Cytogenetic Analysis of Three Sympatric Gymnotus Species (Teleostei: Gymnotidae) from the Fundo Stream, MG, Brazil

Abstract

Summary Three sympatric species of Gymnotus from the Fundo stream, a small tributary of the Sapucaí river, Minas Gerais State, Brazil, were studied in relation to their karyology. Gymnotus sylvius presented 2nϭ40 chromosomes (36 m/smϩ4 st/a), Gymnotus sp. presented 2nϭ50 (26 m/smϩ 24 st/a) and Gymnotus paraguensis had 2nϭ54 (50 m/smϩ4 st/a). C-banding demonstrated positively stained heterochromatic blocks in the centromeric position of few chromosomes on G. sylvius and in the centromeric region of all chromosomes on G. paraguensis samples. The nucleolus organizer region (NOR) was located on the short arm of one st chromosome pair in G. sylvius and Gymnotus sp., and in the interstitial position on the short arm of the pair number one and below the centromere on a third chromosome on G. paraguensis. The cytogenetic data obtained indicate that Gymnotus sp. represent a new Gymnotus specie with a karyotypic constitution never observed on others species from this genus. Some aspects related to the chromosome diversification of these Gymnotus are discussed.

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].…”

Comparative Cytogenetic Study Among Three Fish Species: An Analysis From a Water Divide Region

“…The distribution of constitutive heterochromatin in Gymnotiformes is generally characterized by large blocks scattered over almost all chromosomes, with few interpopulational divergences (FERNANDES-M AT I O L I ; A L M E I D A -TO L E D O , 2 0 0 1 ; LACERDA; MAISTRO, 2007;MARGARIDO et al, 2007, present study). The FISH with 5S rDNA probe shows the most of the chromosomes signals in the pericentromeric region in both G. carapo populations.…”

“…A great diversity in chromosome number has been found in the genus Astyanax, ranging from 2n=36 in A. schubarti to 2n=50 in A. scabripinnis, A. bimaculatus, A. altiparanae (FERREIRA-NETO et al, 2009;KANTEK et al, 2009) and in Gymnotus genus (MARGARIDO et al, 2007;LACERDA;MAISTRO, 2007;MILHOMEN et al, 2007). In turn, the Cichlidae species like Geophagus and others genus showed a minnor chromosomal diversifi cation, usually restrict to micro alterations in the chromosomes (VICARI et al, 2006;PERAZZO et al, 2010).…”

“…The NOR localization is a good taxonomic tool among Gymnotidae because different species showing 2n=54 m/sm chromosomes can be distinguished by the NOR chromosome bearing and localization (GALETTI Jr. et al, 1984;FERNANDES-MATIOLI et al, 1998;PEREIRA et al, 2002;LACERDA;MAISTRO, 2007). The location of NORs present in one chromosome pair is a common feature found among the Gymnotiformes (FONTELES et al, 2008).…”

Comparative Cytogenetic Study Among Three Fish Species: An Analysis From a Water Divide Region

“…This study associated cytogenetic data, biogeographic aspects, and evolutive biology of fishes species located in the headwaters of two isolated rivers basins (Pântano and Feijão streams) in São Paulo State, Brazil. A great diversity in chromosome number has been found in the genus Astyanax, ranging from 2n=36 in A. schubarti to 2n=50 in A. scabripinnis, A. bimaculatus, A. altiparanae (FERREIRA-NETO et al, 2009;KANTEK et al, 2009) and in Gymnotus genus (MARGARIDO et al, 2007;LACERDA;MAISTRO, 2007;MILHOMEN et al, 2007). In turn, the Cichlidae species like Geophagus and others genus showed a minnor chromosomal diversifi cation, usually restrict to micro alterations in the chromosomes (VICARI et al, 2006;PERAZZO et al, 2010).…”