Population genetic structuring in pacu (Piaractus mesopotamicus) across the Paraná-Paraguay basin: evidence from microsatellites

Abstract

The Paraná-Paraguay basin encompasses central western Brazil, northeastern Paraguay, eastern Bolivia and northern Argentina. The Pantanal is a flooded plain with marked dry and rainy seasons that, due to its soil characteristics and low declivity, has a great water holding capacity supporting abundant fish fauna. Piaractus mesopotamicus, or pacu, endemic of the Paraná-Paraguay basin, is a migratory species economically important in fisheries and ecologically as a potential seed disperser. In this paper we employ eight microsatellite loci to assess the population structure of 120 pacu sampled inside and outside the Pantanal of Mato Grosso. Our main objective was to test the null hypothesis of panmixia and to verify if there was a different structuring pattern between the Pantanal were there were no physical barriers to fish movement and the heavily impounded Paraná and Paranapanema rivers. All loci had moderate to high levels of polymorphism, the number of alleles varied from three to 18. The average observed heterozygosity varied from 0.068 to 0.911. After the Bonferroni correction three loci remained significant for deviations from Hardy-Weinberg, and for those the frequency of null alleles was estimated. F ST and R ST pairwise comparisons detected low divergence among sampling sites, and differentiation was significant only between Paranapanema and Cuiabá and Paranapanema and Taquari. No correlation between genetic distance and the natural logarithm of the geographic distance was detected. Results indicate that for conservation purposes and for restoration programs small genetic differences detected in the Cuiabá and Paranapanema rivers should be taken in consideration.A bacia Paraná-Paraguai compreende o oeste do Brasil, nordeste do Paraguai, leste da Bolívia e o norte da Argentina. O Pantanal do Mato Grosso é uma planície inundada com estações de chuva e seca bem definidas, as características do solo e baixa declividade favorecem a retenção de água proporcionando abrigo para uma abundante ictiofauna. O Piaractus mesopotamicus, ou pacu, endêmico da bacia do Paraná-Paraguai, é uma espécie migratória com importância econômica na pesca e ecológica como potencial dispersor de sementes. Neste estudo utilizamos oito loci de microssatélites para verificar a estrutura populacional de 120 pacus coletados dentro e fora do Pantanal do Mato Grosso. Nosso principal objetivo foi testar a hipótese de panmixia e verificar se haviam diferentes padrões de estruturação entre o Pantanal onde não existem barreiras físicas ao movimento migratório desses peixes em relação aos rios Paraná e Paranapanema com suas inúmeras barragens. Todos os loci apresentaram níveis de polimorfismo de moderado a alto e o número de alelos variou de três a 18. A heterozigosidade média observada variou de 0,068 a 0,911. Depois da correção usando o método de Bonferroni três loci permaneceram estatisticamente significantes para desvios de Hardy-Weinberg, para estes a frequência de alelos nulos foi calculada. Comparações par a par de F ST e R ST detectaram...

Microsatellite analysis of pacu broodstocks used in the stocking program of Paranapanema River, Brazil

“…However, it is not possible to verify this hypothesis, since there is no information to report differences between natural populations of these rivers. Calcagnotto and DeSalle (2009) analyzed the genetic structure of P. mesopotamicus natural populations sampled inside and outside the Pantanal of Mato Grosso state, and did not observe a positive correlation between the genetic differentiation and the natural logarithm of geographical distances and when the sampling sites were compared there were also no genetic differentiation among them. Furthermore, Lervolino et al (2010), using the D-loop control region of mtDNA sequence data to investigate genetic variability within and among populations of P. mesopotamicus in the different rivers in the Upper-Paraguay Basin, observed the absence of genetic differentiation, suggesting that the populations could be treated as a single genetic stock.…”

“…Therefore, monitoring the genetic diversity is of fundamental importance to the longterm success of any stocking program , and the microsatellite marker is the foremost method for achieving these purposes (Calcagnotto and DeSalle, 2009;Liu et al, 2005;Ortega-Villaizán Romo et al, 2006).…”

The roles of marginal lagoons in the maintenance of genetic diversity in the Brazilian migratory fishes Prochilodus argenteus and P. costatus

“…The R ST values under the SMM are expected to be greater than the F ST values under the IAM (Slatkin, 1995), although the inverse has been observed in some fish species (e.g., Pereira et al, 2009). Low indexes of F ST have been observed in other studies with characiforms, such as in Colossoma macropomum (Santos et al, 2007), Piaractus mesopotamicus (Calcagnotto & DeSalle, 2009;Iervolino et al, 2010), Prochilodus argenteus (Hatanaka et al, 2006;Sanches et al, 2012), Prochilodus costatus (Carvalho-Costa et al, 2008), Prochilodus lineatus (Revaldaves et al, 1997) and Salminus brasiliensis (Lopes et al, 2007).…”

“…Microsatellites are abundantly distributed along genomes and demonstrate high levels of allelic polymorphism (DeWoody & Avise, 2000). The molecular structure and genetic variability of microsatellites are extensively exploited in evolutionary studies of a wide variety of fish species (see Chistiakov et al, 2006), including some from Neotropical freshwater (Hrbek et al, 2007;Abreu et al, 2009;Calcagnotto & DeSalle, 2009;Matsumoto & Hilsdorf, 2009;Pereira et al, 2009;Sanches et al, 2012).…”

Genetic structuring of Salminus hilarii Valenciennes, 1850 (Teleostei: Characiformes) in the rio Paraná basin as revealed by microsatellite and mitochondrial DNA markers

“…Migratory fish species in large ecosystems, such as the Pantanal in the State of Mato Grosso, Brazil, may be under the influence of hydrological factors, such as seasonal flood pulses, that genetically homogenize populations, thereby bringing them close to panmixia (as in pacu Piaractus mesopotamicus, Calcagnotto & DeSalle, 2009;Iervorlino et al, 2010). In other cases, non-migratory species or those species making but short migrations tend to show more significant levels of population genetic structure (as in Tietê tetra Brycon insignis- Matsumoto & Hilsdorf (2009); and spotted sorubim catfish Pseudoplatystoma corruscans- Pereira et al (2009);Carvalho et al (2012)).…”