Threat-sensitive feeding strategy of immature sticklebacks (Gasterosteus aculeatus) in response to recent experimental infection with the cestode Schistocephalus solidus

Threat-sensitive decision-making might be changed in response to a parasiti c infection that impairs future reproduction. Infected animals should take more risk to gain energy to speed up their growth to achieve early reproduc tion and/or to strengthen their immune response. To avoid correlational evi dence, we experimentally infected and sham-infected randomly selected immat ure three-spined sticklebacks with the cestode Schistocephalus solidus. For 7 weeks we determined the threat-sensitive foraging decisions and growth o f individual sticklebacks in the presence of a live pike (Esox lucius). The experimenters were blind with respect to the infection status of the fish. In contrast to previous studies, our recently infected fish should have be en almost unconstrained by the parasite and thus have been able to adopt an appropriate life history strategy. We found a strong predator effect for b oth infected and uninfected fish: the sticklebacks' risk-sensitive foraging strategy resulted in significantly reduced growth under predation risk. In fected fish did not grow significantly faster under predation risk than uni nfected fish. Since infected fish consumed much less prey in the presence o f the predator than did infected fish in its absence, they obviously did no t use the opportunity to maximize their growth rate to reach reproduction b efore the parasite impairs it.