Varying phylogenetic signal in susceptibility to four bacterial pathogens across species of Drosophilidae

Bacterial host shifts, where bacterial pathogens jump into and establish infection in a new host species, are an important source of emerging infectious diseases. Here, we use four bacterial pathogens to infect a panel of 36 species of fruit fly that shared a common ancestor ~50 million years ago. We found large amounts of variation in susceptibility across host species to these bacterial pathogens. This variation is explained by the host phylogeny to varying degrees, with hosts clustering into clades with distinct levels of susceptibility. However, the magnitude of the effect varies between the four bacterial pathogens. For three out of the four pathogens tested mortality was correlated with bacterial load, suggesting it is a result of bacterial proliferation in the host. This has important implications for our understanding of the emergence of bacterial pathogens, and to date there are few large-scale experimental studies of bacterial host shifts.