Understanding the origin of the remarkable biodiversity in nature is an important goal in biological studies. Despite recent advances in evolutionary developmental biology, our understanding of the interaction between developmental genetic processes and the ecological environment in shaping the phenotype remains largely fragmented. This is mainly because of the difficulty to transfer molecular genetic tools to natural systems where we have a good understanding of the ecology. In this proposal, we combine original natural systems, water-walking insects, with state of the art tools of functional and developmental genetics, to study the interplay between developmental genetic pathways and the ecological environment, and how this interaction can shape adaptive phenotypic change. About 200 million years ago, the common ancestor of water-walking insects (Heteroptera, Gerromorpha) invaded water surface and radiated into a diverse array of niches, from shorelines to open oceans. This ecological transition and specialization is associated with an array of adaptive changes that enabled these insects to support their body weight and generate efficient propulsion on the water surface.In this project, we aim to develop a multilevel functional approach that combines developmental and evolutionary genetics, ecology, and comparative genomics and transcriptomics, to study a set of key morphological traits directly associated with the initial event of transition to water surface life, and the diversification that followed. To achieve this, we chose three water-walking insects, along with a terrestrial and under-water outgroups, based on their morphology, ecology, and amenability for laboratory culturing and functional experiments. We will identify the genes and genetic changes responsible for the development and evolution of the hydrophobic bristles –a key trait that was instrumental in the transition from terrestrial to water surface life. In addition, we will identify the geneti