title: Frequency-dependent assistance as a way out of competitive exclusion between two strains of an emerging virus.
abstract: Biological invasions are the main causes of emerging viral diseases and they favour the co-occurrence of multiple species or strains in the same environment. Depending on the nature of the interaction, co-occurrence can lead to competitive exclusion or coexistence. The successive fortuitous introductions of two strains of Tomato yellow leaf curl virus (TYLCV-Mld and TYLCV-IL) in Réunion Island provided an ideal opportunity to study the invasion of, and competition between, these worldwide emerging pathogens. During a 7-year field survey, we observed a displacement of the resident TYLCV-Mld by the newcomer TYLCV-IL, with TYLCV-Mld remaining mostly in co-infected plants. To understand the factors associated with this partial displacement, biological traits related to fitness were measured. The better ecological aptitude of TYLCV-IL in single infections was demonstrated, which explains its rapid spread. However, we demonstrate that the relative fitness of virus strains can drastically change between single infections and co-infections. An epidemiological model parametrized with our experimental data predicts that the two strains will coexist in the long run through assistance by the fitter strain. This rare case of unilateral facilitation between two pathogens leads to frequency-dependent selection and maintenance of the less fit strain.
authors.affiliation: CIRAD, UMR PVBMT, Pôle de Protection des Plantes, , 97410 Saint-Pierre, Ile de la Réunion, France, Université de La Réunion, UMR PVBMT, Pôle de Protection des Plantes, , 97410 Saint-Pierre, Ile de La Réunion, France, INRA, UMR 0385 BGPI, , 34398 Montpellier Cedex 5, France.
authors.forename: Frédéric
authors.initials: F
authors.lastname: Péréfarres
authors.forename: Gaël
authors.initials: G
authors.lastname: Thébaud
authors.forename: Pierre
authors.initials: P
authors.lastname: Lefeuvre
authors.forename: Frédéric
authors.initials: F
authors.lastname: Chiroleu
authors.forename: Loup
authors.initials: L
authors.lastname: Rimbaud
authors.forename: Murielle
authors.initials: M
authors.lastname: Hoareau
authors.forename: Bernard
authors.initials: B
authors.lastname: Reynaud
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Lett
mesh_terms: D000818:Animals; D053839:Begomovirus / Q000235:genetics / Q000502:physiology*; D021821:Communicable Diseases, Emerging / Q000821:virology*; D006430:Hemiptera / Q000821:virology; D007303:Insect Vectors / Q000821:virology; D058865:Introduced Species; D018551:Solanum lycopersicum / Q000821:virology*; D056265:Microbial Interactions / Q000502:physiology*; D008954:Models, Biological; D060885:Multiplex Polymerase Chain Reaction; D060888:Real-Time Polymerase Chain Reaction; D017508:Reunion; D012641:Selection, Genetic; D013045:Species Specificity; D019562:Viral Load
keywords: biological invasions; coexistence; epidemiological model; fitness; mixed infection; plant virus