In a study of the evolution of DptA and DptB—Diptericin genes encoding antimicrobial peptides that combat pathogens and foster beneficial microbes in fruit flies (Drosophila)—researchers assessed Drosophila melanogaster resistance to pathogenic infections by Providencia rettgeri and Acetobacter sicerae, bacteria common in the flies’ environments. Subjects included flies identified by mutations silencing DptA, DptB, or both DptA and DptB (termed types A, B, and AB, respectively). In conjunction with the observation that resistance to P. rettgeri correlates with DptA activity but is not significantly affected by DptB activity, data in the graph of survival rates post–A. sicerae infection suggest that ______blank