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Karyotypic diversity in four species of the genus Gymnotus Linnaeus, 1758 (Teleostei, Gymnotiformes, Gymnotidae): physical mapping of ribosomal genes and telomeric sequences  [cached]
Priscilla Scacchetti,Jose Pansonato-Alves,Ricardo Utsunomia,Claudio Oliveira
Comparative Cytogenetics , 2011, DOI: 10.3897/compcytogen.v5i3.1375
Abstract: Conventional (Giemsa, C-Banding, Ag-NORs, CMA3) and molecular (5S rDNA, 18S rDNA, telomeric sequences) cytogenetic studies were carried out in specimens of ten distinct fish populations of the genus Gymnotus (G. sylvius Albert and Fernandes-Matioli, 1999, G. inaequilabiatus Valenciennes, 1839, G. pantherinus Steindachner, 1908, and G. cf. carapo Linnaeus, 1758) from different Brazilian hydrographic basins. G. sylvius presented a diploid number of 40 chromosomes (22m+12sm+6st), G. pantherinus presented 52 chromosomes (32m+18sm+2st), while G. inaequilabiatus (42m+10sm+2a) and G. cf. carapo (38m+12sm+4st) presented 54 chromosomes. The C-banding technique revealed centromeric marks in all chromosomes of all species. Besides that, conspicuous blocks of heterochromatin were found interstitially on the chromosomes of G. inaequilabiatus, G. cf. carapo, and G. pantherinus. All four species showed single nucleolus organizing regions confirmed by results obtained through Ag-NORs and FISH experiments using 18S rDNA probes, which showed the NORs localized on the first chromosome pair in G. inaequilabiatus, G. cf. carapo, and G. pantherinus, and on pair 2 in G. sylvius. CMA3 staining revealed additional unrelated NORs marks in G. sylvius and G. pantherinus. The 5S rDNA probes revealed signals on one pair in G. sylvius and two pairs in G. pantherinus; G. inaequilabiatus had about seventeen pairs marked, and G. cf. carapo had about fifteen pairs marked. It is considered that the high amount of heterochromatin identified in the chromosomes of G. inaequilabiatus and G. cf. carapo could have facilitated the dispersion of 5S rDNA in these species. Interstitial signals were detected on the first metacentric pair of G. sylvius by telomeric probes (TTAGGG)n indicating the possible occurrence of chromosomal fusions in this species. The present study reveals valuable cytotaxonomic markers for this group and allows a more precise evaluation of the processes involved in the karyotype differentiation and the interrelationships among different species of the genus Gymnotus.
Chromosomal evidence for a putative cryptic species in the Gymnotus carapo species-complex (Gymnotiformes, Gymnotidae)
Susana SR Milhomem, Julio C Pieczarka, William GR Crampton, Danillo S Silva, Augusto CP De Souza, Jaime R Carvalho, Cleusa Y Nagamachi
BMC Genetics , 2008, DOI: 10.1186/1471-2156-9-75
Abstract: Specimens from one of five localities exhibited a karyotype previously not documented for Gymnotus species in the Amazon basin: 2n = 40 (34M/SM+6ST/A). Samples from the other four localities exhibited a different karyotype: 2n = 42 (30M/SM+12ST/A), which we had previously described. Specimens from all five localities presented constitutive heterochromatin in the centromeric region of almost all chromosomes, including in the distal and interstitial regions. Staining with 4'6-Diamidino-2-phenylindole revealed C-positive banding. In both karyotypes the Nucleolar Organizer Region (NOR) was located on the short arm of pair 20, and Chromomycin A3 stained the NORs. Fluorescent in situ hybridization with telomeric probes showed an Interstitial Telomeric Sequence (ITS) in the proximal short arm of a metacentric pair in the 2n = 40 karyotype.The difference between the two karyotypes on the diploid number and chromosome morphology can be explained by rearrangements of the fusion-fission type and also by pericentric inversions. The presence of ITS in a metacentric pair of the 2n = 40 karyotype suggests that the difference in the diploid number of the karyotypes results from a fusion. The consistent 2n = 42 karyotype at four localities suggests an interbreeding population. However, because fusion-fission and pericentric inversions of this nature typically result in reproductive isolation, we speculate that the form with the 2n = 40 karyotype is a different species to that of the 2n = 42 form. Nonetheless, we did not observe evident differences in external morphology, meristics and pigmentation between the two forms, which suggest that they represent cryptic sympatric species in the G. carapo species complex. We speculate that the chromosomal speciation occurred recently, allowing insufficient time for the fixation of other differences following post-zygotic isolation.Gymnotus (Gymnotiformes, Gymnotidae) is the most diverse known Neotropical electric knife fish genus. It currentl
Electrolocation-communication discharges of the fish Gymnotus carapo L. (Gymnotidae: Gymnotiformes) during behavioral sleep
Stopa, R.M.;Hoshino, K.;
Brazilian Journal of Medical and Biological Research , 1999, DOI: 10.1590/S0100-879X1999001000008
Abstract: technical problems have hampered the study of sleep in teleosts. the electrical discharges of gymnotus carapo l. (gymnotidae: gymnotiformes) were monitored to evaluate their ease and reliability as parameters to study sleep. the discharges were detected by electrodes immersed in a glass aquarium and were recorded on a conventional polygraph. g. carapo showed conspicuous signs of behavioral sleep. during these periods, opercular beat rates were counted, electric discharges recorded, and the "sharp discharge increase" (sdi) of the orienting reflex was investigated. all 20 animals monitored maintained electrical discharges during behavioral sleep. the discharge frequencies during sleep (50.3 ± 10.4 hz) were not significantly different from those observed when the fish was awake and inactive (57.2 ± 12.1 hz) (wilcoxon matched-pairs signed-ranks test, p>0.05). however, the sdi, which was prevalent in the awake fish, was not observed during periods of behavioral sleep. additional observations showed that the species had cannibalistic habits. when presented with electrical discharges from a conspecific, the sleeping fish showed an initial decrease or pause in discharge frequency, while the awake fish did not have this response. we conclude that the electrical discharges of g. carapo were not conspicuous indicators of behavioral sleep. discharges may have been maintained during sleep for sensory purposes, i.e., conspecific detection and avoidance of cannibalistic attacks.
Electrolocation-communication discharges of the fish Gymnotus carapo L. (Gymnotidae: Gymnotiformes) during behavioral sleep  [cached]
Stopa R.M.,Hoshino K.
Brazilian Journal of Medical and Biological Research , 1999,
Abstract: Technical problems have hampered the study of sleep in teleosts. The electrical discharges of Gymnotus carapo L. (Gymnotidae: Gymnotiformes) were monitored to evaluate their ease and reliability as parameters to study sleep. The discharges were detected by electrodes immersed in a glass aquarium and were recorded on a conventional polygraph. G. carapo showed conspicuous signs of behavioral sleep. During these periods, opercular beat rates were counted, electric discharges recorded, and the "sharp discharge increase" (SDI) of the orienting reflex was investigated. All 20 animals monitored maintained electrical discharges during behavioral sleep. The discharge frequencies during sleep (50.3 ± 10.4 Hz) were not significantly different from those observed when the fish was awake and inactive (57.2 ± 12.1 Hz) (Wilcoxon matched-pairs signed-ranks test, P>0.05). However, the SDI, which was prevalent in the awake fish, was not observed during periods of behavioral sleep. Additional observations showed that the species had cannibalistic habits. When presented with electrical discharges from a conspecific, the sleeping fish showed an initial decrease or pause in discharge frequency, while the awake fish did not have this response. We conclude that the electrical discharges of G. carapo were not conspicuous indicators of behavioral sleep. Discharges may have been maintained during sleep for sensory purposes, i.e., conspecific detection and avoidance of cannibalistic attacks.
A new species of Gymnotus (Gymnotiformes: Gymnotidae) from the Fitzcarrald Arch of southeastern Peru
Maxime, Emmanuel L.;Albert, James S.;
Neotropical Ichthyology , 2009, DOI: 10.1590/S1679-62252009000400004
Abstract: herein gymnotus chaviro is described from the alto yuruá (upper rio juruá) of southeastern peru, where it is locally abundant in terra firme streams and floodplain oxbow lakes, and occurs sympatrically and syntopically with the type species of the genus g. carapo. the new species is diagnosed by a unique combination of morphometric, meristic, and osteological traits, and a characteristic color pattern in which the dark band-pairs are unbranched and incompletely separated, and the pale inter-bands rarely reach to the dorsal mid-line on the anterior half of the body, being crescent-shaped in abdominal area. gymnotus chaviro is a member of the g. carapo species group, with which it shares the presence of two pores in the dorsolateral portion of the preopercle, dark pigment bands with wavy margins that become broken and/or loose contrast with the ground color through growth, a clear patch at the caudal end of an otherwise darkly pigmented anal fin, and more than four arrowhead-shaped (anteroposteriorly compressed) teeth in the anterior portion of the dentary. gymnotus chaviro is most similar in external appearance to g. curupira of lowland western amazonia in possessing a slender lateral profile (mean body depth less than 9% total length), a similar color pattern (median number of bands 19 with bands less distinct on dorsum), a large inter-orbital distance (mean greater than 41% head length), a broad head (mean head width greater than 65% head length) and a large mouth (mean mouth width greater than 43% head length). this new species can also be distinguished from g. curupira by the configuration of the preopercular pores, and by several meristic traits of squamation and fin rays. this is the first gymnotiform species described from the interior of the fitzcarrald arch, and the only gymnotiform species known to date that is endemic to this upland region of the western amazon.
Multiple rearrangements in cryptic species of electric knifefish, Gymnotus carapo (Gymnotidae, Gymnotiformes) revealed by chromosome painting
Cleusa Y Nagamachi, Julio C Pieczarka, Susana SR Milhomem, Patricia CM O'Brien, Augusto CP de Souza, Malcolm A Ferguson-Smith
BMC Genetics , 2010, DOI: 10.1186/1471-2156-11-28
Abstract: In this study we use for the first time, whole chromosome probes prepared by FACS of the Gymnotus carapo sensu strictu species, cytotype with 2n = 42. Using two color hybridizations we were able to distinguish pairs 1, 2, 3, 7, 9, 14, 16, 18, 19, 20 and 21. It was not possible to separate by FACS and distinguish each of the following chromosome pairs even with dual color FISH: {4,8}; {10,11}; {5,6,17}; {12,13,15}. The FISH probes were then used in chromosome painting experiments on metaphases of the 2n = 40 cytotype. While some chromosomes show conserved synteny, others are rearranged in different chromosomes. Eight syntenic associations were found.These results show that the karyotype differences between these cryptic species are greater than assumed by classical cytogenetics. These data reinforce the previous supposition that these two cytotypes are different species, despite the absence of morphological differences. Additionally, the homology of repetitive DNA between the two provides evidence of recent speciation.Cross-species FISH using whole chromosome painting is widely used for phylogenomic studies in many vertebrate groups, including primates [1-7], bats [8,9], deer [10], birds [11,12], etc. These studies make important contributions to our understanding of genomic reorganization and mechanisms of chromosome evolution in warm-blooded vertebrates.Research using chromosome painting in fishes is unusual. It has been used only with probes made by microdissection [13-19] or by CGH, the latter without defining chromosome pairs [20]. The probes made by flow cytometry have higher complexity than those made by microdissection, and are more appropriate for cross-species hybridization [21]. However, there are no reports in the literature of FACS (Fluorescent Activated Chromosome Sorting) generated probes for chromosome painting involving a whole fish genome.The chromosome structure of a fish, a cold-blooded vertebrate, lacks both GC-rich and GC-poor compartments. The
Are NORs Always Located on Homeologous Chromosomes? A FISH Investigation with rDNA and Whole Chromosome Probes in Gymnotus Fishes (Gymnotiformes)  [PDF]
Susana S. R. Milhomem, Priscilla C. Scacchetti, Julio C. Pieczarka, Malcolm A. Ferguson-Smith, José C. Pansonato-Alves, Patricia C. M. O’Brien, Fausto Foresti, Cleusa Y. Nagamachi
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0055608
Abstract: Gymnotus (Gymnotiformes, Gymnotidae) is the most diverse known Neotropical electric knife fish genus. Cytogenetic studies in Gymnotus demonstrate a huge karyotypic diversity for this genus, with diploid numbers ranging from 34 to 54. The NOR are also variable in this genus, with both single and multiple NORs described. A common interpretation is that the single NOR pair is a primitive trait while multiple NORs are derivative. However this hypothesis has never been fully tested. In this report we checked if the NOR-bearing chromosome and the rDNA site are homeologous in different species of the genus Gymnotus: G. carapo (2n = 40, 42, 54), G. mamiraua (2n = 54), G. arapaima (2n = 44), G. sylvius (2n = 40), G. inaequilabiatus (2n = 54) and G. capanema (2n = 34), from the monophyletic group G. carapo (Gymnotidae-Gymnotiformes), as well as G. jonasi (2n = 52), belonging to the G1 group. They were analyzed with Fluorescence in situ hybridization (FISH) using 18S rDNA and whole chromosome probes of the NOR-bearing chromosome 20 (GCA20) of G. carapo (cytotype 2n = 42), obtained by Fluorescence Activated Cell Sorting. All species of the monophyletic G. carapo group show the NOR in the same single pair, confirmed by hybridization with CGA20 whole chromosome probe. In G. jonasi the NORs are multiple, and located on pairs 9, 10 and 11. In G. jonasi the GCA20 chromosome probe paints the distal half of the long arm of pair 7, which is not a NOR-bearing chromosome. Thus these rDNA sequences are not always in the homeologous chromosomes in different species thus giving no support to the hypothesis that single NOR pairs are primitive traits while multiple NORs are derived. The separation of groups of species in the genus Gymnotus proposed by phylogenies with morphologic and molecular data is supported by our cytogenetic data.
Sperm ultrastructure in three different families of weakly electric fishes (Teleostei: Gymnotiformes)
Giora, Júlia;Burns, John R.;
Neotropical Ichthyology , 2011, DOI: 10.1590/S1679-62252011005000047
Abstract: this study presents details of sperm ultrastructure for gymnotus aff. carapo (gymnotidae), eigenmannia trilineata (sternopygidae), and three brachyhypopomus species (b. draco, b. bombilla, and b. gauderio - hypopomidae) from southern brazil. differences were found among the representatives of the different families. for example, nuclear rotation was present in e. trilineata and in the brachyhypopomus species, but absent in gymnotus aff. carapo, and the presence of flagellar fins was only observed in e. trilineata. some intraspecific variations could also be noticed among the brachyhypopomus species analyzed. most of the characters found in the spermatozoa of the species studied herein are shared with species of gymnotiformes previously analyzed.
Cytogenetic characterization of the strongly electric Amazonian eel, Electrophorus electricus (Teleostei, Gymnotiformes), from the Brazilian rivers Amazon and Araguaia
Fonteles, Soraia B.A.;Lopes, Carlos E.;Akama, Alberto;Fernandes, Flora M.C.;Porto-Foresti, Fábio;Senhorini, José A.;Daniel-Silva, Maria de Fátima Z.;Foresti, Fausto;Almeida-Toledo, Lurdes Foresti de;
Genetics and Molecular Biology , 2008, DOI: 10.1590/S1415-47572008000200010
Abstract: a karyotype analysis of the electric eel, electrophorus electricus (teleostei, gymnotiformes), a strongly electric fish from northern south america, is presented. two female specimens were analyzed, one from the amazon river and one from the araguaia river. the specimens had a chromosomal number of 2n = 52 (42m-sm + 10a). c-bands were present in a centromeric and pericentromeric position on part of the chromosomes; some interstitial c-bands were also present. heteromorphic nucleolus organizer regions (nors) were detected in two chromosome pairs of the specimen from the amazon river. the chromosome number and karyotype characteristics are similar to those of other gymnotidae species. the genera electrophorus and gymnotus are positioned as the basal lineages in the gymnotiformes phylogeny.
Species diversity and geographic distribution of Gymnotus (Pisces: Gymnotiformes) by nuclear (GGAC)n microsatellite analysis
Fernandes-Matioli, F.M.C.;Matioli, S.R.;Almeida-Toledo, L.F.;
Genetics and Molecular Biology , 2000, DOI: 10.1590/S1415-47572000000400016
Abstract: patterns of amplified dna fragments flanked by (ggac)n microsatellites, obtained by single primer amplification reaction (spar), from 198 gymnotus specimens (pisces: gymnotiformes) sampled from 8 southeastern brazilian river basins were analyzed. the species studied were gymnotus carapo, g. pantherinus, g. inaequilabiatus, and g. sylvius. the indirectly obtained patterns reflected the distribution of simple sequence repeats in the nuclear genome of the specimens. species-specific patterns of dna amplification were found and were useful for the analysis of the geographic distribution of gymnotus species. monomorphic patterns were found in g. carapo, g. pantherinus, and g. inaequilabiatus. three polymorphic patterns were found in g. sylvius populations. the spar technique could be a useful molecular tool in conservation programs involving communities of neotropical freshwater fish.
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