Dinâmica evolutiva do DNAr em cromossomos de peixes da família Eleotridae e revisão citogenética da ordem gobiiformes (Osteichthyes, Teleostei)

Abstract

The Order Gobiiformes, with more than 2200 species is one of the most diversified groups among teleosts. This high diversity of species is accompanied by significant karyotypic diversification, whose the biological causes are not completely established. Among its groups there is the family Eleotridae, with 23 genera and 171 species, of which six inhabits rivers near the coast and estuarine regions in vast areas of the Brazilian coast. In order to extend the cytogenetic data for Eletridae and to review the patterns of karyotype diversification in Gobiiformes, the species Dormitator maculatus, Eleotris pisonis, Erotelis smaragdus and Guavina guavina with occurrence in the South Atlantic were analyzed and a broad review of cytogenetic, biological and ecological aspects of the Order Gobiiformes were performed. The cytogenetic analyses employed conventional techniques (Giemsa staining, silver nitrate impregnation, C-banding), base-specific fluorochromes (MM/DAPI) staining, and fluorescence in situ hybridization with probes of 18S rDNA, 5S rDNA and repeats (CA)15. The species E. smaragdus and E. pisonis presented 2n=46 chromosomes (NF=46). D. maculatus exhibited a structurally diverse karyotype with 36sm+4st+6a (NF=86), while G. guavina had a numerically divergent karyotype with 2n=52, NF=52). The nucleoli organizing regions in the four species are located in different positions of a chromosome, showing its potential to be an efficient cytotaxonomic marker among the species. In situ rDNA mapping indicated a greater variation in the structural arrangements of the 18S and 5S genes, confirming the high evolutionary dynamics of the karyotypes of these species. The cytogenetic data set for the Order Gobiiformes confirms 2n=46 acrocentric chromosomes, as a symplesiomorphic condition for the Order. The varied set of repetitive sequences in the Eleotrid chromosomes, and in Gobiiformes in general, associated to biological biology, such as benthic habits, benthic adhesive eggs can act as trigger for karyotype diversification. The results contributed to a better knowledge on the karyotype evolution in Eleotridae, indicating a variety of rearrangements (inversions, fusions and fissions) and extending the cytogenetic data for Gobiiformes. The heterogeneous structural patterns of the chromosomes of this Order, together with their biological aspects that favor population structure promoting an elevate evolutionary dynamics in their chromosomes, making this group one of the most illustrative models of karyotype megaevolution in marine environments.