Inter-individual transmission of cancer cells represents an intriguing and unexplored complexity of host-pathogen interactions, with significant ecological and evolutionary ramifications. Cancer cells can grow and spread in one individual, but they normally do not spread to others. There are exceptions. In marine shellfish, there is a form of cancer that can spread to other individuals. These cancer cells infect animals like a pathogen and has evolved the ability to spread throughout the population and even move from one bivalve species to the other. Transmissible cancers impair host fitness and castrate infected individuals. Yet, a framework that unravels the ecological and economic implications of this form of cancer is still lacking. How common is it in the wild? What are the factors triggering the transmission of the cancer and how it contributes to mass mortalities? This thesis aims at filling some of the most important these knowledge gaps on Bivalve Transmissible Cancer using the marine mussel Mytilus edulis as host. This is an important ecosystem engineer of intertidal ecosystems and a vital economic and patrimonial resource at the regional level. By contributing to GOALs 12, 13 and 14 of 2030 UN Agenda for Sustainable Development, the work will have multiple implications at the national/international level.
