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Morphological and Genetic Polymorphism in theCoregonus albula Population of Lake Nirza in LatviaJeļena Oreha a , Natalja Škute a & Artūrs Škute a

a Institute of Ecology , Daugavpils University , 13 Vienibas Str., LV-5401 , Daugavpils ,LatviaPublished online: 23 Jul 2012.

To cite this article: Jeļena Oreha , Natalja Škute & Artūrs Škute (2008) Morphological and Genetic Polymorphismin the Coregonus albula Population of Lake Nirza in Latvia, Acta Zoologica Lituanica, 18:4, 248-255, DOI: 10.2478/v10043-008-0031-y

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Acta Zoologica Lituanica, 2008, Volumen 18, Numerus 4

ISSN 1648-6919

DOI: 10.2478/v10043-008-0031-y

Morphological and genetic polyMorphisM in the Coregonus albula population of lake nirza in latvia

Jeļena OREHA, Natalja ŠKUTE, Artūrs ŠKUTE

Institute of Ecology, Daugavpils University, 13 Vienibas Str., LV-5401 Daugavpils, Latvia. E-mail: Natalja.Skute@du.lv

Abstract. A great number of intra-specific forms of local populations of vendace (Coregonus albula) are presumed to be a result of hybridisation between different incipient forms. Morphological and genetic analysis for the study of vendace population of Lake Nirza in Latvia was used. Body length, weight and age in different male and female groups were used for morphological analysis. Genetic polymorphism and genetic structure of the vendace population of Lake Nirza have been evaluated by electrophoresis based on the analysis of isoenzyme systems. Four isoenzyme systems (malic enzyme (Me), esterases (Est), peroxide dismutase (Sod), malate dehydrogenase (Mdh)) and non-specific protein were analysed. Sixteen polymorphic loci were selected for genotype analysis. The genetic analysis of the vendace popu-lation from Lake Nirza showed that homozygotes dominate over heterozygotes. However, distribution of genotypes among different isoenzyme systems is different. The present study provides the first report on the application of isoenzyme markers for genetic investigations of Coregonus albula populations in Latvian lakes.Key words: Coregonus albula, isoenzyme system, homozygote, heterozygote, genotype, population, morphological parameter

species. It has been argued that competition could be the diversifying force due to which character release can lead to differentiation in the absence of other closely related species (Næsje et al. 2004).Some lakes of Europe are inhabited by sympatric forms of vendace, which spawn at different time of the year (spring, autumn, winter) (Schulz & Freyhof 2003). Hence, separate species of vendace should be distin-guished in Europe. It is supposed that the spring-and-winter-spawning vendace are of polyphyletic origin.Genetic differentiation among sympatric populations has been documented in many salmonid species, for example, the lake whitefish (Coregonus clupeaformis (Mitchill)) (Bernatchez 2004); in the whitefish (Core-gonus lavaretus L.), several sympatric forms are often recognised, and management and exploitation is often based on the characterisation of forms based on the number of gillrakers (Sandlund et al. 2002).In Europe, an isoenzyme analysis has been used in the investigation of vendace populations for 20 years already. There is no information on the isoenzyme sys-tems in vendace of Latvian lakes. The purpose of this study is to determine the enzyme systems and compare genotypes of vendace representing the population of Lake Nirza situated in Latvia.

Study area and sample collectionLake Nirza is situated in the Nirza rural municipality of

IntroductIon

Vendace (Coregonus albula) is a widespread fish in the waters of the Holarctic. North salmonid fishes are known to occur as sympatric forms, differing in their morphology and life history characters. At least a part of this diversity has evolved after the last glaciations (Hansen et al. 1999). Due to their short evolutionary history, these sympatric forms represent a potential to study speciation in its early stages (Bernatchez et al. 1999). Usually sympatric forms occur as ‘species pairs’, but in some cases four to six sympatric forms can be distinguished (Schulz & Freyhof 2003).Some authors classify all Eurasian vendace as one spe-cies (Altukhov 2004; Perelygyn 1989; Pokrovskij 1967). There is a possibility that European and Siberian vendace represent two races of the same widespread species.Three evolutionary hypotheses have been proposed to explain this diversity. Firstly, the forms may simply represent phenotypic plasticity within a single spawn-ing population. Phenotypic differentiation may arise in response to variable feeding contexts during ontogeny (Hindar & Jonsson 1993; Sendek 2004). Secondly, the forms may also have diverged in allopatry, subsequently invading the same lake. After double or multiple in-vasions, the forms have been able to maintain their differences. The third scenario is that the forms have developed in sympatry, as has been documented in other

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249Polymorphism of Coregonus albula

the Ludza region of Latvia. The lake area is 552 ha with the maximum depth of 21 meters (the average depth is 8.2 meters). This is a flowing lake. It has one stream and some ditches flowing in, and one stream flowing out.63 vendace individuals from Lake Nirza were investi-gated with regard to the isoenzyme systems and mor-phological parameters. The collecting of the material was carried out in 2004.

MaterIal and Methods

Isoenzyme analysis Samples of muscle and liver tissue were taken from fish placed in individual tubes and frozen until analysis. The liver tissue homogenate of vendace was used for electrophoretic investigations of the isoenzyme sys-tems. The defrosted liver tissue was homogenised in a glass homogeniser, using the buffer 0.2 M Tris-HCl, pH 8.0; 0.01 mg/ml Triton X – 100; 4 mg/ml MgCl2; 0.2 mg/ ml NADP. The homogenisation ratio was 1:2 (tissue: buffer), and 10–20 μl of homogenate was used for electrophoretic analysis.To prevent enzyme degradation, the prepared homoge-nates were kept at a temperature of -20°C (Glazko & Sozinov 1993).Polyacrylamide gel (PAAG) was used as a supporting medium. The vertical gel electrophoresis apparatus was used for isoenzyme electrophoresis in a vertical PAAG block. Gel plates (115 × 15 × 3 mm) were prepared ac-cording to the modified Davis and Raymond’s protocols (Paulauskas & Tubelytė-Kirdienė 2002). To separate malic enzyme (Me), malate dehydrogenase (Mdh) and peroxide dismutase (Sod), the one-layer 5% PAAG was used. The two-layer PAAG (5% and 7.5%) was used for the separation of esterases (Est) and non-specific protein (Nsp) systems. A plate placed into gel before hardening formed cavities in the medium. The cavities were filled with the investigated homogenate before electrophoresis. The polymerisation of gel lasted 15–20 minutes. Electrode vessels were filled with the operating electrode buffer. 40% sacharose solution was added to the homogenate to make samples more viscous and, in order to observe their movement in gel, bromphenol blue was added to the homogenate. For isoenzyme systems Tris-EDTA H3BO3 buffer was used, pH ~ 8.4 (Paulauskas & Tubelytė-Kirdienė 2002).Before electrophoresis, operating buffers were pre-pared from these solutions by adding distilled water 1:10 (buffer: water). Electrophoresis was performed in three stages: pre-electrophoresis (voltage 160 V, duration 30 min); withdrawal of samples from cavities (80 V, 40 mA, 20 min); and an operating mode (250 V,

110–140 mA, 1–3 hours). A cooling system was used to maintain the temperature of 3–5°C in the course of electrophoresis, which lasted for 2–3 hours.After electrophoresis, gels were incubated in stain at 37°C. Dyeing mixtures for the separation of enzyme activity zones were prepared according to the standard protocols (Harris & Hopkinson 1976) with some modi-fications (Paulauskas & Tubelytė-Kirdienė 2002).Electrophoresis of five systems (such as malic enzyme, esterases, non-specific protein, malate dehydrogenase and peroxide dismutase) was performed.The enzyme nomenclature follows the International U nion of Biochemistry Nomenclature Committee (IUBNC) Regulation (Enzyme Nomenclature 1984).When analysing gels, the distribution of protein frac-tions in phoregrams was assessed on the basis of relative electrophoretic mobility. Enzyme activity zones were numbered with respect to their position between the cathode and anode. The zone nearest to the anode was marked as number 1, others being numbered respecti-vely in the ascending order. Protein fractions in the zones were identified as follows: E (fast), D (less fast), C (in-termediate), B (slow moving), A (more slow moving). The genetic control of the corresponding isoenzymes (separate loci and corresponding alleles) was inter-preted in accordance with literature data (Skúlason & Smith 1995) and standard protocols (Harris & Hopkin-son 1976; Pau lauskas & Tubelytė-Kirdienė 2002).The computer program ‘BIOSYS – 2’ was applied for the analysis of isoenzyme systems and frequencies of genes and genotypes (Swofford & Selander 1997).

Morphological analysisThe collected ichthyological material (freshly caught vendace individuals) was treated for morphological analysis in accordance with the methodology described by Pravdin (1966) and widely used nowadays (Peresko-kov & Rogozin 2001; Gurichev & Belousov 2005; La-jus 2001; Lajus et al. 2003; Kaupinis & Bukelskis 2004). Body length (from the snout end to the scales layer edge at the base of the caudal fin), weight and age were used for morphological analysis. In order to determine reli-able distinctions in the morphological parameters and heterozygosity level of males and females aged 3+, 4+, the single factor analysis (ANOVA) was carried out.On the basis of morphometric data, fatness was calcu-lated for each individual separately, and the average fatness for each population was worked out. Fish fatness was determined with the help of the Fulton coefficient Q = w × 100/L3 where Q is fatness coefficient; w fish weight in grams, and L fish length from the snout end to the end of scales layer at the caudal fin base (Pravdin 1966).

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250Oreha J., Škute N., Škute A.

results and dIscussIon

Analysis of genotype frequencies and alleles in the sys-tems uncovers important processes in the population de-velopment. The major problem of genetic monitoring is a long-time keeping track of the state of gene pools of a population, estimation and prediction of their dynamics (changes) in time and space, determination of the limits of allowable changes. We regard it necessary to conduct padding researches of the Lake Nirza population in order to evaluate the actual level of genetic variability and reveal possible tendencies of the loss of alleles.The following four isoenzyme systems and non-specific protein were used for the genetic analysis of the popu-lation:1. Malate dehydrogenase (MDH, Mdh, E. C. 1.1.1.37)NAD-dependent MDH is a dimer. Electrophoresis showed two polymorphic zones, which are genetically controlled by loci Mdh-2 and Mdh-3. However, only one polymorphic zone was found in this isoenzyme system of vendace from Lithuanian lakes (Kaupinis et al. 2004).2. Peroxide dismutase (SOD, Sod, E. C. 1.15.1.1)SOD enzymes show two polymorphic zones on the phoregram. Sod-1 and Sod-2 were analogically detected in this isoenzyme system of vendace from the lakes of Lithuania (Kaupinis et al. 2004). However, only one polymorphic zone was found in this isoenzyme system of vendace populations from Finland and Russia (Vuo-rinen 1984; Sendek 2002).3. Malic enzyme (ME, Me, E. C. 1.1.1.40)ME is a tetramer, NADP-dependent malate dehydro-genase which catalysis the conversion of L-malate into piruvate. The analysis of vendace phoregrams from Latvian lakes as well as from Lithuanian lakes (Kaupinis et al. 2004) revealed two polymorphic zones of this enzyme, which are genetically controlled by loci Me-2 and Me-3. There were two zones in the Finnish vendace population, too. The slower zone was expressed as a single zone, but the faster zone was polymorphic (Vuorinen 1984). In Russian vendace populations only one polymorphic zone was found (Sendek 2002).4. Esterases (EST, Est, E. C. 3.1.1.-)Esterases are enzymes belonging to hydrolases. The analysis of the vendace phoregram from Latvian lakes revealed three polymorphic zones of this enzyme, Est-3, Est-4, and Est-5. In analogical investigation of esterases of Lithuanian vendace, five polymorphic zones of Est were found.Non-specific protein system (NSP, Nsp)Nine zones emerged in that system. Seven zones were analysed. Locus Nsp-1 is monomorphic. Other six loci are polymorphic.

The number of polymorphic loci may be very different across the population. The average parameters of C. al-bula population in Lake Nirza show that the population has a high level of polymorphism (94.12%) and an optimum level of heterozygosity, which differs from the expected data (according to Hardy-Weinberg) only insignificantly: the direct count is 0.464 and the expected count (according to Hardy-Weinberg) is 0.479.The average level of isoenzyme polymorphism, which is appropriate for fish population, is approximately 40% (Kirpichnikov 1987). It is possible that high level of polymorphism in our investigation is caused by a low number of investigated isoenzyme loci/systems. The greatest number of polymorphic loci was established in esterases, but the mean number of alleles per locus was 2.5.The tendency of the presence of deviation from Hardy-Weinberg equilibrium was obtained when analysing heterozygosity of separate loci.We can see that the level of heterozygosity varies in different loci (Fig. 1). The given diagram also reflects the level of expected heterozygosity by Hardy-Weinberg equilibrium. As ideal populations do not exist in nature, some deviations from the expected heterozygosity level are considered normal for a stable natural population. We noticed such deviation from the expected level of heterozygosity in all investigated loci, but in some loci the significance level of this difference was very high (Fig. 1). Furthermore, deficiency of heterozygosity was observed in five loci and excess of heterozygosity in three loci.And on the contrary, we noticed quite a high level of heterozygosity in locus Est-3. For finding out the nature of such a high level of heterozygosity in locus Est-3, we carried out an analysis of allele frequencies in the given locus (Fig. 2). The diagram shows a significant prevalence of allele A in comparison with other alleles in locus Est-3.Distribution of alleles in locus Est-5 is in similar fre-quencies (Fig. 3). Figure 3 reflects the character of allele A prevalence in locus Est-3 and a high level of heterozygosity in this locus against the background of the excess of genotypes with allele A (as a homozygote and all types of heterozygotes). For comparison, on the same diagram we see a more uniform distribution of al-leles in locus Est-5. Having these data, we can assume that the presence of allele A in some individuals has an advantage at selection, or during duplication, or as a factor of viability. However, the prevalence of allele A in locus Est-3 can be caused by genetic drift, too.In particular, it is worth noticing that a possibility of migrants from other lakes is limited.The surplus of heterozygosity could mean their ad-

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251Polymorphism of Coregonus albula

vantage (monogenetic heterosis). This phenomenon can be observed at assortative mating during selection against one of alleles or for the benefit of one of alleles. Assortative mating in fishes, though, is seldom met (Kirpichnikov 1987).The surplus of heterozygotes can be shown as a result of selection against homozygotes, but in our case the selection with an obvious preference of A-allele in the genotype is observed, however, the prevalence of

A- allele might be a result of genetic drift, too. However, the lowered frequency of heterozygotes is observed in loci Sod-2, Mdh-3, Me-2, Me-3 (Fig. 1). The analysis of allele frequency in loci Sod-2 and Mdh-3 shows a clear prevalence of one of the alleles (A-allele in locus Sod-2 and B-allele in locus Mdh-3) (Fig. 3). It means that already the analysis of allele frequencies gives a clear performance of the reasons for the lower frequ-ency of heterozygotes in these loci. These conclusions are also confirmed by the analysis of genotypes in loci Sod-2 and Mdh-3.In locus Sod-2, we noticed an excess of homozygote AA and a low rate of heterozygotes with A-allele in the geno-types in this locus. But in three allelic loci, two alleles, such as B and C, are not practically met. We consider that the prevalence of allele A in locus Sod-2 might be a result of genetic drift, too. The analysis of locus Mdh-3 shows similar results. In two allelic loci, the excess of homozy-gotes BB is expressed, the distribution of heterozygotes is not as rare as in locus Sod-2, but despite that the lack of heterozygotes is appreciable enough (Fig. 4). In this locus, the tendency to lose alleles is similarly shown. The tendency to lose alleles might be caused by a low effective number of individuals in the population or a habit of some age groups in spawning sites when different age groups spawn in a different time range and such behaviour might be ascribed as kind of assortative mating.We consider that there is a drift of genes in loci Est-3, Sod-2, Mdh-3 in spite of the fact that the influence of genetic drift in the loci varies. Any appreciable anthro-pogenous effects infringe the population structure, too, e.g., fast change ratio of miscellaneous groups of genes in a gene pool.In small populations, there is a high probability that

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2.76 9.67** 17.79*** 20.22*** 5.28* 10.83*** 9.86** 1.09 8.94**

Figure 1. Mean heterozygosity per locus and mean heterozygosity in some investigated loci in the Lake Nirza population (Hardy-Weinberg equilibrium), significance level of differen ces between observed and expected heterozygosity levels (* – p < 0.05; ** – p < 0.01; *** – p < 0.001).

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Figure 2. Frequency of genotypes in loci Est-3 and Est-5.

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Figure 3. Frequency of alleles in loci Est-3, Est-5, Sod-1, Sod-2, Mdh-2, Mdh-3, Me-2, Me-3.

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some genotypes will not take part in the reproduction process at all, and in the course of time other alleles will be recorded in the population.Analysis of loci Me-2 and Me-3 showed an interesting result. The analysis of alleles (Fig. 3) shows their uni-form distribution in two allelic loci.But the analysis of genotypes shows that a low frequency of heterozygosity in the mentioned loci is caused by the excess of homozygotes and an insufficient frequency of heterozygotes (Fig. 4). Thus, individuals of the popula-tion in the given locus were divided into two groups ac-cording to homozygotes, and the quantity of individuals with an intermediate genotype was essentially lower than the expected level of heterozygosity (by Hardy-Weinberg equilibrium).Both the loss of heterozygosity and its excessive in-crease are equally adverse for the normal functioning of a population (Vuorinen 1984).To make more concrete conclusions, we find it necessary to confirm (or to deny) by additional investigation of this population the tendency to lose alleles (drift of genes) in loci Mdh-3, Sod-2 and Est-3, and the division of the population into homozygote individuals (formation of races) in loci Me-2 and Me-3.Overall, the level of heterozygosity in all investigated

isoenzyme systems is high (in other researchers’ pub-lications it was reported to be lower (Sendek 2002)); however, there is a little deficiency of heterozygosity. High level of polymorphism (94.12%) in investigated populations can be caused by a low number of investi-gated isoenzyme systems.Morphological distinctions in various populations of vendace are mainly determined by ecological reasons, and in most cases these properties are a result of adapta-tion to living conditions.The sample consists of the individuals of two age groups (3+; 4+). Assessment of the condition of individual fish is an important component of studies of various fish populations. Fish fatness grows in the conditions of good forage reserve. So, fatness coefficients of the vendace from the Nirza population were analysed (Table 1).

Table 1. Fatness of vendace according to Fulton.

AgeMales Females

n Mean Min–max n Mean Min–max3+ 13 1.26 1.16–1.41 13 1.29 1.17–1.454+ 8 1.24 1.14–1.36 28 1.25 1.13–1.37

Fish fatness is closely related to fish age (3+ and 4+) and sex. Fulton’s coefficient for vendace is big enough in the investigated lake, which means that forage reserves in this lake are quite sufficient for vendace. However, Fulton’s coefficient of condition for vendace from some Polish and Russian lakes was lower (from 0.76 to 1.18) (Czerniejewski & Filipiak 2002; Czerniejew-ski & Czerniawski 2004; Czerniejewski et al. 2004; Romanov 2000).The comparison of biological parameters of vendace re-vealed that vendace from Lake Nirza are of ‘small’ form (Table 2), some authors note that two vendace forms can exist in one lake at the same time (‘big’ – ripus and ‘small’ – vendace) (Perelygin 1987; Romanov 2000).Statistics of body weight and length of Lake Nirza for vendace is shown in Table 2.Body length and weight are a little bigger for females than for males (with 95% probability).The length-weight relationship usually assumes the form of a power function. The function exponent de-pends on fish shape, i.e. it does not reach 3 in slender-bodied fish, while higher values are produced by more ‘stocky’ fish (Wootton 1996). In vendace, the parameter oscillates around 3. However, in some lakes with poor crustacean zooplankton resources and environmental conditions unfavourable for the vendace, the exponent does not exceed 2.5 (Czerniejewski & Filipiak 2002; Czerniejewski & Czerniawski 2004; Czerniejewski et al. 2004; Romanov 2000).The relation between the individual length and weight

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253Polymorphism of Coregonus albula

of vendace in the Nirza population is shown on Fig. 6. The value of the exponent n exceeds 2.7. However, in Polish lakes this value was around 2.2–2.5. So, we can assume that crustacean zooplankton resources and environmental conditions in Lake Nirza are favourable for the vendace.

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Figure 6. Relation between vendace individual’s length and weight from Lake Nirza.

The analysis of literature data shows that the depend-ence of heterozygosity frequency on morphometric and physiological parameters of individuals can be shown in fishes. The frequency of heterozygosity is different between males and females (with 95% probability). Figure 5 shows that heterozygosity is a little bigger in males. Similar results were described by other authors (Altukhov 1989).Some authors admit that there is regularity between the frequency of heterozygosity of male individuals of Oncorhynchus nerka in locus Mdh and the size of their body. Heterozygosity of individuals frequently correlates with their morphometrics and ecological parameters (Altukhov 2004). We have conducted an analysis of similar data in the loci which were studied, but such regularity has not been detected.So, the average parameters of C. albula population in Lake Nirza show that the population has a high level of polymorphism (94.12%). It is possible that high level of polymorphism in our investigation is caused of a low number of investigated isoenzyme loci/systems.The level of heterozygosity varies in different loci.

A deficiency of heterozygosity was observed in five loci and excess of heterozygosity in three loci.We can assume that the difference between observed heterozygosity and expected heterozygosity level in investigated loci can be caused by genetic drift. In particular, it is worth to notice that a possibility of migrants from other lakes is limited. Overall, the level of heterozygosity in all investigated isoenzyme systems is high; however, there is a little deficiency of heterozygosity.The value of exponent n in the relation between the individual length and weight of vendace exceeds 2.7. Fulton’s coefficient for vendace is approximately 1.26 in the investigated lake. So, we can assume that crustacean zooplankton resources and environmental conditions in Lake Nirza are favourable for the vendace and this lake is an optimal habitat for the vendace.

references

Altukhov, J. P. 1989. Genetic processes in populations. Mos-cow: Nauka. [Алтухов, Ю. П. 1989. Генетические процессы в популяциях. Москва: Наука.]

Altukhov, J. P. 2004. Dynamics of population genofonds under the influence of anthropogenic factors. Moscow: Nauka. [Алтухов, Ю. П. 2004. Динамика популяцион-ных генофондов при антропогенных воздействиях. Москва: Наука.]

Bernatchez, L. 2004. Ecological theory of adaptive radia-tion. An empirical assessment from Coregonine fishes (Salmoniformes). In: A. P. Hendry and S. C. Stearns (eds) Evolution Illuminated. Salmon and their Relatives, pp. 175–207. Oxford: Oxford University Press.

Bernatchez, L., Chouinard, A. and Lu, G. 1999. Integrating molecular genetics and ecology in studies of adaptive radiation: whitefish, Coregonus sp. as a case study. Bio-logical Journal of the Linnean Society 68: 173–194.

Czerniejewski, P. and Filipiak, J. 2002. Biological and mor phological characteristics of vendace, Coregonus albula L. from lakes Drawsko and Pełcz. Acta Ichthyo-logica et Piscatoria 32 (1): 53–69.

Table 2. Males and females average length and weight.

AgeLength (mm) Weight (g)

Mean ± SE Min–max Mean ± SE Min–maxFemales 3+ 176.9 ± 2.1 162.0–186.0 71.59 ± 2.78 49.93–86.17

4+ 183.1 ± 1.5 168.0–204.0 77.08 ± 1.76 63.67–104.56Males 3+ 171.9 ± 2.1 162.0–188.0 64.08 ± 2.32 50.76–81.36

4+ 174.1 ± 1.5 168.0–180.0 65.31 ± 1.94 54.01–71.24Total 3+ 174.4 ± 1.5 162.0–188.0 67.84 ± 1.93 49.93–86.17

4+ 181.1 ± 1.3 168.0–204.0 74.46 ± 1.65 54.01–104.56

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Czerniejewski, P. and Czerniawski, R. 2004. Age, growth and condition of vendace Coregonus albula (L.) from lakes Morzyczko and Pełcz (NW Poland). Zoologica Poloniae 49 (1–4): 159–170.

Czerniejewski, P., Filipiak, J., Poleszczuk, G. and Wawr-zyniak, W. 2004. Selected biological characteristics of the catchavailable part of the population of vendace, Coregonus albula (L.) from lake Miedwie, Poland. Acta Ichthyologica et Piscatoria 34 (2): 219–233.

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MorfologInIs Ir genetInIs polIMorfIzMas nIr­zos ežero (Latvija) Coregonus albula popu lIa­cijoje

J. Oreha, N. Škute, A. Škute

santrauka

Manoma, kad didelį vietinių seliavų (Coregonus albula) populiacijų vidurūšinių formų skaičių lemia skirtingų pradinių formų hibridizacija. Nirzos ežero (Latvija) selia-vų populiacijos tyrimui buvo naudojama morfologinė ir genetinė analizė. Morfologinei analizei buvo naudojami įvairių patinų ir patelių grupių kūno ilgio, svorio ir amžiaus parametrai. Nirzos ežero seliavų populiacijos genetinis polimorfizmas ir genetinė struktūra buvo įvertinti elek-troforezės metodu, remiantis izoenzimų sistemų analize. Išanalizuotos keturios izoenzimų grupės (malik enzimai (Me), esterazės (Est), peroksid dismutazės (Sod), malat dehydrogenazės (Mdh)) ir nespecifinis proteinas. Ge-notipinei analizei atrinkta šešiolika polimorfinių lokusų. Nirzos ežero seliavų populiacijos genetinė analizė parodė, kad homozigotai dominuoja heterozigotų atžvilgiu. Tačiau genotipų pasiskirstymas atskirose izoenzimų sistemose skiriasi. Pateikiami pirmieji duomenys apie izoenzimų markerių taikymą genetiniuose Coregonus albula popu-liacijų tyrimuose Latvijos ežeruose.

Received: 15 September 2008Accepted: 11 November 2008

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