Raptorial insect forelegs evolved repeatedly but never converged on one winning design

Raptorial insect forelegs evolved repeatedly but never converged on one winning design Sadie Harley Scientific Editor Andrew Zinin Chief Editor The evolutionary paths that created snatching forelimbs in insects multiple times moved in a similar direction but didn't end at a single solution. Kobe University research is pioneering a study of how organs with similar functions evolve, providing a new analytical approach to identify evolutionary dynamics quantitatively. "When we discover that the incredibly functional forms and behaviors of living organisms have emerged repeatedly over time, we naturally wonder why," says Kobe University evolutionary biologist Takami Yasuoki. One often-cited example of such "convergent evolution" is that animals hunting underwater have very similar shapes even though they evolved from very different backgrounds, as seen in sharks, dolphins and extinct ichthyosaurs. Another striking example is snatching forelimbs in insects, which have evolved independently at least seven times, including in the praying mantis. Takami says, "However, no one has studied this across insect lineages." So while the "raptorial forelimbs," as they are called, might look similar, it is unclear whether this is actually convergent evolution. Measuring shape across lineages To address the question, Takami had to develop a new approach. He explains, "Detailed anatomical studies on the repeated evolution of raptorial forelimbs of course exist. But maybe because the more familiar people get with insect anatomy, the less able they are to ignore details. No attempts have been made to quantify the process across lineages." He and his team constructed a framework that allows researchers to statistically distinguish among the different ways evolution can shape a group of organisms: shifts in mean shape, reduced shape variation and similar evolutionary directions. They then conducted their analysis based on the length of various limb and body parts, deliberately ignoring all other detailed structural features, by plotting the shifts in measurements between species without snatching forelimbs and those with them on a multidimensional map of the "morphospace," the space of all possible shape configurations. Similar paths, different outcomes In the journal Scientific Reports, the Kobe University team reports that it did not find evidence for convergent evolution, at least as expressed by the body parts' relative lengths. Takami says, "It seems paradoxical, but while the snatching forelimbs have evolved repeatedly, they are not actually similar." The forelegs and forebody, in particular, evolved in similar directions across the lineages, especially if aquatic ones are excluded, but the essential point is that they haven't settled on a specific final shape. This means that different shapes can capture the same ecological function. Vision changed with the limbs However, there was one more fascinating detail in the data. Along with the evolution of snatching forelimbs, the insects' heads became wider and their "necks" longer, to an extent that comes very close to an overall shift in mean shape in addition to a similar direction of evolution. "The evolution of a broader head is thought to have led to better stereoscopic vision, making it easier to judge the distance to prey. This suggests that there is strong natural selection and little room for shape variation when it comes to visual perception," Takami explains. A framework beyond this case "This work marks the conclusion of our research into the phenomenon of the repeated evolution of snatching appendages," says Takami. Still, the work might have broader implications. He explains, "We believe that the conceptual framework and analytical methods used in this study to analyze repeated evolution will be very useful for future similar research." Publication details Quantifying the repeated evolution of insect raptorial forelegs, Scientific Reports (2026). DOI: 10.1038/s41598-026-57616-w Journal information: Scientific Reports Key concepts morphology (biological)Adaptation, BiologicalAnatomic VariationBiological EvolutionPhylogenyProvided by Kobe University