Toll-like receptors (TLRs) play a crucial role in host defence, since they trigger immune response following recognition of pathogen-associated molecular patterns (PAMPs) in potential infectious agents. TLRs have been found in numerous organisms, including mammals, birds and teleosts. Some TLR members are commonly retained across all species, whilst others were lost, gained or diverged independently during evolution. Our knowledge about the evolution and specific functions of tlr21, tlr22 and tlr23 in teleosts are still scarce. Phylogenetic analysis of 18 tlr13, tlr21, tlr22 and tlr23 genes from 9 different fish species divided them in two groups. All tlr21 genes were under the first clade, while the second comprised tlr22, tlr23 and tlr13 from Atlantic salmon. Evidence of positive selection was detected at three sites within the leucine-rich repeat regions of Tlr22, which may influence PAMP recognition. Immunostimulation experiments revealed that expression of zebrafish tlr22 is modulated by several unrelated PAMPs. Up to a 3-fold increase in tlr21 and tlr22 expression was detected in larvae exposed to immunostimulants such as lipopolysaccharide, peptidoglycan or poly I:C. We found that zebrafish tlrs are expressed mainly in immune-related organs, such as spleen and kidney as well as in testis and temperature stress did not have an effect on the expression of tlr21 and tlr22 in the early stages of development in zebrafish larvae. Our data indicates that these teleost tlrs may play a role in innate host defence. In particular, tlr22 is evolving under positive selection, which indicates functional diversification and adaptation of the response to different PAMPs.

Kuparinen, A., Tuffo, J., Consuegra, S., Hindar, K., Merila, J., Garcia de Leaniz, C. (2010). Effective size of an Atlantic salmon (Salmo salar L.) metapopulation in Northern Spain ? Consevation Genetics, 11 (4), 1559-1565 IMPF: 01.25The genetic diversity of metapopulations is influenced not only by the effective sizes (N e ) of individual subpopulations, but also by the total effective size of the metapopulation (meta-N e ). We estimated meta-N e of four neighbouring Atlantic salmon populations connected by gene flow using genetic estimates of subpopulation N e s and migration rates derived from capture?recapture data. The meta-[^(N)]e meta{\hbox{-}}\hat{N}_{e} was lower than the sum of [^(N)]e \hat{N}_{e} s of the subpopulations, suggesting that genetic diversity harboured by the four river salmon metapopulation is lower than what would have been expected by viewing individual subpopulations separately. In addition, meta-[^(N)]e meta{\hbox{-}}\hat{N}_{e} was found to be sensitive to changes in [^(N)]e \hat{N}_{e} of the subpopulation from which net emigration rate was largest, so as that the genetic diversity of the metapopulation would be best preserved by avoiding any reductions in N e of this subpopulation. Yet, this subpopulation is the one that has historically?and still is?experiencing the highest exploitation rate in the metapopulation system.Peer reviewe

Verspoor, E., Consuegra, S., Fridjonsson, O., Hjorleifsdottir, S., Knox, D., Olafsson, K., Tompsett, S., Wennevik, V., and Garciá de Leániz, C. 2012. Regional mtDNA SNP differentiation in European Atlantic salmon (Salmo salar): an assessment of potential utility for determination of natal origin. – ICES Journal of Marine Science, 69: 1625–1636. The Atlantic salmon, Salmo salar, shows geographically structured differentiation at various classes of molecular genetic variation, among and within river stocks. Nuclear microsatellite locus variation at multiple loci has been exploited for more than a decade as a marker for the continental origin of fish caught at sea in distant-water fisheries. However, a simpler, more cost-effective, but still accurate, assignment can be obtained using a single microsatellite locus in combination with a mitochondrial DNA (mtDNA) single-nucleotide polymorphism (SNP) detected by restriction enzyme digestion. Following on from this, a preliminary study was made of the potential for using mtDNA SNP variation to enhance the resolving power and cost-effectiveness of within-continent assignment of European salmon as determined using microsatellites. Variation in 20 mtDNA regions, encompassing ∼43% of this genome, in 330 salmon from 29 rivers across Europe, was analysed. High levels of inter-individual and inter-river variation were found, as well as evidence of regional differentiation paralleling observed microsatellite differentiation. The observations indicate scope for using mtDNA SNPs along with microsatellites for genetically based assignment of European salmon to region and river of natal origin, but further study is needed.