RESUMEN

Genetic and phylogenetic relationships among seven piranha species of the genera Serrasalmus and Pygocentrus from the Paraná-Paraguay, São Francisco and Tocantins River basins were evaluated in the present study by partial sequences of two mitochondrial genes, Cytochrome b and Cytochrome c Oxidase I. Phylogenetic analysis of Maximum-Likelihood and Bayesian inference were performed. Results indicated, in general, greater genetic similarity between the two species of Pygocentrus (P. nattereri and P. piraya), between Serrasalmus rhombeus and S. marginatus and between S. maculatus, S. brandtii and S. eigenmanni. Pygocentrus nattereri, S. rhombeus and S. maculatus showed high intraspecific genetic variability. These species have each one, at least two different mitochondrial lineages that, currently, occur in sympatry (S. rhombeus) or in allopatry (P. nattereri and S. maculatus). Species delimitation analysis and the high values of genetic distances observed between populations of S. rhombeus and of S. maculatus indicated that each species may corresponds to a complex of cryptic species. The non-monophyletic condition of S. rhombeus and S. maculatus reinforces the hypothesis. The geographic distribution and the genetic differentiation pattern observed for the piranha species analyzed herein are discussed regarding the geological and hydrological events that occurred in the hydrographic basins.(AU)

Relações genéticas e filogenéticas de sete espécies de piranhas dos gêneros Serrasalmus e Pygocentrus das bacias hidrográficas Paraná-Paraguai, São Francisco e Tocantins foram avaliadas com base em sequências parciais dos genes mitocondriais Citocromo b e Citocromo c Oxidase I. Foram realizadas análises filogenéticas de Máxima Verossimilhança e de inferência Bayesiana. Os resultados indicaram, em geral, maior similaridade genética entre as duas espécies de Pygocentrus (P. nattereri e P. piraya), entre Serrasalmus rhombeus e S. marginatus e entre S. maculatus, S. brandtii e S. eigenmanni. Pygocentrus nattereri, S. rhombeus e S. maculatus revelaram ter alta variabilidade genética intraespecífica. Essas espécies têm, cada uma, pelo menos duas linhagens mitocondriais que, atualmente, ocorrem em simpatria (S. rhombeus) ou alopatria (P. nattereri e S. maculatus). Análises de delimitação de espécies e os altos valores de distância genética observados entre as populações de S. rhombeus e de S. maculatus indicam que cada espécie pode, na verdade, corresponder a um complexo de espécies crípticas. A condição não-monofilética de S. rhombeus e S. maculatus reforça essa hipótese. A distribuição geográfica e o padrão de diferenciação genética observados para as espécies de piranhas analisadas são discutidos com relação aos eventos geológicos e hidrológicos que ocorreram nas bacias hidrográficas.(AU)

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RESUMEN

Abstract Genetic and phylogenetic relationships among seven piranha species of the genera Serrasalmus and Pygocentrus from the Paraná-Paraguay, São Francisco and Tocantins River basins were evaluated in the present study by partial sequences of two mitochondrial genes, Cytochrome b and Cytochrome c Oxidase I. Phylogenetic analysis of Maximum-Likelihood and Bayesian inference were performed. Results indicated, in general, greater genetic similarity between the two species of Pygocentrus (P. nattereri and P. piraya), between Serrasalmus rhombeus and S. marginatus and between S. maculatus, S. brandtii and S. eigenmanni. Pygocentrus nattereri, S. rhombeus and S. maculatus showed high intraspecific genetic variability. These species have each one, at least two different mitochondrial lineages that, currently, occur in sympatry (S. rhombeus) or in allopatry (P. nattereri and S. maculatus). Species delimitation analysis and the high values of genetic distances observed between populations of S. rhombeus and of S. maculatus indicated that each species may corresponds to a complex of cryptic species. The non-monophyletic condition of S. rhombeus and S. maculatus reinforces the hypothesis. The geographic distribution and the genetic differentiation pattern observed for the piranha species analyzed herein are discussed regarding the geological and hydrological events that occurred in the hydrographic basins.

Resumo Relações genéticas e filogenéticas de sete espécies de piranhas dos gêneros Serrasalmus e Pygocentrus das bacias hidrográficas Paraná-Paraguai, São Francisco e Tocantins foram avaliadas com base em sequências parciais dos genes mitocondriais Citocromo b e Citocromo c Oxidase I. Foram realizadas análises filogenéticas de Máxima Verossimilhança e de inferência Bayesiana. Os resultados indicaram, em geral, maior similaridade genética entre as duas espécies de Pygocentrus (P. nattereri e P. piraya), entre Serrasalmus rhombeus e S. marginatus e entre S. maculatus, S. brandtii e S. eigenmanni. Pygocentrus nattereri, S. rhombeus e S. maculatus revelaram ter alta variabilidade genética intraespecífica. Essas espécies têm, cada uma, pelo menos duas linhagens mitocondriais que, atualmente, ocorrem em simpatria (S. rhombeus) ou alopatria (P. nattereri e S. maculatus). Análises de delimitação de espécies e os altos valores de distância genética observados entre as populações de S. rhombeus e de S. maculatus indicam que cada espécie pode, na verdade, corresponder a um complexo de espécies crípticas. A condição não-monofilética de S. rhombeus e S. maculatus reforça essa hipótese. A distribuição geográfica e o padrão de diferenciação genética observados para as espécies de piranhas analisadas são discutidos com relação aos eventos geológicos e hidrológicos que ocorreram nas bacias hidrográficas.

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RESUMEN

Genetic and phylogenetic relationships among seven piranha species of the genera Serrasalmus and Pygocentrus from the Paraná-Paraguay, São Francisco and Tocantins River basins were evaluated in the present study by partial sequences of two mitochondrial genes, Cytochrome b and Cytochrome c Oxidase I. Phylogenetic analysis of Maximum-Likelihood and Bayesian inference were performed. Results indicated, in general, greater genetic similarity between the two species of Pygocentrus (P. nattereri and P. piraya), between Serrasalmus rhombeus and S. marginatus and between S. maculatus, S. brandtii and S. eigenmanni. Pygocentrus nattereri, S. rhombeus and S. maculatus showed high intraspecific genetic variability. These species have each one, at least two different mitochondrial lineages that, currently, occur in sympatry (S. rhombeus) or in allopatry (P. nattereri and S. maculatus). Species delimitation analysis and the high values of genetic distances observed between populations of S. rhombeus and of S. maculatus indicated that each species may corresponds to a complex of cryptic species. The non-monophyletic condition of S. rhombeus and S. maculatus reinforces the hypothesis. The geographic distribution and the genetic differentiation pattern observed for the piranha species analyzed herein are discussed regarding the geological and hydrological events that occurred in the hydrographic basins.

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RESUMEN

Abstract Genetic and phylogenetic relationships among seven piranha species of the genera Serrasalmus and Pygocentrus from the Paraná-Paraguay, São Francisco and Tocantins River basins were evaluated in the present study by partial sequences of two mitochondrial genes, Cytochrome b and Cytochrome c Oxidase I. Phylogenetic analysis of Maximum-Likelihood and Bayesian inference were performed. Results indicated, in general, greater genetic similarity between the two species of Pygocentrus (P. nattereri and P. piraya), between Serrasalmus rhombeus and S. marginatus and between S. maculatus, S. brandtii and S. eigenmanni. Pygocentrus nattereri, S. rhombeus and S. maculatus showed high intraspecific genetic variability. These species have each one, at least two different mitochondrial lineages that, currently, occur in sympatry (S. rhombeus) or in allopatry (P. nattereri and S. maculatus). Species delimitation analysis and the high values of genetic distances observed between populations of S. rhombeus and of S. maculatus indicated that each species may corresponds to a complex of cryptic species. The non-monophyletic condition of S. rhombeus and S. maculatus reinforces the hypothesis. The geographic distribution and the genetic differentiation pattern observed for the piranha species analyzed herein are discussed regarding the geological and hydrological events that occurred in the hydrographic basins.

Resumo Relações genéticas e filogenéticas de sete espécies de piranhas dos gêneros Serrasalmus e Pygocentrus das bacias hidrográficas Paraná-Paraguai, São Francisco e Tocantins foram avaliadas com base em sequências parciais dos genes mitocondriais Citocromo b e Citocromo c Oxidase I. Foram realizadas análises filogenéticas de Máxima Verossimilhança e de inferência Bayesiana. Os resultados indicaram, em geral, maior similaridade genética entre as duas espécies de Pygocentrus (P. nattereri e P. piraya), entre Serrasalmus rhombeus e S. marginatus e entre S. maculatus, S. brandtii e S. eigenmanni. Pygocentrus nattereri, S. rhombeus e S. maculatus revelaram ter alta variabilidade genética intraespecífica. Essas espécies têm, cada uma, pelo menos duas linhagens mitocondriais que, atualmente, ocorrem em simpatria (S. rhombeus) ou alopatria (P. nattereri e S. maculatus). Análises de delimitação de espécies e os altos valores de distância genética observados entre as populações de S. rhombeus e de S. maculatus indicam que cada espécie pode, na verdade, corresponder a um complexo de espécies crípticas. A condição não-monofilética de S. rhombeus e S. maculatus reforça essa hipótese. A distribuição geográfica e o padrão de diferenciação genética observados para as espécies de piranhas analisadas são discutidos com relação aos eventos geológicos e hidrológicos que ocorreram nas bacias hidrográficas.

RESUMEN

The genetic relationships of native or introduced Plagioscion squamosissimus in five Brazilian Neotropical basins were evaluated using the mitochondrial atpase6/8 genes. Results revealed that the population of the Tocantins River basin is more basal than the native populations of the Amazon and Parnaíba River basins. Moreover, the populations of P. squamosissimus that were introduced in the São Francisco and upper Paraná River basins originated from the population of the Parnaíba River.

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Abstract Genetic and phylogenetic relationships among seven piranha species of the genera Serrasalmus and Pygocentrus from the Paraná-Paraguay, São Francisco and Tocantins River basins were evaluated in the present study by partial sequences of two mitochondrial genes, Cytochrome b and Cytochrome c Oxidase I. Phylogenetic analysis of Maximum-Likelihood and Bayesian inference were performed. Results indicated, in general, greater genetic similarity between the two species of Pygocentrus (P. nattereri and P. piraya), between Serrasalmus rhombeus and S. marginatus and between S. maculatus, S. brandtii and S. eigenmanni. Pygocentrus nattereri, S. rhombeus and S. maculatus showed high intraspecific genetic variability. These species have each one, at least two different mitochondrial lineages that, currently, occur in sympatry (S. rhombeus) or in allopatry (P. nattereri and S. maculatus). Species delimitation analysis and the high values of genetic distances observed between populations of S. rhombeus and of S. maculatus indicated that each species may corresponds to a complex of cryptic species. The non-monophyletic condition of S. rhombeus and S. maculatus reinforces the hypothesis. The geographic distribution and the genetic differentiation pattern observed for the piranha species analyzed herein are discussed regarding the geological and hydrological events that occurred in the hydrographic basins.

Resumo Relações genéticas e filogenéticas de sete espécies de piranhas dos gêneros Serrasalmus e Pygocentrus das bacias hidrográficas Paraná-Paraguai, São Francisco e Tocantins foram avaliadas com base em sequências parciais dos genes mitocondriais Citocromo b e Citocromo c Oxidase I. Foram realizadas análises filogenéticas de Máxima Verossimilhança e de inferência Bayesiana. Os resultados indicaram, em geral, maior similaridade genética entre as duas espécies de Pygocentrus (P. nattereri e P. piraya), entre Serrasalmus rhombeus e S. marginatus e entre S. maculatus, S. brandtii e S. eigenmanni. Pygocentrus nattereri, S. rhombeus e S. maculatus revelaram ter alta variabilidade genética intraespecífica. Essas espécies têm, cada uma, pelo menos duas linhagens mitocondriais que, atualmente, ocorrem em simpatria (S. rhombeus) ou alopatria (P. nattereri e S. maculatus). Análises de delimitação de espécies e os altos valores de distância genética observados entre as populações de S. rhombeus e de S. maculatus indicam que cada espécie pode, na verdade, corresponder a um complexo de espécies crípticas. A condição não-monofilética de S. rhombeus e S. maculatus reforça essa hipótese. A distribuição geográfica e o padrão de diferenciação genética observados para as espécies de piranhas analisadas são discutidos com relação aos eventos geológicos e hidrológicos que ocorreram nas bacias hidrográficas.

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The pteridophytes Salvinia minima, S. herzogii, and S. auriculata are among the most abundant aquatic macrophytes in the upper Paraná River floodplain. Since some species have highly similar morphological features, it is very difficult to identify members of this genus to the species level. An indication of this difficulty is a set of poorly differentiated taxa comprising S. auriculata and S. herzogii known as the 'S. auriculata complex', which is found in the Paraná River together with other Salvinia species such as S. biloba and S. molesta. Some authors have reported the existence of inter-species hybrids. Despite the complex Salvinia taxonomy, few genetic studies have been performed on purported species within the genus to resolve this complexity. The present study was conducted to determine useful molecular sequences for the discrimination of Salvinia species of the upper Paraná River floodplain. Molecular data were compared with data of other species of the genus to clarify phylogenetic relationships, employing the nucleotide sequence trnL-trnF from the chloroplast DNA. The results revealed that Salvinia populations in the upper Paraná River floodplain belong to different species and indicated that species of the S. auriculata complex may be distinguished from one another after the division of the S. minima group, corroborating results by other researchers. Although the taxonomic position of S. oblongifolia was clarified, as high closeness between S. oblongifolia and the S. auriculata complex was reported, Salvinia kinship is still not thoroughly established and further investigations in morphology and molecular diversity are required.

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Urocleidoides ectoparasites are mainly found on fish of the neotropical regions. Although molecular research on monogeneans is available, no genetic data exist characterizing species in the Urocleidoides genus. Some DNA sequences have been efficacious in systematic studies and in the reconstruction of phylogenies of fish parasites. Relevant roles have been given to the sequence of the mitochondrial gene of cytochrome c oxidase I (COI). This study characterized COI sequences of the parasites Urocleidoides malabaricusi and U. cuiabai in trahira fish Hoplias aff. malabaricus of the flood plain of the Upper River Paraná, Brazil. The two species under analysis were distinguished by sequencing and analysing a 420-bp fragment of the COI gene, which suggested the existence of the cryptic species U. malabaricusi.

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The genetic relationships among 17 species of Astyanax from the Iguaçu River and adjacent river basins in Brazil were examined using nucleotide sequences of the mitochondrial cytochrome b gene (cytb). Congruent trees were constructed using neighbor-joining, maximum-likelihood, and Bayesian methods. The resulting clades suggest that at least three major groups share similar origins with the endemic species of the Iguaçu River. The results indicate that Astyanax is polyphyletic in this location, which suggests that Astyanax did not diversify from a single ancestral group that was isolated when the Iguaçu River basin formed. Astyanax bifasciatus shares an origin with some species of the altiparanae-bimaculatus complex, while A. minor originated from the same group as A. aff. paranae, A. fasciatus, and A. bockmanni. The third group includes A. dissimilis, Astyanax sp F, and A. serratus that are endemic species to the Iguaçu River basin. Geological and hydrological events that influenced the biogeographical patterns of these species are discussed.

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The genetic diversity of invasive and native populations of Plagioscion squamosissimus (Heckel, 1840) from the Paraná, Parnaiba and Araguaia-Tocantins river basins was assessed by using Random Amplified Polymorphic DNA (RAPD) markers. Genetic data confirmed the hypothesis of low genetic variability within and among P. squamosissimus populations introduced in the upper Paraná River basin, and indicated that they likely originated from a common ancestor. Moreover, the data demonstrated that, in agreement with available historical records, the P. squamosissimus populations established in the Paraná River basin were derived from a population native to the Parnaíba River basin. The genetic data presented here are of potential future application for the management of the invasive P. squamosissimus populations and for the preservation of the genetic legacy of native fish.

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The use of molecular markers has contributed to phylogeny and to the reconstruction of species' evolutionary history. Each region of the genome has different evolution rates, which may or may not identify phylogenetic signal at different levels. Therefore, it is important to assess new molecular markers that can be used for phylogenetic reconstruction. Regions that may be associated with species characteristics and are subject to selective pressure, such as opsin genes, which encode proteins related to the visual system and are widely expressed by Cichlidae family members, are interesting. Our aim was to identify a new nuclear molecular marker that could establish the phylogeny of Neotropical cichlids and is potentially correlated with the visual system. We used Bayesian inference and maximum likelihood analysis to support the use of the nuclear opsin LWS gene in the phylogeny of eight Neotropical cichlid species. Their use concatenated to the mitochondrial gene COI was also tested. The LWS gene fragment comprised the exon 2-4 region, including the introns. The LWS gene provided good support for both analyses up to the genus level, distinguishing the studied species, and when concatenated to the COI gene, there was a good support up to the species level. Another benefit of utilizing this region, is that some polymorphisms are associated with changes in spectral properties of the LWS opsin protein, which constitutes the visual pigment that absorbs red light. Thus, utilization of this gene as a molecular marker to study the phylogeny of Neotropical cichlids is promising.

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Astyanax altiparanae, belonging to the bimaculatus group, which includes species with similar colors and morphology, occurs in the upper Paraná River basin. As the use of mitochondrial DNA has made great strides in the diagnosis of species, in previous researches, two strains were detected in A. altiparanae with a high divergence in the D-loop region, provisionally called AltoPR and AltoPR-D. Evidence led to the hypothesis that the two strains did not belong to the same species. Phylogenetic hypotheses were produced by maximum-likelihood. Mean internal distances of the AltoPR and AltoPR-D groups were respectively 0.002 and 0.003, with the distance between them being 0.037. Sequences from GenBank of specimens collected from the Paraíba do Sul River basin were also divided into two groups, of which one may be identified as AltoPR. Since the other group provided an intermediate distance when compared to AltoPR-D, an in-depth investigation was required. The other species analyzed showed a greater distance and was revealed to be a monophyletic taxon. The results suggested that they are really two species and that neither corresponds to the other species used in the current study.

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The genetic divergence among invasive and native populations of Plagioscion squamosissimus from four Neotropical hydrographic basins was assessed using the hypervariable domain of the mitochondrial DNA (mtDNA) control region. Plagioscion squamosissimus is native to the neighbouring hydrographic basins of the Parnaíba and Amazon Rivers, and the latter includes the Araguaia-Tocantins drainage, but it is invasive in other basins due to introductions. The mtDNA nucleotide polymorphism supported the hypothesis that the Amazon and Parnaíba populations constitute the same species and are separated into two independent evolutionary lineages. Absence of nucleotide polymorphism was observed within and among P. squamosissimus populations invasive to the uppper and middle Paraná River basins. Nucleotide divergence was null or low comparing the Paraná invasive populations with the populations native to the Parnaíba River basin, whereas it was significantly high compared to Tocantins populations. These results ascertain that P. squamosissimus populations invasive to the upper Paraná River basin and to the middle Paraná River basin downstream of the Itaipu dam are derived from the Parnaíba River basin. The genetic data presented are potentially useful to assist further studies on P. squamosissimus taxonomic and geographic distribution, development of ecological guidelines for managing populations invasive to the upper Paraná River basin and for preservation of native fish diversity.

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The morphological discrimination between the species Astyanax altiparanae and A. asuncionensis of the upper Paraná River and Paraguay River basins, respectively, has always been difficult. Two D-loop haplogroups of A. altiparanae are known, one with the presence (AltoPR) or the absence (AltoPR-D) of a 32-bp block similar to that in A. asuncionensis. We examined these samples to characterize A. altiparanae and verify whether A. asuncionensis occurred in the upper Paraná River prior to the submergence of the Sete Quedas Falls when Itaipu reservoir was impounded. D-loop sequences were analyzed in A. altiparanae of the upper Paraná and Iguaçu Rivers and those of A. asuncionensis of the upper Paraguay River. The haplogroup AltoPR was found at all sites of the upper Paraná and Iguaçu Rivers, whereas AltoPR-D occurred in the Itaipu reservoir, floodplain and in the Tietê and Grande Rivers. Two haplogroups of A. asuncionensis were identified and both did not have the 32-bp block. However, AltoPR and AltoPR-D differed from one another in 5.1% of their bases and between 8.9 and 12.5% with regard to the haplogroups of the upper Paraguay basin. Further, AltoPR-D occurred in the Grande River upstream the Marimbondo Falls and other older reservoirs than Itaipu. The results reject the hypothesis of the establishment of A. asuncionensis and suggest that the haplogroup AltoPR-D existed in the upper Paraná River before the impounding of the Itaipu reservoir. Moreover, morphological similarity and high genetic variation within the altiparanae/asuncionensis group suggest the existence of a cryptic species complex.

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Fish species of the Zungaro genus (Siluriformes, Pimelodidae) are amongst the largest migratory fish in Latin America and have considerable economic importance for commercial fishing in Brazil. However, natural populations of this large catfish are experiencing a severe decline. There are significant taxonomical inconsistencies for this fish. Two geographically separated species of the fish were initially described, one endemic in the Amazon and another in the Paraná-Paraguay River basins. A taxonomic review had recently proposed that there is only one Zungaro species in Brazil, based on morphological data. We made a molecular study of Zungaro populations in an attempt to solve taxonomical inconsistencies and to analyze genetic diversity in natural populations of this genus. We analyzed two regions of the mitochondrial DNA (the control region and the ATPase 6 gene region) of individuals sampled from the Paraná-Paraguay River and Amazon River basins. Analyses based on p-distances and maximum likelihood phylogenetic models showed a genetic difference between populations corresponding to different species. Genetic differentiation between Zungaro populations was at the same level as that observed between other Siluriformes species, using the same DNA sequences. We conclude that Zungaro species of the Paraná-Paraguay River basin do not belong to the same species found in the Amazon basin. This finding has a significant implication for conservation of this fish, given that populations are disappearing at a high rate in the Paraná-Paraguay River basin, mainly due to impoundments.

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Brycon is one of the main genera of Neotropical freshwater fish. In Brazil, Brycon species have been found in many hydrographic basins, such as the Amazon, Paraná, Paraguay, and Araguaia-Tocantins basins. We examined the phylogenetic relationships among the species Brycon orbignyanus, B. hilarii, B. cf. pesu, B. cephalus, B. falcatus, and B. gouldingi, using mitochondrial and nuclear molecular markers. Specimens of B. orbignyanus were collected in the Paraná River. Specimens of B. hilarii were collected in the Manso River. Specimens of B. cephalus were obtained from a fish farm, and specimens of B. cf. pesu, B. falcatus and B. gouldingi were sampled in the Araguaia-Tocantins basin. DNA extraction was carried out using the phenol/chloroform method. Molecular polymorphism studies of Brycon species were carried out with the inter-simple sequence repeat (ISSR) technique, using the total DNA of six specimens of each species. In DNA amplification of B. cf. pesu, eight specimens were used. The partial sequence of mitochondrial cytochrome b was amplified by PCR. The PCR products were used directly in sequencing reactions. Each ISSR primer produced from 7 to 14 scorable and reproducible bands. The (GGAC)(3)A and (GGAC)(3)C primers produced the greatest number of species-specific bands. A 264-bp fragment, corresponding to the partial region of mitochondrial DNA cytochrome b, was sequenced and used for analysis. According to the phylogenetic tree obtained from the data, these Brycon species can be divided into two clades: one comprised only B. cf. pesu, and the second comprised the remaining Brycon species. We conclude that ISSR primers can be used for the identification of species-specific bands in fish, such as Brycon spp.

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Pseudoplatystoma corruscans (Spix and Agassiz, 1829) and Pseudoplatystoma reticulatum (Eingenmann and Eigenmann, 1889) are large migratory catfishes of high biological importance and great commercial value in South America. Because fertile crossbreeds can be artificially produced in hatcheries, a high genetic proximity between these two Pimelodidae species is conceivable. Possible escape of crossbred specimens from pisciculture stations is a serious environmental concern. Despite their importance, knowledge of P. corruscans and P. reticulatum biology, ecology, population diversity and genetics is limited. In the present work, the genetic divergence between P. corruscans and P. reticulatum populations from the Paraná River Basin was analyzed on the basis of polymorphisms in ISSR fragments and in the hypervariable sequence of the mitochondrial DNA (mtDNA) control region. Estimates of intraspecific haplotype (h > 0.5) and nucleotide diversities (pi < 0.01) indicate that P. corruscans and P. reticulatum have survived a historical population decline, followed by a demographic expansion. The interspecific polymorphisms within the mtDNA control region and ISSR fragments were suitable as diagnostic molecular markers and could be used to discriminate the two species. A unique Pseudoplatystoma specimen, captured in the Upper Paraná River Floodplain, was identified by these DNA diagnostic markers as a hybrid P. reticulatum x P. corruscans, which possibly escaped from pisciculture. The integrity of the natural population of P. corruscans in the Upper Paraná River is at risk of genetic introgression or homogenization due to the presence of hybrids and the transposition of P. reticulatum upstream through the Canal da Piracema at Itaipu Dam. Data presented herein improve the understanding of the genetic relatedness between P. corruscans and P. reticulatum and represent potential tools for future programs of conservation and surveillance of genetic introgression events and the genetic integrity of these populations.

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Diallel analysis was used to obtain information on combining ability, heterosis, estimates of genetic distances by random amplified polymorphic DNA (RAPD) and on their correlations with heterosis, for the popcorn varieties RS 20, UNB2, CMS 43, CMS 42, Zélia, UEM J1, UEM M2, Beija-Flor, and Viçosa, which were crossed to obtain all possible combinations, without reciprocals. The genitors and the 36 F(1) hybrids were evaluated in field trials in Maringá during two growing seasons in a randomized complete block design with three replications. Based on the results, strategies for further studies were developed, including the construction of composites by joining varieties with high general combining ability for grain yield (UNB2 and CMS 42) with those with high general combining ability for popping expansion (Zélia, RS 20 and UEM M2). Based on the RAPD markers, UEM J1 and Zélia were the most genetically distant and RS 20 and UNB2 were the most similar. The low correlation between heterosis and genetic distances may be explained by the random dispersion of the RAPD markers, which were insufficient for the exploitation of the popcorn genome. We concluded that an association between genetic dissimilarity and heterosis based only on genetic distance is not expected without considering the effect of dominant loci.

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Pseudoplatystoma corruscans (Spix and Agassiz, 1829) and Pseudoplatystoma reticulatum (Eingenmann and Eigenmann, 1889) are large migratory catfishes of high biological importance and great commercial value in South America. Because fertile crossbreeds can be artificially produced in hatcheries, a high genetic proximity between these two Pimelodidae species is conceivable. Possible escape of crossbred specimens from pisciculture stations is a serious environmental concern. Despite their importance, knowledge of P. corruscans and P. reticulatum biology, ecology, population diversity and genetics is limited. In the present work, the genetic divergence between P. corruscans and P. reticulatum populations from the Paraná River Basin was analyzed on the basis of polymorphisms in ISSR fragments and in the hypervariable sequence of the mitochondrial DNA (mtDNA) control region. Estimates of intraspecific haplotype (h > 0.5) and nucleotide diversities (π < 0.01) indicate that P. corruscans and P. reticulatum have survived a historical population decline, followed by a demographic expansion. The interspecific polymorphisms within the mtDNA control region and ISSR fragments were suitable as diagnostic molecular markers and could be used to discriminate the two species. A unique Pseudoplatystoma specimen, captured in the Upper Paraná River Floodplain, was identified by these DNA diagnostic markers as a hybrid P. reticulatum x P. corruscans, which possibly escaped from pisciculture. The integrity of the natural population of P. corruscans in the Upper Paraná River is at risk of genetic introgression or homogenization due to the presence of hybrids and the transposition of P. reticulatum upstream through the Canal da Piracema at Itaipu Dam. Data presented herein improve the understanding of the genetic relatedness between P. corruscans and P. reticulatum and represent potential tools for future programs of conservation and surveillance of genetic ...

Pseudoplatystoma corruscans Spix e Agassiz, 1829 e Pseudoplatystoma reticulatum Eigenmann e Eigenmann, 1889 são peixes migratórios de grande porte, com alta importância biológica e elevado valor comercial na América do Sul. Híbridos férteis são obtidos em cativeiro e, portanto, é esperada alta proximidade genética entre essas duas espécies de Pimelodidae. Escapes de espécimes híbridos a partir de estações de piscicultura representam um sério problema ambiental. Apesar da sua importância, conhecimentos sobre a biologia, ecologia, diversidade de populações e genética de P. corruscans e P. reticulatum são escassos. No presente trabalho, foi avaliada a divergência genética entre P. corruscans e P. reticulatum da Bacia do Rio Paraná, com base em fragmentos ISSR e na seqüência D-loop do DNA mitocondrial (mtDNA). As estimativas das diversidades intra-específicas haplotípica (h > 0,5) e nucleotídica (π < 0,01) evidenciaram que P. corruscans e P. reticulatum sobreviveram a um declínio populacional histórico, seguido de expansão demográfica. Os polimorfismos interespecíficos no mtDNA e nos fragmentos ISSR foram eficientes para diagnósticos e discriminaram as duas espécies. Um espécime de Pseudoplatystoma capturado na planície de inundação do Alto Rio Paraná foi identificado com esses marcadores moleculares como híbrido P. reticulatum x P. corruscans, que possivelmente escapou de psicicultura. A integridade da população de P. corruscans no Alto Rio Paraná está ameaçada, por introgressão ou homogeneização genética, pela presença de híbridos e pela transposição para montante de P. reticulatum através do Canal da Piracema em Itaipu. Os dados apresentados constituem um avanço na compreensão do parentesco entre P. corruscans e P. reticulatum e representam ferramentas em potencial para programas de conservação biológica, incluindo o monitoramento de introgressão e de integridade genética das populações.

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RESUMEN

Brycon pesu is a small-sized fish distributed throughout the Amazon and Orinoco Basins and other coastal basins of northeastern South America. Brycon cf. pesu specimens from the Araguaia-Tocantins Basin are currently separated into two morphotypes, Brycon sp1 and Brycon sp2, owing to different coloration of their anal fin. Brycon sp2 has a reddish margin stripe on the anal fin which morphologically distinguishes it from Brycon sp1. In the present research, nuclear and mitochondrial markers were used to test the hypothesis that the Brycon sp1 and Brycon sp2 morphotypes are distinct species. Specimens from the two morphotypes were collected from the Lajeado Hydroelectric Plant and the Palmas River in the Araguaia-Tocantins Basin. Thirty-five loci obtained by the amplification of five inter-simple sequence repeat primers were analyzed but no species-specific bands were detected. Electrophoretic profiles obtained from 5S rDNA non-transcribed spacer amplification failed to show any differentiation in morphotypes. These results were corroborated by nucleotide sequence analysis of the mtDNA control region, in which 24 polymorphic nucleotide sites, representing a polymorphism rate of only 5%, were detected. The low rates of polymorphism detected by inter-simple sequence repeat, non-transcribed spacer and mtDNA D-loop markers strongly reject the hypothesis that the two morphotypes Brycon sp1 and Brycon sp2 represent distinct species within Brycon cf. pesu. Further studies are needed to obtain conclusive data on the notion that the coloration of the anal fin is an intraspecific polymorphism, possibly related to environmental factors.

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