Superspacers shared between viral strains. Superspacers shared between viral strains. Each box represents a pair of viruses; the color indicates the proportion of superspacers in the viral strain on the x axis which are shared with the virus on the y axis. A superspacer is defined as any spacer matching viruses from more than one cluster. Viruses are grouped by cluster (colored boxes to the left and bottom); singletons are grouped together as unclustered (gray box). Whitney E. England et al. mSystems 2018; doi:10.1128/mSystems.00075-18