A total of 56 perches attributed to three different populations of the Baltic Sea, the Curonian Lagoon and the Gulf of Riga were investigated. The amplified mtDNA fragment consisting of 378 bases includes the trnP gene and the 5‘-gale fragment of the control region consisting of 260 bases. Ten variable positions were identified and 15 haplotypes of the European perch of mitochondrial DNA (mtDNA) D-loop were established. Three new haplotypes C4, F8 and G2 characteristic of the perch caught in Lithuanian territorial waters and two haplotypes L1 and L2 characteristic of the perch caught in the Gulf of Riga were determined.
Table 1. Haplotypes of mtDNR trnP gene and control region fragment determined in
the European perch Perca fluviatilis caught in the territorial waters of Lithuania and Latvia (data are compared with the mtDNA sequence PFY14724, haplotype A presented in the Gene Bank)Haplotypes
C4, G2, F8, L1 ir L2 – newly identified haplotypes N – the number of individual studied
T, A and G – substitution of nucleotides - – deletion of nucleotides
Ins* - insertion of ten nucleotides TTGCAAGCAC
The most frequent F haplotype was discovered in the samples of the perch caught both in the Curonian Lagoon and the Baltic Sea near Šventoji. It should be noted that this, as well as other haplotypes of group F (F1-F7) that are close to it by origin, were found most often after many other perch populations of Western Europe had been investigated. Refseth (1998) and Nesbø (1998b) determined a total of 35 haplotypes grouped into eight closely related groups by the nature of base substitutions. The scheme of frequency distribution of haplotypes of the perch presented in the publication based on the data of the said authors (Nesbø and others, 1999) several zones, segregated from the phylogenetic point of view, in which mtDNA variants attributed to different groups of haplotypes prevail, become clear.
As has already been mentioned, in all perch populations of Western Europe haplotypes of group F prevailed, with the exception of the river basins stretching in the territory of Norway where haplotypes (A, A1-A9) of group A prevailed in the perch caught there, as well as the coastal zone of the Adrian Sea and river basins of the Balkan countries in which haplotypes (M, M1) of group M, which are oldest in term of origin, prevailed. Whereas in samples of the perch caught in the continental part of the mainland, in the basins of the Nemunas, Dnieper Rivers, as well as in the remote Baikal Lake, the Angara River basin, haplotypes (C, C1-C3) of group C prevailed, which testify to the attribution of the perch in
the basins of the rivers stretching across this territory to a separate Euro-Asian phyllo-geographical region.
According to our data, haplotype A is found to be second by frequency in the populations of the Lithuanian perch, whereas haplotypes C and E are most often found in the populations of the perch of the Gulf of Riga (Fig. 1).
Haplotypes C1 and A7 were found in all the populations of the perch that we investigated. Five rarer haplotypes were found in the samples of the Lithuanian perch and four – in the samples of the Latvian perch, which characterises the scope of reproductive isolation among the populations of these perches. It should be noted that haplotype E was found with minimum frequency on the coastal zone of the Baltic Sea near Šventoji only in the samples of 2004 and 2005 and could be related to the anadromous behaviour, i.e., a periodical change in the environment when fish feeding in more saline waters of the coastal zone of the Baltic sea swim to spawn to the fresh waters of the river mouths. A repeated discovery of haplotype E in the samples of the perch caught in the coastal strip near Monciškės not far from the settlement of Šventoji in different years can be related to the fact that a larger part of the individuals keep near the spawning site located in the approaches of the mouth of the Šventoji River, and rarer variants of haplotypes (halpotype E), inherited with steady, though small frequency, reflect the fact that the population is in Hardy-Weinberg balance.
1) Gulf of Riga 2) Baltic Sea near Šventoji
3) Curonian Lagoon
Fig. 1. Percentage distribution of all investigated haplotypes of mitrochondrial DNA (mtDNR) D-loop in the populations of the perch in the Gulf of Riga (1), the Baltic Sea near Šventoji (2) and the Curonian Lagoon (3).
13%
Newly identified haplotypes C4 and F8 were found in the samples of the Baltic Sea, G2 – in the samples of the Curonian Lagoon are characteristic of the Lithuanian population of the perch and are related to the group of haplotypes E-F (Fig. 2). The presence of insertion of ten nucleotides characteristic of newly identified haplotypes L1 and L2 could be accounted for by a close phyllogenetic link of these haplotypes, however, on the basis of grouping of these samples in the phyllogenetic tree, according to the nature of single base substitutions haplotype L1 is closest to the group of haplotypes F1-F2, which is related to the group of haplotypes F fully dominating in Western Europe, and haplotype L2 is closest to the group of haplotypes A typical of the western and northern parts of Scandinavia (Norway).
Fig. 2. The Neighbour joining phylogenetic tree representing the origin of haplotypes (the first letter of abbreviation stands for the haplotype, BJ-samples from the Baltic Sea, KM – samples from the Curonian Lagoon, LAT – samples of the perch caught in the Gulf of Riga)
By the way, a combination of these two groups of haplotypes A and F is characteristic of the samples of the perch named the Matsalu population investigated in the geographical range of the Baltic Sea (territorial waters of Estonia) (Table 2), which geographically is one of the closest to the sample of the Latvian perch investigated by us, however, which differs greatly from the Emjajogi and Peipsi populations (the Gulf of Finland, territorial waters of Estonia) in which haplotypes of groups A and C found testify to the influence of the Northern and Eastern phylo-geographical regions on the formation of the perch population of the Gulf of Finland.
Table 2. Sample collection sites and distribution of haplotypes in the population
of the European perchIte
Water basin Haplotypes (N*)
1. Curonian Lagoon Lithuanian
territorial waters 15 Baltic Sea, mouth
of the Nemunas A(2), A7(1), C(1), C1(1), F(9), G2(1) 2. Baltic Sea Lithuanian
territorial waters 18 Baltic Sea near
Šventoji A(2), A2(1), C(1), C4(1), E(2) F(9), F1(1), F8(1) 3. Gulf of Riga Latvian
territorial waters 23 Baltic Sea, the Gulf of Rig near 6. L.Dubrovskoje** Inland waters of
Russia 10 The Dnieper basin C(10) 10. L.Vourasjarve Inland waters of
Norway 10 Karasjakka/Tana A(4), A2(6) 8. The Angara River** Inland waters of 10. The gulf of Bothnia** Territorial
waters of Sweden
20 Baltic Sea A7(2), C(14), F1(4)
11. Anadromous A** Territorial
waters of Sweden
20 Baltic Sea A(2), A7(4), C(8), F(3), F1(2), G(1) 12. Anadromous B** Territorial
waters of
* - the equal number of haplotypes is given in brackets
** - data about the investigated perch populations published in Molecular Ecology, 8, 1387-1404 (Nesbø et al. 1999)
The phylogenetic link between the Estonian and Latvian perch populations is confirmed by the fact that, as in the above-mentioned Matsalu population, haplotypes of A and F groups are most frequently found in the perch population of the Gulf of Riga, however, the Latvian perch population is noted for a rather high frequency of haplotypes C, which, as has been mentioned above, is related to the Euro-Asian phyllo-geographical
region extending in the East. This frequency of haplotypes of group C is three times lower in the populations of the Lithuanian perch in the samples of both the Curonian Lagoon and the coastal zone of the Baltic Sea, hence, the total spectrum of frequencies of haplotypes is closer to the Western European one, though the ‘eastern’ haplotypes of group C entirely dominate in the samples of the perch investigated in the basins of the Vilija and Nemunas Rivers in other than Lithuanian territory.
The smallest diversity of haplotypes (6) was discovered in the perch population of the Curonian Lagoon. The interesting thing is that these data coincide with the data of the investigations carried out into the perch populations of the Gulf of Bothnia in the territorial waters of Sweden, which are noted for a different migration behaviour, where it was determined that the samples of stable, that is, non-migrating perch populations in which 3 and 4 different haplotypes in each were found, respectively, were noted for the smallest diversity of haplotypes, whereas in two samples of the perch noted for an anadromous behaviour 6 different haplotypes in each were discovered (the size of samples fluctuated from 17 to 20 individuals). The data confirming this phenomenon were obtained during our investigation. When analysing the results obtained it was noticed that in brackish coastal waters of the Baltic Sea near Šventoji and in the Gulf of Riga where the perch noted for the anadromous behaviour usually live, a greater diversity of haplotypes, 8 and 9 respectively, was determined. The similarity in the distribution of the most frequently found haplotypes A and F in the samples investigated illustrates closeness of the populations of the Lithuanian perch, substantiating the assumption about possible seasonal migration of the perch between the Curonian Lagoon and the coastal zone of the Baltic Sea, where grown up individuals migrate for summer to the brackish Baltic Sea probably due to low water salinity beneficial effect on the perch growth, whereas in autumn they return to the freshwater Lagoon for winter and spawning the following spring (Ložys, 2004). In this case the smaller diversity of haplotypes reflecting the genetic diversity of the summer population of the perch of the Curonian Lagoon testifies to the assumption about seasonal migrations of part of the perch to the Baltic Sea.
Taking into consideration the results of this investigation and seeking to reveal such subtleties of the structure of populations as the tendency of some part of individuals to seasonally migrate to brackish waters, apart from using mtDNR genetic markers inherited through the maternal lineage, it is necessary to make use of micro-satellite markers, which are especially suitable to the analysis of the population structure (Brunner et al. 1998, Englbrecht et al. 2002), all the more so, that on the basis of the DNA investigations several specific micro-satellite primers have already been created for the species of the yellow perch, which is taxonomically close to the European perch (Leclerc et al., 2000), thus, sufficiently complicated and expensive overcoming of the stage of creating specific primers for the species raises the possibility for the investigators to make use of the available information in continuing investigations into the interspecific genetic diversity and population structure of the European perch.
Acknowledgements
We express our gratitude to the Mutual Funds for the Scientific Co-operation of the joint project of Taiwan, the Republics of Latvia and Lithuania “Application of genetic and micro-chemical markers as implements for diadromous and endangered commercial fish species populations management” for its financial assistance and the provided possibility to carry out this project.
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