title: Genetic gradient of a host-parasite pair along a river persisted ten years against physical mobility: Baltic Salmo salar vs. Gyrodactylus salaris.
abstract: The Atlantic salmon, Salmo salar L., in the Tornio River in the Northern Baltic Sea basin accommodates a monogenean ectoparasite, Gyrodactylus salaris. The aim of the study was to understand the population structure of apparently co-adapted host-parasite system: no parasite-associated mortality has been reported. The parasite burden among salmon juveniles (parr) was monitored along 460km of the river in 2000-2009. Among the parr, 33.0% were infected (nfish=1913). The genetic structure of the parasite population was studied by sequencing an anonymous nuclear DNA marker (ADNAM1, three main genotypes) and mitochondrial CO1 (three clades, six haplotypes). During the ten years, the parasite population was strongly and stably genetically differentiated among up- and downstream nurseries (nADNAM1=411, FST=0.579; nCO1=443, FST=0.534). Infection prevalence among the smolts migrating to sea was higher than in the sedentary parr populations (82.2%, nfish=129). The spatial differentiation observed among the sedentary juveniles was reflected temporally in the smolt run: parasite genotypes dominating the upper part of the river arrived later than downstream dwellers (medians June 4 and June 2) to the trap 7km from the river mouth. The nuclear and mitochondrial markers were in stable disequilibrium which was not relaxed in the contact zone or among the smolts where the parasite clones often met on individual fish. Only five parasite specimens on smolts (nworms=217) were putative recent sexual recombinants. The contribution of extant salmon hatcheries into the infection was negligible. The host salmon population in Tornio River is known to show significant spatial differentiation (FST=0.022). The stable spatial genetic structure of the parasite against the high physical mobility suggested a possibility of local co-adaptation of the host-parasite subpopulations.
authors: Department of Biology, University of Oulu, FI-90014 Oulu, Finland.
authors: Jaakko
authors: J
authors: Lumme
authors: Department of Biology, University of Oulu, FI-90014 Oulu, Finland; Finnish Food Safety Authority Evira, Production Animal and Wildlife Health Research Unit, FI-90590 Oulu, Finland.
authors: Pasi
authors: P
authors: Anttila
authors: Department of Biology, University of Oulu, FI-90014 Oulu, Finland.
authors: Päivi
authors: P
authors: Rintamäki
authors: Finnish Food Safety Authority Evira, Production Animal and Wildlife Health Research Unit, FI-90590 Oulu, Finland. Electronic address: perttu.koski@evira.fi.
authors: Perttu
authors: P
authors: Koski
authors: Natural Resources Institute Finland (Luke), Oulu Game and Fisheries Research, FI-90014 Oulu, Finland.
authors: Atso
authors: A
authors: Romakkaniemi
mesh_terms: D000818:Animals; D001267:Atlantic Ocean; D001454:Baltic States; D018509:DNA, Helminth / Q000235:genetics; D004272:DNA, Mitochondrial / Q000235:genetics; D005393:Fish Diseases / Q000235:genetics / Q000469:parasitology; D006374:Helminthiasis, Animal / Q000235:genetics / Q000469:parasitology; D006790:Host-Parasite Interactions / Q000235:genetics*; D010802:Phylogeny; D010986:Platyhelminths / Q000235:genetics / Q000472:pathogenicity; D045483:Rivers; D020317:Salmo salar / Q000235:genetics / Q000469:parasitology
chemical_list: D018509:DNA, Helminth; D004272:DNA, Mitochondrial
keywords: Asexuality; Atlantic salmon; Infection dynamics; Local adaptation; Parasite dispersal; Tornio river