A New Variant B Chromosome in Auchenipteridae: The Role of (GATA)n and (TTAGGG)n Sequences in Understanding the Evolution of Supernumeraries in Trachelyopterus.

Basic and molecular cytogenetic techniques were carried out in 3 Neotropical region populations of catfishes, two of Trachelyopterus galeatus (one from the marshlands of Paraguay River basin and another from Lago Catalão, Amazon River basin) and one of Trachelyopterus porosus, a sympatric population to T. galeatus from the Amazon River basin. This study aimed to describe and understand the structure and evolution of Trachelyopterus B chromosomes, mainly through physical mapping of repetitive elements. A diploid number of 58 chromosomes was found for all individuals, as well as the presence of B chromosomes. For T. porosus this is the first report of a supernumerary. The sympatric species of T. galeatus and T. porosus from Amazon River had 1-3 B chromosomes and T. galeatus from Paraguay River had 1-2 B chromosomes, all of them showed intra- and interindividual numerical variation. Two females of T. porosus exhibited a new variant B chromosome (B2), previously not seen in Auchenipteridae, which might have originated from B1 chromosomes. All B chromosomes were entirely heterochromatic. In contrast to all complement A and B2 chromosomes, in which the telomeric sequences were found in the telomeric regions, B1 chromosomes of all populations were totally marked by (TTAGGG)n probes. (GATA)n sequence sites were found through all complement A chromosomes, but B1 and B2 chromosomes exhibited only a clustered block in one of the chromosome arms. The most frequent B chromosomes (B1) in all populations/species, including those previously studied in Auchenipteridae catfishes, share the following characteristics: totally heterochromatic, small, metacentric, with accumulation of repetitive (TTAGGG)n sequences, and a low number of (GATA)n copies, which might suggest a common ancient origin in Trachelyopterus species/populations.

Contributions to the taxonomy of Trachelyopterus (Siluriformes): comparative cytogenetic analysis in three species of Auchenipteridae

Auchenipteridae is divided into subfamilies Centromochlinae and Auchenipterinae. Parauchenipterus is included in the latter and is subject of taxonomic discussions concerning its validation or synonymization with Trachelyopterus. Herein, three species from two hydrographic basins were cytogenetically analyzed: Parauchenipterus striatulus from Doce River and two sympatric species, P. galeatus and Trachelyopterus coriaceus, from the Araguaia River. Diploid number of 58 chromosomes was verified for all species, but P. striatulus has different karyotype formula from the others. The three species have heterochromatin located in terminal regions of almost all chromosomes and in pericentromeric region on acrocentric chromosomes. Simple NORs was verified on a subtelocentric chromosome for all species. 5S rDNA sites were detected in three submetacentric chromosome pairs in P. striatulus; in a metacentric chromosome pair and submetacentric pair in T. coriaceus; and in one metacentric chromosome pair in P. galeatus. The similarities found in the karyotypes of the three species suggest the existence of only one genus, Trachelyopterus; therefore, our data refutes the validation of Parauchenipterus. Moreover, the differences in 5S rDNA distribution in P. galeatus in comparison with other populations already studied, indicate the existence of a new taxonomic unit, which suggests a species complex in P. galeatus.(AU)

Auchenipteridae é dividida nas subfamílias Centromochlinae e Auchenipterinae. Parauchenipterus encontra-se incluído na última e tem sido alvo de discussões relacionadas com a problemática taxonômica de validação ou sinonimização com Trachelyopterus. Foram analisadas citogeneticamente três espécies de duas bacias hidrográficas: Parauchenipterus striatulus do rio Doce, P. galeatus e Trachelyopterus coriaceus, simpátricas do rio Araguaia. Todas as espécies analisadas apresentaram número diploide de 58 cromossomos, com diferença na fórmula cariotípica de P. striatulus. A heterocromatina foi localizada nas regiões terminais de quase todos os cromossomos e na região pericentromérica nos cromossomos acrocêntricos das três espécies. AgNORs e DNAr 18S detectaram RONs simples em um par de cromossomos subtelocêntricos nas três espécies. DNAr 5S foi detectado em três pares de cromossomos submetacêntricos em P. striatulus; em um par de cromossomos metacêntricos e um par submetacêntrico em T. coriaceus; e em apenas um par de cromossomos metacêntricos em P. galeatus. As semelhanças encontradas nos cariótipos das três espécies analisadas indicam a existência de somente Trachelyopterus (não validação de Parauchenipterus) e a diferença encontrada na distribuição de DNAr 5S de P. galeatus em relação às outras populações já estudadas sugere a existência de uma nova unidade taxonômica, portanto P. galeatus compreende um complexo de espécies.(AU)