The Genetic Secrets of the Fruit Fly That Hunts Its Prey
In most fruit fly species, females lay eggs on rotting fruit, which hatch into tiny larvae inside the fruit and develop into telltale little flies. But in an article recently published in Current biologyone of the most unusual species of fruit flies, reveals the origins of a completely different way of life.
Enhydrobic Drosophila lives up to its name: it lays its eggs on aquatic plants in African rivers, after which its larvae are entirely aquatic. “We are talking about a fruit fly that has completely turned its lifestyle upside down. From feeding on yeast and rotting fruit, it has become a specialized predator in running water,” Marcus Stensmyr, study leader and biology researcher at Lund University in Sweden, explained in a press release.
Because the last one alive D. enhydrobia was reported in 1981, researchers turned to museum collections to determine its place in the fruit fly family tree. A team of biologists from Lund University and Université Paris Saclay in France recovered a complete genome from a 40-year-old specimen using “museomics” methodology, the latest techniques for extracting historical DNA.
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Its genome places the strange D. enhydrobia within the known subgenus of fruit flies in Asia that live along waterways in riparian areas. This suggests that the aquatic lifestyle of D. enhydrobia was not an evolutionary leap, but rather an extension of the semi-aquatic habits of its ancestors.
When it came to life in the water, D. enhydrobia lost certain genes necessary for life on earth. In particular, the number of its chemical sensing genes has been reduced, leaving a smaller set available for adaptation to aquatic life. But the remaining genes showed intensified selection. “It’s like there are fewer tools in one’s toolbox, but the tools that remain are all the more adapted to this particular environment,” said Hamid Ghanavi, a biologist at Lund University.
Seen up close, the larva D. enhydrobia have unique adaptations for aquatic life. Small hooked pads along their abdomen allow them to cling to submerged rocks. On their bellies are branched openings, or stigmata, typical of insects, allowing air to be sucked in instead of lungs. However, compared to the well-known Earth system Drosophila melanogaster With 5 to 7 stigma openings, these aquatic fruit fly larvae have around 100, probably acting as gills for oxygen exchange underwater. And instead of feeding on detritus like other fruit fly larvae, D. enhydrobia use specialized mouth hooks to catch aquatic insects.
Basically, fruit flies living in bubbling African streams have taken a watery, predatory fork in the road.
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Main image: Ghanavi et al., Cell Press, 2026
