Evolutionary dynamics of rDNA genes on chromosomes of the Eucinostomus fishes: cytotaxonomic and karyoevolutive implications

Abstract

ABSTRACT. Several chromosomal features of Gerreidae fish have been found to be conserved. In this group, it is unclear whether the high degree of chromosomal stasis is maintained when analyzing more dynamic regions of chromosomes, such as rDNA sites that generally show a higher level of variability. Thus, cytogenetic analyses were performed on 3 Atlantic species of the genus Eucinostomus using conventional banding (C-banding, Ag-NOR), AT-and GC-specific fluorochromes, and fluorescence in situ hybridization mapping of telomeric sequences and 5S and 18S rDNA sites. The results showed that although the karyotypical macrostructure of these species is similar (2n = 48 chromosomes, simple Ag-NORs seemingly located on homeologous chromosomes and centromeric heterochromatin pattern), there are differences in the positions of rDNA subunits 5S and 18S. Thus, the ribosomal sites have demonstrated to be effective cytotaxonomic markers in Eucinostomus, presenting a different evolutionary dynamics in relation to other chromosomal regions and allowing access to important evolutionary changes in this group.

Co-located 18S/5S rDNA arrays: an ancient and unusual chromosomal trait in Julidini species (Labridae, Perciformes)

“…The syntenic arrangement of these rDNA classes, as found in Halichoeres and Thalassoma , is not a common feature, although it has already been reported in some main fish orders, such as Perciformes (Ghigliotti et al 2008, Merlo et al 2013), Characiformes (Vicari et al 2006, Bellafronte et al 2009, Cioffi et al 2009), Siluriformes (Mariotto et al 2011, Ziemniczak et al 2012), Anguilliformes (Deiana et al 2006), Salmoniformes (Pendás et al 1994), Nototheniformes (Ghigliotti et al 2007) and Tetraodontiformes (Martinez et al 2010). In fishes, 45S/5S rDNA arrays are phylogenetically stochastic and limited to few species of a clade (Almeida-Toledo et al 2002), and preferentially explained by random events in the course of the evolutionary trajectory of the genome (Calado et al 2014). Thus, the phylogenetic spread of these arrangements in the Julidini clade indicates a noteworthy evolutionary stability.…”

Interregional cytogenetic comparisons in Halichoeres and Thalassoma wrasses (Labridae) of coastal and insular regions of the southwestern Atlantic

“…In the two Halichoeres species, all the 5S rDNA sites exhibit a syntenic 18S/5S arrangement. Syntenic arrangements of ribosomal genes are a derived condition in Perciformes (Nakajima et al, 2012;Calado et al, 2014;Costa et al, 2016) and Characiformes (Voltolin et al, 2013), and this exclusive feature in both Halichoeres species demonstrates that this organization does not interfere with the gene function. The similarity in the organization of ribosomal genes in the Thalassoma and Halichoeres genera indicates a symplesiomorphic condition in the Julidini species.…”

Atlantic surgeonfishes bear only minor microstructural changes in highly derived karyotypes

“…The location of 18S and 5S rRNA genes has been proved to be efficient cytotaxonomic markers in distinct marine fish groups like Gerreidae (Calado et al, 2013(Calado et al, , 2014, Lutjanidae (Rocha and Molina, 2008), and Nototheniidae (Pisano and Ghigliotti, 2009). Usually, both families of these ribosomal genes are not syntenic (Gornung, 2013), as observed in Acanthurus (Fig.…”