Scientists discover the first insects with shell-like armor

Calcareous biominerals have been incorporated by many animals throughout evolutionary history, most notably by crustaceans with their characteristic shells. Surprisingly, this type of protection has never been seen before in insects, which belong to the same group as crustaceans: both are classes of arthropods. But scientists have now found the first evidence of high-magnesium calcite in the armor covering the exoskeletons of leaf cutter ants (Acromyrmex echinatior).

Armored Bacteria Grower

Cameron Currie, a professor of bacteriology at the University of Wisconsin-Madison, studied for several years Streptomyces bacteria. Currie and colleagues showed that these microbes provide leaf-cutting ants with protection against infection, suggesting that both the ants and their microbiome could become a new source of antibiotics. Bearing in mind the frightening increase in antibiotic-resistant bacteria, this research is extremely important, perhaps even crucial.

While studying leaf cutter ants in an attempt to identify what the insects might give in exchange for the protection they receive, Hongjie Li, a postdoctoral scientist at Currie’s lab, discovered crystals on the surface of the exoskeletons. Upon closer inspection, the crystals were found to be biominerals, the first to have been encountered in the insect world.

The morning Li performed X-ray scans of the ants, she couldn’t believe her eyes.

“I immediately texted Cameron saying ‘I found a rock ant’. I can still feel the moment of joy right now, “Li, who is the first author of the new study published in Nature Communications, he told ZME Science.

Subsequent live breeding and in vitro synthesis experiments demonstrated that magnesium-rich calcite armor develops as ants mature, thereby increasing the hardness of their exoskeletons.

The high magnesium content of the armor is particularly exciting, Currie told me, because it is very rare in the biosphere. “So, our ants have very unique and strong armor,” added the researcher.

Worker ants with biomineralized exoskeletons were more likely to survive encounters Atta cephalotes soldier ants, according to observations made by researchers. In addition, the armor also offered protection against infection of the disease-causing fungus Metarhizium anisopliae.

Apparently, there are several reasons why such armor must have been favored by natural selection. But interestingly, the researchers compared bacterial ant breeding to human agriculture.

“Leaf cutter ants evolved about 20 million years ago and are ecologically dominant in the tropics of the new world. Their success parallels the important role agriculture played in the rise of human domination over the planet over the past 10,000 years. There are other parallels between these ants and human farmers. Like crop pathogens that cause pestilence throughout the history of human agriculture, ant crops are highly sensitive to the specialized pathogens that have evolved to exploit them. Just as humans rely on chemicals to defend our crops, ants have developed the use of bacteria to make antibiotics to control crop infection, ”Currie told ZME Science.

“Our discovery of biomineral armor in a leaf cutter ant provides another exciting new parallel for humans: the evolution of protective armor to engage in wars with other farmers,” he added.

There may be more bugs with biomineral armor. One of the reasons they are not common is because most insects already have a tough, sturdy exoskeleton, which generally offers sufficient protection. In the future, Currie and colleagues would like to study in more detail how biomineral is formed, as well as the evolutionary origins of armor through ants growing mushroom gardens.