Repetitive DNAs highlight the role of chromosomal fusions in the karyotype evolution of Dascyllus species (Pomacentridae, Perciformes)

Abstract

The Dascyllus genus consists of 11 species spread over vast regions of the Indo-Pacific, showing remarkable reductions in the diploid chromosome numbers (2n). The present study analyzed the karyotypes and other chromosomal characteristics of D. trimaculatus (2n = 48; 2st + 46a; NF = 50), D. carneus (2n = 48; 2st + 46a; NF = 50) and D. aruanus (2n = 30; 18m + 2st + 10a; NF = 50) from the Thailand Gulf (Pacific Ocean) and D. melanurus (2n = 48; 2st + 46a; NF = 50) from the Andaman Sea (Indian Ocean), employing conventional cytogenetic analyses and the chromosomal mapping of repetitive DNAs, using 18S and 5S rDNA, telomeric sequences and (CA)15, (GA)15, and (CAA)10 microsatellites as probes. The C-positive heterochromatin was found in the centromeric regions of most chromosomal pairs and 18S rDNA phenotypes were single in all species. However, in D. aruanus (2n = 30), which harbors nine metacentric pairs; the 5S rDNA sites were located in the centromeric region of the shortest one. The mapping of the telomeric sequences in D. aruanus revealed the presence of interstitial telomeric sites (ITS) in the centromeric region of four metacentric pairs, with one of these pairs also displaying an additional ITS in the long arms. Distinct chromosomal markers confirmed the reduction of the 2n by chromosomal fusions, highlighting the precise characterization of these rearrangements by the cytogenetic mapping of the repetitive DNAs.

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

“…Indeed, because of their dynamics, they are associated with karyotype rearrangements and diversification in many groups of Perciformes (Getlekha et al, 2016). The three species exhibit 18S/5S rDNA syntenic arrays, also identified in other Halichoeres species (Amorim et al, 2016), which suggest a shared condition in the Tribe Julidini.…”

“…FNA is closer to the mainland (365 km) and 600 km apart from SPSPA. The FNA is influenced by both currents but, due to its proximity to the coast, is also under the effect of the North Brazil Current (Getlekha et al, 2016). The inter-regional variation, concerning the location and frequency of the ribosomal sites in H. radiatus, seems not to be only a polymorphic condition, but instead a response to some level of gene flow restriction between the insular areas.…”

Genomic Organization of Repetitive DNAs and Differentiation of an XX/XY Sex Chromosome System in the Amazonian Puffer Fish, <b><i>Colomesus asellus </i></b>(Tetraodontiformes)

“…In fact, besides the centromeric C-positive heterochromatic bands, C. asellus did not show remarkable accumulation of heterochromatin, with conspicuous blocks only in the sex chromosomes and in chromosome pair 3. This is in contrast to the species from the sister family Diodontidae [Brainerd et al, 2001], which have large heterochromatic blocks containing great amounts of repetitive sequences such as satellite DNAs and transposable elements [Sá-Gabriel and Molina, 2005;Pokorná et al, 2011;Schneider et al, 2013a, b;Getlekha et al, 2016].…”

Chromosomal evolution in large pelagic oceanic apex predators, the barracudas (Sphyraenidae, Percomorpha)

“…Indeed, rDNA regions appear to behave as hotspots for chromosomal rearrangements in fishes. These complex regions, particularly rich in different repetitive sequences (Costa et al, 2015), have been associated with some chromosomal rearrangements, especially with centric fusion events (Getlekha et al, 2016).…”

“…In fact, the occurrence of interstitial telomeric sites seems particularly prevalent in numerical-structural rearrangements, such as tandem and centric fusions (Getlekha et al, 2016), but rare in pericentric inversion events. However, the absence of interstitial telomeric sites could also be related to the loss of these sequences during the chromosomal rearrangements, the small size of the sequences, or even to its mischaracterization due to accumulated changes in this region (Meyne et al, 1990).…”