Variation in the reproductive potential of Schistocephalus infected male sticklebacks is associated with 11-ketotestosterone titre

► 11KT and spiggin titres correlate with reproductive behavior in sticklebacks. ► Reproductive ability of parasitized male stickleback depends on endocrine phenotype. ► Low 11KT and spiggin titres associated with heavy Schistocephalus infections. ► Results do not support endocrine disruption as a mechanism .► Infections probably reduce host reproduction through nutrient theft.