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

Brown trout (Salmo trutta L.) stocking practices in French Mediterranean ri vers 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 bet ween hybrid females (resulting from domestic X Mediterranean genitors) and hatchery males in order to test whether there is genetic incompatibility an d selective phenomena between the genomes. Three crosses between hatchery g enitors 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 si ngle 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 segrega tion tests, only six were significant. One segregation corresponded to "wea k" associations involving one microsatellite locus (Strutta-24) and one enz yme (FBP-1). One case (Strutta-24 and Strutta-12) was clearly caused by dif ferential maternal transmission of alleles. Even if the question of a break down of fitness is only addressed in the hatchery environment, these result s showed the existence of events during meiosis, which have affected the al lelic transmission for hybrids of the two genomes. (C) 2000 Elsevier Scienc e B.V. All rights reserved.