This project aims to characterize immune genes (e.g. MHC class I and II, AMP and TLR genes) in two closely related species B. bufo and B. spinosus to detect differences that could explain contrastive responses to disease. Although B.bufo and B.spinosus are closely related, they have different responses to Bd and ranavirus infections. The effects of environmental factors and host characteristics in the difference of infection outcomes between populations and species are commonly addressed by researchers. However, the relationship between mortality differences between closely related species and their immune gene variation is not well documented. This project constitutes a vital component in a larger research project, and the dissemination of its findings will hold significant relevance for evolutionary biologists. By delving deeply into the characterization of immune genes and their correlation with infection and co-infection, this study promises to contribute valuable insights into the immunogenetics and host-parasite evolution fields. It will be one of the pioneering investigations in its specific field, offering novel perspectives to the scientific community.