Contrastes da evolução cromossômica e diversificação do DNA repetitivo em peixes-anjos (pomacanthidae, teleostei)

Abstract

Karyotypic stasis processes and intense chromosomal changes exemplify extreme phenomena of karyotypic changes. Some groups of marine fish have both conditions reflected in the karyotypes of their species. One of these groups, Pomacanthidae, presents 12% of the species with karyotypes with a high degree of conservatism in the diploid number (2n=48), but with karyotype structures that can be very divergent. Here are presented cytogenetic data of six species of the family, Pomacanthus paru, P. arcuatus, Holacanthus tricolor, H. ciliaris, Centropyge aurantonotus (Atlantic ocean), and C. eibli (Indian ocean), obtained by conventional methods and fluorescent in situ hybridization of four repetitive DNA classes (rDNAs, microsatellites, transposable elements, histones) that demonstrate the karyotypic diversity and contrasting patterns of chromosomal evolution of the group. The analyzed species share the same diploid number (2n=48), with karyotypes formed mainly by acrocentric chromosomes, except for C. aurantonotus, which exhibits a large profusion of bi-brachial elements. Despite the numerical and structural conservatism of karyotypes, there were variations in the distribution and organization of some repetitive DNA classes. All species exhibited only one 18S rDNA loci, while the 5S rDNA regions were more variable, occurring in most chromosomes of C. aurantonotus. P. paru and P. arcuatus, with recent divergence, exhibit very similar karyotypes, including the arrangements of the 18S rDNA sites, but differ in the positioning of the 5S rDNA regions. Holacanthus species showed considerable variation in number and position of histone H4 sites. The occurrence of evolutionary traits related to chromosomal structure and organization of repetitive sequences in some species indicate disruptive events on the limited karyotypic diversification of the group, mediated by pericentric inversions and heterochromatinization processes.