Compatible data from 11 polymorphic allozyme loci were assembled from 14 pu
blished studies and additional unpublished information for 232 native colle
ctions of brown trout sampled over a broad geographical range. Most of the
genetic variation was explained by the distribution of allelic variation at
the LDH-C* and CK-A1* loci. Patterns of geographical distribution coupled
with postglacial geological events supported a model of colonization from t
hree preglacial lineages, each fixed for different sets of alleles at: thes
e two loci. During glacial retreat, recolonization is proposed to have occu
rred mainly into adjacent areas through (i) a north-western migration from
an eastern Mediterranean-Caspian refuge, (ii) a northern expansion from a r
efuge in Atlantic drainages of Iberia and southern France, and (iii) a nort
hern and eastern radiation from a refuge centred near the English Channel.
Extant populations in deglaciated areas are suggested to represent mixed or
pure descendants of these migrating groups. Repopulation from a fourth Med
iterranean refuge distinguished by the presence of the LDH-A2*100QL allele
was excluded based on the absence of this allele in repopulated areas.