Postglacial colonization of brown trout in Europe based on distribution of allozyme variants

Abstract

Compatible data from 11 polymorphic allozyme loci were assembled from 14 published studies and additional unpublished information for 232 native collections of brown trout sampled over a broad geographical range.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 three preglacial lineages, each fixed for different sets of alleles at these two loci. During glacial retreat, recolonization is proposed to have occurred mainly into adjacent areas through (i) a northwestern migration from an eastern Mediterranean-Caspian refuge, (ii) a northern expansion from a refuge in Atlantic drainages of Iberia and southern France, and (iii) a northern 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 Mediterranean refuge distinguished by the presence of the LDH-A2* 100QL allele was excluded based on the absence of this allele in repopulated areas.