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Transposable elements (TEs) are widespread genomic components with substantial roles in genome evolution and sex chromosome differentiation. In this study, we compared the TE composition of three closely related fish with different sex chromosome systems: Megaleporinus elongatus (Z1Z1Z2Z2/Z1W1Z2W2), Megaleporinus macrocephalus (ZZ/ZW) (both with highly differentiated W sex chromosomes), and Leporinus friderici (without heteromorphic sex chromosomes). We created custom TE libraries for each species using clustering methods and manual annotation and prediction, and we predicted TE temporal dynamics through divergence-based analysis. The TE abundance ranged from 16% to 21% in the three mobilomes, with L. friderici having the lowest overall. Despite the recent amplification of TEs in all three species, we observed differing expansion activities, particularly between the two genera. Both Megaleporinus recently experienced high retrotransposon activity, with a reduction in DNA TEs, which could have implications in sex chromosome composition. In contrast, L. friderici showed the opposite pattern. Therefore, despite having similar TE compositions, Megaleporinus and Leporinus exhibit distinct TE histories that likely evolved after their separation, highlighting a rapid TE expansion over short evolutionary periods.

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INTRODUCTION: Eukaryotic genomes are composed of simple, repetitive sequences, including satellite DNAs (satDNA), which are noncoding sequences arranged in tandem arrays. These sequences play a crucial role in genomic functions and innovations, influencing processes such as the maintenance of nuclear material, the formation of heterochromatin and the differentiation of sex chromosomes. In this genomic era, advances in next-generation sequencing and bioinformatics tools have facilitated the exhaustive cataloging of repetitive elements in genomes, particularly in non-model species. This study focuses on the satDNA content of Ancistrus sp., a diverse species of fish from the Loricariidae family. The genus Ancistrus shows significant karyotypic evolution, with extensive variability from the ancestral diploid number. METHODS: By means of bioinformatic approaches, 40 satDNA families in Ancistrus sp., constituting 5.19% of the genome were identified. Analysis of the abundance and divergence landscape revealed diverse profiles, indicating recent amplification and homogenization of these satDNA sequences. RESULTS: The most abundant satellite, AnSat1-142, constitutes 2.1% of the genome, while the least abundant, AnSat40-52, represents 0.0034%. The length of the monomer repeat varies from 16 to 142 base pairs, with an average length of 61 bp. These results contribute to understanding the genomic dynamics and evolution of satDNAs in Ancistrus sp. CONCLUSION: The study underscores the variability of satDNAs between fish species and provides valuable information on chromosome organization and the evolution of repetitive elements in non-model organisms.

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Among the repetitive elements, satellite DNA (SatDNA) emerges as extensive arrays of highly similar tandemly repeated units, spanning megabases in length. Given that the satDNA PboSat01-176, previously characterized in P. boiei, prompted our interest for having a high abundance in P. boiei and potential for centromeric satellite, here, we employed various approaches, including low coverage genome sequencing, followed by computational analysis and chromosomal localization techniques in four Proceratophrys species and, investigating the genomic presence and sharing, as well as its potential for chromosomal centromere marker in Proceratophrys frog species. Our findings demonstrate that PboSat01-176 exhibits high abundance across all four Proceratophrys species, displaying distinct characteristics that establish it as the predominant repetitive DNA element in these species. The satellite DNA is prominently clustered in the peri/centromeric region of the chromosomes, particularly in the heterochromatic regions. The widespread presence of PboSat01-176 in closely related Proceratophrys species reinforces the validity of the library hypothesis for repetitive sequences. Thus, this study highlighted the utility of the satDNA family PboSat01-176 as a reliable centromeric marker in Proceratophrys species, with potential to be applied in other species of anuran amphibians. The observed sharing and maintenance of this sequence within the genus suggest possibilities for future research, particularly through expanded sampling to elucidate parameters that underlie the library hypothesis and the evolutionary dynamics of satDNA sequences.

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Satellite DNAs (satDNAs) are one of the most abundant elements in genomes. Characterized as tandemly organized sequences that can be amplified into multiple copies, mainly in heterochromatic regions. The frog P. boiei (2n = 22, ZZ♂/ZW♀) is found in the Brazilian Atlantic forest and has an atypical pattern of heterochromatin distribution when compared to other anuran amphibians, with large pericentromeric blocks on all chromosomes. In addition, females of Proceratophrys boiei have a metacentric sex chromosome W showing heterochromatin in all chromosomal extension. In this work, we performed high-throughput genomic, bioinformatic, and cytogenetic analyses to characterize the satellite DNA content (satellitome) in P. boiei, mainly due to high amount of C-positive heterochromatin and the highly heterochromatic W sex chromosome. After all the analyses, it is remarkable that the satellitome of P. boiei is composed of a high number of satDNA families (226), making P. boiei the frog species with the highest number of satellites described so far. Consistent with the observation of large centromeric C-positive heterochromatin blocks, the genome of P. boiei is enriched with high copy number of repetitive DNAs, with total satDNA abundance comprising 16.87% of the genome. We successfully mapped via Fluorescence in situ hybridization the two most abundant repeats in the genome, PboSat01-176 and PboSat02-192, highlighting the presence of certain satDNAs sequences in strategic chromosomal regions (e.g., centromere and pericentromeric region), which leads to their participation in crucial processes for genomic organization and maintenance. Our study reveals a great diversity of satellite repeats that are driving genomic organization in this frog species. The characterization and approaches regarding satDNAs in this species of frog allowed the confirmation of some insights from satellite biology and a possible relationship with the evolution of sex chromosomes, especially in anuran amphibians, including P. boiei, for which data were not available.

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Neotropical fishes have highly diversified karyotypic and genomic characteristics and present many diverse sex chromosome systems, with various degrees of sex chromosome differentiation. Knowledge on their sex-specific composition and evolution, however, is still limited. Satellite DNAs (satDNAs) are tandemly repeated sequences with pervasive genomic distribution and distinctive evolutionary pathways, and investigating satDNA content might shed light into how genome architecture is organized in fishes and in their sex chromosomes. The present study investigated the satellitome of Megaleporinus elongatus, a freshwater fish with a proposed Z1Z1Z2Z2/Z1W1Z2W2 multiple sex chromosome system that encompasses a highly heterochromatic and differentiated W1 chromosome. The species satellitome comprises of 140 different satDNA families, including previously isolated sequences and new families found in this study. This diversity is remarkable considering the relatively low proportion that satDNAs generally account for the M. elongatus genome (around only 5%). Differences between the sexes in regards of satDNA content were also evidenced, as these sequences are 14% more abundant in the female genome. The occurrence of sex-biased signatures of satDNA evolution in the species is tightly linked to satellite enrichment associated with W1 in females. Although both sexes share practically all satDNAs, the overall massive amplification of only a few of them accompanied the W1 differentiation. We also investigated the expansion and diversification of the two most abundant satDNAs of M. elongatus, MelSat01-36 and MelSat02-26, both highly amplified sequences in W1 and, in MelSat02-26's case, also harbored by Z2 and W2 chromosomes. We compared their occurrences in M. elongatus and the sister species M. macrocephalus (with a standard ZW sex chromosome system) and concluded that both satDNAs have led to the formation of highly amplified arrays in both species; however, they formed species-specific organization on female-restricted sex chromosomes. Our results show how satDNA composition is highly diversified in M. elongatus, in which their accumulation is significantly contributing to W1 differentiation and not satDNA diversity per se. Also, the evolutionary behavior of these repeats may be associated with genome plasticity and satDNA variability between the sexes and between closely related species, influencing how seemingly homeologous heteromorphic sex chromosomes undergo independent satDNA evolution.

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Cytogenetic data showed a variation in diploid chromosome number in the genus Hyphessobrycon ranging from 2n = 46 to 52, and studies involving repetitive DNA sequences are scarce in representatives of this genus. The purpose of this paper was the chromosomal mapping of repetitive sequences (rDNA, histone genes, U snDNA and microsatellites) and investigation of the amplification of 5S rDNA clusters in the Hyphessobrycon eques genome. Two H. eques populations displayed 2n = 52 chromosomes, with the acrocentric pair No. 24 bearing Ag-NORs corresponding with CMA3+/DAPI-. FISH with a 18S rDNA probe identified the NORs on the short (p) arms of the acrocentric pairs Nos. 22 and 24. The 5S rDNA probe visualized signals on almost all chromosomes in genomes of individuals from both populations (40 signals); FISH with H3 histone probe identified two chromosome pairs, with the pericentromeric location of signals; FISH with a U2 snDNA probe identified one chromosome pair bearing signals, on the interstitial chromosomal region. The mononucleotide (A), dinucleotide (CA) and tetranucleotide (GATA) repeats were observed on the centromeric/pericentromeric and/or terminal positions of all chromosomes, while the trinucleotide (CAG) repeat showed signals on few chromosomes. Molecular analysis of 5S rDNA and non-transcribed spacers (NTS) showed microsatellites (GATA and A repeats) and a fragment of retrotransposon (SINE3/5S-Sauria) inside the sequences. This study expanded the available cytogenetic data for H. eques and demonstrated to the dispersion of the 5S rDNA sequences on almost all chromosomes.

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Astyanax is a genus with a wide distribution ranging from the south United States to north of Patagonia (Argentina). The available cytogenetic data on Astyanax indicate a high karyotypic diversity, with diploid number of 36-52 chromosomes, presence of B chromosomes, heterochromatin polymorphism, and variations with respect to the number and localization of nucleolar organizer regions (NORs) and 18S and 5S ribosomal DNA sites. In the present study, we estimated the evolutionary history and times of divergence for 10 nominal Astyanax species from the South and Central/North American (Cna) continents, which present distinct chromosomal characteristics, based on molecular clocks inferred from mitochondrial DNA sequence. The molecular clock results indicate the origin of three distinct clades (Humeral dark spot [Hds]; Diffuse humeral spot [Dhs]; Cna group) during the late Miocene about 11.2 million years ago (Mya). Thus, Astyanax mexicanus (Cna) represent a species that diverged a long time ago (∼8.6 Mya) from the Hds group, and Astyanax schubarti is the oldest species (∼6.5 Mya) among the Dhs species.

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The Tc1 mariner element is widely distributed among organisms and have been already described in different species of fish. The genus Ancistrus (Kner, 1854) has 68 nominal species and is part of an interesting taxonomic and cytogenetic group, as well as presenting a variation of chromosome number, ranging from 2n=34 to 54 chromosomes, and the existence of simple and multiple sex chromosome system and the occurrence of chromosomal polymorphisms involving chromosomes that carry the nucleolus organizer region. In this study, a repetitive element by restriction enzyme, from Ancistrus sp.1 "Flecha" was isolated, which showed similarity with a transposable element Tc1-mariner. Its chromosomal location is distributed in heterochromatic regions and along the chromosomal arms of all specimens covered in this study, confirming the pattern dispersed of this element found in other studies carried out with other species. Thus, this result reinforces the hypothesis that the sequence AnDraI is really a dispersed element isolated. As this isolated sequence showed the same pattern in all species which have different sex chromosomes systems, including in all sex chromosomes, we could know that it is not involved in sex chromosome differentiation.

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Genus Astyanax is well distributed in Neotropical freshwater environments and its taxonomic position is uncertain, as is the case with other Characidae genera allocated in the group incertae sedis. This study aimed to analyse the karyotype of different populations of Astyanax fasciatus (Corumbataí River basin) using Giemsa staining, C-band technique, and fluorescence in situ hybridization for the H3 histone and 5S rRNA genes, in addition we describe for the first time the chromosomal organization of H3 histone and 5S rRNAgenes in A. marionae (ParaguayRiver basin). Chromosomes of three A. fasciatus populations were analysed (two with 2n = 50 and one with 2n = 48) and the heterochromatin was organized in two forms (blocks with blurred boundaries and distinct blocks). H3 histone and 5S rRNA genes were observed in all the three populations of A. fasciatus on two chromosome pairs (one metacentric chromosome showing H3 histone and 5S rRNA gene clusters). In A. marionae (2n = 48), H3 histone and 5S rRNA genes were observed in one acrocentric chromosome pair (different pairs). Further, differences between karyotypes and heterochromatin, as well as the chromosomal organization of H3 histone and 5S rRNA genes in Astyanax species, focussing on chromosome evolution in the group are discussed.

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Repetitive sequences and their chromosomal locations have been widely studied in species of the Astyanax genus. However, the chromosomal organization of U2 snDNA remains largely unknown. The aims of this study were to examine the chromosomal contexts of U2 snRNA and 5S rRNA genes in Astyanax species and determine the degree of chromosome morphological similarity between species with different diploid numbers. Clusters of U2 snDNA and 5S rDNA were determined in nine species of Astyanax, including two karyomorphs of Astyanax fasciatus Cuvier, 1819. All species exhibited U2 snDNA clusters on two chromosome pairs, except Astyanax mexicanus De Filippi, 1853 (one pair). The 5S rDNA clusters were located on one chromosome pair in Astyanax altiparanae Garutti and Britski, 2000, and Astyanax marionae Eigenmann, 1911, two pairs in Astyanax abramis Jenyns, 1842, Astyanax asuncionensis Géry, 1972, Astyanax bockmanni Vari and Castro, 2007, Astyanax eigenmanniorum Cope, 1894, A. fasciatus (karyomorphs I and II), and Astyanax schubarti Britski, 1964, and four pairs in A. mexicanus. The relationships between the repetitive sequences in different species suggest that A. schubarti and A. mexicanus exhibit an unusual U2 snDNA chromosomal format as a result of events occurring in the evolutionary history of the Astyanax group.

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The genus Astyanax is widely distributed from the southern United States to northern Patagonia, Argentina. While cytogenetic studies have been performed for this genus, little is known about the histone gene families. The aim of this study was to examine the chromosomal relationships among the different species of Astyanax. The chromosomal locations of the 5S rRNA and H3 histone genes were determined in A. abramis, A. asuncionensis, A. altiparanae, A. bockmanni, A. eigenmanniorum, A. mexicanus (all 2n = 50), A. fasciatus (2n = 46), and A. schubarti (2n = 36). All eight species exhibited H3 histone clusters on two chromosome pairs. In six species (A. abramis, A. asuncionensis, A. altiparanae, A. bockmanni, A. eigenmanniorum, and A. fasciatus), syntenic clusters of H3 histone and 5S rDNA were observed on metacentric (m) or submetacentric (sm) chromosomes. In seven species, clusters of 5S rDNA sequences were located on one or two chromosome pairs. In A. mexicanus, 5S rDNA clusters were located on four chromosome pairs. This study demonstrates that H3 histone clusters are conserved on two chromosome pairs in the genus Astyanax, and specific chromosomal features may contribute to the genomic organization of the H3 histone and 5S rRNA genes.

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The Hyphessobrycon are allocated in the incertae sedis group of the Characidae family, one of the genera with more species of the group. The chromosomes of some species of Hyphessobrycon are known, and the diploid number most common for genus is 2n = 50 chromosomes. The aims of this study were to examine the karyotype macrostructure in the Hyphessobryconeques Steindachner, 1882, and show a new origin hypothesis for B chromosomes. The diploid number observed for Hyphessobryconeques was 2n = 52 chromosomes, and a karyotype formulae of 12m + 18sm + 8st + 14a, with FN (fundamental number) = 90 for both sexes. Only two females showed one B chromosome. The heterochromatin was observed mainly on centromeric regions, and in the long arm of the B chromosome. In this paper, the relationship of the B chromosome of Hyphessobryconeques with an occasional chromosome rearrangement was discussed.

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The species of genus Astyanax is widely distributed in freshwater neotropical zones. Astyanax is considered to be taxonomically confused, similar to other genera placed incertae sedis in Characidae. The cytogenetics of this genus is well characterized; species vary widely in diploid number, from 2n=36 chromosomes in Astyanax schubarti to 2n=50 for most species studied. The size, number, and position of different cytological markers vary among species and populations of Astyanax. We analyzed the karyotypes of individuals from three Astyanax species (Astyanax abramis, Astyanax altiparanae, and Astyanax eigenmanniorum) from populations not previously analyzed. We describe variations in several cytogenetic markers and the karyotypic relationships between them, specifically focusing on the characteristics of the conserved and divergent locations of the ribosomal genes. Our data are useful for establishing relationships between species and for investigating the karyotype evolution within the genus.

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BACKGROUND: The Leporinus genus, belonging to the Anostomidae family, is an interesting model for studies of sex chromosome evolution in fish, particularly because of the presence of heteromorphic sex chromosomes only in some species of the genus. In this study we used W chromosome-derived probes in a series of cross species chromosome painting experiments to try to understand events of sex chromosome evolution in this family. RESULTS: W chromosome painting probes from Leporinus elongatus, L. macrocephalus and L. obtusidens were hybridized to each others chromosomes. The results showed signals along their W chromosomes and the use of L. elongatus W probe against L. macrocephalus and L. obtusidens also showed signals over the Z chromosome. No signals were observed when the later aforementioned probe was used in hybridization procedures against other four Anostomidae species without sex chromosomes. CONCLUSIONS: Our results demonstrate a common origin of sex chromosomes in L. elongatus, L. macrocephalus and L. obtusidens but suggest that the L. elongatus chromosome system is at a different evolutionary stage. The absence of signals in the species without differentiated sex chromosomes does not exclude the possibility of cryptic sex chromosomes, but they must contain other Leporinus W sequences than those described here.

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BACKGROUND: Nowadays, the genus Bryconamericus is placed in subfamily Stevardiinae within of Characidae, but not shows consistent evidence of monophyletism. The purpose of this work was to study the chromosomes of three species of Bryconamericus, aiming to add cytogenetic knowledge and contribute to the understanding of the chromosomal evolution of this genus. RESULTS: The chromosomes of three species of Bryconamericus were analyzed using cytogenetic techniques. The karyotype of Bryconamericus stramineus contained 6 metacentric (m) + 10 submetacentric (sm) + 16 subtelocentric (st) + 20 acrocentric (a), the fundamental number (FN) of 84, one silver impregnated (Ag-NOR) pair, one pair bearing the 18S ribosomal DNA sites, another pair bearing the 5S rDNA sites, and a few positive C-bands. Bryconamericus turiuba had a karyotype containing 8 m + 10sm + 14st + 20a (FN = 84), one chromosome pair Ag-NOR, two pairs bearing the 18S rDNA sites, two pairs bearing the 5S rDNA sites, and a few C-band regions. Bryconamericus cf. iheringii had a karyotype containing 10 m + 14sm + 18st + 10a (FN = 94), including one pair with a secondary constriction Ag-NOR positive. In this karyotype the fluorescent in situ hybridization (FISH) showed the 18S and 5S rDNA probe in adjacent position. CONCLUSIONS: The results obtained in this work showed different characteristics in the organization of two multigene families, indicating that distinct evolutionary forces acting on the diversity of rDNA sequences in the genome of three Bryconamericus species.

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In this study, phylogenetic and phylogeographic analyses of populations identified as Hypostomus strigaticeps from the upper Paraná River basin were conducted in order to test whether these different populations comprises cryptic species or structured populations and to assess their genetic variability. The sequences of the mitochondrial DNA ATP sintetase (subunits 6/8) of 27 specimens from 10 populations (one from Mogi-Guaçu River, five from Paranapanema River, three from Tietê River and one from Peixe River) were analyzed. The phylogeographic analysis showed the existence of eight haplotypes (A-H), and despite the ancestral haplotype includes only individuals from the Tietê River basin, the distribution of H. strigaticeps was not restricted to this basin. Haplotypes A, B and F were the most frequent. Haplotypes D, E, F, G, and H were present in the sub-basin of Paranapanema, two (A and B) were present in the sub-basin of the Tietê River, one (C) was exclusively distributed in the sub-basin of the Peixe River, and one (B) was also present in the sub-basin of the Grande River. The phylogenetic analysis showed that the populations of H. strigaticeps indeed form a monophyletic unit comprising two lineages: TG, with representatives from the Tietê, Mogi-Guaçu and Peixe Rivers; and PP, with specimens from the Paranapanema River. The observed degree of genetic divergence within the TG and PP lineages was 0.1% and 0.2%, respectively, whereas the genetic divergence between the two lineages themselves was approximately 1%. The results of the phylogenetic analysis do not support the hypothesis of existence of crypt species and the phylogeographic analysis confirm the presence of H. strigaticeps in other sub-basins of the upper Paraná River: Grande, Peixe, and Paranapanema sub-basins.(AU)

Neste estudo, foram conduzidas análises filogenéticas e filogeográficas de populações identificadas como Hypostomus strigaticeps na bacia do alto rio Paraná a fim de testar se essas populações compreendem espécies crípticas ou populações estruturadas e avaliar a variabilidade genética das mesmas. Foram analisadas sequências do DNA mitocondrial ATP sintetase (subunidades 6/8) de 27 espécimes de 10 populações (uma do rio Mogi-Guaçu, cinco do rio Paranapanema, três do rio Tietê e uma do rio do Peixe). A análise filogeográfica mostrou a existência de oito haplótipos (A-H), e apesar do haplótipo ancestral incluir apenas indivíduos da bacia do rio Tietê, a distribuição de H. strigaticeps não se restringe a esta bacia. Os haplótipos A, B e F foram os mais frequentes. D, E, F, G e H estão presentes na sub-bacia do rio Paranapanema, dois (A e B) estão presentes na sub-bacia do rio Tietê, um (C) está exclusivamente distribuído na sub-bacia do rio do Peixe, e um (B) também está presente na sub-bacia do rio Grande. A análise filogenética mostrou que as populações de H. strigaticeps realmente formam uma unidade monofilética que compreende duas linhagens: TG, com representantes do rio Tietê, rio Mogi-Guaçu e rio do Peixe, e PP, com espécimes do rio Paranapanema. O grau de divergência genética observada nas linhagens de TG e PP foram de 0,1% e 0,2%, respectivamente, enquanto que a divergência genética entre as duas linhagens foi de aproximadamente 1%. Os resultados da análise filogenética não suportam a hipótese da existência de espécies crípticas e a análise filogeográfica confirma a presença de H. strigaticeps em outras sub-bacias do alto rio Paraná: sub-bacias do rio Grande, rio do Peixe e rio Paranapanema.(AU)

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The subfamily Iguanodectinae comprises a group of small Neotropical fishes composed by two genera and 11 nominal species widely distributed in the Atlantic drainages of South America. Piabucus is the only genus of Iguanodectinae found in the Paraguay River basin, especially in the Pantanal of Mato Grosso State, where it is represented by Piabucus melanostomus. Given the wide distribution and the low dispersion capacity of this species, due the ecological constraints, it is possible that many interesting genetic features could be found in different populations. In this way, the aim of his work was to perform the phylogeographic pattern of P. melanostomus populations using mitochondrial DNA sequences. A total of 13 individuals from three rivers belonging the Mato Grosso wetland were sampled. The ATP sintetase (subunits 6 and 8) gene was completely sequenced, the mean of nucleotide base composition in the sequences was 31.2% (T), 30.2% (C), 26.9% (A) and 11.9% (G), with no gene saturation. The population analysis in the TCS program generated a network with six haplotypes (A to F), where the ancestral haplotype (A) has a frequency of 25% and is composed by individuals from Cuiabá and Paraguay Rivers. The phylogenetic analysis showed the occurrence of two mtDNA lineages (1 and 2), the distance observed between the two lineages was 0.6%. The phylogenetic and phylogeographic results as well as the negative values of Fst for some populations, indicate a possible occurrence of gene flow among the analyzed populations. These results highlights the importance of flood pulse existent on wetland as a vehicle that permits a temporary connection among isolated population maintaining the species genetic variability.

A subfamília Iguanodectinae compreende um grupo de pequenos peixes neotropicais composta de dois gêneros e 11 espécies nominais amplamente distribuídas nas drenagens do Atlântico da América do Sul. Piabucus é o único gênero de Iguanodectinae encontrado na bacia do rio Paraguai, especialmente no Pantanal de Mato Grosso, onde é representada por Piabucus melanostomus. Dada a ampla distribuição e a baixa capacidade de dispersão desta espécie, devido às limitações ecológicas, é possível que características genéticas interessantes possam ser encontradas em diferentes populações. Deste modo, o objetivo deste trabalho foi estabelecer os padrões filogeográficos de populações de P. melanostomus utilizando sequências de DNA mitocondrial. Foram amostrados 13 indivíduos de três rios pertencentes ao Pantanal do Mato Grosso. O gene ATP sintetase (subunidades 6 e 8) foi completamente sequenciado, a média da composição de base de nucleotídeos nas sequências foi de 31,2% (T), 30,2% (C), 26,9% (A) e 11,9% (G), não havendo saturação. A análise populacional no programa TCS gerou uma rede com seis haplótipos (A a F), onde o haplótipo ancestral (A) tem uma freqüência de 25% e é composto por indivíduos dos rios Cuiabá e Paraguai. A análise filogenética mostrou a ocorrência de duas linhagens de DNA (1 e 2), a distância observada entre as duas linhagens foi de 0,6%. Os resultados filogenéticos e filogeográficos, bem como os valores negativos de FST para algumas populações, indicam uma possível ocorrência de fluxo de genes entre as populações analisadas. Estes resultados destacam a importância do pulso de inundação existente em zonas úmidas como um veículo que permite uma conexão temporária entre a população isolada, mantendo a variabilidade genética das espécies.

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In this study, phylogenetic and phylogeographic analyses of populations identified as Hypostomus strigaticeps from the upper Paraná River basin were conducted in order to test whether these different populations comprises cryptic species or structured populations and to assess their genetic variability. The sequences of the mitochondrial DNA ATP sintetase (subunits 6/8) of 27 specimens from 10 populations (one from Mogi-Guaçu River, five from Paranapanema River, three from Tietê River and one from Peixe River) were analyzed. The phylogeographic analysis showed the existence of eight haplotypes (A-H), and despite the ancestral haplotype includes only individuals from the Tietê River basin, the distribution of H. strigaticeps was not restricted to this basin. Haplotypes A, B and F were the most frequent. Haplotypes D, E, F, G, and H were present in the sub-basin of Paranapanema, two (A and B) were present in the sub-basin of the Tietê River, one (C) was exclusively distributed in the sub-basin of the Peixe River, and one (B) was also present in the sub-basin of the Grande River. The phylogenetic analysis showed that the populations of H. strigaticeps indeed form a monophyletic unit comprising two lineages: TG, with representatives from the Tietê, Mogi-Guaçu and Peixe Rivers; and PP, with specimens from the Paranapanema River. The observed degree of genetic divergence within the TG and PP lineages was 0.1% and 0.2%, respectively, whereas the genetic divergence between the two lineages themselves was approximately 1%. The results of the phylogenetic analysis do not support the hypothesis of existence of crypt species and the phylogeographic analysis confirm the presence of H. strigaticeps in other sub-basins of the upper Paraná River: Grande, Peixe, and Paranapanema sub-basins.

Neste estudo, foram conduzidas análises filogenéticas e filogeográficas de populações identificadas como Hypostomus strigaticeps na bacia do alto rio Paraná a fim de testar se essas populações compreendem espécies crípticas ou populações estruturadas e avaliar a variabilidade genética das mesmas. Foram analisadas sequências do DNA mitocondrial ATP sintetase (subunidades 6/8) de 27 espécimes de 10 populações (uma do rio Mogi-Guaçu, cinco do rio Paranapanema, três do rio Tietê e uma do rio do Peixe). A análise filogeográfica mostrou a existência de oito haplótipos (A-H), e apesar do haplótipo ancestral incluir apenas indivíduos da bacia do rio Tietê, a distribuição de H. strigaticeps não se restringe a esta bacia. Os haplótipos A, B e F foram os mais frequentes. D, E, F, G e H estão presentes na sub-bacia do rio Paranapanema, dois (A e B) estão presentes na sub-bacia do rio Tietê, um (C) está exclusivamente distribuído na sub-bacia do rio do Peixe, e um (B) também está presente na sub-bacia do rio Grande. A análise filogenética mostrou que as populações de H. strigaticeps realmente formam uma unidade monofilética que compreende duas linhagens: TG, com representantes do rio Tietê, rio Mogi-Guaçu e rio do Peixe, e PP, com espécimes do rio Paranapanema. O grau de divergência genética observada nas linhagens de TG e PP foram de 0,1% e 0,2%, respectivamente, enquanto que a divergência genética entre as duas linhagens foi de aproximadamente 1%. Os resultados da análise filogenética não suportam a hipótese da existência de espécies crípticas e a análise filogeográfica confirma a presença de H. strigaticeps em outras sub-bacias do alto rio Paraná: sub-bacias do rio Grande, rio do Peixe e rio Paranapanema.

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BACKGROUND: Members of the Anostomidae family provide an interesting model system for the study of the influence of repetitive elements on genome composition, mainly because they possess numerous heterochromatic segments and a peculiar system of female heterogamety that is restricted to a few species of the Leporinus genus. The aim of this study was to isolate and identify important new repetitive DNA elements in Anostomidae through restriction enzyme digestion, followed by cloning, characterisation and chromosome mapping of this fragment. To identify repetitive elements in other Leporinus species and expand on studies of repetitive elements in Anostomidae, hybridisation experiments were also performed using previously described probes of LeSpeI repetitive elements. RESULTS: The 628-base pair (bp) LeSpeII fragment was hybridised to metaphase cells of L. elongatus individuals as well as those of L. macrocephalus, L. obtusidens, L. striatus, L. lacustris, L. friderici, Schizodon borellii and S. isognathus. In L. elongatus, both male and female cells contained small clusters of LeSpeII repetitive elements dispersed on all of the chromosomes, with enrichment near most of the terminal portions of the chromosomes. In the female sex chromosomes of L. elongatus (Z2,Z2/W1W2), however, this repeated element was absent. In the remaining species, a dispersed pattern of hybridisation was observed on all chromosomes irrespective of whether or not they were sex chromosomes. The repetitive element LeSpeI produced positive hybridisations signals only in L. elongatus, L. macrocephalus and L. obtusidens, i.e., species with differentiated sex chromosomes. In the remaining species, the LeSpeI element did not produce hybridisation signals. CONCLUSIONS: Results are discussed in terms of the effects of repetitive sequences on the differentiation of the Anostomidae genome, especially with respect to sex chromosome evolution. LeSpeII showed hybridisation patterns typical of Long Interspersed Elements (LINEs). The differential distribution of this element may be linked to sex chromosome differentiation in L. elongatus species. The relationship between sex chromosome specificity and the LeSpeI element is confirmed in the species L. elongatus, L. macrocephalus and L. obtusidens.

RESUMEN

The objective of this study was to evaluate the effectiveness of estradiol valerate in an attempt to feminize the male Astyanax altiparanae. One thousand newly-hatched larvae were randomly distributed in four incubators. During a period of 30 days, estradiol valerate was administered in different dosages (20, 40, and 80 mg/kg of diet); the control group did not receive hormone in the diet. After 161 days of hatching, biometry was performed on 50 fishes per treatment group, and the gonads were analyzed. The hormone treatments were effective in feminizing A. altiparanae, achieving 70-76% of the desired sex, while the control treatment had 44% females. The hormone did not affect the growth of fish.