VARIATION IN MITOCHONDRIAL-DNA AND POSTGLACIAL COLONIZATION OF NORTH-WESTERN EUROPE BY BROWN TROUT

A purified mitochondrial DNA (mtDNA) probe was used to examine restric tion fragment length polymorphisms produced by six restriction enzymes (Xba I, Eco RV, Ava II, HinfI, Hae III, Mbo I) in 915 brown trout fro m western Europe. A total of 20 composite haplotypes were found with o ne to seven haplotypes in individual populations. Icelandic trout samp les from north, south, east, and west coast drainages showed only a si ngle common haplotype in contrast to the high level of polymorphism fo und in Irish and Scottish populations. The phylogeny of mtDNA haplotyp es and the pattern of haplotype distribution suggests that post-glacia l colonization of brown trout in NW Europe was more complex than the d ual colonization model which has been proposed on the basis of differe ntial LDH-5 allele distribution. For example, Lough Melvin (Ireland) appears to have been independently colonised by three distinct types o f trout. (C) 1996 The Fisheries Society of the British Isles