Susana Milhomem - Academia.edu (original) (raw)

Papers by Susana Milhomem

Milhomem et al 2012 G. capanema impresso

Zebrafish, 2015

The electric eel, Electrophorus electricus, the only species of its genus, has a wide distributio... more The electric eel, Electrophorus electricus, the only species of its genus, has a wide distribution in the Amazon and Orinoco drainages. There is little previous information regarding the population variation in E. electricus, with only basic karyotype data from two populations (Amazon and Araguaia Rivers). Karyotypic description and analysis of CO1 barcode sequences were performed for E. electricus from three localities (Caripetuba, Irituia, and Maicuru Rivers). All samples share the 2n = 52 (42 m-sm [meta-submetacentric] + 10 st-a [subteloacrocentric]) with previously studied material. However, the Maicuru River samples differ from the other populations, as they have B chromosomes. The distribution of noncentromeric constitutive heterochromatin between samples is relatively divergent. All samples analyzed present the Nucleolar Organizer Region (NOR) located in a single chromosome pair. In the samples from Caripetuba, NORs were colocalized with a heterochromatin block, whereas the NOR was flanked by heterochromatin in Maicuru River samples and pericentromeric heterochromatin adjacent NOR was found in Irituia River samples. Alignment of CO1 barcode sequences indicated no significant differentiation between the samples analyzed. Results suggest that karyotypic differences between samples from the Caripetuba, Irituia, and Amazon Rivers represent chromosome polymorphisms. However, differences between the samples from the Maicuru and Araguaia Rivers and the remaining populations could represent interpopulation differentiation, which has not had time to accrue divergence at the CO1 gene level.

Reviews in Fish Biology and Fisheries, 2011

Gymnotiformes are an important component of the Neotropical ichthyofauna and they are known for t... more Gymnotiformes are an important component of the Neotropical ichthyofauna and they are known for their ability to generate and detect electrical discharges. Phylogenetic relationships of Gymnotiformes are still not well understood. However, the monophyly of the superfamily Rhamphichthyoidea is well accepted, despite the position of tribe Steatogenini (Steatogenys, Hypopygus and Stegostenopos) within this superfamily is unclear. The genus Steatogenys includes three species that, together with Hypopygus and Stegostenopos, form tribe Steatogenini. Cytogenetic information is currently only available for Hypopygus lepturus.

PLoS ONE, 2013

Gymnotus (Gymnotiformes, Gymnotidae) is the most diverse known Neotropical electric knife fish ge... more 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. Citation: Milhomem SSR, Scacchetti PC, Pieczarka JC, Ferguson-Smith MA, Pansonato-Alves JC, et al. (2013) Are NORs Always Located on Homeologous Chromosomes? A FISH Investigation with rDNA and Whole Chromosome Probes in Gymnotus Fishes (Gymnotiformes). PLoS ONE 8(2): e55608.

Gymnotus capanema, a new species of electric knife fish (Gymnotiformes, Gymnotidae) from eastern Amazonia, with comments on an unusual karyotype

Journal of Fish Biology, 2012

Gymnotus capanema n. sp. is described on the basis of cytogenetic, morphometric, meristic and ost... more Gymnotus capanema n. sp. is described on the basis of cytogenetic, morphometric, meristic and osteological data from nine specimens (one male and eight females) from the municipality of Capanema, Pará, in the eastern Amazon of Brazil. Later, three additional specimens were found in museums and regarded as nontypes (not cytogenetically analysed). Gymnotus capanema, which occurs in sympatry with Gymnotus cf. carapo cytotype 2n = 42 (30m/sm + 12st/a) exhibits a novel karyotype for the genus, with 2n = 34 (20m/sm + 14st/a). Gymnotus capanema can be unambiguously diagnosed from all congeners on the basis of a combination of characters from external anatomy, pigmentation and osteology. The constitutive heterochromatin, rich in adenine-thymine (A-T) base pairs [4',6 diamidino-2-phenylindole dihydrochloride (DAPI) positive], occurs in the centromeric region of all of the chromosomes, and in the pericentromeric and the entire short arm of some chromosomes. The nucleolar organizing region (NOR), stained by silver nitrate, chromomycin A(3) (CMA(3)) and 18S ribosomal (r)DNA fluorescence in situ hybridization (FISH), occurs in the short arm of pair 15. FISH, with telomeric probes did not show interstitial telomeric sequences (ITS), despite the reduced 2n in comparison to the karyotypes of other species of Gymnotus. The karyotype of G. capanema, with a reduced 2n, is strikingly different from all other previously studied congeners.

Genetics and Molecular Biology, 2008

We studied the karyotypes of Hassar cf. orestis and an undescribed Hassar species from the Jarí R... more We studied the karyotypes of Hassar cf. orestis and an undescribed Hassar species from the Jarí River and Opsodoras ternetzi, H. orestis and Platydoras cf. costatus from the Xingú River, all with 2n = 58. Constitutive heterochromatin is located in the centromere in most metacentric pairs; in some chromosomes this banding is not present, or it is located on the whole chromosome arm or in the distal regions. The NOR is located on a single biarmed pair at a distal region of the short arm in H. cf. orestis, H. orestis and P. cf. costatus at a distal region of the long arm in O. ternetzi and at a proximal region of the long arm in the Hassar species. In all species (except for Hassar sp.) the CMA3 analysis revealed a rich G-C region coincident with the NOR. Probably inversions occurred in the NOR chromosome during the chromosomal differentiation of the Doradidae species here described.

Comparative Cytogenetics, 2013

Citation: Cardoso AL, Sales KAH, Nagamachi CY, Pieczarka JC, Noronha RCR (2013) Comparative cytog... more Citation: Cardoso AL, Sales KAH, Nagamachi CY, Pieczarka JC, Noronha RCR (2013) Comparative cytogenetics of two species of genus Scobinancistrus (Siluriformes, Loricariidae, Ancistrini) from the Xingu River, Brazil. Comparative Cytogenetics 7(1): 43-41.

Cytogenetic analysis in catfish species of the genus Peckoltia Miranda Ribeiro, 1912 (Teleostei: Siluriformes: Loricariidae)

Comparative Cytogenetics, 2009

... 2 (Fig. 3, D), which were both caught in the Jari River, located in the town of Monte Dourado... more ... 2 (Fig. 3, D), which were both caught in the Jari River, located in the town of Monte Dourado and Para state, at Cachoeira Santo Antonio (03°18´14.9˝ N/52°03´29.3˝ W). Fish specimens were ... Nucleolar Organizer Re-gions (NOR) was performed according to Howell, Black (1980 ...

BMC Genetics, 2009

Cytogenetic studies were carried out on samples of Eigenmannia virescens (Sternopygidae, Gymnotif... more Cytogenetic studies were carried out on samples of Eigenmannia virescens (Sternopygidae, Gymnotiformes) obtained from four river systems of the Eastern Amazon region (Para, Brazil).

BMC …, Jan 1, 2010

Background: Gymnotus (Gymnotidae, Gymnotiformes) is the Neotropical electric fish genus with the ... more Background: Gymnotus (Gymnotidae, Gymnotiformes) is the Neotropical electric fish genus with the largest geographic distribution and the largest number of species, 33 of which have been validated. The diploid number varies from 2n = 39-40 to 2n = 54. Recently we studied the karyotype of morphologically indistinguishable samples from five populations of G. carapo sensu stricto from the Eastern Amazon of Brazil. We found two cytotypes, 2n = 42 (30 M/SM + 12 ST/A) and 2n = 40 (34 M/SM + 6 ST/A) and we concluded that the differences between the two cryptic species are due to pericentric inversions and one tandem fusion.

BMC …, Jan 1, 2008

In this study we examined the karyotypes of morphologically indistinguishable populations of the ... more In this study we examined the karyotypes of morphologically indistinguishable populations of the electric knifefish Gymnotus carapo sensu stricto from the Eastern Amazon of Brazil. These were identified unambiguously on the basis of external morphology, meristics, and pigmentation.