There is as yet insufficient data to conclude if higher NOS constitutive expression may be linked to clonal differences in resistance or the level of virulence suffered during infection, but a previous study indicated that NOS could play a role in resistance to Pasteuria by supplementing the diet of Daphnia with amino acids that would either enhance or inhibit the production of NO (Labbé et al., 2009), and we suggest that further study of genetic variation in NO production may prove fruitful. Here, NOS1 is linked to infection.