écologie des virus influenza aviaires en Camargue - IRD

« The ecological significance of manipulative parasites »(a)(b)(c)(d)(e)Figure 1. Examples of manipulative parasites.(a) The crustacean amphipod Gammarus insensibilis manipulated by the trematodeMicrophallus papillorobustus (Photo P. Goetgheluck); infected gammarids display a positivephototactism, a negative geotactism and an aberrant evasive behaviour. Indeed, instead ofhiding under stones, they swim towards the surface, and are preferentially eaten by aquaticbirds (definitive hosts) [58]. (b) Cystacanth of Polymorphus minutus (Acanthocephalan)encysted in the body cavity of Gammarus pulex [49] (Photo F. Cezilly). Unlike M.papillorobustus which is encysted in the brain of the gammarid (in (a)), the acanthocephalanis encysted in the body cavity in (b). Remarkably, this acanthocephalan also ends its lifecycle in an aquatic bird and induces similar behavioural changes in the gammarid. Becausetrematodes and acanthocephalans are phylogenetically distant, this illustrates a case ofevolutionary convergence in the manipulative process. (c) Coral polyps infected with atrematode (Podocotyloides stenometra). The parasite induces pink, swollen nodules on thecoral colony and impairs their retraction ability. Infected polyps are, therefore, bothconspicuous and vulnerable to predation by the coral­feeding butterflyfish, Chaetodonmulticinctus (the parasite’s definitive host) [59] (Photo G. Aeby). (d) An ant (Cephalotesatratus) parasitized by a nematode (Myrmeconema neotropicum). The parasite induces fruitmimicry and modifies the ants' behaviour, making them more likely to be ingested by fruiteatingbirds (final hosts) [60] (Photo S.P. Yanoviak). (e) The Gordian worm (Paragordiustricuspidatus) exiting the body of a cricket (Nemobius sylvestris) (Photo P. Goetgheluck).213