicators of oxygen consumption. They used these indicators to estimate the brains' rates of metabolic energy expenditure, or MRs. Finally, the researchers measured the ants' whole-body resting metabolism.
Their analyses compared 11 species belonging to the Pogonomyrmex genus, a group of closely related harvester ants originating from North and South America. The team found no association between the size of ant colonies, which served as an indicator of social complexity, and brain MR. However, the body size of worker ants appeared to be linked to their relative brain size, energy use per unit of brain tissue and the proportion of resting energy expenditure devoted to the brain.
"Worker body size and colony size, a proxy for social complexity, vary significantly among Pogonomyrmex species and were positively correlated," wrote Craig D. Perl and colleagues in their paper. "Species with larger colonies did not have larger brains or higher brain MRs.
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