Comparing mechanisms of host manipulation across host and parasite taxa

Abstract

SummaryParasites affect host behavior in several ways. They can alter activity, microhabitats or both. For trophically transmitted parasites (the focus of our study), decreased activity might impair the ability of hosts to respond to final-host predators, and increased activity and altered microhabitat choice might increase contact rates between hosts and final-host predators. In an analysis of trophically transmitted parasites, more parasite groups altered activity than altered microhabitat choice. Parasites that infected vertebrates were more likely to impair the hostʼs reaction to predators, whereas parasites that infected invertebrates were more likely to increase the hostʼs contact with predators. The site of infection might affect how parasites manipulate their hosts. For instance, parasites in the central nervous system seem particularly suited to manipulating host behavior. Manipulative parasites commonly occupy the body cavity, muscles and central nervous systems of their hosts. Acanthocephalans in the data set differed from other taxa in that they occurred exclusively in the body cavity of invertebrates. In addition, they were more likely to alter microhabitat choice than activity. Parasites in the body cavity (across parasite types) were more likely to be associated with increased host contact with predators. Parasites can manipulate the host through energetic drain, but most parasites use more sophisticated means. For instance, parasites target four physiological systems that shape behavior in both invertebrates and vertebrates: neural, endocrine, neuromodulatory and immunomodulatory. The interconnections between these systems make it difficult to isolate specific mechanisms of host behavioral manipulation.

Possible mechanism of host manipulation resulting from a diel behaviour pattern of eye-dwelling parasites?

“…Alterations to the neurochemistry of the host and infection of the host's central nervous system are the most well-understood mechanisms of parasite-mediated behaviour (Lafferty and Shaw, 2013). A well-known example is Toxoplasma gondii, a protozoan that infects felids as its definitive (primary) (Hill et al 2005).…”

Toxoplasma gondii infection and behaviour – location, location, location?

“…These, often very distantly related, parasites have separately evolved mechanisms to alter the behaviour of their host organism. Classic examples include those involving the alteration of host behaviour as a means to increase transmission of the parasite, such as that of the trematode Dicrocoelium dendriticum, which induces infected ants to 'freeze' at the top of a blade of grass at dusk, enhancing their consumption by grazing ruminants, or another trematode, Euhaplorchis californiensis, which alters the behaviour of the California killifish, increasing the likelihood of its consumption by birds, the parasite's definitive host (Moore, 2013;Lafferty and Shaw, 2013). Another example is the amphipod Gammarus, which becomes attracted to light when infected with Polymorphus paradoxus, an Acanthocephalan, increasing consumption by the parasite's definitive vertebrate host (Helluy, 2013).…”

Animal personality and state–behaviour feedbacks: a review and guide for empiricists

“…For example, behaviour-parasite feedbacks (discussed below) are often mediated by effects of parasites on host hormone levels [41,42] and, in some cases, appear to involve adaptive parasite manipulation of host neuroendocrine pathways [43,44]. Progress in understanding feedbacks between behaviour and multiple, interacting components of the overall neuroendocrine system should be invaluable for better understanding personalities.…”