First chromosomal analysis of Gymnorhamphichthys britskii: the remarkable lowest diploid value within the family Rhamphichthyidae (Gymnotiformes)

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.(AU)

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.(AU)

Karyotypic diversity among three species of the genus Astyanax (Characiformes: Characidae) / Diversidade Cariotípica entre três espécies do gênero Astyanax (Characiformes, Characidae)

Abstract The group Incertae sedis within the Characidae family currently includes 88 genera, previously included in the subfamily Tetragonopterinae. Among them is the genus Astyanax comprising a group of species with similar morphology and widely distributed in the Neotropics. Thus, the present study aimed to analyze the karyotype diversity in Astyanax species from different watersheds by conventional Giemsa staining, C-banding and fluorescence in situ hybridization (FISH rDNA 18S) probe.specimens of Astyanax aff. paranae belonging to the “scabripinnis complex”, Astyanax asunsionensis and Astyanax aff. bimaculatus were analyzed”. Two sympatric karyomorphs were observed in Astyanax.aff paranae, one of them having2n=48andthe other one with 2n=50 chromosomes. Other population of this same species also presented 2n=50 chromosomes, but differing in the karyotype formula and with macro supernumerary chromosome found in 100% of the cells in about 80%of females analyzed. Two population of A. asuncionensis and one population of Astyanax. aff. bimaculatus, also showed a diploid number of 50 chromosomes, but also differing in their karyotype formulas. Therefore, A. asuncionensis was also characterized by intraspecific chromosome diversity. The C-banding analysis was able to demonstrate a distinctable to demonstrate a distinct pattern of heterochromatin differing A. asuncionensis from Astyanax aff. paranae and Astyanax aff. bimaculatus. The supernumerary chromosome of Astyanax aff. paranae proved completely heterochromatic. Only Astyanax.aff. bimaculatus multiple showed multiple sites of nucleolar organizing regions. The other species were characterized by having a simple system of NOR. These data contributes to the know ledge of the existing biodiversity in our fish fauna, here highlighted by the inter- and intraspecific chromosomal diversity in the genus Astyanax.

Resumo O grupo Incertae sedis, dentro da família Characidae inclui atualmente 88 gêneros, anteriormente incluídos na subfamília Tetragonopterinae. Dentre eles encontra-se o gênero Astyanax que compreende um grupo de espécies com morfologia similar e com ampla distribuição na região Neotropical. Assim, o presente estudo teve como objetivo analisar a diversidade cariotípica em espécies de Astyanax de diferentes bacias hidrográficas, através da coloração convencional com Giemsa, bandeamento C e hibridização fluorescente in situ (FISH com rDNA 18S). Exemplares de Astyanax aff. paranae, pertencentes ao “complexo scabripinnis”; Astyanax asunsionensise Astyanax aff. bimaculatus foram analisados. Dois cariomorfos foram observados em A. aff. paranae, um deles com 2n=48 cromossomos e outro com 2n=50 cromossomos. Outra população apresentou 2n=50 cromossomos, ambas diferindo na fórmula cariotípica e um cromossomo supranumerário encontrado em 100% das células, em aproximadamente 80% das fêmeas analisadas. Populações de A.asunsionensis e uma população de Astyanax aff. Bimaculatus também mostraram número diplóide de 50 cromossomos, mas diferindo em suas fórmulas cariotípicas. Portanto, A. asuncionensis foi também caracterizado por uma diversidade cariotípica intraespecífica. As análises de bandeamento C foi capaz de demonstrar um padrão distinto de heterocromatina, diferindo A. asuncionensis de A.aff. paranae e A. aff. bimaculatus. O cromossomo supranumerário de Astyanax aff. paranae mostrou-se completamente heterocromático. Apenas Astyanax aff. bimaculatus mostrou múltiplos sítios de regiões organizadoras de nucléolo(NORs). As outras espécies foram caraterizadas por apresentar um sistema simples de NOR. Estes dados contribuem para o conhecimento da existência de biodiversidade em nossa fauna de peixes, aqui em destaque pela diversidade cromossômica inter e intraespecífica no gênero Astyanax.

Comparative cytogenetics in astyanax (characiformes: characidae) with focus on the cytotaxonomy of the group

Astyanax is a diverse group of Neotropical fishes, whose different forms occupy different environments. This great diversity is also reflected on cytogenetic aspects and molecular markers, which have repeatedly been demonstrated by cytogenetic studies. In order to characterize the karyotype of species of this genus, six species were studied: Astyanax altiparanae, A.argyrimarginatus, A. elachylepis, A. xavante, and two new species provisionally called Astyanax sp. and A. aff. bimaculatus. A detailed cytogenetic study based on conventional staining with Giemsa, AgNORs, C-banding, base-specific fluorochromes, and FISH using ribosomal genes 18S and 5S was conducted, aiming to understand some of the chromosomal mechanisms associated with the high diversification that characterizes this group and culminated with the establishment of these species. The results showed 2n = 50 chromosomes for five species and a karyotype with 52 chromosomes in Astyanax sp. Small variations in the macrostructure of the karyotypes were identified, which were quite relevant when analyzed by classical banding, fluorochromes, and FISH methods. These differences among Astyanax spp. (2n = 50) are largely due to changes in the amount and types of heterochromatic blocks. Astyanax sp (2n = 52), in addition to variations due to heterochromatic blocks, has its origin possibly by events of centric fission in a pair of chromosomes followed by minor rearrangements.These results show an interesting karyotypic diversity in Astyanax and indicate the need of a review of the group referred as A. aff. bimaculatus and the description of Astyanax sp., including the possibility of inclusion of this unit in another genus.

Astyanax é um grupo bastante diverso de peixes neotropicais cujas diferentes formas ocupam distintos ambientes. Esta grande variabilidade também se reflete em aspectos citogenéticos e moleculares, que têm sido repetidamente demonstrados por meio de estudos citogenéticos. A fim de caracterizar o cariótipo de representantes deste gênero, seis espécies foram estudadas: Astyanax altiparanae, A. elachylepis, A. xavante, A. argyrimarginatus e duas espécies novas provisoriamente citadas como Astyanax sp. e A. aff. bimaculatus. Um estudo citogenético detalhado com base na coloração convencional com Giemsa, AgNORs, banda C, fluorocromos base-específicos, e FISH com sondas para genes ribossomais 18S e 5S foi realizado com o objetivo de compreender alguns dos mecanismos cromossômicos associados com a alta diversificação que caracteriza este grupo de peixes e que culminou com o estabelecimento dessas espécies. Os resultados revelaram 2n = 50 cromossomos para cinco espécies e 2n = 52 cromossomos para Astyanax sp. Pequenas variações na macroestrutura dos cariótipos foram identificadas e se mostraram relevantes quando analisadas com base nos bandamentos clássicos, coloração por fluorocromos base-específicos e FISH com sondas de DNA 18S e 5S. Esssa diversidade cariotípica detectada indica a necessidade de uma revisão taxonômica no grupo de indivíduos aqui referidos como A. aff. bimaculatus, inclusive com a descrição de Astyanax sp., incluindo a possibilidade de inserção dessa unidade em outro gênero distinto de Astyanax.

Karyotype characterization of Mugil incilis Hancock, 1830 (Mugiliformes: Mugilidae), including a description of an unusual co-localization of major and minor ribosomal genes in the family

This study reports the description of the karyotype of Mugil incilis from Venezuela. The chromosome complement is composed of 48 acrocentric chromosomes, which uniformly decrease in size. Therefore, the homologues can not be clearly identified, with the exception of one of the largest chromosome pairs, classified as number 1, whose homologues may show a subcentromeric secondary constriction, and of chromosome pair number 24, which is considerably smaller than the others. C-banding showed heterochromatic blocks at the centromeric/pericentromeric regions of all chromosomes, which were more conspicuous on chromosomes 1, given the C-positive signals include the secondary constrictions. AgNO3 and fluorescent in situ hybridization (FISH) with 45S rDNA demonstrated that the nucleolus organizer regions are indeed located on the secondary constrictions of chromosome pair number 1. FISH with 5S rDNA revealed that the minor ribosomal genes are located on this same chromosome pair, near the NORs, though signals are closer to the centromeres and of smaller size, compared to those of the major ribosomal gene clusters. This is the first description of co-localization of major and minor ribosomal genes in the family. Data are discussed from a cytotaxonomic and phylogenetic perspective.

Se presenta la primera descripción del cariotipo de Mugil incilis de Venezuela. El complemento cromosómico está compuesto por 48 cromosomas acrocéntricos uniformemente decrecientes en tamaño. Por lo tanto, los homólogos no pueden ser claramente identificados, con excepción de uno de los pares de mayor tamaño, clasificado como número 1, cuyos homólogos poseen una constricción secundaria subcentromérica, y el par de cromosomas número 24, considerablemente más pequeño que los otros. El bandeo-C reveló bloques heterocromáticos en las regiones centroméricas/pericentroméricas de todos los cromosomas, más conspicuas en el cromosoma 1 en el que las señales C-positivas se encuentra localizada precisamente en la constricción secundaria. La tinción con AgNO3 y la Hibridación Fluorescente in situ (FISH) con sonda 45S rDNA revelaron que las regiones organizadoras del nucléolo están ciertamente localizadas sobre la constricción secundaria del cromosoma número 1. FISH con 5S rDNA reveló que los genes ribosomales menores están ubicados en este mismo par cromosómico, en posición proximal a las NORs, aunque cercanas al centrómero y de menor tamaño en comparación con los clúster de genes ribosomales mayores. Ésta es la primera descripción de co-localización de genes ribosomales mayores y menores en la familia Mugilidae. Los datos se discuten bajo perspectivas citotaxonómicas y filogenéticas.

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

Este estudo apresenta dados cromossômicos de Megalonema platanum do rio Tibagi, Paraná, Brasil e do rio Paraná, Argentina. O número diploide foi igual 54 com composição cariotípica de 24m+16sm+2st+12a em ambas populações. Os sítios AgNORs foram detectados na posição terminal de um par submetacêntrico das duas populações analisadas, coincidindo com constrição secundária no braço curto do par 15. CMA3 e FISH com sonda de DNAr 18S exibiram sinais fluorescentes que correspondem aos sítios AgNORs e à constrição secundária. A presença de um pequeno cromossomo supranumerário acrocêntrico foi observado em M. platanum do rio Tibagi, com heterocromatina centromérica. Outros blocos heterocromáticos foram evidenciados na posição terminal de alguns cromossomos e um par cromossômico submetacêntrico grande, provavelmente o primeiro par, mostrou heterocromatina intersticial. Na população do rio Paraná foram observados ainda blocos heterocromáticos em ambas regiões terminais em alguns cromossomos. Este trabalho mostra pela primeira vez dados citogenéticos de M. platanum, que é uma espécie muito rara na bacia do rio Paraná e pode estar ameaçada de extinção.

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 siteswere 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.

Interspecific chromosomal divergences in the genus Characidium (Teleostei: Characiformes: Crenuchidae)

Karyotypes of seven fish species of the genus Characidium, three of them studied for the first time, were characterized using conventional cytogenetic techniques (Giemsa staining, Ag-NOR, and C-banding). All species presented a diploid number of 2n=50, with only metacentric and submetacentric chromosomes, as observed in all Characidium species studied. In two species cells with one to three B chromosomes were observed. All species analyzed have a single NOR-bearing chromosome pair with morphological differences among them. Characidium cf. zebra shows heterochromatic blocks restricted to the pericentromeric regions of all chromosomes denoting the absence of a sex chromosome system. On the other hand, the species Characidium lanei, C. pterostictum, C. lauroi, C. oiticicai, C. schubarti, and Characidium sp., besides presenting pericentromeric heterochromatic blocks, exhibited large interstitial and/or terminal heterochromatic blocks, and a ZZ/ZW sex chromosome system. The constitutive heterochromatin seems to play a relevant role in the chromosome differentiation process of the studied species, mainly in relation to the sex chromosomes. The geographical isolation of the rivers in which the species were sampled, associated with their way of life restricted to headwaters environments, may have favored the process of fixation of different karyotypes found in each of the analyzed species.

Os cariótipos de sete espécies de peixes do gênero Characidium, três estudadas pela primeira vez, foram caracterizados com o uso das técnicas citogenéticas convencionais (Giemsa, Ag-RONs e bandamento-C). Todas as espécies apresentaram número diplóide de 2n=50 cromossomos, com predominância de cromossomos dos tipos meta e submetacêntricos. Nesse estudo foi também observada a presença de até três cromossomos B em células de duas espécies, C. oiticicai e C. pterostictum. O bandamento C e o tratamento com nitrato de prata revelaram significativas diferenças nos cariótipos das espécies analisadas. A espécie Characidium cf. zebra apresenta heterocromatina restrita às regiões pericentroméricas dos cromossomos e ausência de heteromorfismos cromossômicos relacionados à diferenciação sexual, enquanto as espécies Characidium lanei, C. pterostictum, lauroi, C. oiticicai, C. schubarti e Characidium sp., evidenciaram, além de blocos pericentroméricos também observados em Characidium cf. zebra, grandes blocos heterocromáticos intersticiais e/ou terminais e sistema cromossômico de diferenciação sexual do tipo ZZ-ZW. A heterocromatina constitutiva parece exercer papel relevante no processo de diferenciação cromossômica destas espécies, principalmente em relação à diferenciação de cromossomos sexuais. O isolamento geográfico dos rios em que essas espécies foram amostradas, bem como o seu modo de vida restrito às regiões de cabeceira, podem ter favorecido o processo de diferenciação cromossômica e a fixação dos cariótipos particulares encontrados em cada uma das espécies analisadas.

Cytogenetic analysis of three sea catfish species (Teleostei, Siluriformes, Ariidae) with the first report of Ag-NOR in this fish family

Despite their ecological and economical importance, fishes of the family Ariidae are still genetically and cytogenetically poorly studied. Among the 133 known species of ariids, only eight have been karyotyped. Cytogenetic analyses performed on Genidens barbus and Sciades herzbergii revealed that both species have 2n = 56 chromosomes and Cathorops aff. mapale has 2n = 52 chromosomes: Genidens barbus has 10 Metacentrics (M), 14 Submetacentrics (SM), 26 Subtelocentrics (ST), and 6 Acrocentrics (A), Sciades herzbergii has 14M, 20SM, 18ST and 4A, whereas Cathorops aff. mapale has 14M, 20SM, and 18ST. The nucleolus organizer regions (NORs) were found in a single chromosome pair on the short arm of a large-sized ST pair in Genidens barbus and on the short arm of a middle-size SM pair in Cathorops aff. mapale. Multiple NORs on the short arms of two large-sized ST pairs were found in Sciades herzbergii. The occurrence of diploid numbers ranging from 2n = 52 through 56 chromosomes and the presence of different karyotypic compositions, besides the number and position of NORs suggest that several numeric and structural chromosome rearrangements were fixed during the evolutionary history of this fish family.

Karyology of the Atlantic forest rodent Juliomys (Cricetidae): a new karyotype from southern Brazil

Juliomys is a small rodent from the family Cricetidae which inhabits the Atlantic forest and forests from Argentina to eastern Brazil. The three species recognized so far have different karyotypes. In this paper, we describe a new karyotype with 2n = 32, FN = 48 found in Juliomys specimens from a high-altitude area in the Atlantic forest of southern Brazil. The karyotype was analyzed after G- and C-banding and silver staining of the nucleolus organizer regions (Ag-NOR) and its G-banding patterns were compared with those of the newly described species Juliomys ossitenuis (2n = 20, FN = 36). The 2n = 32 karyomorph presented peculiar features and was very different from those of the other species of the genus: J. pictipes (2n = 36, FN = 34), J. rimofrons (2n = 20, FN = 34) and J. ossitenuis (2n = 20, FN = 36). Differences were mostly due to centric and tandem fusions, pericentric inversion and loss of heterochromatin. The karyotype represents a powerful tool to differentiate Juliomys species and our data suggest that the karyotype described herein belongs to a new species.

Comparative cytogenetics of three species of Dichotomius (Coleoptera, Scarabaeidae)

Meiotic and mitotic chromosomes of Dichotomius nisus, D. semisquamosus and D. sericeus were analyzed after conventional staining, C-banding and silver nitrate staining. In addition, Dichotomius nisus and D. semisquamosus chromosomes were also analyzed after fluorescent in situ hybridization (FISH) with an rDNA probe. The species analyzed had an asymmetrical karyotype with 2n = 18 and meta-submetacentric chromosomes. The sex determination mechanism was of the Xy p type in D. nisus and D. semisquamosus and of the Xyr type in D. sericeus. C-banding revealed the presence of pericentromeric blocks of constitutive heterochromatin (CH) in all the chromosomes of the three species. After silver staining, the nucleolar organizer regions (NORs) were located in autosomes of D. semisquamosus and D. sericeus and in the sexual bivalent of D. nisus. FISH with an rDNA probe confirmed NORs location in D. semisquamosus and in D. nisus. Our results suggest that chromosome inversions and fusions occurred during the evolution of the group.

Karyotype and genome size of Iberochondrostoma almacai (Teleostei, Cyprinidae) and comparison with the sister-species I. lusitanicum

This study aimed to define the karyotype of the recently described Iberian endemic Iberochondrostoma almacai, to revisit the previously documented chromosome polymorphisms of its sister species I. lusitanicum using C-, Ag-/CMA3 and RE-banding, and to compare the two species genome sizes. A 2n = 50 karyotype (with the exception of a triploid I. lusitanicum specimen) and a corresponding haploid chromosome formula of 7M:15SM:3A (FN = 94) were found. Multiple NORs were observed in both species (in two submetacentric chromosome pairs, one of them clearly homologous) and a higher intra and interpopulational variability was evidenced in I. lusitanicum. Flow cytometry measurements of nuclear DNA content showed some significant differences in genome size both between and within species: the genome of I. almacai was smaller than that of I. lusitanicum (mean values 2.61 and 2.93 pg, respectively), which presented a clear interpopulational variability (mean values ranging from 2.72 to 3.00 pg). These data allowed the distinction of both taxa and confirmed the existence of two well differentiated groups within I. lusitanicum: one that includes the populations from the right bank of the Tejo and Samarra drainages, and another that reunites the southern populations. The peculiar differences between the two species, presently listed as "Critically Endangered", reinforced the importance of this study for future conservation plans.

Cytogenetic characterization of Rhomboplites aurorubens and Ocyurus chrysurus, two monotypic genera of Lutjaninae from Cubagua Island, Venezuela, with a review of the cytogenetics of Lutjanidae (Teleostei: Perciformes)

Lutjanidae, commonly known as snappers, includes 105 species, grouped in four subfamilies. In spite of the high number of species and of its worldwide distribution, the family has been little investigated and the phylogenetic relationships among some of its genera and species are still cause for debate. Only a small number of the species has been cytogenetically analysed. This study reports the first description of the karyotype of Rhomboplites aurorubens as well as data concerning the distribution of the constitutive heterochromatin and the location of the 18S rRNA and the 5S rRNA genes. Specimens of Ocyurus chrysurus from Venezuela were also investigated for the same cytogenetic features. Both species have a 48 uniarmed karyotype, but R. aurorubens has a single subtelocentric chromosome pair, the smallest of the chromosome complement, among the other acrocentric chromosomes. The C-positive heterochromatin is limited to the pericentromeric regions of all chromosomes. Both species show a single chromosome pair bearing the Nucleolus Organizer Regions, but NORs are differently located, in a terminal position on the short arms of the smallest chromosomes in R. aurorubens and in a paracentromeric position in a chromosome pair of large size in O. chrysurus. In O. chrysurus, the 5S rDNA gene cluster is located on a medium-sized chromosome pair, whereas in R. aurorubens it is syntenic with the 18S rDNA gene cluster on chromosome pair number 24. The obtained cytogenetic data, along with previous cytogenetic, morphological and molecular data for the family, reinforce the proposal to synonymize genus Ocyurus with Lutjanus. A review of Lutjanidae cytogenetics is also included.

Lutjanidae, comumente conhecidos como snappers, inclui 105 espécies, reunidas em quatro subfamílias. A despeito do grande número de espécies e de sua distribuição mundial, a família tem sido pouco estudada e as relações filogenéticas entre alguns de seus gêneros e espécies ainda é motivo de debates. Apenas um pequeno número de espécies foi citogeneticamente analisada. Esse estudo apresenta a primeira descrição do cariótipo de Rhomboplites aurorubens assim como dados relativos à distribuição de heterocromatina constitutiva e localização dos genes 18S rRNA e 5S rRNA. Espécimes de Ocyurus chrysurus da Venezuela foram também analisados quanto às mesmas características citogenéticas. Ambas as espécies têm cariótipos compostos de 48 cromossomos com um único braço, entretanto R. aurorubens tem um único par de cromossomos subtelocêntrico, o menor do complemento cromossômico, entre os outros cromossomos acrocêntricos. A heterocromatina C-positiva é limitada à região pericentromérica de todos os cromossomos. Ambas as species apresentam um único par com Regiões Organizadoras de Nucléolo, mas as RONs são localizadas em posições diferentes, em posição terminal no braço curto dos menores cromossomos de R. aurorubens e em posição paracentromérica no braço longo de um par de cromossomos grandes de O. chrysurus. Em O. chrysurus, os genes 5S rDNA estão localizados em um par de cromossomos de tamanho médio, enquanto em R. aurorubens eles são sintenicamente localizados com os genes 18S rDNA no par de cromossomos número 24. Os dados citogenéticos obtidos, junto com os dados morfológicos e moleculares disponíveis para a família reforçam a proposta de sinonimizar o gênero Ocyurus com Lutjanus. Uma revisão da citogenética dos Lutjanidae é também apresentada

Karyotype characterization and nucleolar organizer regions of marsupial species (Didelphidae) from areas of Cerrado and Atlantic Forest in Brazil

The karyotypes of 23 specimens belonging to 16 species from nine genera of Brazilian marsupials (family Didelphidae) were studied. The animals were collected in eight localities of Cerrado or Atlantic Forest biomes in the states of Goiás, Tocantins and São Paulo. The karyotypes were analyzed after conventional Giemsa staining and silver staining of the nucleolus organizer regions (Ag-NORs). New karyotypic data were obtained for Gracilinanus microtarsus (2n = 14, FN = 24),Marmosops paulensis (2n = 14, FN = 24), Micoreus paraguayanus (2n = 14, FN = 20) and Monodelphis rubida (2n = 18, FN = 32) and are discussed in detail. The karyotypes of G. microtarsus, M. paulensis and M. paraguayanus include three large pairs of submetacentrics (pairs 1, 2 and 3) and a medium-sized metacentric or submetacentric pair 4. Pairs 5 and 6 are small submetacentrics in G. microtarsus and M. paulensis and acrocentrics in M. paraguayanus. M. paulensis presented a single Ag-NOR in pair 6 (6p6p), while M. paraguayanus exhibited multiple Ag-NORs in pairs 5 and 6 (5pq5pq6p6p). There was variation in size and morphology of the sex chromosomes among these species. Monodelphis rubida presented a karyotype with 2n = 18 and FN = 32 composed of a large submetacentric pair 1, a medium-sized metacentric pair 2 and six pairs of submetacentrics (pairs 3 through 8). The X was a small acrocentric and the Y was dot-like. A single Ag-NOR bearing pair (5p5p) characterized M. rubida. Relevant karyotypic information was obtained for 19 specimens belonging to 12 species collected in areas sampled for the first time [Caluromys lanatus and C. philander (2n = 14, FN = 20), Gracilinanus emiliae (2n = 14, FN = 24), Marmosa murina, Metachirus nudicaudatus and Micoureus demerarae (2n = 14, FN = 20), Monodelphis americana (2n = 18, FN = 32) and M. domestica (2n = 18, FN = 20), and Didelphis marsupialis, Philander frenata, P. opossum and P. sp (2n = 22, FN = 20)]. Although the karyotypes...

Patterns of ribosomal DNA distribution in hylid frogs from the Hypsiboas faber and H. semilineatus species groups

We performed a comparative analysis of the nucleolus organizer region (NOR) distribution in the karyotypes of hylid frogs from two different taxonomic groups, Hypsiboas faber and H. semilineatus. Silver nitrate staining of NORs (Ag-NORs) and fluorescence in situ hybridization (FISH) with a rDNA probe were used to investigate the chromosomal location of rDNA loci in two species. The karyotype of H. semilineatus and the Ag-NORs distribution of the four species are presented herein for the first time. After conventional staining, the four species presented very similar karyotypes with 2n = 24, but Ag-NORs analyses revealed species-specific characteristics. H. albomarginatus, H. faber and H. semilineatus had one pair of interstitial Ag-NORs in the short arm of pairs 2, 11, and in the long arm of pair 7, respectively. H. pardalis presented telomeric NORs in the long arm of pair 11. Ag-NORs were heteromorphic in three of the species (H.pardalis, H. semilineatus and H. albomarginatus) and FISH confirmed the differential activity of rDNA genes in H. semilineatus. In the present study, 2n = 24 karyotypes could be distinguished by their Ag-NORs distribution. Our results further the knowledge about the cytogenetics of hylids from Brazil.

B chromosomes in a population of Astyanax eigenmanniorum (Characiformes, Characidae) from the Araguari River Basin (Uberlândia, MG, Brazil)

A cytogenetic study was conducted on an Astyanax eigenmanniorum population from the Caetano Stream (18º 44' 56" S/ 048º 18' 39" W) - in Uberlândia, MG, Brazil - showing a modal diploid number of 48 chromosomes in the standard male and female karyotypes. However, in several specimens it was also possible to observe metaphases with one or two B chromosomes, increasing the diploid number to 49 or 50 chromosomes, respectively. The supernumerary chromosomes were totally heterochromatic and highlighted after C-banding. The silver-stained nucleolus organizing regions (Ag-NORs) were located in at least five chromosomes of the standard karyotype, thus characterizing a multiple NOR system in the species. This is the first occurrence of an A. eigenmanniorum population with 2n = 48 chromosomes, bearing supernumerary chromosomes.

Chromosomal variability in the wild ornamental species of Symphysodon (Perciformes: Cichlidae) from Amazon

Cytogenetic studies were conducted on three discus species which inhabit the Amazon in Brazil: Symphysodon haraldi from Manacapuru, S. aequifasciatus from Tefé and S. discus from Barcelos. All individuals showed 2n=60 chromosomes, most of them biarmed. No sexual chromosomal heteromorphism was verified. However, different karyotypic formulae, owing to the presence of subtelocentric chromosomes, were verified for S. aequifasciatus and S. discus. One of the karyotypic formulae from S. aequifasciatus (cytotype 2) differs from the others, due to one of the homologues in the first chromosome pair being significantly larger than the other. A large variability was observed toward the nucleolar organizer regions (NOR) of S. haraldi and S. aequifasciatus. Although the number of silver-stained blocks varied from 2 to 5, confirming different NOR patterns, at least seven homologue pairs were involved with NORs. In S. discus only two marks were observed, however two chromosome pairs were involved, characterizing a multiple NOR system for the three species. The heterochromatic blocks were mainly located in the pericentromeric region of all chromosomes but, in some of them, they are also located in the proximal regions, both in the short and long arms. Moreover, in the cytotype 2 from S. aequifasciatus, an interstitial heterochromatic block was observed on the long arm of the largest homologue of the first pair. A direct comparison of karyotypes from more related genera (Heros, Uaru, Mesonauta and Pterophyllum), makes it clear that a succession of chromosomal rearrangements, mainly pericentric inversions, translocations and fissions/fusions occurred resulting in the present diploid number and intraspecific karyological variability found in Symphysodon.

Estudos citogenéticos foram conduzidos em três espécies de acará-disco que habitam a Amazônia no Brasil: Symphysodon haraldi coletada em Manacapuru, S. aequifasciatus coletada em Tefé e S. discus em Barcelos. Todos os indivíduos apresentaram 2n=60 cromossomos, a maioria deles com dois braços. Heteromorfismo de cromossomos sexuais não foi detectado. Porém, diferentes fórmulas cariotípicas, devido à presença de cromossomos subtelocêntricos, foram verificadas em S. aequifasciatus e em S. discus. Uma das fórmulas cariotípicas (citótipo 2) de S. aequifasciatus difere das outras, devido a um dos homólogos do primeiro par cromossômico ser significativamente maior que o outro. Uma grande variabilidade foi observada em relação à região organizadora do nucléolo (RON) de S. haraldi e de S. aequifasciatus. Embora, o número de marcações coradas por Nitrato de Prata variou de 2 a 5, confirmando diferentes padrões de RON, pelo menos sete pares de homólogos foram envolvidos com a RON. Em S. discus foram observadas apenas duas marcas, envolvendo, contudo, dois pares de cromossomos, caracterizando um sistema de RONs múltiplas, para as três espécies. Os blocos heterocromáticos estão localizados, principalmente, na região pericentromérica de todos os cromossomos, sendo que alguns deles também foram observados em regiões próximas aos centrômeros, tanto nos braços curtos quanto nos braços longos. Além disso, no citótipo 2 de S. aequifasciatus, um bloco heterocromático foi observado, intersticialmente no braço longo do maior homólogo do primeiro par. Uma comparação direta dos cariótipos dos gêneros mais relacionados (Heros, Uaru, Mesonauta e Pterophyllum), deixa claro que ocorreu uma sucessão de rearranjos cromossômicos, principalmente inversões pericêntricas, translocações e fissões/fusões, que resultou no presente número diplóide e na variabilidade cariotípica encontrada em Symphysodon.

Relationships among growth and different NOR phenotypes in a specific stock of rainbow trout (Oncorhynchus mykiss)

Growth is one of the most important aspects in the genetic improvement of cultured fish species. Consequently, genetic parameters related to this feature and their response to selection have been the focus of most research in this area. Such research indicates that, in general, there is enough additive genetic variance related to growth, justifying the use of selection. Based on the usefulness of cytogenetic and molecular markers in the fish culture, the aim of the present work was to analyze the possible relationships among cytogenetic characteristics, specifically the NOR phenotypes, and the increase in length and weight in specimens of the rainbow trout (Oncorhynchus mykiss), resultant from directed mating between homozygous females and heterozygous males according to their NOR phenotypic patterns. The equations of the relationship between length and weight of the analyzed specimens followed the model Wt = a Lt b, showing b values higher than 3, determinant of a positive allometric growth. The results showed that the different NOR phenotypes were not related with the growth values for length and weight in any statistical test.

O crescimento é um dos mais importantes aspectos considerados no melhoramento genético de espécies de peixes cultivadas. Conseqüentemente, a ênfase das pesquisas na área tem sido avaliar os parâmetros genéticos relacionados com esta característica e sua resposta à seleção. Essas pesquisas indicam, em geral, haver variância genética aditiva suficiente para justificar o uso da seleção. Considerando que a utilização de marcadores citogenéticos ou moleculares pode ser de grande valia para a piscicultura, o presente trabalho teve como objetivo analisar a possível relação entre as características citogenéticas, de modo específico os padrões fenotípicos das NORs e o crescimento em comprimento e em peso dos exemplares de trutas arco-íris (Oncorhynchus mykiss) resultantes de acasalamentos dirigidos entre fêmeas homozigotas e machos heterozigotos, conforme caracterização do padrão fenotípico da NOR. As equações da relação comprimento e peso dos indivíduos analisados seguiram o modelo onde Wt = a Lt b, mostrando valores de b maiores que 3, determinante de um crescimento do tipo alométrico positivo. Os resultados mostraram que os padrões fenotípicos da NOR dos indivíduos homozigotos e dos heterozigotos não apresentaram diferenças estatisticamente significativas entre seus valores de crescimento em comprimento ou peso.

Astylus variegatus (Coleoptera, Melyridae): Cytogenetic study of a population exposed to agrochemical products

In this work we describe the cytogenetic analyses performed in specimens of Astylus variegatus (Germar, 1824) collected in two localities: one area of natural vegetation and one of agricultural crops, where agrochemical products were used. Astylus variegatus had karyotypes with 2n(male) = 16+Xy p and 2n (female) = 16+XXp, with exclusively metacentric chromosomes. Pachytene spermatocytes showed synapsed autosomal bivalents and non-associated sex chromosomes. In diplotene, the autosomal bivalents exhibited one or two terminal chiasmata and the Xy p had a typical parachute configuration. In meiotic cells of some specimens, an extra chromosome, interpreted as a B chromosome, was observed. C-banding showed constitutive heterochromatin in the pericentromeric region of all chromosomes, with the exception of the y p. Silver nitrate staining revealed one nucleolus organizer region (NOR) on the terminal region of the short arm of the second autosome pair. Silver staining of meiotic cells confirmed the NOR pattern detected in mitotic cells and revealed an argentophilous material on the Xy p. A cytogenetic comparison between the two populations of A. variegatus showed a statistically significant divergence (chi2 = 117.10; df = 1) in the number of aneuploid cells and a higher frequency of B chromosome in the population exposed to agrochemicals.

Preponderance of GC-rich sites in silver-stained nucleolus organizing regions of Rita rita (Hamilton) and Mystus gulio (Hamilton) (Bagridae, Pisces), as revealed by chromomycin A3-staining technique and scanning electron microscopic studies

The karyotypes of two species of catfish, Rita rita (Hamilton) (2n = 54; 14m + 34sm + 6st; NF = 102) and Mystus gulio (Hamilton) (2n = 58; 30m + 12sm + 2st + 14t, NF = 100) were studied through Giemsa-, silver- and chromomycin A(3)-staining techniques. The silver-stained karyotypes in both sexes of R. rita and M. gulio revealed that the nucleolus organizing regions were located terminally at the shorter arms (Tp) of one pair of submetacentric chromosomes, placed at positions Nos. 2 and 1, respectively, which was confirmed by scanning electron microscopy. Staining with a GC-specific fluorochrome, chromomycin A(3), produced bright fluorescence in the Ag-positive nucleolus organizer regions, suggesting thereby that nucleolus organizing regions actually included GC-rich sites of active r-RNA genes in metaphase chromosomes of these two bagrids. Further such studies are needed due to the extreme paucity of data on fish.

Effect of Thyroxine and Propylthiouracil in Ehrlich Ascitic Tumor Cells / Efecto de la Tiroxina y Propiltiouracilo en las Células del Tumor Ascítico de Ehrlich

The main purpose of this study was to investigate the effect of thyroxine and PTU in ascitic Ehrlich tumor cells. Tumor was implanted in 30 female mice distributed in three groups: treated with PTU, treated with thyroxine and control. Each group received an intraperitoneal injection of neoplastic cells, pre-incubated with sterile solutions of PTU, thyroxine and distilled water, respectively. On the fifth and seventh days after inoculation, animals received an intraperitoneal injection of the respective solutions. On the tenth day after inoculation, animals were sacrificed. Volume of ascitic liquid, number of neoplastic cells/ml and percentage of viable cells were determined. Ascitic liquid smears were carried out for tumor cytological evaluation. There was no difference among groups regarding ascitic liquid and as for the number and viability of tumor cells. However, cells under the effect of thyroxine presented significantly larger mean of nuclear diameter, size and number of nucleolus organizer regions. In this group, there was a predominance of clear, round cells with abundant eosinophilic and very vacuolated cytoplasm with little defined edges. Under the PTU effect, tumor cells were small with hyperchromatic nucleus and the same number of NORs as the control group. It was concluded that PTU and thyroxine have not changed the number and viability of cells after 10 days of tumor inoculation but they changed significantly cell characteristics. Whilst thyroxine increases cell size and the number of NORs of ascitic Ehrlich tumor cells, PTU causes an opposite effect.

El propósito principal de este estudio ha sido investigar el efecto de la tiroxina y del propiltiouracilo (PTU) en las células del tumor de Ehrlich. El tumor fue implantado en 30 ratones hembras distribuidas en tres grupos: tratado con PTU, tratado con tiroxina y control. Cada grupo recibió una inyección intraperitoneal de células neoplásicas, pre-incubadas con las soluciones estériles de PTU, tiroxina y agua, respectivamente. En el quinto y séptimo días después de la inoculación, los animales recibieron una inyección intraperitoneal de las soluciones respectivas. En el décimo día después de la inoculación, se sacrificaron los animales. Fueron determinados el volumen de líquido ascítico, el número de células/ml y el porcentaje de células viables. Además se realizaron frotis del líquido ascítico para la evaluación de la citología del tumor. No hubo ninguna diferencia entre los grupos con respecto al volumen del líquido ascítico y el número y viabilidad de las células del tumor. Sin embargo, las células bajo el efecto de la tiroxina presentaron una media significativamente superior del diámetro nuclear, tamaño y número de regiones organizadoras de nucleélos. En este grupo, había un predominio de células claras, redondas con citoplasma abundante, eosinofílico y vacuolado con poca definición de los bordes. Bajo el efecto del PTU, las células del tumor eran pequeñas con el núcleo hipercromático y el mismo número de NORs como el grupo control. Se concluye que el PTU y tiroxina no afectaron el número y viabilidad de las células después de 10 días de inoculación del tumor, pero sí cambiaron las características celulares. Aunque la tiroxina aumenta el tamaño celular y el número de NORs de las celulas del tumor de Ehrlich, PTU causa efectos opuestos.

Caracterização cariotípica de um estoque de tilápia do Nilo, Oreachromis niloticus, da Universidade Estadual de Londrina, mediante diversas técnicas de bandamento cromossômico / Karyotypical characterization from stock of Nile tilapia, Oreochromisniloticus, at Londrina State University, PR, Brazil, through severaltechniques of chromosomes band

Foram analisados citogeneticamente 14 indivíduos de tilápia do Nilo, Oreochromis niloticus que fazem parte do estoque de reposição de reprodutores da Estação de Piscicultura da Universidade Estadual de Londrina, Paraná, Brasil. Todos os indivíduos apresentaram o mesmo número diplóide de 44 cromossomos. As NORS foram observadas em quatro cromossomos com marcações em posição terminal do braço curto e a hibridação "insitu" (FISH) com sonda de 18S também evidenciou a presença de dois pares de cromossomos contendo cístrons ribossômicos. O tratamento com os fluorocromos CMA d DAPI, respectivamente, não mostrou bandas brilhantes em nenhum cromossomo do complemento. A banda C (CBG)evidenciou, regiões de heterocromatina distribuídas em vários cromossomos nas regiões centroméricas, sendo observadas algumas marcações em regiões teloméricas, principlamente no maior par de cromossomos do complemento, um par apresentou-se quase totalmente heterocromático. Os resultados obtidos estão de acordo com os dados disponíveis na literatura, porém, quando analisadas as bandas C e as NORs, foram evidenciadas algumas diferenças que aparentemente caracterizam a população local de peixes da Universidade Estadual de Londrina

14 specimens of Nile's tilapia were analyzed cytogenetically, Oreochromis niloticus, that belong to thestock of fish breeding from the Freshwater Aquaculture Station of the Londrina State University in theParaná, Brazil. All specimens presented the same disploid number of 44 chromosomes. The NORs wereobserved in four chromosomes with marks in terminal position of the short arm and the hybridization "insitu" (FISH) with probe of 18 S also evidenced the presence of two pairs of chromosomes containingribbosomic cistrons. The treatment with the fluochromes CMA3 and DAPI, respectively, didn't showshinning bands in any chromosome of the complement. The band C (CBG) evidenced regions ofheterochromatin distributed on several chromosomes in the centromeric regions, being observed somemarks in telomeric regions, mainly on the biggest pair of chromosomes of the complement, a pair presenteditself almost totally heterochromatic. The obtained results are in accordance with the data found inliterature, nevertheless when the C bands and NORs were analyzed, were evidenced some differencesthat apparently characterized the local fish population of the Londrina State University