Karyotypic variation of two populations of the small freshwater stingray Potamotrygon wallacei Carvalho, Rosa & Araújo 2016: A classical and molecular approach.

Potamotrygoninae comprises a group of Neotropical fishes with an ancient relationship with marine environments. In the last few years, 11 new Potamotrygon species were described, including Potamotrygon wallacei Carvalho, Araújo e Rosa 2016. Cytogenetic data about this species are limited to classical markers (Giemsa, C-Banding and Ag-NOR techniques), these studies highlighted a rare sexual chromosome system XX/X0 with males presenting 67 chromosomes and females 68 chromosomes. The classical analyses performed here reveled populational variation in the karyotype formula, as well as, in the heterochromatin regions. Besides the classical markers, our molecular experiments showed multiple sites for 18S rDNA sequence (including in the X chromosomes) and single sites for 5S rDNA sequence, we did not find interstitial telomeric sequences. In addition, (AC)15, (AG)15, and (CAC)15 microsatellites showed association with the several autosome pair, and the (GT)15 clutters were found in only one population. On the other hand, (GATA)4 sequence showed association with the sexual chromosomes X in all males and females analyzed. Our results showed that pericentric inversions, in addition to fusions, shaped the karyotype of P. wallacei once we found two populations with distinct karyotype formula and this could be a result of the past events recovered by our modeling experiments. Besides, here we described the association of 18S and (GATA)4 motifs with sexual chromosomes, which indicated that these sequences had a novel in the differentiation of sexual chromosomes in P. wallacei.

Molecular analysis reveals high diversity in the Hoplias malabaricus (Characiformes, Erythrinidae) species complex from different Amazonian localities

ABSTRACT DNA barcoding proposes that a fragment of DNA can be used to identify species. In fish, a fragment of cytochrome oxidase subunit I (COI) has been effective in many studies with different foci. Here we use this molecular tool to provide new insights into the cryptic diversity found in the Hoplias malabaricus species complex. Popularly known as trahira, H. malabaricus is widely distributed in South America. The clade shows molecular and cytogenetic diversity, and several studies have supported the occurrence of a complex of species. We performed molecular and karyotypic analysis of H. malabaricus individuals from eight Amazonian localities to assess the diversity present in the nominal taxon, and to clarify relationships within this group. We used 12 samples in cytogenetic analyses and found two karyomorphs: 2n = 40 (20m + 20sm) (karyomorph C) and 2n = 42 (22m + 20sm) (karyomorph A). We used 19 samples in molecular analyses with COI as a molecular marker, maximum likelihood analyses, and the Kimura-2-parameter evolutionary model with bootstrap support. We found karyomorph-related differentiation with bootstrap of 100%. However, we found high molecular diversity within karyomorph C. The observed pattern allowed us to infer the presence of cryptic diversity, reinforcing the existence of a species complex.

RESUMO O DNA barcoding propõe que um fragmento de DNA possa servir para identificar espécies. Em peixes, um fragmento do gene COI tem se mostrado eficaz em muitos estudos com focos diferentes. Nós usamos essa ferramenta molecular para fornecer novas informações sobre a diversidade críptica encontrada no complexo de espécies Hoplias malabaricus. Popularmente conhecida como traíra, H. malabaricus tem uma ampla distribuição na América do Sul. Esse clado mostra diversidade molecular e citogenética, e vários estudos dão suporte à ocorrência de um complexo de espécies. Realizamos análises molecular e cariotípica em indivíduos de H. malabaricus de oito localidades amazônicas, para acessar a diversidade no taxon nominal e elucidar as relações nesse grupo. Usamos 12 amostras em análises citogenéticas e encontramos dois cariomorfos: 2n = 40 (20m + 20sm) (cariomorfo C) e 2n = 42 (22m + 20sm) (cariomorfo A). Usamos 19 amostras em análise molecular, utilizando COI como marcador molecular, análises de máxima verossimilhança e o modelo evolutivo de Kimura-2-parâmetros com estimativa de bootstrap. Encontramos diferenciação relacionada aos cariomorfos com bootstrap de 100%. No entanto, encontramos alta diversidade molecular no cariomorfo C. O padrão observado nos permitiu inferir a presença de diversidade oculta, reforçando a existência de um complexo de espécies.

Análise molecular revela alta diversidade no complexo de espécies Hoplias malabaricus (Characiformes, Erythrinidae) de diferentes localidades amazônicas / Molecular analysis reveals high diversity in the Hoplias malabaricus (Characiformes, Erythrinidae) species complex from different Amazonian localities

O DNA barcoding propõe que um fragmento de DNA possa servir para identificar espécies. Em peixes, um fragmento do gene COI tem se mostrado eficaz em muitos estudos com focos diferentes. Nós usamos essa ferramenta molecular para fornecer novas informações sobre a diversidade críptica encontrada no complexo de espécies Hoplias malabaricus. Popularmente conhecida como traíra, H. malabaricus tem uma ampla distribuição na América do Sul. Esse clado mostra diversidade molecular e citogenética, e vários estudos dão suporte à ocorrência de um complexo de espécies. Realizamos análises molecular e cariotípica em indivíduos de H. malabaricus de oito localidades amazônicas, para acessar a diversidade no taxon nominal e elucidar as relações nesse grupo. Usamos 12 amostras em análises citogenéticas e encontramos dois cariomorfos: 2n = 40 (20m + 20sm) (cariomorfo C) e 2n = 42 (22m + 20sm) (cariomorfo A). Usamos 19 amostras em análise molecular, utilizando COI como marcador molecular, análises de máxima verossimilhança e o modelo evolutivo de Kimura-2-parâmetros com estimativa de bootstrap. Encontramos diferenciação relacionada aos cariomorfos com bootstrap de 100%. No entanto, encontramos alta diversidade molecular no cariomorfo C. O padrão observado nos permitiu inferir a presença de diversidade oculta, reforçando a existência de um complexo de espécies. (AU)

Cytogenetic Analysis of Panaqolus tankei Cramer & Sousa, 2016 (Siluriformes, Loricariidae), an Ornamental Fish Endemic to Xingu River, Brazil.

Despite conservation of the diploid number, a huge diversity in karyotype formulae is found in the Ancistrini tribe (Loricariidae, Hypostominae). However, the lack of cytogenetic data for many groups impairs a comprehensive understanding of the chromosomal relationships and the impact of chromosomal changes on their evolutionary history. Here, we present for the first time the karyotype of Panaqolus tankei Cramer & Sousa, 2016. We focused on the chromosomal characterization, using conventional and molecular cytogenetic techniques to unravel the evolutionary trends of this tribe. P. tankei, as most species of its sister group Pterygoplichthini, also possessess a conserved diploid number of 52 chromosomes. We observed heterochromatin regions in the centromeres of many chromosomes; pairs 5 and 6 presented interstitial heterochromatin regions, whereas pairs 23 and 24 showed extensive heterochromatin regions in their q arms. In situ localization of 18S rDNA showed hybridization signals correlating with the nucleolus organizer regions, which are located in the q arms of pair 5. However, the 5S rDNA was detected in the centromeric and terminal regions of the q arms of pair 8. (TTAGGG)n hybridized only in the terminal regions of all chromosomes. Microsatellite in situ localization showed divergent patterns, (GA)15 repeated sequences were restricted to the terminal regions of some chromosomes, whereas (AC)15 and (GT)15 showed a scattered hybridization pattern throughout the genome. Intraspecific comparative genomic hybridization was performed on the chromosomes of P. tankei to verify the existence of sex-specific regions. The results revealed only a limited number of overlapping hybridization signals, coinciding with the heterochromatin in centromeric regions without any sex-specific signals in both males and females. Our study provides a karyotype description of P. tankei, highlighting extensive differences in the karyotype formula, the heterochromatin regions, and sites of 5S and 18S rDNA, as compared with data available for the genus.

Comparative cytogenetic of six species of Amazonian Peacock bass (Cichla, Cichlinae): intrachromosomal variations and genetic introgression among sympatric species.

Cytogenetic data for the genus Cichla Bloch et Schneider, 1801 are still very limited, with only four karyotype descriptions to date. The sum of the available cytogenetic information for Cichla species, points to a maintenance of the diploid number of 48 acrocentric chromosomes, considered a typical ancestral feature in cichlids. In the current study, we performed molecular and classical cytogenetic analyses of the karyotype organization of six species of Cichla, the earliest-diverging genus of Neotropical cichlids. We cytogenetically analysed Cichla kelberi Kullander et Ferreira, 2006, Cichla monoculus Agassiz, 1831, Cichla piquiti Kullander et Ferreira, 2006, Cichla temensis Humboldt, 1821, Cichla vazzoleri Kullander et Ferreira, 2006 and Cichla pinima Kullander et Ferreira, 2006, including three individuals that showed mixed morphological characteristics, likely from different species, suggesting they were hybrid individuals. All individuals analysed showed 2n = 48 acrocentric chromosomes, with centromeric heterochromatic blocks on all chromosomes and a terminal heterochromatic region on the q arm of the 2nd pair. Mapping 18S rDNA gave hybridization signals, correlated with the nucleolus organizer regions, on the 2nd pair for all analyzed individuals. However, we found distinct patterns for 5S rDNA: interstitially at the proximal position on 6th pair of four species (C. kelberi, C. pinima, C. piquiti and C. vazzoleri), and on the distal of the 4th pair in two (C. monoculus and C. temensis). Accordingly, we present here new data for the genus and discuss the evolutionary trends in the karyotype of this group of fish. In addition, we provide data that supports the occurrence of hybrid individuals in the Uatumã River region, mainly based on 5S rDNA mapping.

Transposable DNA Elements in Amazonian Fish: From Genome Enlargement to Genetic Adaptation to Stressful Environments.

Transposable elements have driven genome evolution and plasticity in many ways across a range of organisms. Different types of biotic and abiotic stresses can stimulate the expression or transposition of these mobile elements. Here, we cytogenetically analyzed natural fish populations of the same species living under different environmental conditions to test the influence and organization of transposable elements in their genome. Differential behavior was observed for the markers Rex 1, Rex 3, and Rex 6 in the chromosomes of individuals of the same species but coming from different environments (polluted and unpolluted). An increase in the number of Rex transposable elements in the chromosomes and their influence on the genome of populations living in a polluted environment indicates that they must be under constant adaptive evolution.