Journal ArticleFunctional innovation promotes diversification of form in the evolution of an ultrafast trap-jaw mechanism in antsBooher, Douglas B.; Gibson, Joshua C.; Liu, Cong; Longino, John T.; Fisher, Brian L.; Janda, Milan; Narula, Nitish; Toulkeridou, Evropi; Mikheyev, Alexander S.; Suarez, Andrew V.; Economo, Evan P.Khila, AbderrahmanEvolutionary innovations underlie the rise of diversity and complexity—the 2 long-term trends in the history of life. How does natural selection redesign multiple interacting parts to achieve a new emergent function? We investigated the evolution of a biomechanical innovation, the latch-spring mechanism of trap-jaw ants, to address 2 outstanding evolutionary problems: how form and function change in a system during the evolution of new complex traits, and whether such innovations and the diversity they beget are repeatable in time and space. Using a new phylogenetic reconstruction of 470 species, and X-ray microtomography and high-speed videography of representative taxa, we found the trap-jaw mechanism evolved independently 7 to 10 times in a single ant genus ( Strumigenys ), resulting in the repeated evolution of diverse forms on different continents. The trap mechanism facilitates a 6 to 7 order of magnitude greater mandible acceleration relative to simpler ancestors, currently the fastest recorded acceleration of a resettable animal movement. We found that most morphological diversification occurred after evolution of latch-spring mechanisms, which evolved via minor realignments of mouthpart structures. This finding, whereby incremental changes in form lead to a change of function, followed by large morphological reorganization around the new function, provides a model for understanding the evolution of complex biomechanical traits, as well as insights into why such innovations often happen repeatedly.2021-03-0210283278PLOS Biology193e30010311545-7885https://doi.org/10.1371/journal.pbio.30010311755336; 1932405; 1655076National Science Foundation