Aphids, important as agricultural pests, are also remarkably valuable biological models for studying two disparate processes, symbiosis and genome evolution. Their usefulness derives from two unrelated features of their biology. First, aphids host bacterial symbionts that alter their fitness. Second, aphids vary in reproductive mode within a species affording an unparalleled opportunity to understand the role of sex in eukaryotic genome evolution. In my lab at the University of Miami, we are assessing the role of symbiont genome evolution as a driving force in aphid speciation and examining how reproductive mode effects eukaryotic genome evolution.