THE MANIPULATION OF RAT BEHAVIOR BY TOXOPLASMA-GONDII

We review recent work testing the hypothesis that the parasite Toxopla sma gondii manipulates one of its intermediate hosts to make it behave in a way that would enhance the parasite's chance of completing its o wn life cycle. Both experimental and inferential evidence from wild ra ts and/or captive rats in semi-naturalistic environments suggest that infected rats differed from non-infected individuals in a suite of beh aviours that may enhance their likelihood of being predated by cats, t he parasite's definitive host: T. gondii-infected rats were found to b e more active, more exploratory, less cautious of novel stimuli and mo re easily trapped. Also in accordance with the manipulation hypothesis , these alterations appear specific rather than due to the symptoms of some general illness. There were no differences in food intake, condi tion indices, other parasite load or growth rates. Moreover, infected rats did as well as non-infected individuals in terms of social status and mating success, both the products of costly and competitive activ ities which would be expected to be changed if the alterations were ge neral rather than specific.