The jawbone is the fastest in the world – and has evolved independently several times into ants

Trap-jaw ants are notorious for one of the strongest bites among all animals, but we didn’t really understand how they evolved from more traditional jaws. A new study looking at their evolutionary history found that the distinctive mechanism behind trapping jaws has evolved independently several times around the world.

Unlike normal gripping jaws that open and close through the contraction of muscles, trap jaws use a complex mechanism to grip themselves open and fix down when needed. This mechanism allows the jaws to store energy similar to a spring, and this can be released to produce a lot of force quickly.

A bitten piece

“One of the central questions in biology is: how does something complex come from something simple?” said Professor of Economics, who heads the Biodiversity and Biocomplexity Unit at the Graduate University of Okinawa Institute of Science and Technology (OIST).

“Structures like the trap jaw depend on many interrelated parts to function properly. At first it may be difficult to see how such complexity can arise with the gradual gradual changes of development. However, when we look closely biologists can discover evolutionary pathways to complexity. “

A new study led by Professor Economics and Dr. Douglas Booher of Yale University has tracked the evolutionary history of trap jaws, finding that they have evolved independently, several times, around the world. Many of the species that have such jaws are descended from the Strumigenys a genus that includes more than 900 species found in tropical and subtropical regions.

For the study, the team sequenced the genetic information of 470 species in this genus recovered from around the world, including two types of trapping jaws (ancestral and with modified trapping jaws). From this, they reconstructed their family tree, which shows how various species relate.

Finally, they analyzed the jaws and ants themselves using micro-CT scanners, allowing them to create 3D models.

One of the first observations the team made was that only small changes in structure were needed to turn a trapping jaw into a trapping jaw. They further report that after this transition, the heads of (now trap-jaw) ants also began to morph quite drastically. Muscle restructuring and changes in the length and open width of the jaws were among the main changes.

“Previously we thought that all trap jaws have both divergent shape and divergent function, so it was much less obvious whether the function change could occur at the beginning or whether many changes to the shape were first needed as a precondition,” said Professor Economo.

“But it has been shown that there are many intermediate forms of the trap-jaw mechanism that people have not recently identified before, some that differ only slightly from the ancestral form.”

In collaboration with Andrew Suarez’s lab at the University of Illinois, the team also used high-speed video cameras to capture the jaws of Strumigenys ants in motion. They were thus able to determine that the trap jaws have the fastest yet “acceleration of any animal part that can return to its original position”. Such jaws have been seen to accelerate a hundred times faster than standard mandibles, closing a thousand times faster than a human eye can blink. Which sounds impressive fast.

But they need all the speed they can get. Strumigenys ants use their jaws to catch spring tails, their favorite prey, which use a spring escape mechanism (hence the name). We still don’t understand much about their hunting habits, but we do know that ants with shorter trap jaws tend to be passive hunters, hiding in leaf litter with open jaws, waiting to bite any prey passing by. Meanwhile more jaw ants meanwhile are actively looking for prey to bite.

Both types of ants can be found in all regions around the world, the authors add. They believe that differences in behavior may explain why there are so many different forms of trap jaws out there. However, what is not yet clear is whether the genetic background that supported the change from normal to trapped jaws is the same for all species, or whether they all achieved the same solution through different genetic changes.

“It was really striking how we saw the same varieties evolve over and over again on different continents. It illustrates how repeatable development can be, finding similar solutions to life’s challenges, ”said Professor Economo.

Going forward, the team plans to follow the genomes of a representative Strumigenys species around the world to determine this.

The journal “Functional innovation promotes diversification of form in the development of an ultra-fast trap-jaw mechanism in ants” was published in the journal PLOS Biology.