While analyzing interactions between parasites and hosts, a substantial amount of research has been devoted to studying the methods parasitic organisms use to control host behavior. In “Invisible Designers: Brain Evolution Through the Lens of Parasite Manipulation,” published in the September 2019 issue of The Quarterly Review of Biology, Marco Del Giudice explores an overlooked aspect of this relationship by systematically discussing the ways in which parasitic behavior manipulation may encourage the evolution of mechanisms in the host’s nervous and endocrine systems. Examining this evolutionary history, Del Giudice investigates the hypothetical methods hosts may have adopted to counteract attempts at behavioral hijacking.
Parasites, such as viruses, insects, helminths, and bacteria, seek to manipulate host behavior for numerous reasons. Parasitic organisms may induce behavioral changes in order to increase their chances of transmission from one host to another. In a similar vein, parasites may disrupt a host’s normal neural functioning to prompt the organism to travel to an environment that is more hospitable for the parasite or more conducive for reproduction. Host bodies are sometimes co-opted and utilized as safe environments for the development of the parasite’s offspring.
The means by which parasites attempt to alter host behavior also vary. Parasites may use an immunological approach by disrupting responses in an organism’s immune system. A more direct option may be to employ neuropharmacological manipulation by secreting substances that interfere with the host’s neurotransmitters. Parasites may also take the genomic/proteomic route by changing gene expression.
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