Large ant colonies prefer many bad workers to few good ones.

Would you rather fight one duck the size of a horse or one hundred horses the size of a duck? The question, which presents the dilemma between quantity and quality, is transferable to evolutionary biology, which always selects the best for each species.

According to a study published in Science Advances, in most ant coloniesevolution prioritizes quantity over quality, that is, it prefers to manufacture a large number of workers with more fragile or vulnerable exoskeletons but metabolically «cheap» to produce, Less quantity of more resistant and powerful ants.

The study concludes that choosing quantity over quality has been an evolutionarily successful strategy in a large number of ant colonies and sheds light on what happens to individuals when complex societies, such as humans, evolve.

Their colonies range from dozens to millions of individuals (Twitter).

«There is this question in biology about what happens to individuals as the societies they are in become more complex. For example, individuals can become simpler because the tasks that a solitary organism would need to complete can be handled by a collective,» explains lead author Evan Economo, head of the Department of Entomology at the University of Maryland (United States).

Part of this is because individuals can become «cheaper», meaning they are easier to produce in greater numbers, but individually less resilient, as the study has shown with large-scale analysis of insects with a certain social order such as ants.

Evolution in complex societies

Ants are an ideal way to test how complex societies arise because their colonies range from tens to millions of individuals.

«Ants are everywhere but the fundamental biological strategies that allowed them to form massive colonies and extraordinary diversification remain unclear,» says Arthur Matte, lead author of the study and a doctoral student in zoology at the University of Cambridge (United Kingdom).

The authors intuited that there is a relationship between the size of the colony and the investment in the cuticle, a structure that protects the ants and supports their muscles.

But to have a resistant cuticle, ants need to obtain scarce elements such as nitrogen and certain minerals, that is, it is nutritionally expensive and that could limit the number of individuals that a colony can maintain.

To find out, made 3D X-ray tomography of 880 specimens of 507 species of ants and they measured the thickness of their cuticle and body.

They then poured the data into evolutionary models and discovered that ants in larger colonies have weaker exoskeletons. They weren’t smaller, they just had less protection.

The authors believe that having a weaker exoskeleton may be beneficial for ants because they need to search for less food, and since they are more numerous, it is easier to defend the nest and distribute tasks in the colony.

As they are more numerous, it is easier to defend the nest and distribute tasks in the colony (EFE).

«Ants reduce the investment per worker in one of the most nutritionally expensive tissues for the good of the collective,» Matte explained.

Furthermore, lower investment in the cuticle was associated with higher diversification rates, a measure of speciation events that biologists often use as an indicator of evolutionary success.

«Not many traits associated with diversification have been found in ants,» Economo said, making the finding particularly intriguing.

It is not yet known why reducing investment in the cuticle leads to speciation, but one hypothesis is that it allows ants to occupy new habitats with scarce nutrients. «Needing less nitrogen could make them more versatile and capable of conquering new environments,» concludes Matte.

EFE Agency.