1. ¹Department of Ecology and Genetics, University of Aarhus, Aarhus C, Denmark
2. ²Department of Inland Fisheries, Danish Institute for Fisheries Research, Silkeborg, Denmark

Correspondence: Dr LF Jensen, Department of Ecology and Genetics, University of Aarhus, Building 540, Ny Munkegade, Aarhus C DK-8000, Denmark. E-mail: lasse.fast@gmail.com

Received 25 May 2007; Revised 30 August 2007; Accepted 31 August 2007; Published online 7 November 2007.

Abstract

Temporal samples of Danish brown trout (Salmo trutta) from populations representing varying geographical scales were analysed using eight putatively neutral microsatellite loci and two microsatellite loci embedded in TAP genes (Transporter associated with Antigen Processing). These genes encode molecules that are central to the major histocompatibility complex (MHC) class I restricted antigen presentation and thus integral components in the adaptive immune system. As such, they could be influenced by selection, driven by pathogens and parasites in a manner similar to MHC genes. Analysis of allele frequencies at presumably neutral microsatellite loci revealed a temporally unstable population structure within regions, while the population structure was stable over time among regions. Analyses of the two TAP markers indicated an effect of selection at both a regional and micro-geographical spatial scale. Moreover, signals of divergent selection among temporal samples within localities suggest that selection also might fluctuate at a temporal scale. These results suggest that immune genes other than the classical MHC class I and II might be subject to selection and warrant further studies of functional polymorphism of such genes in natural populations.