Chromosomal differentiation and speciation in sister-species of Grammatidae (Perciformes) from the Western Atlantic

Abstract

In the tropical Atlantic, the ichthyofauna between the coast of Brazil and the Caribbean regions, divided by the Amazon barrier, is very similar presenting several geminate species, including Gramma brasiliensis, endemic in Brazil, and its Caribbean counterpart Gramma loreto. Morphological and molecular studies have helped establish evolutionary patterns that sister-species of these two marine habitats are subjected to. However, their chromosomal characteristics are only beginning to be better characterized. Accordingly, a comparative cytogenetic analysis was carried out in G. brasiliensis and G. loreto, seeking evidence of cytotaxonomic markers implicated in the karyotypic diversiWcation of these species and likely associated with speciation events. Heterochromatic regions and their aYnity to Xuorochromes GC-or AT-speciWc were identiWed, as well as the distribution of ribosomal DNA sites in chromosomes, either by silver nitrate impregnation (Ag-NORs) or dual-color FISH mapping with 18S and 5S rDNA probes. While displaying the same diploid number, 2n = 48 chromosomes, considered basal for Perciformes, the two species diVered in karyotype structure, showing karyotypic formulas and species-speciWc heterochromatin pattern. The cytological characters found support the diVerentiating status of these species, possibly achieved under the conditions of allopatry due to the Amazon/Orinoco barrier, showing chromosomal peculiarities in Grammatidae species when compared to other groups of Perciformes.

Physical mapping of 18S and 5S genes in pelagic species of the genera Caranx and Carangoides (Carangidae)

“…In fact, C. lugubris that are GC-rich in most chromosomes show the most cytogenetic differences among the 3 species. High GC+ content dispersed throughout all chromosomes, although uncommon, has been identified in some marine families such as Tetraodontidae and Grammatidae (Martinez et al, 2011;Molina et al, 2012).…”

Karyoevolutionary aspects of Atlantic hogfishes (Labridae–Bodianinae), with evidence of an atypical decondensed argentophilic heterochromatin

“…Cioffi et al, 2009). Although equilocation between Ag-NORs and 18S rDNA is normally expected (Nirchio et al, 2007;Molina et al, 2011), numerous cases of lack of correspondence between these sites have been reported (e.g. Vicari et al, 2003), justifying the use of both methodologies for a more thorough study of the presence and distribution of nucleolus organizer regions in the karyotypes.…”

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

“…The species Bodianus rufus, B. pulchellus, and B. insularis exhibit an atypical chromosomal region, exceptionally decondensed and argentophilic, but without affinity with 18S rDNA probes and not a GC-rich region (Molina et al, 2012a). On the contrary, in the species now analyzed, the heterochromatin has a predominantly centromeric distribution, seemingly little variable, with low intra-and interspecific discriminatory power.…”