Insects of the genus Rhagovelia are unusual among water striders, because they can move on fast-flowing water. They are also the only organisms to have propelling fan structures on their midlegs (pictured; scale bar, 100 micrometres). Writing in Science, Santos et al. examine this evolutionary innovation (M. E. Santos et al. Science 358, 386–390; 2017).

Credit: Abderrahman khila

The authors identify two genes that control fan development. One, geisha, is specific to Rhagovelia and evolved when another, mother-of-geisha, was duplicated early in the insect's lineage. The duplicates acquired expression only in the cells from which the fans arise.

Santos et al. demonstrate that the fans facilitated Rhagovelia's adaptation to fast-flowing water, by enabling fast and manoeuvrable running against a current. Thus, their work provides insights into how the evolution of lineage-specific genes can enable organisms to inhabit previously inaccessible environments.

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