Abstract
The production of hybrids of the 'pintado', Pseudoplatystoma corruscans (Spix & Agassiz, 1829) and 'cachara', Pseudoplatystoma reticulatum (Eigenmann & Eigenmann, 1889) in captivity has generated many concerns about the possibility of introduction of farmed hybrids into natural environments. In the last decade, hybrids between these species, known as 'pintachara' or 'cachapinta', were reported from different regions of the Upper Parana River basin. Prospection of these hybrids is important in order to orient conservation programs for the species involved. Knowledge of the presence of these hybrids will direct conservation strategies towards prevention and/or mitigation of the effects of cross breeding in natural populations of P. corruscans (the native species of the genus) and farmed hybrids. In this study, surveyed the larval population using molecular tools to detect the presence and assess the origin (natural hybridization or escapes from fish farms) of hybrids in natural water bodies. Nine microsatellite markers were used to detect signals of hybridization and introgression of P. reticulatum in larvae and adults of P. corruscans in Upper Parana River basin, between Itaipu Dam and Porto Primavera Dam. The specimens were sampled in the Upper Parana channel and in tributaries where hybrids had been detected in the past, during two reproductive seasons. Despite of that, no sign of hybridization and introgression was found in the 171 larvae and 75 adults sampled, suggesting that the specimens detected in previous studies had originated from escapes of aquaculture farms.
Highlights
The production of hybrids of the ‘pintado’, Pseudoplatystoma corruscans (Spix & Agassiz, 1829) and ‘cachara’, Pseudoplatystoma reticulatum (Eigenmann & Eigenmann, 1889) in captivity has generated many concerns about the possibility of introduction of farmed hybrids into natural environments
Hybrids are becoming more common in natural environments as a result of environmental degradation, introduction of foreign species, breeding of artificial interspecific hybrids for aquaculture, and shifts in the distribution of species associated with climate changes (Rhymer & Symberloff 1996, Allendorf et al 2001, Scribner et al 2001, Walther et al 2009)
Hybrids between P. corruscans and P. reticulatum are often reported from the Aquidauana River (Paraguay River basin), the Mogi-Guaçu River and the Ivinheima River sub-basin (Upper Paraná River basin) (Prado et al 2012a, Vaini et al 2014)
Summary
A total of 171 larvae of Pseudoplatystoma species, all identified as P. corruscans by morphological and DNA barcode methods (GenBank accession numbers KU220028-KU220190), were collected and genotyped for the 9 loci of microsatellites (Table 1). Adults of P. corruscans and P. reticulatum presented different values of genetic diversity (0.61 and 0.49, respectively – Table 2) and numbers of alleles (mean of 9.8 and 6.6, respectively). Adults of P. corruscans presented 88 alleles of which 69 are private. Tests of genetic differentiation support disjunction between the adults of species according to AMOVA, Fst, and Rst analyses. The analysis in Structure using the most probable number of groups is 2 (K = 2), according to the method of Evanno et al (2005), indicates that 99.7% of the genotype of adults of P. corruscans and 99.7% of the genotype of the P. reticulatum
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