Karyotype description of possible new species of the Hypostomus ancistroides complex (Teleostei: Loricariidae) and other Hypostominae - doi: 10.4025/actascibiolsci.v34i2.9318

Cytogenetic analyses were performed in four species of the Hypostominae subfamily, three from Hypostomus (Hypostomini) genus and Rhinelepis aspera (Rhinelepini). Three populations of Hypostomus ancistroides were analyzed, which had 2n=68 chromosomes, but presented different karyotype formulas. Hypostomus regani and H. strigaticeps, both from Ivaí river, showed 2n=72 chromosomes with two distinct cytotypes. In turn, R. aspera of the upper Paraná river basin presented 2n=54 chromosome. Multiple Nucleolar Organizer Regions (NORs) have been evidenced by silver nitrate staining in species of Hypostomus and single NOR in R. aspera. The observed variation in the chromosome number and the marked variability in karyotype formulas and NORs reveal a certain amount of karyotype variation in the genus Hypostomus suggesting the probable existence of cryptic species with independent chromosome traits. Therefore, our data can be of great value in discriminating species and understanding their chromosomal evolution.

Observation of an invasion of the piranha Serrasalmus marginatus Valenciennes, 1847 (Osteichthyes, Serrasalmidae) into the Upper Paraná River, Brazil / Invasão da piranha Serrasalmus marginatus Valenciennes, 1847 no alto rio Paraná, Brasil (Osteichthyes, Serrasalmidae)

The building of Itaipu Dam, 150 km downstream from Sete Quedas Falls, resulted in the natural geographical barrier drowning, with subsequent mixing of the fish faunas. Serrasalmus marginatus (Osteichthyes, Serrasalmidae), a species that had been restricted to the river segment downstream from Sete Quedas, invaded the Upper Paraná River. The catching of Serrasalmus spilopleura, a resident species, decreased drastically after the invasion, contrary to S. marginatus, which increased in abundance. In the Piquiri River, where the latter species does not occur, the abundance of S. spilopleura remained high, due to the presence of Nhá Bárbara and Apertado Falls.

A construção da barragem de Itaipu, 150 km a jusante do salto de Sete Quedas, resultou no afogamento da barreira geográfica natural, com conseqüente mistura das ictiofaunas. Serrasalmus marginatus (Osteichthyes, Serrasalmidae), uma espécie que apresentava distribuição restrita ao segmento a jusante de Sete Quedas, invadiu o alto rio Paraná. A captura de Serrasalmus spilopleura, uma espécie residente, diminuiu drasticamente após a invasão, ao contrário de S. marginatus que aumentou em abundância. No rio Piquiri, onde a espécie invasora não ocorreu, a abundância de S. spilopleura permaneceu alta por causa das quedas de Nhá Bárbara e Apertado.

Observation of an invasion of the piranha Serrasalmus marginatus Valenciennes, 1847 (Osteichthyes, Serrasalmidae) into the Upper Paraná River, Brazil / Invasão da piranha Serrasalmus marginatus Valenciennes, 1847 no alto rio Paraná, Brasil (Osteichthyes, Serrasalmidae)

The building of Itaipu Dam, 150 km downstream from Sete Quedas Falls, resulted in the natural geographical barrier drowning, with subsequent mixing of the fish faunas. Serrasalmus marginatus (Osteichthyes, Serrasalmidae), a species that had been restricted to the river segment downstream from Sete Quedas, invaded the Upper Paraná River. The catching of Serrasalmus spilopleura, a resident species, decreased drastically after the invasion, contrary to S. marginatus, which increased in abundance. In the Piquiri River, where the latter species does not occur, the abundance of S. spilopleura remained high, due to the presence of Nhá Bárbara and Apertado Falls.

A construção da barragem de Itaipu, 150 km a jusante do salto de Sete Quedas, resultou no afogamento da barreira geográfica natural, com conseqüente mistura das ictiofaunas. Serrasalmus marginatus (Osteichthyes, Serrasalmidae), uma espécie que apresentava distribuição restrita ao segmento a jusante de Sete Quedas, invadiu o alto rio Paraná. A captura de Serrasalmus spilopleura, uma espécie residente, diminuiu drasticamente após a invasão, ao contrário de S. marginatus que aumentou em abundância. No rio Piquiri, onde a espécie invasora não ocorreu, a abundância de S. spilopleura permaneceu alta por causa das quedas de Nhá Bárbara e Apertado.

Genetic differentiation among populations of Pseudoplatystoma corruscans (Agassiz, 1829) (Osteichthyes, Pimelodidae) isolated by the Guaíra Falls in the Paraná River / Diferenciação genética entre populações de Pseudoplatystoma corruscans (Agassiz, 1829) (Osteichthyes, Pimelodidae) isoladas pelos saltos de Guaíra do rio Paraná

Until 1982, the Guaíra Falls, also named the Seven Falls, constituted a barrier to the dispersion of migratory fish in the Paraná River. The objective of this work was to verify if populations of Pseudoplatystoma corruscans (Osteichthyes, Pimelodidae) were isolated by the Guaíra Falls. Samples from the Upper Paraná River floodplain (PL), the Itaipu reservoir (IT), and downstream Yacyretá reservoir (YA) were compared by RAPD markers. Lynch"s FST was significant between PL and IT (0.090), and PL and YA (0.112). Estimated gene flow (Nm) varied from 2.0 between PL and YA to 8.1 between IT and YA. Nei"s genetic distance varied from D = 0.0638 between PL and YA to D = 0.0174 between IT and YA. These results indicate the existence of genetic differentiation and that, possibly, the Guaíra Falls isolated the populations reproductively. They also suggest the possibility of different spawning areas, partially avoiding the genetic homogenization of the IT and PL populations.

Os saltos de Guaíra, também denominados Sete Quedas, constituíam até 1982 uma barreira para a dispersão de peixes migradores. Este trabalho teve por objetivo verificar se populações de Pseudoplatystoma corruscans (Osteichthyes, Pimelodidae) eram isoladas pelos saltos de Guaíra. Amostras provenientes da planície de inundação do alto rio Paraná (PL), do reservatório Itaipu (IT) e de jusante de Yacyretá (YA), foram comparadas por RAPD. O FST de Lynch foi significativo entre PL e IT (0,090) e PL e YA (0,112). O fluxo gênico estimado (Nm) variou de 2,0 entre PL e YA a 8,1 entre IT e YA, e a distância genética de Nei de D = 0,0638 entre PL e YA a D = 0,0174 entre IT e YA. Estes resultados indicam existência de diferenciação genética e que, possivelmente, Sete Quedas isolavam reprodutivamente as populações. Sugerem, também, a possibilidade de áreas diferentes de desova, impedindo parcialmente a homogeneização genética das populações IT e PL.

Genetic differentiation among populations of Pseudoplatystoma corruscans (Agassiz, 1829) (Osteichthyes, Pimelodidae) isolated by the Guaíra Falls in the Paraná River / Diferenciação genética entre populações de Pseudoplatystoma corruscans (Agassiz, 1829) (Osteichthyes, Pimelodidae) isoladas pelos saltos de Guaíra do rio Paraná

Until 1982, the Guaíra Falls, also named the Seven Falls, constituted a barrier to the dispersion of migratory fish in the Paraná River. The objective of this work was to verify if populations of Pseudoplatystoma corruscans (Osteichthyes, Pimelodidae) were isolated by the Guaíra Falls. Samples from the Upper Paraná River floodplain (PL), the Itaipu reservoir (IT), and downstream Yacyretá reservoir (YA) were compared by RAPD markers. Lynch"s FST was significant between PL and IT (0.090), and PL and YA (0.112). Estimated gene flow (Nm) varied from 2.0 between PL and YA to 8.1 between IT and YA. Nei"s genetic distance varied from D = 0.0638 between PL and YA to D = 0.0174 between IT and YA. These results indicate the existence of genetic differentiation and that, possibly, the Guaíra Falls isolated the populations reproductively. They also suggest the possibility of different spawning areas, partially avoiding the genetic homogenization of the IT and PL populations.

Os saltos de Guaíra, também denominados Sete Quedas, constituíam até 1982 uma barreira para a dispersão de peixes migradores. Este trabalho teve por objetivo verificar se populações de Pseudoplatystoma corruscans (Osteichthyes, Pimelodidae) eram isoladas pelos saltos de Guaíra. Amostras provenientes da planície de inundação do alto rio Paraná (PL), do reservatório Itaipu (IT) e de jusante de Yacyretá (YA), foram comparadas por RAPD. O FST de Lynch foi significativo entre PL e IT (0,090) e PL e YA (0,112). O fluxo gênico estimado (Nm) variou de 2,0 entre PL e YA a 8,1 entre IT e YA, e a distância genética de Nei de D = 0,0638 entre PL e YA a D = 0,0174 entre IT e YA. Estes resultados indicam existência de diferenciação genética e que, possivelmente, Sete Quedas isolavam reprodutivamente as populações. Sugerem, também, a possibilidade de áreas diferentes de desova, impedindo parcialmente a homogeneização genética das populações IT e PL.

Karyotype description of possible new species of the Hypostomus ancistroides complex (Teleostei: Loricariidae) and other Hypostominae - doi: 10.4025/actascibiolsci.v34i2.9318

Cytogenetic analyses were performed in four species of the Hypostominae subfamily, three from Hypostomus (Hypostomini) genus and Rhinelepis aspera (Rhinelepini). Three populations of Hypostomus ancistroides were analyzed, which had 2n=68 chromosomes, but presented different karyotype formulas. Hypostomus regani and H. strigaticeps, both from Ivaí river, showed 2n=72 chromosomes with two distinct cytotypes. In turn, R. aspera of the upper Paraná river basin presented 2n=54 chromosome. Multiple Nucleolar Organizer Regions (NORs) have been evidenced by silver nitrate staining in species of Hypostomus and single NOR in R. aspera. The observed variation in the chromosome number and the marked variability in karyotype formulas and NORs reveal a certain amount of karyotype variation in the genus Hypostomus suggesting the probable existence of cryptic species with independent chromosome traits. Therefore, our data can be of great value in discriminating species and understanding their chromosomal evolution.