title: When should a trophically and vertically transmitted parasite manipulate its intermediate host? The case of Toxoplasma gondii.
abstract: Parasites with complex life cycles are expected to manipulate the behaviour of their intermediate hosts (IHs), which increase their predation rate and facilitate the transmission to definitive hosts (DHs). This ability, however, is a double-edged sword when the parasite can also be transmitted vertically in the IH. In this situation, as the manipulation of the IH behaviour increases the IH death rate, it conflicts with vertical transmission, which requires healthy and reproducing IHs. The protozoan Toxoplasma gondii, a widespread pathogen, combines both trophic and vertical transmission strategies. Is parasite manipulation of host behaviour still adaptive in this situation? We model the evolution of the IH manipulation by T. gondii to study the conflict between these two routes of transmission under different epidemiological situations. Model outputs show that manipulation is particularly advantageous for virulent strains and in epidemic situations, and that different levels of manipulation may evolve depending on the sex of the IH and the transmission routes considered. These results may help to understand the variability of strain characteristics encountered for T. gondii and may extend to other trophically transmitted parasites.
authors.affiliation: National Institute for Mathematical and Biological Synthesis, University of Tennessee, Knoxville, TN 37996, USA. lelu@nimbios.org
authors.forename: Maud
authors.initials: M
authors.lastname: Lélu
authors.forename: Michel
authors.initials: M
authors.lastname: Langlais
authors.forename: Marie-Lazarine
authors.initials: ML
authors.lastname: Poulle
authors.forename: Emmanuelle
authors.initials: E
authors.lastname: Gilot-Fromont
authors.forename: Sylvain
authors.initials: S
authors.lastname: Gandon
mesh_terms: D000818:Animals; D002415:Cats; D005260:Female; D006790:Host-Parasite Interactions / Q000235:genetics; D018445:Infectious Disease Transmission, Vertical; D008018:Life Cycle Stages; D008297:Male; D008954:Models, Biological; D011157:Population Dynamics; D051381:Rats; D014122:Toxoplasma / Q000235:genetics* / Q000472:pathogenicity / Q000502:physiology*; D014124:Toxoplasmosis, Animal / Q000453:epidemiology / Q000469:parasitology / Q000635:transmission*; D014774:Virulence
keywords: adaptive dynamics; behavioural manipulation; population genetics approach; trophic transmission; vertical transmission; virulence