The trade-off between quality and quantity is a fundamental economic dilemma. Now, a team of British, American, and Japanese researchers describes how it applies to biology, as well. They have discovered that this dilemma most likely shaped the evolutionary trajectory of ants, one of Earth’s most successful groups of organisms.
Their study reveals that, as ant societies grew in complexity and numbers, they didn’t just make their workers smaller—they also made them cheaper.
The cost of armor
In the insect world, the exoskeleton known as the cuticle serves as a protective barrier against predators, pathogens, and desiccation, while providing the structural framework for muscle attachment. But this protection comes at a price. Building a robust cuticle requires significant amounts of nitrogen and rare minerals like zinc and manganese. While skimping on armor for an individual insect may be a death sentence, the evolution of ants apparently found a way around it.
“There’s this question in biology of what happens to individuals as societies they are in get more complex?” said Evan Economo, an entomologist at the University of Maryland and co-author of the study. “For example, the individuals may themselves become simpler because tasks that a solitary organism would need to complete can be handled by a collective.”
Economo’s team hypothesized that the metabolic balance behind investing in cuticles in social insects like ants could favor the collective over the individual. The idea was that a colony of 10,000 workers could lose a few individuals to a predator without much consequence, so investing heavily in each worker’s defenses would seem like a waste of precious nutrients. To test this hypothesis, they examined whether ant lineages that maintain massive, specialized workforces reduce the investment in their individual workers’ exoskeletons.
Scanning superorganisms
To test this idea, the researchers needed to pull off a comparative study on the anatomy of ants at an unprecedented scale. “We worked with scans of ant specimens and species from all over the world to capture the global diversity of ants,” Economo says. The team used a massive database called Antscan, which contains three-dimensional X-ray microtomography imaging of ants from around the globe.