Dividing up the bill: Interactions between how parasitoids manipulate host behaviour and who pays the cost.

Controlling host behaviour can be costly for parasites. In some parasitic systems, such as insect parasitoids, this physiological cost can be paid for by the mother parasite, her offspring or both.Parasitoid wasps provide examples of how individual parasites in a host–parasite system can vary in their opportunity, means and motive (i.e. fitness benefits) for manipulating host behaviour.Changes in host behaviour that occur very soon after infection are typically paid for by the mother parasitoid. She has the greatest opportunity (offspring are often still eggs), the means (neuroactive venoms) and benefits by promoting her offspring's success.Changes in host behaviour that occur late in the development of the offspring (e.g. host bodyguard behaviour) often hinge on some behaviour of the offspring (e.g. the exiting of the host). In these cases, the cost is paid largely by the offspring. The offspring have the greater opportunity, the means (e.g. secreting compounds into the host) and directly benefit by their increased survival.Gene delivery agents, such as symbiotic viruses, allow a reduction in the direct cost of parasitic manipulation to the parasite because the host is induced to use its own resources to produce the compounds needed to alter its behaviour. However, this method leads to indirect costs that are paid for by the offspring, due to a reduction in the host's resources that are available for their own growth.In gregarious systems, the possibility of cheating among the offspring (i.e. some individuals paying less than others to alter host behaviour) may select for modes of control that make cheating difficult.Determining who pays the physiological cost of manipulating host behaviour, and why, promises exciting insights into the evolution of parasitic manipulation in these systems. Read the free Plain Language Summary for this article on the Journal blog. [ABSTRACT FROM AUTHOR]