Small shape changes could lead to innovative breakthroughs in features, a new study reveals.
- Researchers have revealed how an ant’s trap – a powerful, fast and complex evolutionary trait – evolved from a simpler ancestral jaw mechanism
- The study found that the trap mechanism developed 7-10 times independently around the world
- The trap function could develop with only small changes in the shape of the jaw, followed by the development of different trap shapes
- Researchers have seen the same variations of traps that develop independently on different continents, showing the repeatability of the evolution of this complex trait.
- High-speed videography has shown that the trap is the fastest accelerated animal body part that can be repaired
Powerful and deadly, the bite of a trap ant is known in the animal kingdom. Unlike normal gripping jaws, which rely on muscles to open and close, the trap clamps itself open and stores energy like an elongated spring. When they are released, the jaws of the ant lock their prey in one quick strike.
Trap jaws are a record-breaking evolutionary innovation, but scientists still do not understand how this complex mechanism of simpler ancestors evolved. Now it appears today (March 2, 2021) in PLOS Biology, a research team led by Professor Evan Economo of the Okinawa Institute of Science and Technology Graduate University (OIST) and Dr. Douglas Booher van Yale University, New Haven CT, along with an international team of collaborators, showed how traps originated and then diversified several times around the world.
The animation shows the shape changes as the fall-jaw mechanism becomes more deviant from the ancestral shape. The jaws (yellow) develop small protrusions that can cling to the labrum (purple). The labrum changes from functioning as a sensor in the ancestral gripping jaw to a latch in the trap. The muscles in the head that control the jaw and the labrum undergo major changes in structure.
“One of the most important questions in biology is: how does something complicated come from something simple?” says Professor Economo, who heads the unit for biodiversity and biocomplexity at OIST. “Structures such as the trap depend on various interactions to function correctly. Initially, it can be difficult to see how such complexity can arise from the gradual step-by-step changes in evolution. Nevertheless, biologists may uncover evolutionary paths to complexity. ‘
Many ant species with catching jaws form part of the Strumigenys genus – a very diverse group with more than 900 species found in tropical and subtropical regions around the world.
“This species contains many closely related species where the trap is present or not, which really gives us a unique opportunity to understand how it originated,” Professor Economo said.
Fast videography captures motion at a rate of 480,000 frames per second (fps) and plays it at 30 fps (16,000 x slow motion). The trap accelerates faster and reaches higher speeds than the simpler gripping mechanism.
In OIST, in collaboration with Professor Alexander Mikheyev’s unit for ecology and evolution, the research team withdrew and gave order DNA of 470 Strumigenys ant species worldwide, including those with ancestral gripping jaws and those with modified traps.
The researchers reconstructed a tree showing the evolutionary relationships between the species. They then analyzed the jaw mechanism using micro-CT scanners to create 3D images and models of the ants.
The researchers found that the trap mechanism developed 7-10 times independently around the world.
What is important is that only a very small shape change was needed to drastically change the function of the jaw from the grip mechanism to the fall mechanism. After the change in function occurred, the head of fall jaw ants began to undergo massive restructuring of the muscles and diversified in the length of the jaw and how wide the jaw opened.
Trap jaw ants show remarkable diversity in the length of the jaw and how wide it opens.
‘Previously we thought that all traps had a different shape and a different function, so it was much less obvious whether the change in function could take place at the beginning or that many changes to the shape were needed first, a condition, said Professor Economo. “But it turned out that there are many intermediate forms of the fall-jaw mechanism that people just have not identified before, some differing only slightly from the ancestral form.”
The researchers collaborated with the laboratory of Andrew Suarez at the University of Illinois, who used high-speed videography to capture Strumigenys anteaters in motion. They found that the trap has the fastest known acceleration of any animal body part that can return to its original position.
“The acceleration of the lower jaw is one hundred thousand times greater than the standard lower jaw,” said Professor Economo. “And they close thousands of times faster than the blink of an eye.”
Strumigenys ants need speed, and use their fast jaws to stop the spring-loaded escape mechanism of springtails, their most abundant prey.
It is not yet known how all these different ant species hunt, but ants with shorter trap caps are typically passive hunters, hiding in the leaf litter with their jaws waiting to close any unsuspecting prey that ventures too close. Meanwhile, the ants with longer jaws are active hunters looking for prey to strike.
According to the researchers, the ants can use their jaws to catch prey, helping to explain the surprising level of diversity in the form of trap caps. In every region of the world, at continental level and at local community level, long and short traps are found.
‘It was really striking how we saw the same variations develop on different continents over and over again. It illustrates how sustainable evolution can be, by finding similar solutions to the challenges of life, ”said Professor Economo.
What is less clear is whether the underlying genetic changes required to build the trap are the same, and whether the ants have achieved these similar outcomes in different ways.
Therefore, the research team now plans to sequence the genomes of representative Strumigenys species around the world. ‘We want to bridge the gap between the changes we see on a genetic and molecular level, and what we see on a morphological level. This is the next big project. ”
Reference: “Functional innovation promotes form diversification in the evolution of a rapid fall-jaw mechanism in ants” by Douglas B. Booher, Joshua C. Gibson, Cong Liu, John T. Longino, Brian L. Fisher, Milan Janda , Nitish Narula, European Toulkeridou, Alexander S. Mikheyev, Andrew V. Suarez and Evan P. Economo, 2 March 2021, PLOS Biology.
DOI: 10.1371 / joernaal.pbio.3001031
Funding: Okinawa Institute of Science and Technology Postgraduate University, Japan Association for the Advancement of Science, National Science Foundation, Tinker Foundation at UIUC’s Center for Latin American and Caribbean Studies