Single and joint gene segregation in intraspecific hybrids of brown trout ( Salmo trutta L.) lineages

Abstract

Brown trout ( Salmo trutta L.) stocking practices in French Mediterranean rivers often result in artificial secondary contact and introgression between substantially differentiated genomes. Single and joint segregation at five protein and four microsatellite loci were analysed in two back-crosses between hybrid females (resulting from domestic×Mediterranean genitors) and hatchery males in order to test whether there is genetic incompatibility and selective phenomena between the genomes. Three crosses between hatchery genitors were performed and followed in the same time to measure and compare survival among back-cross (2) and hatchery (3) families. Only one of 23 single segregation tests ( LDH-5 for family 2) was significant with an excess of allele of the domestic origin in the F 1 hybrid. Out of 70 joint segregation tests, only six were significant. One segregation corresponded to “weak” associations involving one microsatellite locus ( Strutta-24) and one enzyme ( FBP-1). One case ( Strutta-24 and Strutta-12) was clearly caused by differential maternal transmission of alleles. Even if the question of a breakdown of fitness is only addressed in the hatchery environment, these results showed the existence of events during meiosis, which have affected the allelic transmission for hybrids of the two genomes.