écologie des virus influenza aviaires en Camargue - IRD

Annexe 2(e.g. light, humidity, temperature) between living under (uninfected) or above (infected) thesurface of the mud, manipulated cockles clearly constitute a new habitat for sessile species.As a result, echinostomes increase the diversity of the invertebrate community by providinghabitats for species like limpets and anemones that would normally be absent from the softsedimenthabitat [40­42] (Box 2).Probably the most important role of parasites as ecosystem engineers takes placeinside host species, since living organisms are themselves an ecosystem for numerousparasite species [43]. Depending on their life cycle and transmission routes, shared interestsor, conversely, conflicts of interests, may occur within parasite communities. For instance,behavioural alterations induced by M. papillorobustus (Figure 1a) are not neutral for theother parasites co­occurring inside G. insensibilis. In field gammarids, there is a positiveassociation between M. papillorobustus and another trematode, Maritrema subdolum, whichdoes not manipulate the behaviour of the amphipod but has the same definitive hosts as themanipulative M. papillorobustus [44]. Because the infective stages of M. subdolum swimcloser to the water's surface compared to those of M. papillorobustus, they more frequentlyencounter and infect manipulated gammarids than uninfected ones (i.e. the ‘hitch­hiking’strategy [44]). Leung and Poulin [45] recently investigated how the presence of manipulativeechinostomes in New Zealand cockles impacts the whole community of parasites andsymbionts co­occurring in these bivalves. They found a novel potential case of a hitch­hikerparasite: another trematode (a gymnophallid) that shares the same transmission route asechinostomes but is not capable of manipulation preferentially infects manipulated cockles(but see Ref [46]). These examples illustrate well how manipulative parasites, by modifyingtheir living habitats (i.e. the intermediate host), can change the selective pressures acting onother species and consequently influence the structure of communities.Just as shared interests exist between manipulative parasites and other parasitesexploiting the same host species, conflicts are also likely to occur. The nematodeGammarinema gammari (Figure 3) uses G. insensibilis as a habitat and source of nutrition,not as a ‘vehicle’ for transmission to birds. There is evidence that this nematode prefers nonmanipulatedgammarids and seems also able to reverse the manipulation induced by M.papillorobustus, changing gammarids from an altered behaviour back to a normal behaviour[47]. A similar situation has been reported within the gammarid G. roeseli between the bird200