Abstract Among the Neotropical fish fauna, suckermouth armored catfishes (Hypostomus - Loricariidae) stands out as one of the most difficult groups to diagnose morphologically. So the use of different molecular markers, as is the case of cytogenetics, has been fundamental for a precise identification of some species. In the present study, we characterize the karyotypes of two allopatric Hypostomus spiniger populations, using classical and molecular cytogenetic methods. This species was described by Hensel (1870) but later synonymized with Hypostomus commersoni, and recently it was again recognized as a valid species. Taking to account this taxonomic problematic, the aim of this study is to determine chromosomal characters that may be useful to validate the taxonomic status of H. spiniger and to complement its diagnosis in relation to H. commersoni populations. The karyotype of H. spiniger is composed by 66 chromosomes (10m+16sm+14st+26a), few heterochromatin and a multiple nucleolar organizer regions (NORs) system. Despite, the currently geographic isolation among the samples collected in Forquetinha River (Patos Lagoon basin) and Quadros Lagoon (Tramandaí River basin), both shared the same karyotypic structure, this cytogenetic evidence, suggest that both populations belongs to the same species. Additionally, our results clearly distinguish H. spiniger from H. commersoni populations collected along the Paraná River basin, that exhibited 2n=68 chromosomes and several divergences in heterochromatin and NORs pattern. In sum, the present study reinforces the valid status of H. spiniger and demonstrated the importance of basic cytogenetic analysis to understand conflictuous taxonomic matters.

RESUMO 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.

ABSTRACT 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.

Abstract Doradinae (Siluriformes: Doradidae) is the most species-rich subfamily among thorny catfishes, encompassing over 77 valid species, found mainly in Amazon and Platina hydrographic basins. Here, we analyzed seven Doradinae species using combined methods (e.g., cytogenetic tools and Mesquite ancestral reconstruction software) in order to scrutinize the processes that mediated the karyotype diversification in this subfamily. Our ancestral reconstruction recovered that 2n=58 chromosomes and simple nucleolar organizer regions (NOR) are ancestral features only for Wertheimerinae and the most clades of Doradinae. Some exceptions were found in Trachydoras paraguayensis (2n=56), Trachydoras steindachneri (2n=60), Ossancora punctata (2n=66) and Platydoras hancockii whose karyotypes showed a multiple NOR system. The large thorny catfishes, such as Pterodoras granulosus, Oxydoras niger and Centrodoras brachiatus share several karyotype features, with subtle variations only regarding their heterochromatin distribution. On the other hand, a remarkable karyotypic variability has been reported in the fimbriate barbells thorny catfishes. These two contrasting karyoevolution trajectories emerged from a complex interaction between chromosome rearrangements (e.g., inversions and Robertsonian translocations) and mechanisms of heterochromatin dispersion. Moreover, we believe that biological features, such as microhabitats preferences, populational size, low vagility and migratory behavior played a key role during the origin and maintenance of chromosome diversity in Doradinae subfamily.

RESUMO Gymnorhamphichthys britskii é um peixe neotropical da família Rhamphichthyidae descrita no sistema Paraná-Paraguai. Este estudo relata a primeira descrição cariotípica de G. britskii coletado na bacia do alto rio Paraná, que apresentou 2n = 38 cromossomos, cariótipo composto por 14 metacêntricos, 8 submetacêntricos, 2 subtelocêntricos e 14 acrocêntricos, e número fundamental 62 para ambos sexos. Cromossomos sexuais heteromórficos estavam ausentes. Um único par de regiões organizadoras de nucléolos (RONs) foi detectado no par de cromossomos submetacêntricos número 9 por coloração com prata e confirmado pela sonda DNAr 18S. O DNAr 5S foi localizado em um único par cromossômico. Regiões heterocromáticas foram claramente observadas nos braços curtos do par de cromossomos que carrega a RON e nas posições teloméricas da maioria dos cromossomos acrocêntricos. Além dos dados presentes serem valiosos para auxiliar na compreensão da evolução cariotípica em Rhamphichthyidae, dados de RONs confirmaram a tendência desta família em apresentar sítios simples de RONs, semelhantes aos demais clados de Gymnotiformes. No entanto, a presença de um grande bloco heterocromático no cromossomo portador da RON, pode ser usado como marcador citogenético para G. britskii e as fusões cêntricas parecem ser um mecanismo importante na evolução e diferenciação cariotípica entre as espécies de Gymnotiformes.

ABSTRACT Gymnorhamphichthys britskii is a Neotropical electric fish of family Rhamphichthyidae described from the Paraná-Paraguay system. This study reports the first karyotypic description of G. britskii collected from the upper Paraná river basin, which presented 2n=38 chromosomes, karyotype composed of 14 metacentric, 8 submetacentric, 2 subtelocentric and 14 acrocentric chromosomes, and fundamental number as 62 for both sexes. Heteromorphic sex chromosomes were absent. A single pair of nucleolar organizing regions (NORs) was detected in the submetacentric chromosome pair number 9 by silver staining and confirmed by the 18S rDNA probe. The 5S rDNA was located in a single chromosome pair. Heterochromatic regions were clearly observed in the short arms of the NOR-bearing chromosome pair and in the telomeric positions of most acrocentric chromosomes. Besides the present data are valuable to help in understanding karyotypic evolution in Rhamphichthyidae, data from NORs confirmed the tendency of this family in presenting simple NORs sites, similar to the other Gymnotiformes clades. Yet, the presence of a large heterochromatic block in the NOR-bearing chromosome can be used as cytogenetic markers for G. britskii, and that centric fusions appear to be an important mechanism in the karyotype evolution and differentiation among Gymnotiformes species.

RESUMO Fornecemos dados citogenéticos para a espécie ameaçada Gymnogeophagus setequedas, e o primeiro registro da espécie coletado no rio Iguaçu, na área de preservação ambiental do Parque Nacional do Iguaçu, a qual é uma área de ocorrência inesperada para esta espécie. Verificamos em G. setequedas 2n = 48 cromossomos (4sm + 24st + 20a) e heterocromatina presente nas regiões centroméricas e pericentroméricas, as quais indicam caracteres conservados em Geophagini. Múltiplas regiões organizadoras de nucléolos foram observadas em G. setequedas e são consideradas características apomórficas em Geophagini, enquanto cístrons de DNAr 5S simples e localizados intersticialmente no braço longo de cromossomos subtelocêntricos representam uma característica plesiomórfica. Visto que G. setequedas é uma espécie ameaçada de extinção que ocorre em águas lóticas, recomendamos a manutenção de ambientes livre de barragens em sua área de distribuição.

ABSTRACT We provide cytogenetic data for the threatened species Gymnogeophagus setequedas, and the first record of that species collected in the Iguaçu River, within the Iguaçu National Park’s area of environmental preservation, which is an unexpected occurrence for that species. We verified a diploid number of 2n = 48 chromosomes (4sm + 24st + 20a) and the presence of heterochromatin in centromeric and pericentromeric regions, which are conserved characters in the Geophagini. The multiple nucleolar organizer regions observed in G. setequedas are considered to be apomorphic characters in the Geophagini, whereas the simple 5S rDNA cistrons located interstitially on the long arm of subtelocentric chromosomes represent a plesiomorphic character. Because G. setequedas is a threatened species that occurs in lotic waters, we recommend the maintenance of undammed environments within its known area of distribution.