Investigação da distribuição de elementos repetitivos no genoma de espécies de Trachelyopterus (Valenciennes, 1840)

Abstract

Trachelyopterus is a Neotropical catfish genus with a controversial taxonomic history and more than 200 years of revisions due to similar morphology among species. Cytogenetically, it is still poorly explored and there is no physical mapping of repetitive elements beyond the rDNAs 18S and 5S. Only the microsatellite (GATA)n distribution pattern was analyzed in some species, having a crucial role in the origin and evolution of B chromosomes, but without efficiency in distinguishing species through complement A chromosomes. In this study, the mapping of the repetitive elements 18S and 5S rDNA, H3 and H4 histone genes, snRNA U2 and the microsatellite (GATA)n were performed in six Trachelyopterus species: T. striatulus, T. galeatus and T. porosus of the Amazon River Basin; T. coriaceus and Trachelyopterus aff. galeatus (possible new species) from the Araguaia River basin; and Trachelyopterus aff. coriaceus (possible new species) of the Paraguay River basin. The 5S DNAr was evidenced in 1-3 chromosome pairs. The H3 and H4 histone genes were found in 1-2 chromosome pairs and, in most species, synthenic with DNAr 18S. The U2 snRNA was found in only one chromosome pair, however, Trachelyopterus aff. galeatus had a chromosomal inversion polymorphism, which is in Hardy-Weinberg equilibrium and had homologous chromosomes with distinct size. Cytotaxonomically, the 5S rDNA revealed autapomorphies of four species, while the H3 and H4 histone genes and 18S rDNA distinguished two species and U2 snRNA only one species. As a result, all species could be distinguished, including Trachelyopterus aff. coriaceus and Trachelyopterus aff. galeatus, both possible new species. Once the distribution pattern of the 18S and 5S rDNA, U2 snRNA and H3/H4 histone genes was known, it was used as a guide to compare the microsatellite (GATA)n distribution pattern in the homologous chromosomes of the six species. As a result, most species had a similar (GATA)n distribution pattern in the 18S rDNA chromosome carriers. However, T. galeatus presented a chromosomal polymorphism, which is in Hardy-Weinberg equilibrium and possibly originated through amplification events. On the other hand, the mapping of the (GATA)n sequence in the carriers of the 5S rDNA and H3 / H4 histone genes did not reveal new information about the structure of these chromosomal pairs, however, it indicated a more precisely chromosomal homeologies between the species and reaffirmed the existence of the chromosomal polymorphism in T. galeatus. Similar to the carriers of the 18S rDNA, most species presented a conserved distribution pattern of microsatellite (GATA)n on the chromosomes of the U2 snRNA. However, Trachelyopterus aff. galeatus presented a new chromosomal polymorphism in Hardy-Weinberg disequilibrium and six possible cytotypes. Thus, through combined mapping of these markers, we could evidence cytotaxonomic autapomorphies that can distinguish all species, including both possible new species, as well as new evolutive e diversity aspects in the controvertial neotropical genus Trachelyopterus, which can lead to a better understanding of its taxonomy, evolution and biodiversity.