Aspectos cariogenômicos em espécies marinhas de Haemulidae (Perciformes) e Labridae (Labriformes): uma perspectiva evolutiva

Abstract

Percomorpha series is the largest division among vertebrates, constituting the largest and most derived clade of teleostean fishes. Among its Orders, Perciformes and Labriformes constitue adequated models for the investigation of conservatism and chromosomal diversification. In Perciformes the chromosomal conservatism is represented by basal karyotypes with 2n = 48 acrocentric, extensively shared by a considerable portion of species. The causes and extent of the karyotypic conservatism in various families of this Order are not entirely clear. In front of the diversity of species in Labriformes, more detailed aspects of its karyotype evolution or even the taxonomic status of some species deserve particular attention. In order to contribute with new information on these issues, it was implemented conventional chromosome analysis (conventional staining with Giemsa, C-banding and Ag- NORs, base-specific fluochromes) and cytomolecular (in situ hybridization with 18S rDNA, 5S rDNA) probes were implemented. Eight species of the genera Anisotremus and Haemulon of the family Haemulidae (Perciformes) were analyzed, including samples from different areas of the Atlantic, as a model of conservative evolution. In 2 species of the Bodianus genus Labridae (Labriformes), it was also analyzed aspects of the evolution of particular repetitive sequences (DNAr 18S, DNAr 5S, Alu and Tol2) in the chromosomes by hybridization with 5 methylcytosine (5mC). Additionally, phylogenetic comparisons were performed using mitochondrial (COI and 16S) and nuclear (Rhodopsin) DNA sequences to verify the taxonomic status of the Bodianus insularis species, endemic to the Meso-Atlantic islands. All Haemulidae species presented 2n = 48a, single Ag-NORs sites and reduced centromeric heterochromatin, besides considerable sharing of rDNA 5S and 18S sites, confirming the occurrence of karyotype stasis in the family. The karyotypic patterns of the populations of A. virginicus and H. chrysargyreum between the Caribbean and the South Atlantic did not reveal chromosomal variations due to the barrier of the discharges of the Amazonas / Orinoco rivers. In Bodianus, the analyzes identified a remarkable decondensed region in a subtelocentric chromosomal pair, denominated BOD region. Among its particular constitutive and functional characteristics, it is DAPI-, Argentofílica (Ag +), markedly hypomethylated and saturated with transposable elements, suggesting that the participation of these mobile elements may have contributed to its genesis and complex epigenetic dynamics. In relation to the endemic species B. insularis its genetic divergence is much inferior to that presented by differentiated species suggesting that although it represents a geographically isolated group, it constitutes a synonym of B. pulchellus. The divergence in the rates of karyotype diversification between Haemulidae and Labridae is discussed here in the light of intrinsic karyotype characteristics that may favor the buffering and the fixation of chromosomal changes and biological aspects of the species that contributes to particular conditions of karyotype evolution of these two groups of marine fish.