How Do Caterpillars Acquire Chubby Extra Legs? Singapore Scientists Trace Origins to Ancient Genetic Program Associated with Crabs

Adult insects, including butterflies and moths, typically have only three pairs of legs. But the existence of extra legs in caterpillars – chubby abdominal appendeages also known as “prolegs” – has long posed an evolutionary mystery to biologists. A recent study by researchers from the National University of Singapore (NUS) linked this novel trait to crustaceans. Caterpillars use their prolegs to grab on to twigs and leaves, while using their thoracic or “true” legs to hold on to other plant parts for feeding. “The three main theories regarding prolegs suggested that they might be modified thoracic legs, completely novel traits, or modified lobes (endites) of primitive thoracic legs,” explained Professor Antónia Monteiro, who led the team of researchers from the Department of Biological Sciences at the National University of Singapore (NUS) Faculty of Science. “Our study proposes that prolegs are indeed novel traits unrelated to thoracic legs. However, they are derived from a genetic program that specifies lobes that were originally found in the proximal region of crustacean limbs, but had remained inactive in this limb region for millions of years.” The NUS team published its findings in Science Advances on October 13, 2023. The open-access article is titled “Lepidopteran Prolegs Are Novel Traits, Not Leg Homologs.”