Work is using a primarily quantitative genetic approach in the Caenorhabditis species to understand the control of variation in complex traits, particulary those involved in adaptation to differing environments. Key questions are to determine: 1) the extent to which complex trait evolution is reproducible, 2) the role of conditionally deleterious and compensatory mutations in this process and 3) the role of such complex traits in the early stages of speciation. The aim of this is to use results from the model systems to understand environmental responses in both detrimental plant parasitic species (Meloidogyne spp.) and beneficial entomopathogenic species (Steinernema spp.).