Chromosomal diversity in three species of Lycosa Latreille, 1804 (Araneae, Lycosidae): Inferences on diversification of diploid number and sexual chromosome systems in Lycosinae

Lycosa is one of the most speciose genera in Lycosidae, including species with different sexual chromosome systems (SCS). We carried out cytogenetic analyses in three species of Lycosa, revealing that L. erythrognatha and L. sericovittata share 2n ♂ = 22 and SCS X₁X₂0 while L. gr. nordenskjoldi presents 2n ♂ = 19 and SCS XO, composed only of acrocentric chromosomes. All species shared pericentromeric heterochromatin. Nonetheless, one specimen of L. sericovittata carried two chromosomes with terminal heterochromatin and L. gr. nordenskjoldi showed four chromosomes with interstitial heterochromatin plus another chromosome with terminal C-bands. The pericentromeric heterochromatin of all species as well as the terminal heterochromatic blocks in L. sericovittata were CMA₃⁺. The 18S rDNA sites varied in number and type of bearing chromosomes both at inter and intrapopulational levels, with the highest variation in L. gr. nordenskjoldi. These differences may be related to gene dispersal due to the influence of transposition elements and translocation events. Despite these variations, all species shared ribosomal sites in pair 5. This study demonstrated intra and interspecific chromosomal variability of Lycosa, suggesting that chromosomal rearrangements are related to the diversification of diploid number and SCS in this group of spiders.

First chromosomal analysis in Deinopidae (Araneae) reveals Sex Chromosome System X1X2X3X4, B chromosomes and polymorphism for centric fusion

Here we present the first cytogentic study concerning Deinopidae and their controversial phylogenetic position. This study karyologically analyzed one population of Deinopis biaculeata Simon, 1906 and five populations of Deinopis plurituberculata Mello-Leitão, 1925. The majority of specimens of D. plurituberculata exhibited 2n♂ = 40 and 2n♀ = 44 telocentric chromosomes (however some of them showed B chromosomes, belongs to Aquidauana and Botucatu population). The Deinopis biaculeata and D. plurituberculata meiosis of males showed 18 autosomal bivalents + X₁X₂X₃X₄, n = 22 and n = 18, a rare sex chromosome system (SCS) in spiders. Some individuals of D. plurituberculata from the Campo Grande population exhibited 2n♂ = 39 and 2n♀ = 43, with a metacentric chromosome (heterozygotes for centric fusion). The D. plurituberculata males with the rearrangement exhibit diplotenes with 16 autosomal bivalents + 1 autosomal trivalent + X₁X₂X₃X₄ and metaphases II with n = 22 (18 telocentric autosomes + X₁X₂X₃X₄), n = 21 (16 telocentric autosomes + a metacentric autosome + X₁X₂X₃X₄), n = 18 (18 telocentric autosomes) and n = 17 (16 telocentric autosomes + a metacentric autosome). The Ag-NORs (silver impregnation) are terminally located in a pair, coinciding with secondary constriction, which is the most common configuration for Araneae. The relatively high diploid number in Deinopis corroborates phylogenies that place it in a basal position among Entelegynes, in the UDOH grade (Uloboridae, Deinopidae, Oecobiidae and Hersiliidae). Centric fusion in only one population of D. plurituberculata suggests low dispersion capacity of this species and an absence of homozygotes for fusion suggests their low viability or a need to increase the population sampling of D. plurituberculata exhibiting the rearrangement. B chromosomes were detected in D. plurituberculata, with interpopulacional, intrapopulacional and intraindividual numerical variation, with cells presenting 0 - 3 and 0 - 6 B chromosomes in populations of Aquidauana and Botucatu, respectively.

Chromosome comparison among five species of Neotropical cichlids of Cichlasoma and Gymnogeophagus (Perciformes)

The genera Cichlasoma and Gymnogeophagus belong to the subfamily Cichlinae, the only one in Neotropical cichlids. Cichlasoma dimerus, C. paranaense, C. portalegrense, Gymnogeophagus rhabdotus, and G. lacustris were collected at different points in the Paranapanema and Paraguay basins and the Lagoon of Patos hydrographic system. In addition to conventional analysis, CMA3 fluorochrome staining, and FISH with 18S rDNA probe were performed. All species had a diploid number equal to 48, with interand intraspecific differences in karyotype formulae. All species presented a single AgNOR site, except G. rhabdotus and the C. paranaense population of the Paranapanema River, which revealed more than one pair of nucleolar chromosomes. AgNORs were coincident to 18S rDNA and CMA3. Heterochromatin was distributed in the pericentromeric chromosomal regions and coincident with NORs. For the first time, this work shows cytogenetic data for C. portalegrense, G. lacustris, and G. rhabdotus. Although some results reinforce the idea of conservative chromosome evolution of 2n in Cichlinae, interspecific and populational variations observed confirm that chromosomal rearrangements affect the microstructural karyotype diversification in this group of fish.

Insights on repetitive DNA behavior in two species of Ctenus Walckenaer, 1805 and Guasuctenus Polotow and Brescovit, 2019 (Araneae, Ctenidae): Evolutionary profile of H3 histone, 18S rRNA genes and heterochromatin distribution

Ctenidae represents one of the most representative spider families in the tropical forests of Brazil. Its largest genus, Ctenus, has approximately 220 species out of the more than 520 Ctenidae species described, and several authors consider it polyphyletic. Chromosomal data are only available for four species of Ctenus, representing a large gap in the cytogenetic knowledge about the group. This study provided cytogenetic data on two Ctenus species and one Guasuctenus (previously described as Ctenus). All showed 2n♂ = 28 (26+X1X20). Guasuctenus longipes presented two chromosome pairs containing 18S rDNA genes and C. medius, however C. ornatus showed only one chromosome pair with the 18S rDNA gene. Hybridization data using histone H3 probe indicated specific profiles: histone H3 genes were found in one chromosome pair in G. longipes, in three pairs in C. medius, and in four pairs in C. ornatus. Furthermore, supernumerary chromosomes were identified in C. ornatus presenting a meiotic behavior similar to that of sex chromosomes; and a trivalent was found in C. medius, formed by the association of one sex chromosome and an autosomal bivalent, indicating the importance of these events for the diversification of sex chromosomes in spiders. The C-banding pattern was similar between C. medius and C. ornatus with regard to the number and locations of heterochromatic bands, suggesting that heterochromatin amplification and dispersion, affect karyotypic evolution in the genus. Cytogenetic data showed similarity between C. medius and C. ornatus, and differentiation of G. longipes congruent with morphological data. Moreover, although more comparative analyses are needed to specify composition of the dispersed heterochromatin in Ctenus, the mapping of heterochromatic bands provided insights about the evolution of the karyotypes in this genus.

The Karyotypic Diversification of Calophysines and the Exallodontus-Propimelodus Clade (Pimelodidae, Siluriformes): A Cytotaxonomic and Evolutionary Approach in Pimelodidae Based on Ancestral State Reconstruction

Pimelodidae family is one of the most diverse and widely distributed fish groups in South America. Phylogenetic analysis in the family have recently indicated the existence of two main clades: "sorubiminae" and the OCP clade, including Pimelodus ornatus, "calophysines" and "pimelodines." The aim of this study was to investigate the karyotype of three Amazonian Pimelodidae species: Calophysus macropterus, Propimelodus eigenmanni, and Exallodontus aguanai associating them to the literature, seeking to reconstruct probable ancestral characters. C. macropterus has 2n = 50, 20m+20sm+10a (fundamental number [FN] = 90), simple interstitial nucleolar organizing regions (NORs), and four 5S rDNA sites terminals, two in synteny with the 18S rDNA. P. eigenmanni has 2n = 56, 28m+20sm+2st+6a (FN = 106), simple NORs, and two 5S rDNA sites terminals. E. aguanai has 2n = 56, 36m+12sm+2st+6a (FN = 106) and 18S and 5S rDNA sites interstitial syntenic in the chromosome 1. All species exhibited a higher amount of heterochromatin, differing from the pattern of the family, and strong marking associated with NORs. The integration between molecular phylogenetic data and karyotype data indicated a high probability that 2n = 56 and simple terminals NORs in the short arm are ancestral characters in Pimelodidae, evidenced in "sorubiminae." In the OCP clade derived traits were observed resulting from chromosomal changes that played a critical role in the karyotype evolution of the group.

Blocking and remanence properties of weakly and highly interactive cobalt ferrite based nanoparticles

We compare both magnetic blocking properties and remanence curves for dilute ferrofluid and powder samples of ferrite magnetic nanoparticles. Low field DC magnetization, AC susceptibility, isothermal remanent magnetization and DC demagnetization techniques are employed to investigate the role of interparticle magnetic interactions on the superparamagnetic relaxation, the magnetic anisotropy and on the super-spin-glass state in closely packed particles. The samples used herein are 3 nm sized spinel-type nanocrystals made of a cobalt ferrite core covered by a layer of maghemite on its outermost surface and can be obtained as aqueous colloidal dispersions thanks to this core-shell strategy. They show large anisotropy attributed to an enhanced surface contribution and the blocking temperature is shifted towards higher values as interparticle distance decreases. For all investigated diluted liquids and powder samples the frequency dependency of the peak temperature is well accounted by a Vogel-Fulcher law, with the insertion of a phenomenological temperature associated to the magnitude of interparticle dipolar interactions. The fractional change of the peak temperature per decade of frequency enlights the presence of interactions between particles in dilute liquids and of a spin-glass-like state in powder samples. The remanence curves always show global demagnetizing behavior, attributed to the combination of both spin surface disorder and interparticle dipolar interactions, the former being predominant in isolated nanoparticles and the latter in powder samples. However, in the most compacted powder, exchange interaction between surface ions of different particles becomes more pronounced and promotes an additive magnetizing effect.

Karyotype diversity between species of Crenicichla (Perciformes, Cichlidae) from different Brazilian hydrographic basins

Crenicichla is the largest genus in the Cichlidae family in South America. The genus includes 100 valid species that are popularly known in Brazil as jacundás or joaninhas and are widely distributed in rivers east of the Andes. Cytogenetic analyses were carried out on seven species in this genus. All species showed a diploid number of 48 with interspecific differences in karyotype formulas and AgNORs located in interstitial position on the short arm of the largest metacentric pair, except for the two populations from C. britskii. Population A showed terminal markings on the long arm of the fifth pair of the complement, and population B showed up to two marked chromosome pairs. FISH with an 18S rDNA probe was coincident with AgNORs and CMA₃, except for pair 6 from population B of C. britskii that did not presented positive CMA₃ sites. This work presents first cytogenetic data for C. haroldoi, C. maculata, and C. punctata, and the results show karyotypic patterns similar to those in the literature. However, the diversity found in populations of C. britskii represents new information about the evolution of the karyotype of the Cichlidae family, which has been conservative. Furthermore, the data could assist in phylogenetic studies of Crenicichla.

Genetic and Chromosomal Differentiation of Rhamdia quelen (Siluriformes, Heptapteridae) Revealed by Repetitive Molecular Markers and DNA Barcoding

Rhamdia quelen, a species of Heptapteridae, is considered to be a complex because of taxonomic and phylogenetic inconsistencies. Determining the physical location of repetitive DNA sequences on the chromosomes and the DNA barcode might increase our understanding of these inconsistencies within different groups of fish. To this end, we analyzed R. quelen populations from two river basins in Brazil, Paraguay and Parana, using DNA barcoding and different chromosomal markers, including U2 snDNA, which has never been analyzed for any Rhamdia species. Cytochrome c oxidase I gene sequence analysis revealed a significant differentiation among populations from the Miranda and Quexada rivers, with genetic distances compatible to those found among different species in neotropical fishes. Our results, in general, revealed a conservative chromosomal evolution in R. quelen and a differential distribution of some markers, such as 5S rDNA and U2 snDNA, in different populations. We suggest that R. quelen must undergo a major revision in its morphological, genetic, and cytogenetic molecular and taxonomic structure to elucidate possible operational taxonomic units.

Cytogenetic Trends in Two Families of the Neotropical Catfishes: Heptapteridae and Pseudopimelodidae (Siluriformes)

Several neotropical Siluriformes groups suffered important taxonomic revisions based on the evaluation of morphological and molecular characteristics that allow the construction of new phylogenetic hypothesis. In the present study were cytogenetically analyzed six species belonging to Heptapteridae (Cetopsorhamdia iheringi, Phenacorhamdia tenebrosa, Rhamdella eriarcha, Pimelodella meeki, Pimelodella australis, Heptapterus mustelinus) and two to Pseudopimelodidae families (Microglanis cottoides and Microglanis cibelae) by means of differential staining techniques to describe more precisely cytogenetic similarities and differences. The diploid number of R. eriarcha with 2n = 58 and M. cibelae with 2n = 56 were reported for the first time. Also, the lowest chromosome number (2n = 48) for P. tenebrosa was described. The chromosome-banding techniques for to put in evidence nucleolar organizers impregnated by silver nitrate ([AgNORs], chromomycin A₃ [CMA₃], and rDNA 18S) showed for all studied species conserved patterns, characteristic for each family. The rDNA 5S showed high variability among species or populations of both families, these regions could be simple or multiple, syntenic, or not with rDNA18S. The chromosome markers showed that both families are related not only from a morphologic point of view but also by their karyotypic characteristics, however, some of the present cytogenetic results evidence the importance of new morphologic, molecular, and phylogenetic studies to improve the knowledge of these fish groups.

Primeiros dados Cariotípicos em Cupiennius sp. (Araneae, Ctenidae)

Os dados citogenéticos em Ctenidae são reportados apenas para 8 espécies, que apresentam juntas uma variação no número diplóide de 2n = 22, 2n = 28 e 2n = 29, sendo 28 cromossomos o número mais frequente na família, até o momento. Também são descritos dois sistemas de cromossomos sexuais, X1X20 observado nas espécies com números diploides pares (2n = 22 e 28) e X1X2X30 para as espécies com 29 cromossomos. Dados acerca da distribuição de regiões ricas em pares de bases AT e GC são insistentes em Ctenidae, porém são observados geralmente nas regiões terminais dos cromossomos em Araneae. A impregnação com nitrato de prata para detectar as regiões organizadoras de nucléolo (RONs) também foi pouco empregada nas análises citogenéticas dessa família, sendo que 3 espécies apresentam RONs simples (Ctenus ornatus, Ctenus sp., Ctenus indicus) e 1 RONs múltiplas (Viracucha andicola), com dois pares portadores. O presente estudo teve como objetivo analisar citogeneticamente cinco indivíduos machos de Cupiennius sp., coletados no Parque Nacional do Superagui, de modo a descrever o número diploide e o sistema de cromossomos sexuais, o número de RONs e a distribuição das regiões AT e GC ricas (por meio do emprego dos fluorocromos base-específcos CMA3 e DAPi). Foi observado um número diplóide até então não relatado para Ctenidae, de 2n= 24 + X1X20. Os fluorocromos revelaram bandas GC ricas distribuídas nas regiões pericentroméricas e intersticiais proximais da maioria dos cromossomos, que foram identificados como acrocêntricos. Foi possível observar um par cromossômico com uma grande constrição terminal CMA3+, coincidente com a impregnação com nitrato de prata, e com a FISH com sonda de DNAr 18S, que revelaram um único par portador das RONs. O presente estudo amplia para 7 o número de gêneros com descrição citogenética, sendo eles: Ctenus, Nothroctenus, Parabatinga, Phoneutria, Anahita, Asthenoctenus e agora Cupiennius. Além de trazer também a primeira descrição de 2n = 24 + X1X20 para uma espécie da família.

Dados citogenéticos preliminares de quatro espécies de Siluriformes da bacia Amazônica

Dentre as famílias pertencentes à ordem Siluriformes, Heptapteridae e Pimelodidae estão entre as mais diversificadas apresentando, respectivamente, 210 e 109 espécies válidas. Entretanto, considerando o número de espécies existentes, são escassos os trabalhos citogenéticos nestes grupos de peixes: Heptapteridae possui dados cariotípicos para apenas 41 espécies e Pimelodidae para 45. O objetivo do presente estudo foi caracterizar citogeneticamente quatro espécies de peixes da ordem Siluriformes, coletadas no rio Solimões, bacia Amazônica, por meio de técnicas convencionais de coloração e bandamento cromossômico. Foram analisadas uma espécie de Heptapteridae, Pimelodella cristata, e três espécies de Pimelodidae, Callophysus macropterus, Propimelodus sp. e Exallodontus aguanae. Os resultados mostram que P. cristata apresentou 2n=46, com número fundamental (NF) igual a 86, sendo 24m+16sm+6st-a. Callophysus macropterus apresentou 2n=50 e NF igual a 90, com 22m+18sm+10st-a. As espécies Propimelodus sp e Exallodontus aguanae apresentaram 2n=56, mas diferiram quanto à fórmula cariotípica, sendo que Propimelodus apresentou 24m+22sm+10st-a e NF=102 e E. aguanae mostrou 32m+16sm+8st-a e NF=104. As regiões organizadoras de nucléolos (Ag-RONs) se mostraram simples para todas as espécies analisadas e, com exceção de Callophysus macropterus, todas apresentaram uma constrição secundária, coincidente com as RONs, sendo terminal em Propimelodus sp. e Pimelodella cristata, e intersticial em Exallodontus aguanae, sendo este o primeiro relato em Pimelodidae. As AgRONs foram localizadas em um par acrocêntrico exceto em E. aguanae, evidenciadas no primeiro par metacêntrico. Em P. cristata e E. aguanae foi evidenciado um heteromorfismo de tamanho da constrição secundária entre os cromossomos homólogos. Na coloração com fluorocromos, todas as constrições secundárias apresentaram sinal positivo para cromomicina A3 sendo, portanto, regiões ricas em bases GC. Callophysus macropterus foi a única espécie que mostrou sinais positivos para o fluorocromo DAPI, além do par cromossômico positivo para CMA3, provavelmente correspondente à RON. Os dados aqui apresentados são os primeiros para este grupo de peixes da bacia Amazônica, exceto para C. macropterus e, apesar de preliminares, já fornecem interessantes informações citogenéticas sobre estas espécies, que poderão contribuir para um melhor entendimento da evolução e estrutura cariotípica das famílias Heptapteridae e Pimelodidae.

Diferenciação cromossômica e molecular no complexo Rhamdia quelen (Siluriformes, Heptapteridae) evidenciado pelo mapeamento físico de genes ribossomais, de RNAsn U2 e DNA barcoding

Análises de sequências de DNAs repetitivos proporcionam uma caracterização cromossômica mais apurada, auxiliando na compreensão de problemas taxonômicos e filogenéticos. Rhamdia quelen é considerada um complexo de espécies e, apesar de ser a espécie mais estudada dentro de Heptapteridae, pouco se sabe sobre sequências de DNA repetitivo no grupo. Sendo assim, o objetivo deste trabalho foi realizar uma análise citogenética comparativa entre seis populações de R. quelen. Foi confirmado o número diplóide igual 58, com variação nas fórmulas cariotípicas sendo: 40m+10sm+4st+4a e número fundamental (NF) igual 112, para a população do rio Quexada/PR; 40m+12sm+6st (NF=116) para exemplares do Ribeirão do Penacho/PR; 34m+16sm+8st (NF=116) para rio Miranda/MS e 32m+8sm+18st (NF=116) para a população do rio Cambé. A região organizadora de nucléolos (AgRONs) foi evidenciada na região terminal de um cromossomo submetacêntrico, nas quatro populações de R. quelen, sendo coincidente com a coloração pelo fluorocromo CMA3. A população do rio Quexada apresentou um heteromorfismo de tamanho das AgRONs entre os cromossomos homólogos. O mapeamento cromossômico de genes ribossomais 18S e 5S, e de U2 DNAsn foi realizado nas quatro  populações citadas de R. quelen, mais as do rio Taquari e do ribeirão Lindóia, ambas do estado do Paraná. A distribuição dos genes de DNAr 18S confirmou o padrão simples da RON, em todas as populações, estando co-localizados com alguns sítios de U2 DNAsn. Os resultados mostraram uma variação das sequências de DNAs repetitivos na população do rio Miranda em comparação com as demais populações. Apenas os indivíduos desta localidade apresentaram um único par portador da sequência de U2 DNAsn, assim como foi a única população a mostrar um padrão múltiplo de distribuição do DNAr 5S. Esta heterogeneidade da população do rio Miranda em relação às demais populações de R. quelen, foi confirmada pela análise da sequência que codifica a subunidade I da enzima citocromo oxidase C, mostrando uma diferenciação em relação à população do rio Quexada. Os dados revelam uma variação interpopulacional na microestrutura cromossômica da espécie nunca antes evidenciada, caracterizando essas famílias de DNA repetitivos como importantes ferramentas em estudos filogenéticos e taxonômicos.  

Análise do padrão de distribuição da heterocromatina e da região organizadora do nucléolo em Pimelodus microstoma (Pimelodidae)

Pimelodus microstoma é uma espécie de peixe que pertence à família Pimelodidae, da ordem Siluriformes. Estudos citogenéticos na família Pimelodidae mostraram que 2n=56 é o mais comum neste grupo, sendo encontradas algumas espécies com 2n=50, 54 e 58. As regiões organizadoras de nucléolos são localizadas em região terminal de um par de cromossomos subtelo-acrocêntrico em todas as espécies da família Pimelodidae analisadas até o momento, indicando um caráter basal para o grupo. Nos pimelodídeos, é característica a pouca quantidade de heterocromatina, geralmente distribuída em regiões pericentroméricas e/ou terminais dos cromossomos. Tanto as RONs como o padrão de distribuição da heterocromatina são importantes marcadores citogenéticos, que permitem diferenciar espécies e populações. O objetivo do presente estudo foi caracterizar citogeneticamente Pimelodus microstoma do rio Laranjinha/PR, bacia do rio Paranapanema e, para isso, foram analisados 12 espécimes. Utilizou-se técnicas convencionais de coloração com Giemsa e de bandamento cromossômico: impregnação pelo nitrato de prata para observar as regiões organizadoras de nucléolo, bandamento C para evidenciar o padrão de distribuição da heterocromatina e coloração com fluorocromos base específicos cromomicina A3 (CMA3)e DAPI para observar regiões ricas em CG e AT, respectivamente. As análises mostraram 2n=56 com fórmula cariotípica de 24 cromossomos metacêntricos, 18 submetacêntricos, 8 subtelocêntricos e 6 acrocêntricos e o número fundamental igual 106. As regiões organizadores de nucléolo foram localizadas na região terminal do braço longo de um par de cromossomos subtelocêntricos. Na análise com fluorocromos observou-se que a RON é CMA3 positiva e DAPI negativa, sendo rica em pares de bases GC. A heterocromatina mostrou-se distribuída em regiões terminais, na maioria dos cromossomos, sendo observadas algumas marcações biteloméricas, com alguns cromossomos apresentando blocos terminais. Foram observadas poucas regiões heterocromáticas pericentroméricas. Após a coloração da Banda C com fluorocromos, algumas regiões heterocromáticas mostraram-se CMA3 positivas, portanto ricas em pares de bases GC e marcações com DAPI não puderam ser observadas. Os dados relatados para P. microstoma do rio Laranjinha seguem o mesmo padrão observada as demais espécies do gênero e da família. Um estudo mais amplo com fluorocromos deverá ser realizado para melhor analisar a composição da heterocromatina neste grupo de peixes.

Mapeamento físico de snDNA U2 em espécies da família Cichlidae

O processo de splicing do RNA mensageiro é realizado pelo spliceossomo em um dos maiores e mais complexos mecanimos moleculares da célula. O spliceossomo consiste em cinco RNAs nucleares (snRNAs) – U1, U2 U4,U5 e U6 que, unidos com vários fatores proteicos, formam uma  ribonucleoproteína nuclear (snRNPs). Os ciclídeos são um dos maiores e mais diversificados grupos de peixes, sendo importantes modelos de evolução biológica, além de serem apreciados na aquariofilia e aquicultura. Apesar disso, ainda são poucos os trabalhos citogenéticos, com somente 154 espécies cariotipadas até o momento e este número se restringe ainda mais quando se trata de análises com sequências de DNAs repetitivos, principalmente em ciclídeos neotropicais. Sendo assim, o presente estudo tem como objetivo a localização cromossômica do gene snRNA U2 em diferentes espécies da família Cichlidae. Foi realizada a extração de DNA de Cichlasoma e utilizada como molde para amplificação do gene U2, com os primers U2F (59-ATC GCT TCT CGG CCT TAT G–39) e U2R (59-TCC CGG CGG TAC TGC AAT A-39). Essa PCR foi marcada com Cy3dUTP. O fragmento da PCR obtido no presente trabalho foi de, aproximadamente, 200 pb o que parece ser semelhante ao encontrado para o mesmo gene no genoma humano, que mostra uma região codificante de 188 pb. A hibridação fluorescente in situ (FISH) foi realizada em seis espécies de ciclídeos neotropicais. Cichlasoma portalegrense, Gymnogeophagus gymnogenys, Crenicichla lepdota, Crenicichla maculata  e Crenicichla niederleinii  apresentaram um par portador do sitio de DNAsn U2, enquanto Crenicichla britski apresentou dois pares. Os estudos com a sequência de DNAsn U2 em peixes ainda são muito restritos, mas em sua maioria evidenciam essa sequência em um único par cromossômico contudo, estudos recentes demonstram uma variabilidade maior em relação ao mapeamento físico desta sequência. Em ciclideos existem análises de DNAsn U1 para 12 espécies, todas com um único sítio portador da sequência entretanto, para DNAsn U2 os dados aqui apresentados são os primeiro neste grupo de peixes e, apesar de preliminares, já indicam que análises desta e outras sequências de DNA repetitivo podem contribuir para um maior entendimento da organização genômica da família Cichlidae.

Repetitive DNA in the Catfish Genome: rDNA, Microsatellites, and Tc1-Mariner Transposon Sequences in Imparfinis Species (Siluriformes, Heptapteridae)

Physical mapping of repetitive DNA families in the karyotypes of fish is important to understand the organization and evolution of different orders, families, genera, or species. Fish in the genus Imparfinis show diverse karyotypes with various diploid numbers and ribosomal DNA (rDNA) locations. Here we isolated and characterized Tc1-mariner nucleotide sequences from Imparfinis schubarti, and mapped their locations together with 18S rDNA, 5S rDNA, and microsatellite probes in Imparfinis borodini and I. schubarti chromosomes. The physical mapping of Tc1/Mariner on chromosomes revealed dispersed signals in heterochromatin blocks with small accumulations in the terminal and interstitial regions of I. borodini and I. schubarti. Tc1/Mariner was coincident with rDNA chromosomes sites in both species, suggesting that this transposable element may have participated in the dispersion and evolution of these sequences in the fish genome. Our analysis suggests that different transposons and microsatellites have accumulated in the I. borodini and I. schubarti genomes and that the distribution patterns of these elements may be related to karyotype evolution within Imparfinis.

Cytogenetic analysis of five Ctenidae species (Araneae): detection of heterochromatin and 18S rDNA sites

The present study aimed to cytogenetically analyse five Ctenidae species Ctenus ornatus (Keyserling, 1877), Ctenus medius (Keyserling, 1891), Phoneutria nigriventer (Keyserling, 1891), Viracucha andicola (Simon, 1906), and Enoploctenus cyclothorax (Philip Bertkau, 1880), from Brazil. All species presented a 2n♂ = 28 except for V. andicola, which showed 2n♂ = 29. Analysis of segregation and behavior of sex chromosomes during male meiosis showed a sex chromosome system of the type X₁X₂0 in species with 28 chromosomes and X₁X₂X₃0 in V. andicola. C banding stained with fluorochromes CMA₃ and DAPI revealed two distributions patterns of GC-rich heterochromatin: (i) in terminal regions of most chromosomes, as presented in C. medius, P. nigriventer, E. cyclothorax and V. andicola and (ii) in interstitial regions of most chromosomes, in addition to terminal regions, as observed for C. ornatus. The population of Ubatuba (São Paulo State) of this same species displayed an additional accumulation of GC-rich heterochromatin in one bivalent. Fluorescent in situ hybridization revealed that this bivalent corresponded to the NOR-bearing chromosome pair. All analyzed species have one bivalent with 18S rDNA site, except P. nigriventer, which has three bivalents with 18S rDNA site. Karyotypes of two species, C. medius and E. cyclothorax, are described for the first time. The latter species is the first karyotyped representative of the subfamily Acantheinae. Finally, 18S rDNA probe is used for the first time in Ctenidae at the present study.

Seminoma and sertolioma in a male pseudohermaphrodite dog with unilateral cryptorchidism: short communication

A male miniature Schnauzer with cryptorchidism and a mass growth in the right inguinal canal was admitted to the clinical center of a veterinary hospital. During surgical resection of the mass, tubular formations were found, connecting the mass to the left testicle. Histopathology revealed that the tubular formations were uterine tubes and the mass was a seminoma associated with a sertolioma of the right testicle. Further analysis also showed atrophy of the left testicle. Cytogenetic evaluation revealed normal chromosomes of male gender, 78, XY, which led to the conclusion that this was a male pseudohermaphrodite.

Chromosomal Mapping of Repetitive DNA Sequences in the Genus Bryconamericus (Characidae) and DNA Barcoding to Differentiate Populations

The mapping of repetitive DNA sites by fluorescence in situ hybridization has been widely used for karyotype studies in different species of fish, especially when dealing with related species or even genera presenting high chromosome variability. This study analyzed three populations of Bryconamericus, with diploid number preserved, but with different karyotype formulae. Bryconamericus ecai, from the Forquetinha river/RS, presented three new cytotypes, increasing the number of karyotype forms to seven in this population. Other two populations of Bryconamericus sp. from the Vermelho stream/PR and Cambuta river/PR exhibited interpopulation variation. The chromosome mapping of rDNA sites revealed unique markings among the three populations, showing inter- and intrapopulation variability located in the terminal region. The molecular analysis using DNA barcoding complementing the cytogenetic analysis also showed differentiation among the three populations. The U2 small nuclear DNA repetitive sequence exhibited conserved features, being located in the interstitial region of a single chromosome pair. This is the first report on its occurrence in the genus Bryconamericus. Data obtained revealed a karyotype variability already assigned to the genus, along with polymorphism of ribosomal sites, demonstrating that this group of fish can be undergoing a divergent evolutionary process, constituting a substantive model for studies of chromosomal evolution.

Isolation and characterization of 5S rDNA sequences in catfishes genome (Heptapteridae and Pseudopimelodidae): perspectives for rDNA studies in fish by C0t method

Sequences of 5S ribosomal RNA (rRNA) are extensively used in fish cytogenomic studies, once they have a flexible organization at the chromosomal level, showing inter- and intra-specific variation in number and position in karyotypes. Sequences from the genome of Imparfinis schubarti (Heptapteridae) were isolated, aiming to understand the organization of 5S rDNA families in the fish genome. The isolation of 5S rDNA from the genome of I. schubarti was carried out by reassociation kinetics (C0t) and PCR amplification. The obtained sequences were cloned for the construction of a micro-library. The obtained clones were sequenced and hybridized in I. schubarti and Microglanis cottoides (Pseudopimelodidae) for chromosome mapping. An analysis of the sequence alignments with other fish groups was accomplished. Both methods were effective when using 5S rDNA for hybridization in I. schubarti genome. However, the C0t method enabled the use of a complete 5S rRNA gene, which was also successful in the hybridization of M. cottoides. Nevertheless, this gene was obtained only partially by PCR. The hybridization results and sequence analyses showed that intact 5S regions are more appropriate for the probe operation, due to conserved structure and motifs. This study contributes to a better understanding of the organization of multigene families in catfish's genomes.

Patient perceptions concerning clinical trials in oncology patients

Background

Clinical trials are critical to scientifically evaluate promising new therapies in oncology, but patient accrual to these studies is persistently low. Patient preference plays an important role in enrollment in these trials. We performed this survey to evaluate the perceptions of newly diagnosed oncology patients about clinical trials and the reasons why they wish to or not to participate in these trials.

Methods

Patients were given a ten question survey reflective of their attitudes regarding clinical trials as a treatment option at their initial visit. The self-directed questionnaire was scored on an ordinate scale from strongly agree [1] to strongly disagree [5].

Results

Ninety three patients were surveyed in the cancer specific multispecialty clinics in an academic center. Our patients expected their providers to discuss all information relating to clinical trials and eligibility at the first visit (65.4% agree and 15.4% neutral, p < 0.0001). Patients felt their privacy and safety would be safeguarded in the University sponsored trials (56.8% agree, and 25.7% neutral, p < 0.0001). Over 80% patients showed their unwillingness to participate in randomized clinical trials (disagree 61%, neutral 19.5%, p < 0.001). Patients also showed less likelihood to participate in clinical trials as a first treatment option (48.7% disagree and 28.9% neutral, p0.0161), but were willing to consider participating in a clinical trial if the conventional treatment failed. Industry sponsored trials, phase 1 trials, investigator initiated trials with the involved tests and time commitment and altruistic reasons did not significantly deviate from the mean preference analyzed using Fisher's exact test analysis.

Conclusions

Patients consider the option of clinical trials as important in their treatment, and expect to be informed by their oncologist about such trials. Newly diagnosed cancer patients perceive randomization and first line trials negatively. Since randomization data provides new standards of care and hope for improved treatment, patients and their families must be educated of their importance.

Evolutionary trends in the family Curimatidae (Characiformes): inferences from chromosome banding

The family Curimatidae is a fish group usually considered chromosomally conserved in their diploid number. However, some studies show small changes in the karyotype microstructure, and the presence of B chromosomes, indicating a chromosomal diversification within the group, even if structural changes in the karyotypes are not visible. Few studies associate this trait with an evolutionary pattern within the family. This study aimed to characterize the karyotype, nucleolus organizer regions (NORs), and heterochromatin distribution of six species of Curimatidae of the genera Cyphocharax Fowler, 1906 and Steindachnerina Fowler, 1906: Cyphocharax voga (Hensel, 1870), Cyphocharax spilotus (Vari, 1987), Cyphocharax saladensis (Meinken, 1933), Cyphocharax modestus (Fernández-Yépez, 1948), Steindachnerina biornata (Braga et Azpelicueta, 1987) and Steindachnerina insculpta (Fernández-Yépez, 1948) and contribute data to a better understanding of the mechanisms involved in the chromosomal evolution of this group of fish. All specimens had 2n=54, m-sm, and B microchromosomes. Five species exhibited single NORs, except for Steindachnerina biornata, which showed a multiple pattern of ribosomal sites. NORs were chromomycin A3 positive (CMA3 (+)) and 4'-6-diamino-2-phenylindole (DAPI(-)) negative, exhibiting differences in the pair and chromosomal location of each individual of the species. FISH with 5S rDNA probe revealed sites in the pericentrometic position of a pair of chromosomes of five species. However, another site was detected on a metacentric chromosome of Cyphocharax spilotus. Heterochromatin distributed both in the pericentromeric and some terminal regions was revealed to be CMA3 (+)/DAPI(-). These data associated with the previously existing ones confirm that, although Curimatidae have a very conservative karyotype macrostructure, NORs and heterochromatin variability are caused by mechanisms of chromosome alterations, such as translocations and/or inversions, leading to the evolution and diversification of this group of fish.

Physical mapping of 18S rDNA and heterochromatin in species of family Lygaeidae (Hemiptera: Heteroptera)

Analyses conducted using repetitive DNAs have contributed to better understanding the chromosome structure and evolution of several species of insects. There are few data on the organization, localization, and evolutionary behavior of repetitive DNA in the family Lygaeidae, especially in Brazilian species. To elucidate the physical mapping and evolutionary events that involve these sequences, we cytogenetically analyzed three species of Lygaeidae and found 2n (♂) = 18 (16 + XY) for Oncopeltus femoralis; 2n (♂) = 14 (12 + XY) for Ochrimnus sagax; and 2n (♂) = 12 (10 + XY) for Lygaeus peruvianus. Each species showed different quantities of heterochromatin, which also showed variation in their molecular composition by fluorochrome staining. Amplification of the 18S rDNA generated a fragment of approximately 787 bp. The alignment of the consensus sequence with sequences from other species of Heteroptera deposited in the GenBank revealed a similarity of 98% with small differences. Fluorescent in situ hybridization with the 18S rDNA fragment revealed that this ribosomal gene was located in 1 autosomal pair at different positions in the three species. No cytogenetic data are available for these Brazilian species. The basal number and the possible chromosomal changes that occurred among the different species, as well as the evolution of these DNA sequences, are discussed.

Karyotypic diversity in a population of Bryconamericus aff. iheringii (Characidae)

Bryconamericus comprises 56 species distributed into three groups, on the basis of the position and shape of the maxillary teeth: B. exodon, B. microcephalus and B. iheringii groups. Few cytogenetic data are available for this genus, but the diploid number of 52 chromosomes is quite common, although the karyotypic variability is extensive. This study aimed to characterize a population of B. aff. iheringii and thus contribute more cytogenetic information and better understanding of the structure and karyotypic evolution of this genus. We found 6 cytotypes with different NOR patterns: cytotype I showed a karyotype formula of 12m+10sm+16st+14a (FN = 90) and single NORs; cytotype II with 18m+14sm+10st+10a (FN = 94) and cytotype III with 20m+18sm+4st+10a (FN = 94), showing both single and multiple NORs; cytotype IV with 20m+14sm+12st+6a (NF = 98), cytotype V with 22m+18sm+8st+4a (FN = 100) and cytotype VI with 18m+24sm+6st+4a (FN = 100), all with multiple NORs. Cytotype I is the most different in relation to FN and NOR pattern, and can be regarded as belonging to another species of the genus Bryconamericus, living in sympatry in Três Bocas Stream. The remaining cytotypes may have been generated by crosses between them and by pericentric inversions. Meiotic cells were also analyzed and showed that despite the high karyotypic variability, chromosome pairing occurred normally. The great variability found in B. aff. iheringii may be related to a high degree of polymorphism; nevertheless, the possibility of occurrence of more than one species in this location is not ruled out, demonstrating the need for conservation of the Três Bocas Stream.

Activity patterns of nucleolar organizer region during spermatogenesis of different curimatid species (Characiformes: Curimatidae)

The nucleolus is an important nuclear structure where transcription of ribosomal DNA (rDNA) takes place. During mitotic division, the nucleolus passes through different processes that inactivate rDNA transcription; in meiosis, its reassembly takes place during telophase II. The objective of this study was to identify the activity patterns and localization of nucleolar organizer regions (NORs) during meiotic division in fish species of the family Curimatidae. For this analysis, the meiotic division in five curimatid species was studied using silver nitrate impregnation, fluorescent in situ hybridization (FISH), and base-specific fluorochrome staining. Silver nitrate staining indicated the presence of a nucleolus in interphase nuclei, one chromosome pair in the spermatogonial metaphases, and one bivalent at the pachytene stage. No Ag-NORs were identified for cells at the diplotene, diakinesis, metaphase I, or metaphase II stages; however, FISH confirmed the presence of Ag-NORs in the nuclei, in spermatogonia, and at the pachytene phase. FISH identified this region during the other stages of meiosis, as did fluorochrome CMA3 staining, which revealed fluorescent marks corresponding to NORs during all stages of meiosis analyzed. The gene activity and localization of this ribosomal sequence during the different stages involved will also be discussed.

Comparative cytogenetics between two species of the family Pseudopimelodidae (Siluriformes): occurrence of natural triploidy and supernumerary chromosomes

The Pseudopimelodidae family comprises 35 species however, cytogenetic studies have been performed in only six species. This study uncovered karyotypic data on Pseudopimelodus pulcher and Microglanis cottoides. Both species possessed 2n = 54, with 20m + 16sm + 10st + 8a and FN = 100 for P. pulcher and 30m + 14sm + 6st + 4a and FN = 104 for M. cottoides. A female of M. cottoides with 45m + 21sm + 9st + 6a (2n = 81) plus two extra small chromosomes was found, indicating a natural triploidy with supernumerary chromosomes. The formation of the polyploid individual seems to have come from a diploid female gamete, due to the presence of a marker chromosome pair partially heterochromatic presents only in females and common to that exemplar. This triploid female showed three chromosomes with nitrate staining (AgNOR), 18S rDNA probe and chromomycin A3 (CMA3) staining. AgNORs were observed on pairs 12 and 23 in P. pulcher and pair 24 in M. cottoides, results that were confirmed with an 18S rDNA probe and CMA3 fluorochrome. These are the first chromosomal data for P. pulcher and provide the first description of natural triploidy with the presence of supernumerary chromosomes in this family and emphasizing well the chromosomal rearrangements diversification between this species.

Remarkable karyotypic homogeneity in a widespread tropical fish species: Hoplosternum littorale (Siluriformes, Callichthyidae)

The first chromosomal data in Hoplosternum littorale from an isolated South American drainage in north-eastern Brazil are presented. All specimens were characterized by a diploid number (2n) of 60 chromosomes divided into three metacentric, one submetacentric and 26 acrocentric pairs; single nucleolar organizer regions (NOR) on the sixth pair; centromeric and interstitial heterochromatin; GC-rich sites on four large acrocentric chromosomes, including the NOR-bearing pair, and 5S ribosomal genes at terminal region on short arms of two acrocentric pairs. These data are invariably similar to previous reports in H. littorale from distant localities throughout South America, which contrasts with the chromosomal diversity of Callichthyidae and reinforces the role of human activities on the dispersal and colonization of this fish.

Sex chromosome differentiation in Belostoma (Insecta: Heteroptera: Belostomatidae)

Belostoma, a genus of the family Belostomatidae, includes species of great ecological importance as biocontrol agents. Few species of these species have been the subject of cytogenetic analyses. Karyotypic evolution in this genus involves agmatoploidy and simploidy; there are also different sex chromosome systems. We examined two Belostoma species (B. dilatatum and B. candidulum) collected from the Paranapanema River Basin (Brazil). Mitotic and meiotic analysis revealed 2n(♂) = 26 + X₁X₂X₃Y for B. dilatatum and 2n(♂) = 14 + XY for B. candidulum; both karyotypes have holokinetic chromosomes. Differences in heterochromatin distribution were also observed between the species, besides variation in the localization of CMA₃⁺/DAPI⁻ blocks. The existence of different types of sex chromosome systems in these species was confirmed based on arrangements of the chromosomes in different meiotic stages. We identified a new sex system in B. dilatatum, and make the first cytogenetic report on B. candidulum.

Population divergence and peculiar karyoevolutionary trends in the loricariid fish Hypostomus aff. unae from northeastern Brazil

Loricariidae (Siluriformes, Hypostominae) is one of the most diverse catfish families. In spite of the wide distribution of loricariids in South America, cytogenetic reports are available for only a few species, mostly from southern and southeastern Brazil. We made the first chromosomal analysis of Hypostomus aff. unae from the Contas River basin in northeastern Brazil. Four populations isolated by short distances but from distinct landscapes were studied based on conventional staining, C-banding, argyrophilic nucleolar organizer regions (Ag-NOR), CMA(3)/DAPI fluorochrome staining, and fluorescent in situ hybridization with 18S rDNA probes. Although sharing the same diploid number (2n = 76) and NOR locations, each population presented exclusive karyotype formulae and specific patterns of heterochromatic and AT-rich regions. The derived karyotypes of H. aff. unae (2n >54; high number of acrocentrics bearing AT-rich interstitial heterochromatin) indicated a divergent karyoevolution, mostly driven by centric fissions, pericentric inversions and particular heterochromatin dispersion models. This finding of distinct evolutionary units in H. aff. unae will be useful for understanding the natural history of loricariids from relatively unexplored coastal basins in South America.

Sympatric occurrence of four cytotypes and one extra chromosome in Bryconamericus ecai (Characidae): 18S rDNA polymorphism and heterochromatin composition

In the present study, specimens of Bryconamericus ecai collected from the Forquetinha River/RS, were cytogenetically analyzed, disclosing a wide karyotypic diversity in this species. All individuals had 2n = 50, with different karyotypic formulae, resulting in four cytotypes and one B macrochromosome observed in cytotype III. Heterochromatin was distributed in the pericentromeric region of most chromosomes on the four cytotypes and also on a chromosome pair with interstitial markings in cytotype IV. Staining with CMA(3) and DAPI fluorochromes revealed a C-band region rich in AT base pairs in cytotypes I, II and III, and a pair with GC-rich heterochromatin in cytotypes II and III. Cytotype IV presented CMA(3) and DAPI positive heterochromatin. Silver nitrate impregnation, in situ hybridization, and fluorochrome staining showed a multiple system of AgNORs, 18S rDNA and CMA(3) sites in cytotypes I, III and IV, with both inter-and intraindividual variability in the number and location of these sites. Cytotype II had only one pair of NORs coincident with the 18S rDNA and CMA(3) sites, indicating a simple system. The chromosomal polymorphism observed among the specimens of B. ecai added to the literature data show that chromosomal rearrangements, especially pericentric inversions, play an important role in the karyotypic evolution of this group of fish. It can also be implied that more than one species of Bryconamericus is probably occurring, living in sympatry in the Forquetinha River/RS.

B microchromosomes in the family Curimatidae (Characiformes): mitotic and meiotic behavior

Cyphocharax voga (Hensel, 1870), Cyphocharax spilotus (Vari, 1987), Cyphocharax saladensis (Meinken, 1933), Cyphocharax modestus (Fernández-Yépez, 1948), Steindachnerina biornata (Braga & Azpelicueta, 1987) and Steindachnerina insculpta (Fernández-Yépez, 1948) collected from two hydrographic basins. All samples presented 2n=54 meta-submetacentric (m-sm) chromosomes and FN equal to 108, and 1 or 2 B microchromosomes in the mitotic and meiotic cells of the six sampled populations showing inter-and intraindividual variation. The analysis of the meiotic cells in Cyphocharax saladensis, Cyphocharax spilotus, and Cyphocharax voga showed a modal number of 54 chromosomes in the spermatogonial metaphases and 27 bivalents in the pachytene, diplotene, diakinesis and in metaphase I stages, and 27 chromosomes in metaphase II; in Cyphocharax modestus, Steindachnerina biornata, and Steindachnerina insculpta, spermatogonial metaphases with 54 chromosomes and pachytene and metaphase I with 27 bivalents were observed. The B microchromosome was observed as univalent in the spermatogonial metaphase of Cyphocharax spilotus, in the pachytene stage in the other species, with the exception of Cyphocharax saladensis, and Steindachnerina biornata in metaphase I. New occurrences of the B microchromosome in Cyphocharax voga, Cyphocharax saladensis and Steindachnerina biornata were observed, confirming that the presence of this type of chromosome is a striking characteristic of this group of fish.

Cytogenetic comparison between two allopatric populations of Astyanax altiparanae Garutti et Britski, 2000 (Teleostei, Characidae), with emphasis on the localization of 18S and 5S rDNA

Two populations of Astyanax altiparanae (Garutti & Britski, 2000) of the Água dos Patos stream/SP and lake Igapó/PR were analyzed. All individuals showed 2n = 50, however, different karyotypic formulae were observed. The population of the Água dos Patos stream showed 8m +24sm+6st+12a (NF=88) and the population of lake Igapó, 8m+28sm+4st+10a (NF=90). Nucleolus organizing regions (AgNORs) were observed in the terminal position on the short and long arm of different chromosomes of both populations, showing a variation from 3 to 4 chromosomes. Fluorescent in situ hybridization (FISH) using 18S rDNA probes revealed only one pair of chromosomes with fluorescent signals in the terminal site on the short arm in the Igapó lake population, while the population of Água dos Patos stream showed 4 fluorescence terminal signals, characterizing a system of simple and multiple NORs, respectively. 5S rDNA fluorescent signals were detected in the interstitial position of a pair of chromosomes in the two studied populations. Some AgNOR sites revealed to be GC-rich when stained with Chromomycin A3 (CMA3), however, AT positive regions were not observed. The data obtained show that, despite the conservation of the diploid number and location of 5S DNAr, differences in both the distribution of 18S rDNA and karyotypic formula among the populations were found, thus corroborating the existing data on chromosome variability in Astyanax altiparanae that can be significant for cytotaxonomy in this group.

Chromosomal analyses in Megalonema platanum (Siluriformes: Pimelodidae), an endangered species from South American rivers

This study presents chromosomal data of Megalonema platanum from rio Tibagi, Paraná, Brazil and from rio Paraná, Argentina. The diploid number was equal 54 with karyotype composition of 24m+16sm+2st+12a in both populations. The AgNOR sites were detected in the terminal position of a submetacentric pair of the two analyzed populations, coinciding with secondary constrictions on the short arm of pair 15. CMA3 and FISH with 18S rDNA probe displayed fluorescent signals that correspond to the AgNOR sites and secondary constriction. The presence of a small acrocentric supernumerary chromosome can be observed in M. platanum from rio Tibagi, with centromeric heterochromatin. Others heterochromatic blocks were evidenced in the terminal position of some chromosome and one metacentric large chromosome pair, probably the first pair, showed an interstitial heterochromatin. In the population of the rio Paraná were still observed heterochromatic blocks in both ends in some chromosomes. This work brings for the first time cytogenetic date of M. platanum, which is a very rare species in the rio Paraná basin and may be endangered.

Karyotypes of two species of the genus Pimelodus (Siluriformes, Pimelodidae)

A cytogenetic study was conducted on two species of the genus Pimelodus that were collected from the Piquiri river, Paraná, Brazil: Pimelodus paranaensis and Pimelodus heraldoi. Both had a diploid number of 2n=56 chromosomes and a fundamental number (FN) of 104. In P. paranaensis, the karyotype consisted of 22m+22sm+4st+8a chromosomes, whereas the karyotype of P. heraldoi consisted of 18m+24sm+6st+8a. The AgNORs were localized in the terminal region of the long arm in one pair of subtelocentric chromosomes, pair 24 in P. paranaensis and pair 23 in P. heraldoi. The latter species showed size heteromorphism of these regions between the chromosome homologues. Heterochromatin was distributed mainly in the terminal regions in the two species. CMA3-positive staining was observed in some chromosomes, besides being associated with NORs, which were all DAPI-negative, in both species of Pimelodus. C-banding plus CMA3 and DAPI showed that most of the heterochromatic regions were rich in AT bases in P. paranaensis and P. heraldoi.

Banding chromosome pattern of two species of Pimelodus (Siluriformes, Pimelodidae) from the Parana River basin of Brazil

Cytogenetic studies were carried out on seven specimens of Pimelodus heraldoi and sixteen specimens of Pimelodus sp., both from the Parana River basin. The two species had the same diploid number of 56 chromosomes: P. heraldoi with 22M+22SM+6ST+6A and FN of 106 and Pimelodus sp. with 24M+26SM+4ST+2A and FN of 110. NORs were found at the terminal position of the long arm of one pair of ST chromosomes. C-banding (CB) showed in the two species heterochromatin distributed in various chromosomes of the complement, mainly in telomeric regions and in a pair of metacentric chromosomes with strong heterochromatic staining in both telomeres. Treatment only with the fluorochrome CMA3 confirmed in Pimelodus heraldoi and Pimelodus sp. the nucleolar chromosome pair and showed other fluorescent bands. Combined treatment with CB+CMA3 enhanced fluorescent staining of chromosomes in the two fish species evidencing several bands, including in P. heraldoi a chromosome pair showing fluorescent staining in both telomeres.

Structural chromosome polymorphism in a Pimelodus maculatus La Cepède, 1803 population (Siluriformes, Pimelodidae) from the Paranapanema River basin, PR, Brazil

In the present cytogenetic study of Pimelodus maculatus, 13 specimens (8 males and 5 females) from the Congonhas Stream in Paraná State, Brazil, were examined using conventional staining. All of them showed a karyotype of 2n=56, with a chromosome distribution of 20m + 20sm + 10st + 6a. However, four individuals (2 males and 2 females) were found to have a variant karyotype (cytotype) with two heteromorphic chromosomes in the group of submetacentric chromosomes--one of them corresponds to the second largest chromosome of this group and the other is a chromosome of small size. This variation suggests the existence of a structural polymorphism in the studied population.

Cytogenetic study of two species of the family Pimelodidae (Siluriformes) collected in lago Guaíba, Rio Grande do Sul, Brazil

A cytogenetic study was conducted on specimens of Parapimelodus nigribarbis and Pimelodus maculatus collected in the lago Guaíba drainage, Porto Alegre, Rio Grande do Sul, Brazil. The two species had a diploid number of 56 chromosomes, with P. nigribarbis showing a karyotype of 20m + 20sm + 4st + 12a with FN of 100, and P. maculatus showing a karyotype of 24m + 20sm + 6st + 6a with FN of 106. NORs were demonstrated in both species in only one pair of subtelocentric chromosomes, in the terminal region of the long arm, which was coincident with C- banding and CMA3 staining, while DAPI staining was negative in these regions. Parapimelodus nigribarbis had a greater number of heterochromatic bands than did P. maculatus, which were distributed mainly in the terminal regions, where the latter species showed an interstitial band on the short arm of the first metacentric pair. C-banding plus CMA3 demonstrated heterochromatin that was associated with GC-rich NORs in both P. nigribarbis and P. maculatus, although other fluorescent regions were also observed in the former species. With C-banding plus DAPI, various chromosomal regions were stained in the two species, along with interstitial staining in P. maculatus, indicating that heterochromatin contained a greater quantity of AT-rich regions.

Occurrence of B chromosomes in Cyphocharax modestus (Fernández-Yépez, 1948) and Steindachnerina insculpta (Fernández-Yépez, 1948)(Characiformes, Curimatidae) from the Tibagi River basin (Paraná State, Brazil)

We cytogenetically analyzed 18 individuals of Cyphocharax modestus, and 41 individuals of Steindachnerina insculpta from the Tibagi River basin (Paraná State, Brazil). All the specimens had 2n=54 chromosomes, all meta-submetacentric (M-SM). The presence of 1 or 2 B chromosomes was seen in some individuals of C. modestus of the two sampled populations, showing inter- and intra individual variation. In S. insculpta, B chromosomes were also observed but only in one population, also showing inter- and intra individual variation. C-banding was used to show that the identified B chromosomes were totally heterochromatic in the two examined species.

Cytogenetic characterization of Rhamdia quelen (Siluriformes, Heptapteridae) from the Bodoquena Plateau, Mato Grosso do Sul, Brazil

We made a cytogenetic study of the fish Rhamdia quelen collected from the Bodoquena Plateau, an isolated national park region in Mato Grosso do Sul State, Brazil. The diploid number was 2n = 58, with 36 metacentric + 16 submetacentric + 6 subtelocentric chromosomes. We found one to three B chromosomes, which were metacentric and submetacentric and of medium size, showing both intra- and interindividual variation. The nucleolus organizer region (NOR) was located in the terminal region of the short arm of submetacentric pair 20. Staining with CMA3 fluorochrome revealed the NOR location, while there was no evidence of fluorescent staining with DAPI. C banding revealed heterochromatin mainly in the terminal regions of the chromosome arms, including the NOR pair. In addition, metacentric pair 2 showed three heterochromatic blocks in the terminal portions and in the pericentromeric region. The B chromosomes appeared euchromatic. The CB + CMA3 staining combination demonstrated only one chromosome pair with fluorescence, probably the NOR-bearing one, while CB + DAPI gave various fluorescent signals, including metacentric pair 2, indicating that these heterochromatic regions are AT-rich in this population of R. quelen. The R. quelen population in this isolated region of Brazil is chromosomally distinct from that of other populations that have been studied.

Heteromorphic sex chromosome system with an exceptionally large Y chromosome in a catfish Steindachneridion sp. (Pimelodidae)

The chromosomes and banding patterns of Steindachneridion sp., a large catfish (Pimelodidae), endemic to the Iguaçu River, Brazil, were analyzed using conventional (C-, G-banding) and restriction enzyme banding methods. The same diploid number (2n = 56) as in other members of the genus and the family was found but the karyotype displayed an XX/XY sex chromosome system. The X chromosome was the smallest submetacentric, while the Y was the largest chromosome in the karyotype. Meiotic analysis showed 27 autosomal bivalents plus one heteromorphic XY bivalent during spermatogenesis. Sex chromosomes had no particular pattern after C-banding but G- and restriction enzyme bandings showed specific banding characteristics. The present finding represents the first report of a well-differentiated and uncommon sex chromosome system in the catfish family Pimelodidae.