Cytogenetic analysis of three sympatric Gymnotus (Gymnotiformes, Gymnotidae) species verifies invasive species in the Upper Paraná River basin, Brazil

Abstract

Cytogenetic analyses were performed on three Gymnotus species, Gymnotus paraguensis, Gymnotus sylvius and Gymnotus pantanal, collected in sympatry in the region of Guaı´ra, ParanaŚ tate (Brazil). Gymnotus paraguensis presented 54 chromosomes (52m-sm þ 2st) in both sexes, G. sylvius presented 40 chromosomes (36m-sm þ 4a) in both sexes and G. pantanal presented 40 chromosomes (14m-sm þ 26a) in females and 39 (15m-sm þ 24a) in males, with an X 1 X 1 X 2 X 2 / X 1 X 2 Y multiple sex chromosome system. All three species had single nucleolar organizing regions and heterochromatin in the centromeric region of most chromosomes. Gymnotus pantanal, previously collected only in the Lower Parana´and Paraguay River basins, was confirmed for the first time in the Upper Parana´River basin. This species constitutes one of several examples of species that have colonized the region after flooding of the great Sete Quedas waterfalls by the construction of the Itaipu hydroelectric dam. The probable absence or infertility of hybrids is indicated by the high level of chromosome differentiation between these species.

Repetitive DNA and Meiotic Behavior of Sex Chromosomes in <i>Gymnotus pantanal</i> (Gymnotiformes, Gymnotidae)

“…Although Gymnotus is the most species-rich genus of the order Gymnotiformes, with 35 species described [Froese and Pauli, 2011], cytogenetic studies remain scarce; only 10 species have karyotype descriptions [Lacerda and Maistro, 2007;Margarido et al, 2007]. Moreover, some authors suggest the occurrence of cryptic species and this number may therefore be larger [Milhomem et al, 2008].…”

Genetic variability in three species of Gymnotus Linnaeus, 1758 (Gymnotiformes: Gymnotidae) from Caracu stream of the upper Paraná River basin, Brazil

“…The Gymnotus species have been object of ecological studies (Barbieri & Barbieri, 1984;Cognato & Fialho, 2006;Ferreira & Casatti, 2006), cytogenetic analysis (Foresti et al, 1984;Murofushi & Yosida, 1984;Fernandes-Matioli et al, 1997, 1998a, 1998bMargarido et al, 2007), phylogenetic approaches (Albert, 2001;Fernandes-Matioli & AlmeidaToledo, 2001;Albert et al, 2005) and systematic studies (Albert & Miller, 1995;Campos-da-Paz, 1996, 2000Albert et al, 1999;Fernandes-Matioli et al, 2000;Crampton & Albert, 2004;Fernandes et al, 2005). However, genetic variability estimates of the Gymnotus species have never been made.…”

Evidence of the color pattern variation in populations of Gymnotus pantanal (Gymnotiformes) from three streams in the upper Paraná River basin, Brazil

“…The occurrence of G. pantanal in the upper Paraná River basin was already described by Margarido et al (2007) and by Graça & Pavanelli (2007). The formers used cytogenetic analysis to identify this invasive species, and pointed out the usefulness of this analysis for taxonomic diagnosis in this fish group due to its specific karyotype.…”

“…Fernandes et al (2005) used morphological, cytogenetic, and molecular data to describe that species; in their diagnosis color pattern was the main morphological trait: 'Gymnotus pantanal differs from other members of the G. pantherinus Steindachner speciesgroup (except G. anguillaris Hoedeman) in possessing a color pattern composed of thin obliquely-oriented pale pigment bands (about one third the width of the dark bands) with wavy margins restricted to the ventral portion of the body (rarely extending above the lateral line) on the anterior half of the body'. Later, Graça & Pavanelli (2007) and Margarido et al (2007) reported this species for the upper Paraná River basin.…”