Origins and relationships of native populations of Salmo trutta (brown trout) in Spain

Abstract

Allele frequency variation at 25 protein-coding loci was compared among collections from 24 naturally spawning brown trout populations in Spain. Evidence of introgression was apparent but alleles of indigenous fish predominated in each of the nine populations sampled in areas where exogenous hatchery fish had been released. Native Spanish gene pools were characterized by strong individuality based on distinct allele frequencies of both adjacent and distant rivers (GST = 0.64), the locally high frequency of rare and previously unreported alleles, and low heterozygosities (H = 0.03 1). Two major Spanish lineages are proposed within a previously postulated 'ancestral' grouping of populations existing in southern Europe, based on predominant alleles at the CKA1* locus. An 'Atlantic' group (comprising populations in Atlantic flowing streams) extends to unglaciated areas of the southern British Isles and Britanny, and is characterized by high frequencies of the *115 allele. Mediterranean flowing streams are populated by a 'Mediterranean' group extending eastward through the Caspian basin and characterized by high frequencies of the *100 allele.

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

“…Only the *100 allele was observed in the seven Greek samples. Fixation of the *115 allele in eight Spanish and one French sample was consistent with this allele serving as a marker for a south-western glacial refuge for brown trout (García-Marín & Pla, 1996). Also noteworthy is the high frequency of the *115 allele in some Swedish, Norwegian and Russian samples (0.609-0.916), in contrast to a maximum value of 0.500 in the British Isles.…”

“…Based on these criteria, we used data representing presumably native fish from 232 discrete locations: 90 from the British Isles (Fleming, 1983;Crozier & Ferguson, 1986;Ferguson & Taggart, 1991;Cross et al, 1992); 15 from France (Krieg & Guyomard, 1985;Barbat-Leterrier et al, 1989); seven from Greece (Karakousis & Triantaphyllidis, 1990); 51 from Norway (Skaala & Jørdstad, 1987;Skaala & Nëvdal, 1989;Hindar et al, 1991;Skaala, 1992); six from Russia (Osinov, 1984); 33 from Sweden (Ryman, 1983); and 30 from Spain (García-Marín & Pla, 1996;and 6 unpublished locations). A detailed description of these collections, including the allele frequency for the most widespread variant at the four more polymorphic loci is available from the authors on request or accessible in the URL entry: http://fc.udg.es/~genetica/LIG/curri/appendix/ tabla1.html.…”

“…esterases, malic enzyme) were excluded because of the difficulty in establishing homologies of loci and alleles among the different published sources. Ultimately, we chose a set of 11 loci (Table 1) Following the practice in brown trout genetic studies, all variation at the sMDH-B1,2* isolocus was assigned to sMDH-B1*; variation assigned simultaneously to both isoloci is restricted to a few Spanish rivers (García-Marín & Pla, 1996). Thus the sMDH-B2* locus was excluded from the present data set.…”

“…The fixation of the CK-A1*100 allele distinguishes these two refuges from lineage II populations. The restricted occurrence of the LDH-A2*100QL allele in the Mediterranean basin (Apostolidis et al, 1996;García-Marín & Pla, 1996;Largiardèr & Scholl, 1996) provides a useful marker to distinguish populations of lineage IV from those of lineage III. The absence of this allele from postglacially colonized regions and the palaeohydrographical features associated with the geography of this fourth lineage suggest little if any Table 4 Frequency ranges of main variant alleles of four polymorphic loci of brown trout in countries with genetic evidence of stocking practices in the analysed locations.…”

“…1). Two lineages (I and II) among Atlantic drainages are characterized, respectively, by high allelic frequencies of LDH-C*90 and of CK-A1*115 (Hamilton et al, 1989;García-Marín & Pla, 1996). MtDNA haplotypes distinguish populations of lineage III in the Black, Caspian and Aral seas and those of the more western lineage IV in the Mediterranean Sea (Osinov & Bernatchez, 1996).…”