How does natural selection redesign multiple interacting parts to achieve a new emergent function? Booher et al. investigated the evolution of a biomechanical innovation, the latch-spring mechanism of trap-jaw ants, to address two 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, they found that the trap-jaw mechanism evolved independently seven to ten 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. The authors found that most morphological diversification occurred after evolution of latch-spring mechanisms, which evolved via minor realignments of mouthpart structures. The image shows the ultrafast mandible system of the trap-jaw ant Strumigenys cacaoensis rendered from an X-ray microtomography scan.

Image Credit: Julian Katzke