Monogenean parasites in two cyprinid species (Parachondrostomatoxostoma and Chondrostoma nasus) in sympatric zones ofsouthern France

Our study was aimed to investigate the composition of metazoan parasite communities in fish specimens collected from one allopatric population for each species and six localities where both fish species live in sympatry. During four field studies (performed in 2008-2011), fish were examined for all metazoan parasites – ectoparasites (Monogenea, Crustacea, Mollusca, Hirudinea) and endoparasites (Trematoda, Cestoda, Acanthocephala, Nematoda). Molecular identification of fish specimens (pure species vs. hybrids) was performed using cytochrome b gene and 41 microsatellite loci. Moreover, to estimate the potential threat to endemic species linked to the introduction of invasive species, we focused on the structural variability and expression profiles of the functional MHC IIB genes (DAB1 and DAB3) because of their adaptive significance and role in parasite resistance. The variability of the genes, the selection pattern shaping MHC polymorphism and extent to which trans-species evolution and intergeneric hybridization affect MHC polymorphism were investigated. Our results suggest that differences in parasites between two studied species and their hybrids are linked not only to different feeding and habitat conditions but also host-parasite evolutionary associations play an important role in determining the presence of Chondrostoma-specific monogeneans. The frequencies of both pure host species in the localities studied determine the composition of metazoan parasite communities.