Evidence of chromosome fusion in Gymnotus sylvius Albert & Fernandes-Matoli, 1999 (Teleostei: Gymnotiformes) detected by telomeric probes and R-banding

Abstract

Gymnotus cf. carapo and Gymnotus sylvius are two fi sh species inhabiting the Upper Parana River Basin, presenting respectively 2n = 54 and 2n = 40 chromosomes. In the present cytogenetic analysis, R-banding and telomere-sequence hybridization were carried out in order to determine the possible relationship between the karyotipes of these two species. Incorporation bands (R-bands) obtained for the two species allowed the identifi cation of chromosome similarities, showing to be an usefull alternative to the G-banding methods, which fail in producing satisfying results in most of analyzed fi sh species. This approach, associated with the hybridization of telomeric sequences, permited to identify chromosomal rearrangements that could be used as indicators of karyotypic evolution within the group. In the present case, telomeric sequences were detected in the centromeric region of two metacentric chromosome pairs of Gymnotus sylvius. The results obtained after hybridization with the telomere sequences, coupled with the chromosome homeologies detected by R-banding, showed that G. cf. carapo and G. sylvius should present a common ancestor, and this may also be corroborated by the similarities found in three chromosome pairs, that seem to have been conserved during the evolution of the two species. Based on the data here presented we propose that G. sylvius may have undergone a recent process of chromosome fusion that resulted in the diminution of its chromosome number.

Telomere organization and the interstitial telomeric sites involvement in insects and vertebrates chromosome evolution

“…These kinds of ITS were described in species into 12 fish orders ( Ocalewicz, 2013 ). In some groups with chromosomal remodeling, most of the pericentromeric ITS was described as relicts of chromosome fusion events ( Rocco et al, 2001 , 2002 ; Chew et al, 2002 ; Harvey et al, 2002 ; Milhomem et al, 2008 ; Ocalewicz et al , 2009 ; Felippe and Foresti, 2010 ; Mota-Velasco et al, 2010 ; Scacchetti et al, 2011 ; Blanco et al, 2012 , 2017 ; Errero-Porto et al, 2014 ; Favarato et al, 2016 ; Barbosa et al, 2017 ; Barros et al, 2017 ; Glugoski et al, 2018 , 2022 ; Deon et al, 2022a ) or as unstable sites triggering DSBs and chromosome rearrangements ( Rosa et al, 2012 ; Deon et al , 2020 , 2022b ). In other cases, e.g., in some Characidium species, a conserved karyotype with ITS was proposed due to ectopic transposition or events of homologous and non-homologous recombination ( Scacchetti et al , 2015 ; Oliveira et al, 2021a ).…”