How trap-jaw ants got the fastest bite in the animal kingdom

The latch-spring mechanism of trap-jaw ants evolved up to 10 different times independently throughout the world, according to a new study from the Okinawa Institute of Science and Technology Graduate University (OIST)

Trap-jaw ants are famous for their powerful mandibles, which close about 2,300 times faster than the blink of an eye. To catch prey and dodge predators, the ants’ jaws accelerate at 100,000 times the force of gravity, and this force up to 500 times their body weight.

The trap-jaw does not rely on muscles to open and close, but instead latches itself open, storing energy like a stretched spring. When released, the jaws snap shut in one strike. The OIST team wanted to know how this complex mechanism evolved from simpler ancestors.

The experts have now discovered that the core mechanism that drives the extraordinary speed of the trap-jaw arose multiple times, followed by the diversification of the mandible shape.

The researchers reconstructed the evolutionary relationships among 470 species of Strumigenys miniature trap-jaw ants. They also observed the jaws in motion using X-ray microtomography, 3D modeling, and high-speed videos.

The study revealed that the trap-jaw mechanism evolved 7 to 10 times independently across the world.

The experts found that only a very small change in form was required to drastically change the function of the jaw from the gripping mechanism to the trapping mechanism. After the new function evolved, the muscles in the head of trap-jaw ants began to dramatically restructure, and their jaws became longer and grew to open wider. 

“Previously, we had thought that all trap-jaws had both divergent form and divergent function, so it was much less obvious as to whether the change in function could occur at the start or whether a lot of changes to the form were first needed as a precondition, but it turned out there are many intermediate forms out there of the trap-jaw mechanism that people just hadn’t identified before, some which differ only slightly from the ancestral form,” explained Professor Evan Economo.

“One of the central questions in biology is: how does something complex arise from something simple? Structures like the trap-jaw depend on multiple interacting parts to function correctly.”

“At first it can be hard to see how such complexity can arise through the gradual stepwise changes of evolution. Nevertheless, when we look closely biologists can uncover evolutionary pathways to complexity.”

The study is published in the journal PLOS Biology 

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By Chrissy Sexton, Earth.com Staff Writer