He and his lab are interested in symbioses. They work with a number of model systems, including sap-feeding insects and their endosymbiotic bacteria, ambrosia beetles and their ectosymbiotic fungi, and the consortia of fungal and photosynthetic partners that form lichens. They use a variety of approaches—genomics, microscopy, molecular biology, molecular evolution, cell biology, and field biology—to address their questions. John is an Associate Editor at Genome Biology and Evolution and is on the Editorial Board at Current Biology.