Host behaviour alteration by its parasite: from brain gene expression to functional test.

Many parasites with complex life cycles modify their intermediate hosts' behaviour, presumably to increase transmission to their final host. The threespine stickleback () is an intermediate host in the cestode life cycle, which ends in an avian host, and shows increased risky behaviours when infected. We studied brain gene expression profiles of sticklebacks infected with to determine the proximal causes of these behavioural alterations.

Testing the parasite mass burden effect on alteration of host behaviour in the -stickleback system.

Many parasites with complex life cycles modify the behaviour of their intermediate host, which has been proposed to increase transmission to their definitive host. This behavioural change could result from the parasite actively manipulating its host, but could also be explained by a mechanical effect, where the physical presence of the parasite affects host behaviour. We created an artificial internal parasite using silicone injections in the body cavity to test this mechanical effect hypothesis.

Can the behaviour of threespine stickleback parasitized with Schistocephalus solidus be replicated by manipulating host physiology?

Sticklebacks infected by the parasitic flatworm Schistocephalus solidus show dramatic changes in phenotype, including a loss of species-typical behavioural responses to predators. The timing of host behaviour change coincides with the development of infectivity of the parasite to the final host (a piscivorous bird), making it an ideal model for studying the mechanisms of infection-induced behavioural modification. However, whether the loss of host anti-predator behaviour results from direct manipulation by the parasite, or is a by-product (e.