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Among Greek Brown Trout (Salmo Trutta L.) Populations

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Among Greek Brown Trout (Salmo Trutta L.) Populations Heredity 64 (1990) 297-304 The Genetical Society of Great Britain Received 14 August 1989 Genetic structure and differentiation among Greek brown trout (Salmo trutta L.) populations Y. Karakousis and Division of Genetics, Development and Molecular C. Triantaphyllidis Biology, University of Thessaloniki, T.K. 54006, Greece. Twenty five loci have been screened in four Greek brown trout (Salmo truttaL.)populations using starch gel electrophoresis. A number of alleles which were unique for the Greek populations were found. The degree of genetic differentiation within and among seven Greek brown trout populations was calculated. The values of genetic distance between these seven populations are similar to those reported for other populations of the same species. These results contradict the classification of Greek brown trout populations into five subspecies. Furthermore, the phylogenetic relationships between 19 European populations were investigated. The high values of genetic identity between the Mediterranean and the Black Sea populations indicate that they might be of common origin. INTRODUCTION Ferguson, 1986), France (Krieg and Guyomard, 1983; 1985; Guyomard and Krieg, 1983) and Sincethe recognition of multiple molecular forms Russia (Osinov, 1984) have been researched. of enzymes (Markert and Moller, 1959), these gene However, only a few studies have been carried out products, called isozymes, have served as probes on brown trout populations in Greece, especially for the evaluation of the genetic diversity, popula- on distribution (Economidis, 1973) and biology tion structuring and evolutionary relationships of (Papageorgiou et a!., 1984a, b), even though there many fish species (Allendorf and Utter, 1979; are several reasons to study them: Ferguson, 1980). This appraisal is particularly use- (a) Brown trout is a fish of high preference as ful among members of the family Salmonidae regards sport fishing and constitutes a poten- whose striking diversity in morphology, ecology tial species for extensive breeding in Greece. and behaviour is found to reflect their evolutionary (b) The populations of brown trout have not been relationships and population structuring (Behnke, subjected to a massive transplantation pro- 1968). Furthermore, genetic variability constitutes gramme, so they represent undisturbed natural a primary biological resource and must be preser- populations. ved (Smith and Chesser, 1981). For instance, future (c) Based on morphological characters five sub. breeding programmes will require genetically species have been recognised: S. trutta macro- diverse material upon which to act (Vuorinen, stigma, S. trutta dentex, S. trutta peristericus, 1984). Thus, there is a current awareness of the S. trutta pelagonicus and S. trutta macedonicus need to identify and document the genetic diver- (Heckel and Knerr 1858; Dumeril, 1858; sity, as well as to clarify the complex taxonomic Karaman, 1924; 1927; 1937). However, the use status (Ryman, 1981) as a sound basis for the future of morphological characters in taxonomy has management and conservation of the salmonid some limitations because they are polygeni- species. cally inherited with low heritability, so the The genetic diversity and population structure taxonomic status of these populations is of brown trout (Salmo trutta) in lakes and rivers actually unclear. The origin of the populations in Scandinavia (Allendorf et a!., 1976; Ryman et of brown trout in Greece in relation to other a!., 1978; Ryman, 1983), Ireland (Ferguson and European populations is also unclear. Mason, 1981; Ferguson and Flemming, 1983; In a former paper we reported the genetic struc- Flemming and Ferguson, 1983; Crozier and ture of three populations of brown trout belonging 298 Y. KARAKOUSIS AND C. TRIANTAPHYLLIDIS to the subspecies S. trutta pelagonicus (Karakousis and Triantaphyllidis, 1988). The aim of this paper is to expand our previous research including four other populations belonging to different sub- species, in an effort to understand their genetic structure and to clarify their evolutionary relation- ships. These studies also constitute a necessary step towards the aims of rational management and conservation of this valuable resource. MATERIALSAND METHODS Samplesof brown trout were collected between 1985 and 1987 from seven streams in N. Greece 'I (fig. 1). Fishes were obtained by electrofishing, specimens were transferred to the laboratory either alive or in ice and stored at —20°C until used. Samples of skeletal muscle, liver, heart, eye and brain were excised and homogeneised in an equal volume of distilled water, centrifuged and the supernatant used for electrophoresis. Horizon- tal starch gels were prepared with 10 per cent hydrolysed starch. Buffers, electrophoretic condi- tions and the staining methods for each system are Figure 1 Geographical locations of rivers and streams where shown in table 1. brown trout were sampled. 1. Nestos river, 2. Tripotamos stream, 3. Drosopigi stream, 4. Skopos stream, 5. Agios Eleven enzymic systems were studied corre- Germanos stream, 6. Voidomatis river, 7.Lourosriver. sponding to 25 loci. The nomenclature used to designate loci and alleles was that proposed by Allendorf et al. 1977) and Taggart et al. (1981). The allele frequency estimates result from allele are k alleles at a locus then the x2statisticis given counting. Average polymorphism level, total by: expected heterozygosity, standard genetic distance and genetic identity (Nei, 1972) were computed. The heterogeneity of the allele frequencies at the 2N()J I PJ polymorphic loci was calculated by the Workman where P and r2parethe weighted mean and and Niswander (1970) homogeneity test. If there variance of the frequencies of the Jth allele at the Table 1 Enzyme systems studied, abbreviations and electrophoretic conditions Migration Staining Number System Abbreviations EC No buffer* methodst of loci Aspartate aminotransferase AAT (GOT) 2.6.1.1 AM 3 3 a-glycerophosphte dehydrogenase a-GPDH 1.1.1.8 TP 1 1 Creatine kinase CK 2.7.3.2 TCB 2 2 Isocitrate dehydrogenase IDH 1.1.1.42 AM 1 2 Lactate dehydrogenase LDH 1.1.1.27 TCB 3 4 Malate dehydrogenase MDH 1.1.1.37 AM 1 4 Malic enzyme ME 1.1.1.40 TP 1 3 Phosphoglucomutase PGM 2.7.5.1 A 3 1 6-phosphogluconate dehydrogenase 6-PGDH 1.1.1.44 AM 1 1 Phosphoglucose isomerase PGI 5.3.1.9 A 3 3 Superoxide dismutase SOD 1.15.1.1 A 3 1 *A=ft,Jlendorf et aL (1977); AM and TCB=Taggart et at. (1981); TP=Guyomard and Krieg (1983). = t1 Allendorfet aL (1977); 2 =Brewer(1970); 3 =Harrisand 1-Iopkinson (1976). GENETIC STRUCTURE AND DIFFERENTIATION AMONG TROUT POPULATIONS 299 Table 2 Allelic frequencies of studied loci, mean heterozygosity (H), proportion of polymorphic loci (P)andinterpopula- tion heterogeneity (x2) Louros Voidomatis Ag. Germanos Paranesti Loci Alleles n =75 n =35 n =52 n =69 x2 Aat-1,2 100 100 100 0.4706** 06463 70 000 0•00 05294 0.3537 8577++ Aat-4 100 05978 04848 08181 100 74 Ø.4fl 05152 01819 000 7161++ cs-Gpdh-2 100 100 07576 100 100 50 0.00 02424 000 000 90•10++ Ck-i 100 1•00 100 100 100 Ck-2 100 1•00 100 0.00 100 50 000 0.00 100 000 Idh-l 100 1•00 1.00 1.00 100 Idh-2 100 100 100 100 1.00 Ldh-1 100 094 1.00 09904 0.9265** 0 006 000 00096 00735 1032+ Ldh-2 100 1•00 09143 100 09044 0 000 00857 0.00 00956 24•47++ Ldh-4 100 100 1.00 100 100 Ldh-5 100 000 0•00 0.00 0.0444** 105 100 1.00 100 09556 967+ Mdh-1,2 100 100 1.00 100 100 Mdh-3,4 100 100 1.00 1.00 100 Me-i 100 100 100 F00 100 Me-2 100 06933 00714 0.00 05 50 03067 09286 1•00 0•5 16333++ Me-3 100 100 1.00 100 100 Pgm-1 100 100 100 1.00 100 6-Pgdh-1 100 100 100 100 100 Pgi-1 100 100 100 100 100 Pgi-2 100 100 100 100 100 Pgi-3 100 100 100 100 100 Sod-i 100 100 100 1.00 100 (H) 00407 00462 00326 00541 (P) 12% 16% 12% 20% n =samplesize; + significant at the P =005;++ significant at the P=001 level; **significantat the P=005 level under the Hardy-Weinberg equilibrium. locus. For each allele the weighted mean is: previous authors. The enzymic systems examined are discussed below. AAT Three polymorphic loci were studied in this where p, is the frequency of the allele in the ith enzymic system. The sAat-l,2 which are pre- population. The weighted variance is: dominantly expressed in skeletal muscle and the a= (N1/N)p—p2. sAat-4 which is expressed in liver. A variant allele, sAat-1,2(70), was observed in this investigation. Wright's (1965) standardised genetic variance This allele is probably identical with the sAat- (FST) was also calculated. 1,2(75) allele reported by Osinov (1984), which exists only in Black Sea basin trout. c-GPDH. Only one population was polymorphic RESULTS with two alleles ce-Gpdh-2(50) and a-Gpdh-2(100). In all other populations a constant three banded Mostof the enzymic systems (tables 1 and 2) have phenotype was observed in the skeletal muscle previously been analysed in other populations extracts examined. (Allendorf et a!., 1977; Taggart et a!., 1981; Guyomard and Krieg, 1983). Our description and CK. Utter et a!. (1979) reported a common three genetic interpretation were in agreement with the banded phenotype for brown trout muscle extracts. 300 Y. KARAKOUSIS AND C. TRIANTAPHYLLIDS These isozymes have been identified as the prod- PGM, 6-PGDH and SOD. A single invariant band ucts of two loci, Ck-1 and Ck-2. Polymorphism has been observed for each of these enzymes. They was reported at the Ck- 1 locus.
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