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Arquivo Brasileiro de Medicina Veterinária e Zootecnia

Print version ISSN 0102-0935

Arq. Bras. Med. Vet. Zootec. vol.63 no.5 Belo Horizonte Oct. 2011

https://doi.org/10.1590/S0102-09352011000500034 

COMMUNICATION

 

Utilization of microsatellite markers to form families of "pejerrey" Odontesthes bonariensis in a genetic breeding program

 

Utilização de marcadores microssatélites para formação de famílias de "pejerrey" Odontesthes bonariensis em um programa de melhoramento genético

 

 

R.A. TavaresI; M.D. NunesI; D.B. AlmeidaI; J.C. SilvaI; B.S. VazI; C.G.A. MoreiraII; N.J.L. DionelloIII; S.R.N. PiedrasIII; H.L.M. MoreiraIII

IAluno de pós-graduação - UFPel - Pelotas, RS
IIAluno de pós-graduação - UFRGS - Porto Alegre, RS
IIIUniversidade Federal de Pelotas - UFPEL. Caixa Postal 453 96010-970 - Pelotas, RS

 

 


Keywords: fish, genetic variability, polymorphism


RESUMO

Foram identificadas a divergência e a variabilidade genética, por meio do polimorfismo de seis marcadores microssatélites, de duas populações de Odontesthes bonariensis, utilizadas em manejos de cultivo e com potencial para fornecimento de reprodutores para programas de melhoramento genético. Do total de seis loci, cinco demonstraram eficiência para análise genética nas duas populações de O. bonariensis. A diferenciação genética significante nas populações analisadas pode fornecer a base para futuros programas de melhoramentos genéticos, através da combinação de material das populações divergentes para o desenvolvimento de linhagens ou execução de um programa de seleção.

Palavras-chave: peixe, variabilidade genética, polimorfismo


 

 

The freshwater "pejerrey" (Odontesthes bonariensis Valenciennes, 1835) is a South American atherinid species with economic importance due to its high economic and nutritional value (Tsuzuki et al., 2007). This species originally colonized lakes and lagoons of Argentina and Rio Grande do Sul state (Brazil). Also, it has been successfully stocked in basins and dams in other areas of Brazil, Argentina an other South American countries, in view of its fishing values (Piedras et al., 2009). The high quality of this fish has created an incentive for its cultivation in regions distant from its native occurrence, like Japan and Italy (Baigún et al., 2009).

The starting point for the success of O. bonariensis is the consolidation of a genetic breeding program. Therefore, it is necessary to acquire breeders for the foundation of families; and the analysis of the founding genetic population is necessary to avoid or minimize effects of endogamy and loss of genetic variability (Tave, 1999). The maintenance of genetic variability in management practices in aquaculture is another factor to be considered, since this parameter confers adaptability and resistance, affecting growth and reproduction (Povh et al., 2009).

Molecular markers of the microsatellite types are being used to analysis of endogamy coefficients, population differentiation indexes and stock variability (Yue et al., 2009; Patel Das et al., 2010), showing efficacy and sensibility, giving support to acquaculture management programs. Genetic variability and divergence were identified, through polymorphism of six microsatellite markers, in two populations of O. bonariensis raised under cultivation practices and with a potential source of reproducers for genetic improvement.

Six clones of microsatellites of O. bonariensis were selected out of 23 clones maintained in the GenBank, and used for genetic analysis (Koshimizu et al, 2009). The primers were designed with the aid of PerlPrimer (Ferreira et al., 2009), in which the size of distinct fragments, of each locus, allowed the optimization of genotyping through the pairs combination of loci (Table 1).

The polymorphism of the microsatellite loci was evaluated from 80 samples of two populations of O. bonariensi:40 samples were collected at the Chascomús lake (Section of Buenos Aires, Argentina - 35º 35'S, 58º 02'W) and 40 samples at the Chasqueiro dam (Arroio Grande, Brazil - 32º10'S 53º00W). Chascomús is considered an oligohaline (<5gL-1) lake, with average temperature of 14ºC, average pH of 8.6 and high concentration of suspended materials (Capítulo and Freire, 1995; Berasain et al., 2005). In 1925, atherine fish ("pejerrey") incubators were installed in the city of Chascomús, Argentina, furnishing fertilized eggs and larvae for introduction in public and private waters. However, these programs were precarious with little support and were limited to embryo allotment or newly ecloded larvae and without supervision of water courses (Somoza et al., 2008). The Chasqueiro dam, built at the end of the 1970s, has a channel system approximately 50km long and physical infrastructure contributing for regional agricultural production (ALM, 1994). The region presents a sub-tropical climate, average water temperature varying from 11 to 27ºC, pH of 6.8 to 7.4 and alkalinity from 30 to 45 mgL-1 (ALM, 1994). The presence of "pejerrey" is a consequence from the introduction made with the purpose of increasing the local fishery production, since this species does not occur naturally in artificial reservoirs (Piedras, unpublished).

Genomic DNA was extracted from the caudal flipper (200-300 mg), stored in 95% ethanol and kept at -20ºC, using a modified salt protocol (Barrero et al., 2008). Amplifications of PCR were made in a final volume of 25µL, containing 20ng of genomic DNA, 5pmol of each locus specific primers, 100µM of dNTPs, 1X buffer of Taq reaction buffer and 0.25U of DNA Taq polymerase (Fermentas, Burlington, Canada). Amplification conditions were 5min at 94ºC, followed by 35 cycles of 45s at 94ºC, 45s according to the temperature of each locus and45s at 72ºC, with a final extension time of 8 min at 72ºC. The PCR products were verified in agarose gel at 1% stained with GelGreenTM (Biotium, Hayward, USA). All products were submitted to gel electrophoresis in Spreadex EL 600 Wide Mini S-2x25TM (Elchrom Scientific, Zurich, Switzerland). Gels were performed at 60V, for 4.5 min and afterwards elevated to 120V and 254mA for 360 min, with constant temperature of 20ºC. The alleles were obtained using the scale Marker M3TM (Elchrom Scientific, Zurich, Switzerland). The confirmation of allele sizes was done through selection of samples with different alleles, submitted to genotyping in automatic sequential ABI 377 Genetic Analyzer (Applied Biosystems, Foster City, USA) and analyzed with software Genotyper 2.0R (Applied Byosystems, Foster City, USA). The number of alleles of each locus, expected (He) and observed (Ho) heterozygosity, index of endogamy (Fis), Hardy-Weinberg equilibrium test of probability (HWE) and genetic differentiation (Fst) were obtained using the GENOPOP version 4.0 software (Rousset, 2008).

From the total of six loci, five demonstrated efficiency for genetic analysis in the two populations of O. bonariensis. Seventeen microsatellites were amplified by Koshimizu et al. (2009) among 25 individuals of "pejerrey" collected from natural water bodies in Argentina (Laguna Chascomús, n=9). The locus 0bo64TUF showed low amplification in the samples from Argentina and no amplification in Brazilian samples. The number of alleles varied from 4 to 15 and for all samples a total of 49 alleles was obtained, with positive values of 8.16 alleles per locus. Similar results were obtained by Koshimizu et al. (2009), who reported a number of alleles per locus in "pejerrey" ranging from 3 to 18 (mean of 10). Beheregeray and Sunnucks (2000) successfully amplified in species O. bonariensis and O. humensis twelve microsatellite loci developed for the species O. argentinensis. O. perugiae showed a number of alleles per locus ranging from 2 to 11. The index of endogamy with positive values suggests a deficit of heterozygote for all loci analyzed in the two populations. For the Brazilian population, only the locus 0bo77TUF appears to be in equilibrium of Hardy-Weinberg while in the Argentine population the loci 0bo19tuf, 0bo64TUF and 0bo79TUF are in Hardy-Weinberg; equilibrium (Table 2). Koshimizu et al. (2009) reported significant deviations from Hardy-Weinberg equilibrium detected in Obo19TUF. No significant linkage disequilibrium was evidenced between loci. The more accentuated deficit of heterozygote in the population of Chasqueiro (Brazil) can be explained by the foundation effect at the time of the animal introduction in the dam (Hartl and Clark, 1997). Probably, few spawns were used and there was no common source control. Because of a few founders, exists the possibility of accentuated break of genetic variability of the new populations, when compared to the original population. There also exists a high probability of endogamy occurrence.

The value of Fst between the two populations was 0.1303, which supports that the populations show moderate differentiation (P<0.05), caused by geographical separation, through the obstruction of gene flow (Liu et al., 2009).

The loss of the genetic variability decreases the capacity that a population has to adapt to different environmental conditions, being of extreme importance the selective reproduction. However, the genetic variation is difficult to estimate without polymorphic genetic markers. The high polymorphism, analyzed in five microsatellite loci, provided an efficient tool to the study of genetic variation of O. bonariensis.

The significant genetic differentiation in the analyzed populations can supply the basis for future programs of genetic improvements, through the combination of material from divergent populations to develop lines or accomplishment of a selection program. These markers will be used in the orientation of crossings to form a base-population for the genetic improvement that is in progress.

 

ACKNOWLEDGEMENTS

The authors are grateful to CNPq and to the Animal Science Graduate Program at the Universidade Federal de Pelotas for financial support. We also wish to thank the Laboratory of Ictiología y Acuicultura, Instituto de Investigaciones Biotecnológicas-Instituto Tecnológico de Chascomús (IIB-INTECH), Argentina, for providing the samples.

 

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Recebido em 20 de outubro de 2010
Aceito em 11 de agosto de 2011

 

 

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