MITOCHONDRIAL-DNA DIFFERENTIATION OF SYMPATRIC POPULATIONS OF BROWN TROUT, SALMO-TRUTTA L, FROM LOUGH-MELVIN, IRELAND

RFLP analysis of mitochondrial DNA (mtDNA) was used to study variation within and between ferox, sonaghen, and gillaroo, the local names of three types of brown trout, Salmo trutta L., which live sympatrically in Lough Melvin, northwest Ireland. They spawn in separate rivers or sections of rivers and thus maintain reproductive integrity by their innate homing behaviour. In this study, 12 restriction enzymes were used to survey 4.9% of the genome in 37 trout. Five of the enzymes were informative (AvaII, HaeIII, HinfI, MboI, and XbaI) and these were used to examine an additional 139 trout. Seven mtDNA haplotypes were found in the first 37 trout and one further haplotype, owing to variation at MboI sites, was found in the larger sample of trout. All of the ferox were monomorphic at all sites examined whereas six haplotypes were found among the gillaroo, three of which were unique to this group. Five haplotypes were found among the sonaghen, two of which were found only in this group. Sonaghen and gillaroo share three haplotypes but they are present in each at different frequencies. Relative to morphological, allozyme, and multilocus probe results, mtDNA provides the most discriminating marker system for these trout.