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The immunocompetence handicap hypothesis (ICHH) provides a functional explanation for how sexual ornaments can provide honest signals of male quality. A key aspect of this hypothesis is that testosterone (T) has a bimodal effect: a higher T level enhances the expression of ornaments (increasing mating success and, ultimately, fitness); however, at the same(More)
The extreme polymorphism found at some major histocompatibility complex (MHC) loci is believed to be maintained by balancing selection caused by infectious pathogens. Experimental support for this is inconclusive. We have studied the interaction between certain MHC alleles and the bacterium Aeromonas salmonicida, which causes the severe disease(More)
The mutational mechanism underlying the striking diversity in MHC (major histocompatibility complex) genes in vertebrates is still controversial. In order to evaluate the role of inter- and intragenic recombination in MHC gene diversification, we examined patterns of nucleotide polymorphism across an exon/intron boundary in a sample of 31 MHC class IIB(More)
The two main trade-offs considered determining reproductive patterns in iteroparous organisms are the one between current and future reproduction, and the one between the number and quality of offspring. Recently, it has been suggested that these trade-offs may be mediated by stress-induced reduction in immunocompetence. To test the hypothesis that stress(More)
We compared three different molecular methods currently used for screening of Mhc variation in population studies of Atlantic salmon. Restriction fragment length polymorphism (RFLP) of the entire class II gene detected 22 haplotypes. Seventeen exon 2 sequences were obtained from individuals carrying the 22 haplotypes, two of which had not been detected by(More)
We have tested the importance of genetic variation in the major histocompatibility complex (MHC) class IIB in Atlantic salmon (Salmo salar) for survival after challenge with a highly virulent bacterial pathogen. Forty juvenile full siblings from each of 120 families were infected with the bacterium Aeromonas salmonicida, which causes high mortality in(More)
We sequenced exon 2 of the MHC class II B gene in Atlantic salmon from the Baltic Sea and identified 17 different exon 2 alleles among 22 different restriction fragment length polymorphism haplotypes. The sequences differed at between 1 and 34 bases. Two different tests were used to estimate the importance of recombination in the generation of new alleles.(More)
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