This blog post is provided by Pedro Pequeno and Douglas Glazier and tells the #StoryBehindThePaper for the article “Divergent evolution of colony-level metabolic scaling in ants”, which was recently published in the Journal of Animal Ecology. In their study, Pequeno and Glazier investigate variation in the metabolisms of ant colonies, revealing similar metabolic principles to those observed at the individual level.

Metabolism and body size: it’s complicated

Life runs on energy, and bigger animals need more of it. For a long time, many biologists believed that the way metabolism changes with body size followed a fixed rule — almost like a law of nature. But in the last couple of decades, it has become increasingly evident that this pattern is much more flexible and often shaped by ecological traits like what animals eat or how active they are.

Things are further complicated by eusocial animals like ants and termites. These animals evolved a new kind of “body”: they live in family groups or colonies, with different individuals doing different jobs — like the cells of a multicellular organism. So, we wondered: do whole colonies adapt their metabolism to their environment the same way individual animals do?

Ant colony metabolism, diet and division of labour

In our recent paper in the Journal of Animal Ecology, we looked at ant species from around the world to study how colony metabolism changes with colony mass and lifestyle. Researchers estimate metabolic rate or energy use through a method called “respirometry”: as animals breathe in oxygen and burn food, they release carbon dioxide, which can be measured to estimate energy use per time.

We found that energy use increased more quickly with colony mass in predatory ants than in plant-eating ants. That makes sense — predatory colonies may need to hunt larger or harder-to-catch prey to get enough food as they grow, which requires more energy. Herbivorous ants, by contrast, may rely on more abundant and easier-to-access plant resources even when their colonies are larger.

We also found that polymorphic species — those with different types of workers for different tasks — used more energy as colonies got larger than monomorphic species. This is surprising because division of labour is often expected to make colonies more efficient and thus less costly. But more specialized workers might do their tasks faster or more intensely, and overall colony activity might increase when different specialists work simultaneously, driving up energy costs. Since worker polymorphism tends to increase with colony size, this may help explain the higher energy use of larger, polymorphic colonies. Still, the extra cost might be worth it: having a wider range of worker types may help colonies compete better for resources.

Individuals and colonies: shared rules?

Measuring the metabolism of whole ant colonies is tricky, especially in species with very large colonies, for which we still lack data. Even so, by bringing together existing studies, we found a novel pattern: like individual animals, eusocial colonies evolved different rules of energy use depending on their ecology. This opens the door to future work exploring shared metabolic principles across levels of biological organization.

Read the paper

Read the full paper here: https://doi.org/10.1111/1365-2656.70055