From antifreeze genes in fish to fungal pigment genes in aphids, horizontal gene transfer (HGT) – the non-sexual movement of DNA between species – has occurred between all major eukaryotic lineages, with implications for their development, physiology, and evolution. However, this powerful evolutionary force is critically understudied, especially in animals, and the most fascinating aspects remain mysterious. How do genes jump between species? What are the vectors of HGT? Why are some genes preferentially transferred over others? We recently discovered that Mavericks, ancient transposable elements with viral properties that are found across eukaryotes, are one of the long-sought vectors of HGT between animals. By studying the biology of Mavericks and the cargo genes they have repeatedly transferred between nematode species on a global scale, my lab will uncover molecular mechanisms of animal HGT for the first time using genetic, molecular and computational approaches