LAUSR

Significance When organisms access unexploited ecological opportunities, species diversification often follows, yet the mechanisms underlying such transitions are poorly understood. Water striders transited from terrestrial to water surface life some 200 Mya, aided by the evolution of superhydrophobic bristles and increased leg length, both required for standing and moving on water. We identified genes involved in both bristle density and leg length, suggesting that these two traits are genetically correlated. Strikingly, these genes are involved in cell division, thus explaining their dual role in leg growth and bristle density. In addition, we identified molecular changes that account in part for the differences in bristle density across species. We propose that pleiotropy might facilitate diversification by impacting several adaptive traits simultaneously.