Sixty-four samples from 46 salmon populations totalling 2369 specimens were used for polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) analysis of the mitochondrial ND1 region. The final analyses included 3095 specimens from 60 populations in Northern Europe. A subsample was analysed by RFLP of ND3/4/5/6. Representative RFLP haplotypes from different parts of the distribution area were sequenced and the phylogeny of European haplotypes and their relations to the North American lineage was described. The four common European haplotypes derive from the ancestral ND1-BBBA (rooting the European clade to the North American) by one-step substitutions: AAAA < AABA < BBBA > BBBB. The Swedish west-coast populations differ from the geographically close southern Baltic, indicating absence of inward and limited outward gene flow through the Danish straits during the last 8000 years. Within the Baltic Sea, only three ND1 haplotypes were detected and there was no variation for ND3/4/5/6. In the whole southern Baltic and in lakes Vänern, Ladoga and Onega the haplotype AABA dominated. Proposed postglacial colonization routes to the Baltic Sea are discussed in relation to the haplotype distribution pattern.

Mitochondrial and microsatellite DNA markers were applied to infer the phylogeography, intraspecific diversity and dynamics of the distributional history of European grayling (Thymallus thymallus) with focus on its central and northern European distribution range. Phylogenetic and nested clade analyses revealed at least four major mtDNA lineages, which evolved in geographical isolation during the Pleistocene. These lineages should be recognized as the basic evolutionary significant units (ESUs) for grayling in central and northern Europe. In addition, and in contrast to previous work on grayling, the results of Bayesian analysis of individual admixture coefficients, two-dimensional scaling analysis and spatial analysis of molecular variance provided evidence for a high level of admixture among major lineages in contact zones between drainages (e.g. the low mountain range of Germany), most likely resulting from glacial perturbations and ancient river connections between drainages during the Pleistocene glaciations. Even within river systems, a high level of differentiation among populations was revealed as indicated by the microsatellite data. Grayling sampled from 29 sites displayed high levels of differentiation (overall F(ST) = 0.367), a high number of private alleles and high bootstrap support for the genetic distance-based population clusters across 12 loci. We specifically discuss our results in context of phylogeograpic studies on other European freshwater fish species with habitat preferences similar to those of grayling. Our study shows that both large-scale phylogeographical and detailed genetic analyses on a fine scale are mandatory for developing appropriate conservation guidelines of endangered species.

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Summary Parasites and pathogens can have an important effect on their host's thermal resistance. The impact of parasite infection on host physiological performances has traditionally been studied in controlled laboratory conditions, and much less is known about its actual effects in wild populations. Nonetheless, such knowledge is critical when assessing the effect of climate change on the future survival of the host. Tetracapsuloides bryosalmonae is a myxozoan endoparasite causing proliferative kidney disease (PKD) in salmonids. Infection and clinical symptoms of PKD are dependent on environmental temperature and PKD has become an emerging disease of primary importance for farmed and wild salmonids in the last decades. Despite important achievements in understanding PKD pathology in recent years, there are still crucial gaps in the knowledge of the disease ecology, notably in how the parasite affects host performance in the wild. We sampled juvenile (0+) brown trout (Salmo trutta) from the wild during early and late summer and assessed relative parasite load (DNA quantification with qPCR) and disease severity (kidney hyperplasia). We also measured haematocrit, leucocyte formula, aerobic scope and upper thermal tolerance in a field‐physiology approach in order to better understand the relationships between PKD severity and host performance. By using wild‐caught individuals and performing measurements directly on location, we aimed to gain insights into host physiology in a natural environment while avoiding biases caused by laboratory acclimation. We found that most physiopathological symptoms in the wild were strongly correlated with kidney hyperplasia, but more weakly linked to parasite load. Disease severity was positively correlated with anaemia and abundance of circulating thrombocytes, and negatively correlated with aerobic scope and thermal tolerance. Our results suggest that impaired aerobic performances and thermal tolerance in infected fish may potentially result in decreased host survival in the wild, especially in relation with predicted higher average summer temperatures and increased frequency of extreme events (summer heatwaves) in the context of global climate change. A http://onlinelibrary.wiley.com/doi/10.1111/1365-2435.12701/suppinfo is available for this article.

The genetic structure and phylogeography of Atlantic salmon (Salmo salar) across the Baltic Sea basin and neighbouring areas (eastern Atlantic Ocean, North Sea, Barents Sea, White Sea, and two Russian lakes, Onega and Ladoga) were studied to resolve the partly contradictory hypotheses of the species' postglacial colonization history. Thirty-eight populations (total of 2180 individuals) were studied for nine DNA microsatellite loci. Within the Baltic Sea, the anadromous populations formed three clear groups, corresponding to the northern (Gulf of Bothnia), eastern (Gulf of Finland and eastern Baltic Main Basin), and southern regions (western Baltic Main Basin). The genetic differences among these three groups were clearly greater (G GB 5.6%; G GB being the proportion of diversity components between regions within basins) than were those among population groups in the eastern Atlantic Ocean (G GB 2.2%) from Ireland to the White Sea. The isolation-by-distance model explained part of the differentiation within, but not between, the regions. The results strongly indicate colonization of the Baltic Sea by at least three glacial lineages. Potential refugium areas for each lineage are proposed.Résumé : Nous avons étudié la structure génétique et la phylogéographie du saumon atlantique (Salmo salar) de part en part du bassin de la Baltique et dans les régions avoisinantes (est de l'Atlantique, mer de Barents, mer Blanche et deux lacs russes, les lacs Onega et Ladoga) pour résoudre les hypothèses en partie contradictoires sur l'histoire de la colonisation postglaciaire de l'espèce. Nous avons analysé neuf locus ADN microsatellites chez 2180 individus appartenant à 38 populations. Au sein de la Baltique, les populations anadromes forment trois groupes distincts qui correspondent aux régions du nord (golfe de Bothnie), de l'est (golfe de Finlande et bassin principal de l'est de la Baltique) et du sud (bassin principal de l'ouest de la Baltique). Les différences génétiques entre ces trois groupes sont nettement plus importantes (G GB 5,6 %; G GB représente la proportion d'éléments de diversité entre les régions à l'intérieur des bassins) que celles qui existent entre les groupes de populations de l'est de l'Atlantique (G GB 2,2 %), de l'Irlande à la mer Blanche. Le modèle de l'isolement en fonction de la distance explique une partie de la différentiation au sein des régions, mais non entre elles. Nos résultats indiquent fortement une colonisation de la Baltique par au moins trois lignées glaciaires. Nous proposons des zones possibles de refuge pour chaque lignée.[Traduit par la Rédaction] Säisä et al. 1904

Health after pathogen contact varies among individuals because of differences in pathogen load (which is limited by resistance) and disease severity in response to pathogen load (which is limited by tolerance). To understand pathogen-induced host evolution, it is critical to know not only the relative contributions of nongenetic and genetic variation to resistance and tolerance but also how they change environmentally. We quantified nongenetic and genetic variation in parasite load and the associated temperature-dependent disease among trout siblings from two rivers. We detected a genetic variance for parasite load 6.6 times as large in the colder river. By contrast, genetic variance for disease traits tended to be larger in the warmer river, where the disease was manifested more severely. The relationships between disease severity and pathogen load (tolerance) exhibited plateaus at low pathogen load and stronger steepening slopes at high pathogen load in the warmer river. Our study demonstrates the environmental influence on disease severity, nongenetic and genetic variance for health-damage-limiting host abilities, and the shape of tolerance curves. Environmental variability is predicted to govern the presence and intensity of selection, change the relative contributions of nongenetic and genetic variance, and therefore hamper evolution toward more resistant and tolerant hosts.

Genetic homogenization has been recognized as a serious threat in an increasing number of species, including many salmonid fishes. We assessed the rate and impact of immigration from the main hatchery stocks of Atlantic salmon in the Gulf of Bothnia into one of the largest wild salmon populations in the Baltic Sea, the River Vindelä lven, within a temporal framework of 18 years (from 1985-2003). We provide genetic evidence based on mtDNA and microsatellite markers, using mixed-stock analysis, that a large proportion (66%) of fin-damaged spawners (n ¼ 181) caught in the Ume/ Vindelä lven during 1997-2003 originated from the hatcheries in the Rivers Å ngermanä lven, Luleä lven and Ljusnan. The maximum-likelihood estimate of immigration rate from these hatcheries into the wild Vindelä lven population was 0.068 (95% CI 0.021-0.128) over the studied time period (1985)(1986)(1987)(1988)(1989)(1990)(1991)(1992)(1993)(1994)(1995)(1996)(1997)(1998)(1999)(2000)(2001)(2002)(2003) and reached up to a quarter (m ¼ 0.249, 95% CI 0.106-0.419) of the total population during 1993-2000. This resulted in significant (Po0.01) genetic homogenization trend between the wild Vindelä lven population and hatchery stocks of the Å ngermanä lven and Luleä lven. Our results demonstrate extensive straying from geographically distant hatchery releases into wild salmon population and emphasize the genetic risks associated with current large-scale stocking practices in the Baltic Sea. Heredity (2005) 95, 76-83.

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