Turnover of multiple sex chromosomes in Harttia catfish (Siluriformes, Loricariidae): a glimpse from whole chromosome painting

The remarkable fish biodiversity encompasses also great sex chromosome variability. Harttia catfish belong to Neotropical models for karyotype and sex chromosome research. Some species possess one of the three male-heterogametic sex chromosome systems, XY, X1X2Y or XY1Y2, while other members of the genus have yet uncharacterized modes of sex determination. Particularly the XY1Y2 multiple sex chromosome system shows a relatively low incidence among vertebrates, and it has not been yet thoroughly investigated. Previous research suggested two independent X-autosome fusions in Harttia which led to the emergence of XY1Y2 sex chromosome system in three of its species. In this study, we investigated evolutionary trajectories of synteny blocks involved in this XY1Y2 system by probing six Harttia species with whole chromosome painting (WCP) probes derived from the X (HCA-X) and the chromosome 9 (HCA-9) of H. carvalhoi. We found that both painting probes hybridize to two distinct chromosome pairs in Amazonian species, whereas the HCA-9 probe paints three chromosome pairs in H. guianensis, endemic to Guyanese drainages. These findings demonstrate distinct evolutionary fates of mapped synteny blocks and thereby elevated karyotype dynamics in Harttia among the three evolutionary clades.

Evolutionary breakpoint regions and chromosomal remodeling in Harttia (Siluriformes: Loricariidae) species diversification

The Neotropical armored catfish genus Harttia presents a wide variation of chromosomal rearrangements among its representatives. Studies indicate that translocation and Robertsonian rearrangements have triggered the karyotype evolution in the genus, including differentiation of sex chromosome systems. However, few studies used powerful tools, such as comparative whole chromosome painting, to clarify this highly diversified scenario. Here, we isolated probes from the X₁ (a 5S rDNA carrier) and the X₂ (a 45S rDNA carrier) chromosomes of Harttia punctata, which displays an X₁X₁X₂X₂/X₁X₂Y multiple sex chromosome system. Those probes were applied in other Harttia species to evidence homeologous chromosome blocks. The resulting data reinforce that translocation events played a role in the origin of the X₁X₂Y sex chromosome system in H. punctata. The repositioning of homologous chromosomal blocks carrying rDNA sites among ten Harttia species has also been demonstrated. Anchored to phylogenetic data it was possible to evidence some events of the karyotype diversification of the studied species and to prove an independent origin for the two types of multiple sex chromosomes, XX/XY₁Y₂ and X₁X₁X₂X₂/X₁X₂Y, that occur in Harttia species. The results point to evolutionary breakpoint regions in the genomes within or adjacent to rDNA sites that were widely reused in Harttia chromosome remodeling.

Molecular data reveal a complex population genetic structure for Psalidodon scabripinnis (Teleostei: Characidae) in the Atlantic Rainforest, Brazil

Recently renamed, Psalidodon scabripinnis populations of Serra da Mantiqueira, previously known as Astyanax scabripinnis have been deeply studied in the last years. These populations are small and isolated and occur very close to the watershed between Paraíba do Sul River basin and Upper Paraná River basin, in Serra da Mantiqueira region in the Atlantic Rainforest. These conditions arouse the interest in knowing theor genetic conservation status and how they responded to the separation between the two rivers basins. Therefore, we accessed the genetic diversity of five P. scabripinnis populations of this region with microsatellites and mitochondrial data. The results showed a complex structure pattern that doesn’t match the simple basin separation and a reasonably conservation status when compared with other populations of the same family or with similar natural history.

Chromosome analysis in Saccodon wagneri (Characiformes) and insights into the karyotype evolution of Parodontidae

ABSTRACT Parodontidae is a relatively small group of Neotropical characiform fishes consisting of three genera (Apareiodon, Parodon, and Saccodon) with 32 valid species. A vast cytogenetic literature is available on Apareiodon and Parodon, but to date, there is no cytogenetic data about Saccodon, a genus that contains only three species with a trans-Andean distribution. In the present study the karyotype of S. wagneri was described, based on both conventional (Giemsa staining, Ag-NOR, C-bands) and molecular (repetitive DNA mapping by fluorescent in situ hybridization) methods. A diploid chromosome number of 2n = 54 was observed in both sexes, and the presence of heteromorphic sex chromosomes of the ZZ/ZW type was detected. The W chromosome has a terminal heterochromatin band that occupies approximately half of the long arm, being this band approximately half the size of the Z chromosome. The FISH assay showed a synteny of the 18S-rDNA and 5S-rDNA genes in the chromosome pair 14, and the absence of interstitial telomeric sites. Our data reinforce the hypothesis of a conservative karyotype structure in Parodontidae and suggest an ancient origin of the sex chromosomes in the fishes of this family.

Chromosomal distribution of the retroelements Rex 1, Rex 3 and Rex 6 in species of the genus Harttia and Hypostomus (Siluriformes: Loricariidae)

ABSTRACT The transposable elements (TE) have been widely applied as physical chromosome markers. However, in Loricariidae there are few physical mapping analyses of these elements. Considering the importance of transposable elements for chromosomal evolution and genome organization, this study conducted the physical chromosome mapping of retroelements (RTEs) Rex1, Rex3 and Rex6 in seven species of the genus Harttia and four species of the genus Hypostomus, aiming to better understand the organization and dynamics of genomes of Loricariidae species. The results showed an intense accumulation of RTEs Rex1, Rex3 and Rex6 and dispersed distribution in heterochromatic and euchromatic regions in the genomes of the species studied here. The presence of retroelements in some chromosomal regions suggests their participation in various chromosomal rearrangements. In addition, the intense accumulation of three retroelements in all species of Harttia and Hypostomus, especially in euchromatic regions, can indicate the participation of these elements in the diversification and evolution of these species through the molecular domestication by genomes of hosts, with these sequences being a co-option for new functions.

Mapeamento cromossômico das histonas H1 e H4 em espécies de Parodontidae (Characiformes)

Parodontidae é composta por três gêneros: Parodon, Saccodon e Apareiodon, os quais abrangem 31 espécies consideradas válidas. Do ponto de vista cromossômico, apresentam 2n=54 cromossomos conservado, com variações nas fórmulas cariotípicas, número e localização dos DNAs ribossomais 45S e 5S e presença/ausência de cromossomos sexuais. O presente trabalho teve como objetivo contribuir para o conhecimento da diversidade cromossômica de Parodontidae, analisando, através de hibridizações in situ fluorescentes, a localização cromossômica dos genes das histonas H1 e H4 em sete espécies da família: Apareiodon cavalcante, Apareiodon machrisi, Apareiodon sp. 1, Apareiodon sp. 2, Apareiodon argenteus, Apareiodon davisi e Parodon cf. pongoensis. As sondas utilizadas foram amplificadas a partir do genoma de A. cavalcante. As sequências obtidas na amplificação das histonas H1 e H4 apresentaram 626 e 213 pares de bases, respectivamente, exibindo similaridade com sequências parciais destes genes de outras espécies de peixes. Além disso, a sequência de H1 amplificada apresentou similaridade com um fragmento interno do elemento transponível ERV1-2 FCa-I. As hibridizações revelaram a ocorrência de co-localização destes genes em porção intersticial de um único par cromossômico (par 20 em P. cf. pongoensis e par 13 nas demais espécies), ocorrendo também um sítio adicional de H1 em A. davisi e pequenos sítios dessa sequência dispersos pelos cariótipos de todas as espécies. Os resultados sugerem que o cluster H1-H4 alocado em apenas um par cromossômico seja a tendência para Parodontidae, indicando assim uma possível conservação desta clusterização em todas as espécies do grupo. Os pequenos sítios de H1 dispersos pelos cariótipos e o sítio adicional de A. davisi provavelmente estão associados ao retroelemento inserido nesta sequência. Além disso, o sítio adicional de A. davisi também pode ser resultado de rearranjos cromossômicos, bem como o par portador do cluster H1-H4 em P. cf. pongoensis. Apesar de ser sugerida a conservação da localização dos genes das histonas H1 e H4 em Parodontidae, as particularidades apresentadas por algumas espécies indicam que, em alguns casos, estes genes estão envolvidos em processos evolutivos que resultam em maior nível de diferenciação.Órgãos financiadores: FAPESP, CAPES e CNPqApoio de coleta: ICM-Bio (licença Nº 10538-1)

Análise citogenética de Leporinus cf. obtusidens e Leporellus vittatus (Characiformes, Anostomidae) da bacia do rio São Francisco

Anostomidae é uma família altamente especiosa entre os Characiformes, compreendendo 156 espécies válidas, as quais estão distribuídas na região Neotropical. Estudos citogenéticos com anostomídeos revelam que sua estrutura cariotípica é altamente conservada, com variações quanto a presença de cromossomos sexuais. O presente estudo teve como objetivo realizar a caracterização cariotípica de Leporinus cf. obtusidens e Leporellus vittatus da bacia do rio São Francisco, por meio de técnicas citogenéticas. As coletas foram realizadas no rio Piumhi, bacia do rio São Francisco, em Minas Gerais. Foram utilizados procedimentos citogenéticos convencionais (Giemsa, Ag-Rons e bandamentos C) aliados a citogenética molecular (hibridação in situ fluorescente com sondas de DNA ribossômico 18S e 5S). Ambas as espécies analisadas apresentaram 2n = 54 cromossomos, tipo metacêntricos e submetacêntricos, com número fundamental igual a 108. Leporinus cf. obtusidens apresentou sistema de cromossomos sexuais tipo ZZ/ZW, identificados pelo padrão de distribuição da heterocromatina constitutiva, com o cromossomo W quase inteiramente heterocromático e o cromossomo Z com apenas a região terminal heterocromática. Para Leporellus vittatus foram observadas marcações heterocromáticas nas regiões centroméricas e ausência de cromossomos sexuais. A FISH com sondas de rDNA 18S revelou marcação nas regiões terminais de um único par cromossômico para as duas espécies. O rDNA 5S também foi observada em apenas um par de cromossomos, localizado na posição terminal em Leporinus cf. obtusidens e intersticial de Leporellus vittatus. Estes dados corroboram o conservadorismo da macroestrutura cromossômica e indicam a necessidade de um aprofundamento no tocante a distribuição dos DNAs repetitivos nos genomas de Anostomidae.

Citogenética comparativa em Neoplecostomus (Hypoptopomatinae: Neoplecostomini) em afluentes do rio Paraná

O gênero Neoplecostomus compreende espécies de tamanho pequeno que habitam riachos da região sul e sudeste do Brasil. O gênero apresenta interesse em estudos citogenéticos e genéticos por apresentar cariótipos conservados e indícios de ausência de fluxo gênico entre populações de subafluentes do rio Paraná. Das dezesseis espécies válidas descritas até o momento para este gênero, oito foram descritas para a bacia do rio Paraná e há evidências da ocorrência de novas espécies para esta bacia. Sendo assim, este trabalho teve como objetivo estudar a diferenciação cariotípica no gênero Neoplecostomus nas bacias hidrográficas dos rios Iguaçu, Itararé, Cinzas e Tibagi com vistas ao entendimento da evolução cariotípica e descrição da biodiversidade. Para isso, foram realizas coletas em quatro localidades: rio Pinhão – bacia do rio Iguaçu (Neoplecostomus sp. 1), rio Samambaias – bacia do rio Itararé (Neoplecostomus cf. botucatu), rio das Pedras – bacia do rio das Cinzas (Neoplecostomus sp. 2) e no rio São João – bacia do rio Tibagi (Neoplecostomus yapo). Os dados citogenéticos revelaram um número diploide de 54 cromossomos, fórmula cariotípica 18m+20sm+16st e número fundamental 108 para as quatro espécies analisadas. O bandamento C detectou poucas regiões heterocromáticas. A hibridização in situ do gene ribossomal 18S demonstrou a localização do sítio ribossomal 45S em um único par cromossômico e, em dois sítios cromossômicos para o gene ribossomal 5S. Os estudos citogenéticos realizados demonstram que as espécies pertencentes ao gênero Neoplecostomus apresentam estruturas cariotípicas similares, com cariótipo constituído basicamente de regiões eucromáticas sugerindo uma aparente conservação cariotípica a qual também já foi observada em outras espécies deste gênero e em outras espécies de Neoplecostomini.Apoio: CNPq, CAPES, Fundação Araucária, SETI, FAPESP

Mapeamento cromossômico comparativo de DNAs repetitivos em duas espécies de Pimelodidae (Siluriformes): Bergiaria westermanni (Liitken, 1874) e Pimelodus pohli (Ribeiro e Lucena, 2006)

Bergiaria westermanni e Pimelodus pohli são espécies pertencentes à família Pimelodidae (Siluriformes) e endêmicas da bacia do rio São Francisco. Estudos citogenéticos no grupo já evidenciaram cromossomos B, sistemas de cromossomos sexuais heteromórficos e diversificação cariotípica. O presente trabalho objetivou analisar citogeneticamente duas espécies de Pimelodidae coletadas na bacia do rio São Francisco (MG): B. westermanni (26? e 3?) e P. pohli (28? e 19?). Para ambas, o 2n foi de 56 cromossomos sem a ocorrência de cromossomos sexuais e, em B. westermanni uma variação intra e interindividual de 0 a 4 cromossomos B foi observada. As fórmulas cariotípicas são diferenciadas para as duas espécies (28m+14sm+10st+4a, NF = 94 para B. westermanni) e (20m+18sm+12st+6a, NF=106 para P. pohli). A heterocromatina alocou-se preferencialmente nas regiões centroméricas e terminais, sendo os cromossomos B de B. westermanni totalmente heterocromáticos. Evidenciou-se NOR simples, terminal, ativa e coincidente com os sítios de rDNA 18S no par cromossômico 27 em B. westermanni, e no par 24 de P. polhi, além de sítios do rDNA 45S nos cromossomos B de B. westermanni com evidências de atividade transcricional. Sítios intersticiais de rDNA 5S foram detectados nos pares cromossômicos 1 e 5 em B. westermanni e nos pares 1 e 18 em P. pohli. A localização in situ da sonda do snRNA U2 foi sintênica a um par cromossômico portador do rDNA 5S, par 5 em B. westermanni e par 18 em P. pohli. A sequência (TTAGGG)n foi evidenciada nas porções terminais dos cromossomos das espécies, inclusive nos cromossomos B de B. westermanni. Em P. pohli, sítios teloméricos intersticiais (ITS) foram detectados em três pares cromossômicos, os quais podem ser resultado de rearranjos cromossômicos ou quebras da dupla fita com mecanismo de reparo mediado pela telomerase. Os resultados citogenéticos para estas duas espécies evidenciam uma conservação do número diplóide. Entretanto, variações nas fórmulas cariotípicas, presença de cromossomos B em B. westermanni, com genes rRNA 45S provavelmente ativos, e ITS em P. pohli, demonstraram diferenciação na estrutura dos cromossomos e no conteúdo genômico. Esses dados contribuem para a caracterização citogenética da família, e auxiliam no entendimento de sua evolução cromossômica.Órgãos financiadores: FAPESP, CAPES e CNPqApoio de coleta: ICM-Bio (licença Nº 10538-1)

rDNA 5S e rearranjos cromossômicos em Rineloricaria (Siluriformes: Loricariidae)

Dados citogenéticos de Loricariidae (Siluriformes) revelam uma extensiva variação de número diploide e plasticidade cromossômica no grupo. Nestes peixes, a localização in situ de sítios de rDNA 5S em regiões co-localizadas a sítios teloméricos intersticiais (ITS) evidenciaram o envolvimento de múltiplos clusters de rDNA 5S em rearranjos cromossômicos nas subfamílias Loricariinae e Ancistrinae. Vestígios de sequências (TTAGGG)n em sítios internos podem corresponder à locais de rearranjos cromossômicos e também são considerados como pontos quentes para quebras cromossômicas, os “sítios frágeis”. Este trabalho teve como objetivo a caracterização molecular de segmentos duplicados (SD) de rDNA 5S, discutir seu envolvimento como sítio frágil, além da sua localização in situ em duas populações de Rineloricaria latirostris. Rineloricaria latirostris (rio das Pedras) apresentou 2n = 46 cromossomos e 5 pares marcados com rDNA 5S, além de um par portador de ITS/rDNA 5S co-localizado, enquanto R. latirostris (rio Piumhi) apresentou 2n = 48 cromossomos, 2 pares com sítios para rDNA 5S e ausência de ITS. Fragmentos isolados de rDNA 5S de 222 pb mostraram identidade com rDNAs 5S de outras espécies, além disso um amplificado de 702 pb apresentou inserção de um segmento do TE hAT em sua sequência, clone rDNA 5S degenerado. Ensaios de dupla-FISH evidenciaram a co-localização de rDNA 5S/rDNA 5S degenerado, rDNA 5S/hAT e ITS/rDNA 5S em R. latirostris do rio das Pedras, enquanto na outra população estudada apenas marcações de rDNA 5S foram detectadas. Segundo nossos dados, a invasão do TE hAT no rDNA 5S gerou a região de SD rDNA 5S degenerado, a qual atuou como sítio frágil para quebras cromossômicas e fusão Robertsoniana (Rb) em Rineloricaria. Assim, a evidência do SD rDNA 5S em pontos de fusão Rb em outras espécies sugerem que esta região é um sítio frágil para genomas de Loricariidae e, poderia explicar parte dos eventos Robertsonianos neste grupo de peixes.APOIO: Fundação Araucária, CNPq.

Origem e evolução do sistema de cromossomos sexuais XY 1 Y 2 no peixe Hoplias malabaricus: (Characiformes, Erythrinidae)

O peixe Hoplias malabaricus (Characiformes, Erythrinidae) é caracterizado por uma ampla diversidade cariotípica, com uma ampla variação em seus números diploides e tipos cromossômicos, incluindo distintos sistemas de cromossomos sexuais entre seus cariomorfos. Até o presente momento, três sistemas XY [um altamente diferenciado (Cariomorfo B) e outros dois em estágios iniciais de diferenciação (Cariomorfos C e F)] e um sistema X1X2Y (Cariomorfo D), foram extensivamente estudados por procedimentos de citogenética convencional e molecular, elucidando seus processos de diferenciação e evolução. Os resultados apontaram para uma origem independente dos sistemas XY, onde distintos autossomos se diferenciaram nos cromossomos sexo-específicos nos distintos cariomorfos. Neste estudo, foi analisada a origem e evolução do sistema XX/XY1Y2, presente no cariomorfo G desta espécie, utilizando procedimentos citogenéticos convencionais e moleculares, incluindo bandamento C, mapeamento cromossômico de DNAs repetitivos, hibridação genômica comparativa (CGH) e pintura cromossômica total (WCP). Os dados obtidos possibilitaram evidenciar os rearranjos cromossômicos envolvidos na gênese deste raro sistema de cromossomos sexuais múltiplos observado entre os peixes. Os experimentos de CGH foram resolutivos para identificar a ocorrência de uma região cromossômica macho-específica no cromossomo Y1, onde as sequencias ali existentes podem estar associadas à fase inicial da diferenciação deste cromossomo. Ficou também evidenciada uma estreita correlação entre o sistema XY1Y2 do cariomorfo G e o sistema XY do cariomorfo F de H. malabaricus, reforçando a maior proximidade evolutiva entre eles, bem como a origem independente destes sistemas em relação à outros encontrados nesta mesma espécie. Os resultados destacam o excelente modelo fornecido por este grupo taxonômico nos estudos dos cromossomos sexuais.Apoio: CAPES, CNPq, FAPESP, SEDUC-MT

Contributions to the cytogenetics of the Neotropical fish fauna

Brazilian fish cytogenetics started as early as the seventies in three pioneering research groups, located at the Universidade Estadual Paulista (UNESP, Botucatu, SP), Universidade Federal de São Carlos (UFSCar, São Carlos, SP) and Universidade de São Paulo (USP, São Paulo, SP). Investigations that have been conducted in these groups led to the discovery of a huge chromosomal and genomic biodiversity among Neotropical fishes. Besides, they also provided the expansion of this research area, with the genesis of several other South American research groups, in view of a number of dissertations and doctoral theses developed over years. The current authors were encouraged to make their thesis catalog accessible from a public source, in order to share informations on the taxa and subject matter analyzed. Some of the key contributions to evolutionary fish cytogenetics are also being highligthed.

Karyotype Diversity and Evolutionary Trends in Armored Catfish Species of the Genus Harttia (Siluriformes: Loricariidae)

Most species of the genus Harttia inhabits the headwaters of small tributaries, but some species are restricted to the main channel of some rivers. This feature, combined with limited dispersal ability, leads to the formation of small isolated populations with reduced gene flow. Currently, there are 23 taxonomically defined and recognized species, and 17 of these are found in Brazil, distributed in several hydrographic basins. Despite this diversity, few chromosomal data for the species belonging to this genus are found in the literature. Thus, this study analyzed, by classical and molecular cytogenetics methodologies, the chromosomal diversity of this genus, to discuss the processes that are involved in the evolution and karyotype differentiation of the species of the group. Seven species of Harttia were analyzed: H. kronei, H. longipinna, H. gracilis, H. punctata, H. loricariformis, H. torrenticola, and H. carvalhoi. The chromosomal diversity found in these species includes different diploid and fundamental numbers, distinct distribution of several repetitive sequences, the presence of supernumerary chromosomes in H. longipinna and multiple sex chromosome systems of the type XX/XY1Y2 in H. carvalhoi and X1X1X2X2/X1X2Y in H. punctata. Lastly, our data highlight the genus Harttia as an excellent model for evolutionary studies.

The role of chromosomal fusion in the karyotypic evolution of the genus Ageneiosus (Siluriformes: Auchenipteridae)

Ageneiosus is the most widely distributed genus of the family Auchenipteridae among South American river basins. Although chromosome studies in the family are scarce, this genus has the largest number of analyzed species, with 2n = 54 to 56 chromosomes, differing from the rest of the family (2n = 58). This study aimed to analyze Ageneiosus inermis from the Araguaia River basin. The diploid number found was of 56 chromosomes. Heterochromatin was allocated in terminal region of most chromosomes, plus a pericentromeric heterochromatic block in pair 1, a pair distinguished by size in relation to other chromosomes pairs. AgNORs were detected in only one submetacentric chromosome pair, which was confirmed by FISH. 5S rDNA was present in only one metacentric chromosome pair. Hybridization with [TTAGGG]n sequence marked the telomeres of all chromosomes, in addition to an ITS in the proximal region of the short arm of pair 1. The repetitive [GATA]n sequence was dispersed, with preferential location in terminal region of the chromosomes. Ageneiosus has a genomic organization somewhat different when compared to other Auchenipteridae species. Evidences indicate that a chromosomal fusion originated the first metacentric chromosome pair in A. inermis, rearrangement which may be a basal event for the genus

Comparative chromosomal analysis and evolutionary considerations concerning two species of genus Tatia (Siluriformes, Auchenipteridae)

Auchenipteridae is divided in two subfamilies, Centromochlinae and Auchenipterinae. Centromochlinae has 31 valid species, from which 13 are included in the genus Tatia Miranda Ribeiro, 1911. Among these, Tatia jaracatia Pavanelli & Bifi, 2009 and Tatia neivai (Ihering, 1930) are the only two representative species from the Paraná-Paraguay basins. This study aimed to analyze cytogenetically these two species and thus provide the first chromosomal data for the genus. Although Tatia jaracatia and Tatia neivai presented 2n=58 chromosomes, some differences were observed in the karyotypic formula. The heterochromatin was dispersed in the centromeric and terminal regions of most chromosomes of Tatia jaracatia, and only in the terminal region of most chromosomes of Tatia neivai. The AgNORs were detected in the subtelocentric pair 28 for both species, which was confirmed by FISH with 18S rDNA probe. The 5S rDNA sites were detected in four chromosome pairs in Tatia jaracatia and three chromosome pairs in Tatia neivai. Both species of Tatia presented great chromosomal similarities among themselves; however, when compared to other species of Auchenipteridae, it was possible to identify some differences in the karyotype macrostructure, in the heterochromatin distribution pattern and in the number and position of 5S rDNA sites, which until now seems to be intrinsic to the genus Tatia.

Sex chromosome system ZZ/ZW in Apareiodon hasemani Eigenmann, 1916 (Characiformes, Parodontidae) and a derived chromosomal region

Parodontidae fish show few morphological characteristics for the identification of their representatives and chromosomal analyses have provided reliable features for determining the interrelationships in this family. In this study, the chromosomes of Apareiodon hasemani from the São Francisco River basin, Brazil, were analyzed and showed a karyotype with 2n = 54 meta/submetacentric chromosomes, and a ZZ/ZW sex chromosome system. The study revealed active NORs located on pair 11 and additional 18S rDNA sites on pairs 7 and 22. The 5S rDNA locus was found in pair 14. It showed a pericentric inversion regarding the ancestral condition. The satellite DNA pPh2004 was absent in the chromosomes of A. hasemani, a shared condition with most members of Apareiodon. The WAp probe was able to detect the amplification region of the W chromosome, corroborating the common origin of the system within Parodontidae. These chromosomal data corroborate an origin for the ZW system of Parodontidae and aid in the understanding of the differentiation of sex chromosome systems in Neotropical fishes.

Karyotypic diversity between allopatric populations of the group Hoplias malabaricus (Characiformes: Erythrinidae): evolutionary and biogeographic considerations

Three populations of the group Hoplias malabaricus from the hydrographic basins of the São Francisco, Araguaia/Tocantins and Xingu Rivers in Brazil were analyzed using classic cytogenetic methods (Giemsa staining, C-banding and Ag-NORs) and molecular methods (fluorescent in situ hybridization with 18S rDNA, 5S rDNA and 5SHindIII satellite DNA probes). The chromosome markers allowed the characterization of these populations as belonging to karyomorph A and the detection of inter-population divergences. These differences likely stem from different evolutionary histories resulting from geographic isolation between populations associated to the dispersive mode of these organisms, reinforcing genetic diversity in the group Hoplias malabaricus.

Chromosome polymorphism in Ancistrus cuiabae Knaack, 1999 (Siluriformes: Loricariidae: Ancistrini)

Cytogenetic and FISH analyses were performed in 30 Ancistrus cuiabae specimens from a bay near the town of Poconé, in the Pantanal of Mato Grosso, Brazil. The observed diploid number was 2n = 34 chromosomes for both sexes and three distinct katyotypic formulae were found, namely cytotype A (20m, 8sm, 6st, Fundamental Number/FN = 68; 6 males and 11 females), cytotype B (19m, 8sm, 6st, 1a, FN = 67; 8 males and 4 females) and cytotype C (18m, 8sm, 6st, 2a, FN = 66; a single male). NORs's analyses showed that these regions were located in distinct sites on the NOR-bearing chromosome pair, according to cytotypes. Thus, in cytotype A, NORs were located in the terminal region of the short arm of the second metacentric chromosome pair; in cytotype B, they were detected in the short arm of the metacentric chromosome and interstitially on the acrocentric chromosome and, in cytotype C, NORs were observed in the interstitial region of the acrocentric chromosome pair. C-positive heterochromatic bands were adjacent to the rDNA sites in the corresponding chromosomes. Thus, the chromosomal polymorphism of A. cuiabae was probably originated through a pericentric inversion in chromosome pair nº 2 involving the NOR sites, which represents a novelty in the Ancistrini tribe. The results also broaden the knowledge of the chromosomal evolution in Ancistrus, the most derived genus of the Ancistrini tribe.

Constitutive heterochromatin, 5S and 18S rDNA genes in Apareiodon sp. (Characiformes, Parodontidae) with a ZZ/ZW sex chromosome system

Karyotype, sex chromosome system and cytogenetics characteristics of an unidentified species of the genus Apareiodon originating from Piquiri River (Paraná State, Brazil) were investigated using differential staining techniques (C-banding and Ag-staining) and fluorescent in situ hybridization (FISH) with 5S and 18S rDNA probes. The diploid chromosome number was 2n = 54 with 25 pairs of meta- (m) to submetacentric (sm) and 2 pairs of subtelocentric (st) chromosomes. The major ribosomal rDNA sites as revealed by Ag-staining and FISH with 18S rDNA probe were found in distal region of longer arm of st chromosome pair 26, while minor 5S sites were observed in the interstitial sites on chromosome pairs 2 (smaller cluster) and 7 (larger one). The C-positive heterochromatin had pericentromeric and telomeric distribution. The heteromorphic sex chromosome system consisted of male ZZ (pair 21) and female middle-sized m/st Z/W chromosomes. The pericentric inversion of heterochromatinized short arm of ancestral Z followed by multiplication of heterochromatin segments is hypothesized for origin of W chromosome. The observed karyotype and chromosomal markers corresponded to those found in other species of the genus.

A poorly known case of watershed transposition between the São Francisco and upper Paraná river basins

During construction of the Furnas hydroelectric power dam in the upper rio Paraná basin in the early 1960s, the rio Piumhi drainage outflow was diverted into the headwaters of the São Francisco river basin. The rio Piumhi was a right bank tributary of the rio Grande, which unites with the rio Paranaíba to form the rio Paraná. The transposition allowed the entire fish fauna of the rio Piumhi and associated swamps, lakes, and tributaries to intermingle with the fish fauna of the São Francisco basin via the ribeirão Sujo, a right bank tributary of the São Francisco. The transposition of the watershed may have had a major impact on the current composition of the fish fauna of the upper rio São Francisco watershed.

Cytogenetical analyses in three fish species of the genus Pimelodus(Siluriformes: Pimelodidae) from rio São Francisco: considerations about the karyotypical evolution in the genus

Karyotypes and other chromosomal markers were investigated in three species of the catfish genus Pimelodus, namely P. fur, P. maculatus and Pimelodus sp., from municipality of Três Marias, Minas Gerais, Brazil, using differential staining techniques (C-banding, Silver nitrate and CMA3 staining). The diploid chromosome number was 2n = 56 in P. maculatus and Pimelodus sp., while in P. fur 2n = 54. The karyotype of P. fur consisted in 32M + 8SM + 6ST + 8A with fundamental number (NF) of 100, that of P. maculatus 32M + 12SM + 12A with NF = 112, and that of Pimelodus sp. had 32M + 12Sm + 6ST + 6A with NF = 106.The nucleolar organizer regions (NORs) in all three species were invariably detected in telomeres of longer arm of the 20th chromosome pair. These sites were also positive after CMA3 and C-banding. No heteromorphic sex chromosomes were detected and C-banding pattern was species specific. Inferences about the karyotype differentiation in Pimelodus and putative chromosomal rearrangements are hypohesized.

Origin and differentiation of a sex chromosome system in Parodon hilarii (Pisces, Parodontidae). Satellite DNA, G- and C-banding

A satellite DNA sequence of Parodon hilarii (named pPh2004) was isolated, cloned and sequenced. This satellite DNA is composed of 200bp, 60% AT rich. In situ hybridization (FISH) results revealed that the satellite DNA pPh2004 is located in the terminal regions of several chromosomes, forming highly evident blocks in some and punctual marks in others. The comparison between the FISH and C-banding results showed that the location of this satellite DNA coincides with that of most terminal heterochromatins. However, some regions are only marked by FISH whereas other regions are only marked by C-banding. The possible existence of more than one satellite DNA family could explain these partial differences. The in situ hybridization with the satellite DNA and the G- and C-bandings confirmed the presence of a sex chromosome system of the ZZ/ZW type in P. hilarii, as well as the correct identification of the Z chromosome in the karyotype. This chromosome displays a segment of terminal heterochromatin in the long arm, similar to the segment observed in the short arm of the W chromosome, also showing a G-banding pattern similar to that of the short arm and part of the long arm of the W chromosome. A hypothesis on the origin of the W chromosome from an ancestral chromosome similar to the Z chromosome is presented.

Aphaereta sp. (Hymenoptera: Braconidae: Alysiinae) as a natural enemy to Peckia chrysostoma (Wiedemann) (Diptera: Sarcophagidae), in Brazil

This paper reports the first occurence of the parasite Aphaereta sp. (Hymenoptera: Braconidae: Alysiinae) which was collected from Peckia chrysostoma pupae (Diptera: Sarcophagidae) by means of traps containing some fish baits in a wood area close to the Agronomy college (Faculdade of Agronomia) in Itumbiara, Goiás, in the period from March to September, 2001. A total of 362 gregarious specimens of parasitoids from 26 pupae of P. chrysostoma. Aphaereta sp. was collected, with several individuals emerging from the same pupae.

Morphological differentiation and possible origin of B chromosomes in natural Brazilian population of Astyanax scabripinnis (Pisces, Characidae)

Specimens of Astyanax scabripinnis from three different altitudes (1920, 1800 and 700 m) along the Ribeirão Grande stream in the Campos do Jordão region (São Paulo State, Brazil) were investigated. The same diploid number, 2n = 50, was detected in the three populations, with the following karyotypic constitution: 6M, 22SM, 10ST and 12A. The populations located at 1920 and 1800 m altitude presented a high incidence of B chromosomes varying in number (0-2), shape (meta- and submetacentrics), size (large and small) and sex-related frequency (they were more frequent among females). The two morphologically variant B chromosomes probably evolved from a metacentric macrochromosome, which is the most commonly observed B chromosome in several A. scabripinnis populations.

Altitudinal variation for B chromosome frequency in the characid fish Astyanax scabripinnis

The analysis of three populations of the characid fish Astyanax scabripinnis located at different altitudes along the same stream has revealed the presence of a macro B chromosome in two high-altitude populations (1800 m and 1920 m) but its absence from a low-altitude population (700 m). Because the stream flows through very rugged mountains, with numerous falls ensuring that any gene flow occurs downstream only, the absence of B chromosomes from the low-altitude populations is best interpreted in the light of the parasitic theory of B chromosome evolution. Under this theory, we would expect B chromosomes to be more frequent where environmental conditions are more favourable for the species, because Bs are best tolerated there. The widespread presence of these B chromosomes in numerous Brazilian river headwaters, which are the preferred habitat for this species, support this possibility.

Biological aspects of Amazonian fishes. IX. Cytogenetic studies in two species of the genus Semaprochilodus (Pisces, Prochilodontidae)

The karyotype of Semaprochilodus insignis and Semaprochilodus taeniurus were analyzed through the conventional Giemsa staining, C-banding, and the nucleolar organizer regions. The diploid number is the same (2n = 54) in both species, but S. taeniurus shows a chromosomic system of the ZZ/ZW type. This and some other differences between the two karyotypes will be useful in further studies on the possible hybrid origin of the "jaraqui açú," a low frequency form that is observed together with S. insignis and S. taeniurus.

Key words: fish, ZZ/ZW system, constitutive heterochromatin, nucleolar organizing regions.