[show abstract][hide abstract] ABSTRACT: Potamotrygonidae is a representative family of South American freshwater elasmobranchs. Cytogenetic studies were performed in a Potamotrygon species from the middle Negro River, Amazonas, Brazil, here named as Potamotrygon sp. C. Mitotic and meiotic chromosomes were analyzed using conventional staining techniques, C-banding, and detection of the nucleolus organizing regions (NOR) with Silver nitrate (Ag-NOR). The diploid number was distinct between sexes, with males having 2n = 67 chromosomes, karyotype formula 19m + 8sm + 10st + 30a, and fundamental number (FN) = 104, and females having 2n = 68 chromosomes, karyotype formula 20m + 8sm + 10st + 30a, and FN = 106. A large chromosome, corresponding to pair number two in the female karyotype, was missing in the male complement. Male meiotic cells had 33 bivalents plus a large univalent chromosome in metaphase I, and n = 33 and n = 34 chromosomes in metaphase II. These characteristics are consistent with a sex chromosome system of the XX/XO type. Several Ag-NOR sites were identified in both male and female karyotypes. Positive C-banding was located only in the centromeric regions of the chromosomes. This sex chromosome system, which rarely occurs in fish, is now being described for the first time among the freshwater rays of the Amazon basin.
[show abstract][hide abstract] ABSTRACT: The Astyanax species of the bimaculatus group include morphologically similar representatives that share the same color pattern, corresponding to at least 20 species. Specimens from the São Francisco River basin and from the Grande River (Upper Paraná basin) are included in this group. In the early 1960’s, the Piumhi River, an original tributary of the Grande River, was transposed to the São Francisco River basin due to the construction of the Furnas Hydroelectric Power, in the state of Minas Gerais, Brazil. In this context, we characterized representatives of the bimaculatus group from both basins and from the transposition region of the Piumhi River, using chromosome characteristics obtained by conventional analyzes and fluorescence in situ hybridization with rDNA probes. All the analyzed specimens presented 2n = 50 chromosomes and similar localization of the nucleolus organizer regions (Ag-NORs), 18S rDNA and 5S rDNA sites. However, diagnostic chromosome differences were detected concerning the number of submetacentric and acrocentric chromosomes in the karyotypes, making possible the characterization of five distinct karyotypes (Cytotypes A–E), where the specimens from the São Francisco and from the Grande River correspond to Cytotypes A and B, respectively. In addition, these two Cytotypes were sympatrically found in the Piumhi River with specimens carrying a clear intermediate karyotype (Cytotype C), as well as with others harboring different karyotypes (Cytotypes D and E). Our data indicate that Cytotypes A and B probably diverged from each other during the prior geographic isolation. However, despite their chromosomal differentiations, they still maintain a close relationship which allows interbreeding and the formation of a secondary hybrid zone, due to the breakdown of the geographic isolation.
Reviews in Fish Biology and Fisheries 08/2013; 22(2). · 2.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Extensive phenotypic diversity (size, colors and shapes) among species of Haemulidae is practically dissociated from the conservative cytogenetic pattern observed in this family. Detailed analyses indicate that karyotypic stasis is maintained even under the scrutiny of different chromosome investigation methods. Chromosomal banding patterns (endophenotype) of five Atlantic species are presented here: Conodon
plumierii and H. steindachneri, obtained by incorporating the base analog 5-BrdU, C-banding and staining with base-specific fluorochromes. Despite a few chromosomal specificities, relative karyotypic conservation was confirmed, corroborating earlier studies on this family. On the other hand, phenotypic patterns (exophenotype), identified by geometric morphometrics contrast visibly with the chromosomal conservation of this group. As such, the evolutionary rates of chromosomes and body morphology demonstrate clear asynchrony. Possible causes of karyotypic stasis in Haemulidae are discussed as well as the sharing of this condition with other Perciformes.
Reviews in Fish Biology and Fisheries 08/2013; 22(2). · 2.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: The genus Pareiorhina, formerly considered monotypic, was recently described to comprise two new species P. carrancas and P. brachyrhyncha. Karyotype analysis allowed to infer cytotaxonomical diagnostic characters for P. rudolphi and P. brachyrhyncha in the present study. The species showed the same diploid number (2n = 54) and karyotypes with 18 m, 32sm, 4st and 18 m, 30sm, 6st chromosomes, respectively. In addition, we found that the nucleolus organizer regions (NORs) are located on different chromosomes. Localization of NORs has been ascertained by fluorescent in situ hybridization (FISH) and colloidal silver nitrate stain (Ag-NORs). P. rudolphi shows NORs in interstitial position of the long arm of chromosome pair number 11, while P. brachyrhyncha shows subterminal NORs only in the short arm of chromosome pair 25. Occurrence of diploid chromosome number and presence of only one pair of NOR bearing chromosomes makes these species to comprised of most plesiomorphic karyotype of Loricariidae and supports its clustering with the genus Neoplecostomus. The chromosome types and diversification in the location of NORs corroborate the description of the species P. brachyrhyncha.
[show abstract][hide abstract] ABSTRACT: Harttia is a genus of the subfamily Loricariinae that posses a broad chromosomal variation. In addition to interspecific karyotype diversity within this group, a multiple sex chromosome system, XX/XY1Y2, has been described for Harttia carvalhoi. Thus, this study aimed to determine the role of chromosomal rearrangements in karyotype differentiation in Harttia by classical and molecular cytogenetic procedures. The results show that Robertsonian rearrangements have a prominent role in the chromosomal diversification of the species analysed, which initially leads to hypothesize a diploid number reduction in Harttia torrenticola and H. carvalhoi. The metacentric chromosome 1, shared between H. torrenticola and H. carvalhoi, could have originated from centric fusions from the ancestral karyotype. A centric fission event associated with the first metacentric pair allowed for the origination of a multiple sex chromosome system XX/XY1Y2, specific to H. carvalhoi. This study highlights the relevance of Robertsonian rearrangements in karyotypic differentiation of the species studied and demonstrates that the occurrence of a centric fission, as opposed to a previously hypothesised chromosome fusion, is directly implicated in the origin of the sex chromosome system of H. carvalhoi.
Reviews in Fish Biology and Fisheries 08/2013; 23(1). · 2.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Despite the theoretical and experimental progress, our understanding on sex chromosome differentiation is still diagrammatic. The accumulation of repetitive DNA sequences is believed to occur in early stages of such differentiation. As fish species present a wide range of sex chromosome systems they are excellent models to examine the differentiation of these chromosomes. In the present study, the chromosomal distribution of 9 mono-, di- and trinucleotide microsatellites were analyzed using fluorescence in situ hybrization (FISH) in rock bream fish (Oplegnathus fasciatus), which is characterized by an X1X2Y sex chromosome system. Generally, the males and females exhibited the same autosomal pattern of distribution for a specific microsatellite probe. The male specific Y chromosome displays a specific amount of distinct microsatellites repeats along both arms. However, the accumulation of these repetitive sequences was not accompanied by a huge heterochromatinization process. The present data provide new insights into the chromosomal constitution of the multiple sex chromosomes and allow further investigations on the true role of the microsatellite repeats in the differentiation process of this sex system.
[show abstract][hide abstract] ABSTRACT: All Triportheus species show the conserved diploid number of 52 chromosomes and a ZZ/ZW sex chromosome system. Previous studies conducted on Triportheus nematurus reported a syntenical location of 18S and 5S sites on this species, in addition to some indications that this condition could be shared by other Triportheus species, possibly constituting a synapomorphy for this genus. In the present study, fluorescence in situ hybridization (FISH) experiments were performed in seven Triportheus species in view of a comparative analysis of the distribution of the 18S and 5S ribosomal DNAs on the chromosomes. The double-FISH experiments have showed that the synteny of the 18S and 5S rDNA genes is not a synapomorphy for the genus, since it is not present in all the species investigated, although it is present in most of them. The findings suggest that the syntenical location of the ribosomal genes is an ancestral trait in Triportheus, which was changed during the course of evolution of this group.
[show abstract][hide abstract] ABSTRACT: Evidence of population fragmentation and speciation processes has been reported for several species of marine fish, including small cryptobenthics forms of Atlantic. Four populations of the frillfin goby Bathygobius soporator, which cover a wide geographical area of the Atlantic coast in North/Northeast Brazil, were cytogenetically analyzed and their morphological patterns compared. Continental populations of this species (denominated MA, RN, and BA) exhibited divergences in morphological and chromosomal characteristics compatible with interpopulation differentiation. However, specimens from Rocas Atoll (RA) displayed notable divergences in these parameters, corroborating molecular data that suggest they are a different species. Furthermore, the RN population showed intrinsic chromosomal markers, revealing a certain level of population structuring. Chromosomal and morphological patterns found confirm the biodiversity of B. soporator, substantiating an evolutionary scenario of population divergences and adaptation to new habitats.
Journal of Experimental Marine Biology and Ecology 10/2012; s 434–435:63–70. · 2.26 Impact Factor
[show abstract][hide abstract] ABSTRACT: This study presents an adaptation of current methodologies for preparing mitotic chromosomes from fishes, optimized for use in the field. The high-quality preparations obtained using this modified methodology is suitable for subsequent chromosomal analysis. Importantly, this method is particularly useful when specimen collection sites are far from research laboratories or when researchers are working with highly sensitive species that do not survive long outside of their natural habitats.
Journal of Fish Biology 07/2012; 81(1):351-7. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Fish from the family Labridae elicit considerable ecological interest, especially due to their complex interactions with the reef environment. Different karyoevolutionary tendencies have been identified in the subfamilies Bodianinae, Corinae and Cheilinae. Chromosomal analyses conducted in the Atlantic species Bodianus rufus (2n=48; 6m+12sm+14st+16a, FN=80), Bodianus pulchellus (2n=48; 4m+12sm+14st+18a, FN=78) and Bodianus insularis (2n=48; 4m+12sm+14st+18a, FN=78) identified Ag-NOR/18SrDNA sites located only in the terminal region of the short arm (p) of the largest subtelocentric pair. The 5S rDNA genes were mapped in the terminal region of the long arm (q) of the largest acrocentric pair and the p arm of chromosome 19 in B. insularis. The karyotype of the three species shows an extensive heterochromatic and argentophilic region, exceptionally decondensed, located in the p arm of the second subtelocentric pair. This region does not correspond to a NOR site, since it is not hybridized with 18S rDNA probes, and is not GC-rich, as generally occurs with nucleolus organizer regions of lower invertebrates. Heterochromatin in the three species is reduced and distributed over the centromeric and pericentromeric regions of chromosomes. The elevated number of two-armed chromosomes in species of Bodianus, in relation to other Labridae, shows karyotype diversification based on pericentric inversions, differentiating them markedly in terms of evolutionary tendencies that occur in subfamilies Corinae and Cheilininae. Structural cytogenetic similarities between B. pulchellus and B. insularis, in addition to the conserved chromosomal location pattern of ribosomal multigenic families, indicate phylogenetic proximity of these species.
[show abstract][hide abstract] ABSTRACT: Despite substantial progress, there are still several gaps in our knowledge about the process of sex chromosome differentiation. The degeneration of sex-specific chromosome in some species is well documented, but it is not clear if all species follow the same evolutionary pathway. The accumulation of repetitive DNA sequences, however, is a common feature. To better understand this involvement, fish species emerge as excellent models because they exhibit a wide variety of sex chromosome and sex determining systems. Besides, they have much younger sex chromosomes compared to higher vertebrates, making it possible to follow early steps of differentiation. Here, we analyzed the arrangement of 9 repetitive DNA sequences in the W chromosomes of 2 fish species, namely Leporinus reinhardti and Triportheus auritus, which present well-differentiated ZZ/ZW sex system, but differ in respect to the size of the sex-specific chromosome. Both W chromosomes are almost fully heterochromatic, with accumulation of repeated DNAs in their heterochromatic regions. We found that microsatellites have strongly accumulated on the large W chromosome of L. reinhardti but not on the reduced-size W chromosome of T. auritus and are therefore important players of the W chromosome expansion. The present data highlight that the evolution of the sex chromosomes can diverge even in the same type of sex system, with and without the degeneration of the specific-sex chromosome, being more dynamic than traditionally appreciated.
[show abstract][hide abstract] ABSTRACT: During the evolutionary process of the sex chromosomes, a general principle that arises is that cessation or a partial restriction of recombination between the sex chromosome pair is necessary. Data from phylogenetically distinct organisms reveal that this phenomenon is frequently associated with the accumulation of heterochromatin in the sex chromosomes. Fish species emerge as excellent models to study this phenomenon because they have much younger sex chromosomes compared to higher vertebrates and many other organisms making it possible to follow their steps of differentiation. In several Neotropical fish species, the heterochromatinization, accompanied by amplification of tandem repeats, represents an important step in the morphological differentiation of simple sex chromosome systems, especially in the ZZ/ZW sex systems. In contrast, multiple sex chromosome systems have no additional increase of heterochromatin in the chromosomes. Thus, the initial stage of differentiation of the multiple sex chromosome systems seems to be associated with proper chromosomal rearrangements, whereas the simple sex chromosome systems have an accumulation of heterochromatin. In this review, attention has been drawn to this contrasting role of heterochromatin in the differentiation of simple and multiple sex chromosomes of Neotropical fishes, highlighting their surprising evolutionary dynamism.
Journal of Fish Biology 05/2012; 80(6):2125-39. · 1.83 Impact Factor
[show abstract][hide abstract] ABSTRACT: Chromosome analyses were carried out for several fish species in a region impacted by the connection between two hydrographic
basins, where a river originally pertaining to the Paraná River basin was transposed to the São Francisco River basin in the
state of Minas Gerais, Brazil. The purpose was to assess the dispersal of invasive species from one hydrographic basin to
the other and the consequent new geographical distributions of species that had been previously isolated from each other.
Species of the families Parodontidae (Apareiodon piracicabae, A. ibitiensis, Parodon hilarii, and P. nasus), Sternopygidae (Eigenmannia virescens), and Gymnotidae (Gymnotus sylvius) were studied. The four species of Parodontidae had 2n=54 chromosomes, but species-specific karyotype structures, including
the presence of the ZZ/ZW sex chromosome system in A. ibitiensis and P. hilarii. Two distinct karyomorphs (A and B) were identified for E. virescens, although with the same diploid number (2n=38 chromosomes). G. sylvius had 2n=40 chromosomes. P. hilarii and E. virescens (karyomorph B) are considered to be native to the São Francisco River basin, whereas A. piracicabae, A. ibitiensis, E. virescens (karyomorph A), and G. sylvius are known for the Paraná River basin, and P. nasus is known for the Paraná-Paraguay basin. The presence of the last five species in the São Francisco River basin indicates
that they migrated from the Parana River to the São Francisco River basin due to the transposition of the river, and can therefore
be considered invasive species in this basin. Moreover, a natural migratory pathway through the former wetland may have affected
KeywordsChromosomes-Biological invasion-Characiformes-Gymnotiformes-River transposition
[show abstract][hide abstract] ABSTRACT: Six hundred and twenty-seven specimens of neotropical fishes belonging to thirteen species/populations from southern field
(Paraná, State, Brazil) were karyotypicaly analyzed between 2000 and 2006. The study biogeographic region is characterized
as a divisor of waters presenting tributaries and headboards of the hydrographic basins of the rivers Tibagi, Iguaçu, Ivaí,
and Paranapanema (Upper Paraná Basin) and Ribeira river (East Basin). Two patterns of karyotypic diversification were verified,
being one more conserved in the karyotypic macrostructure and the other more diversified. The understanding at of this variability
with views to the citotaxonomy and biological conservation was interpreted at the light of (1) the historical biogeography,
(2) of the evolutionary time, and (3) of the biology of the species, indicating the study area as highly relevant for the
selection of evolutionary potential.
Reviews in Fish Biology and Fisheries 04/2012; 19(3):393-401. · 2.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Karyotypic analyses were performed in fishes from the genus Hoplias (H.
malabaricus and H. lacerdae groups) from the São Francisco River basin (Brazil), in an impacted region by a river transposition which altered the local
ecology and fish fauna. The karyotypes were investigated using chromosomal markers obtained from classic and molecular cytogenetics
(Giemsa, CMA3 and DAPI staining, C-banding, Ag-NORs, and FISH with 18S rDNA, 5S rDNA and 5SHindIII satellite DNA probes). Two karyotypic forms were found for the H. malabaricus group—karyomorph F, corresponding to the native form from the São Francisco River basin, and karyomorph A, corresponding
to the invading form from the Upper Paraná River basin. Specimens from the H. lacerdae group exhibited striking chromosome differences in relation to the H. malabaricus group, thereby enabling good cytotaxonomic characterization and inferences regarding the karyotype evolution of these groups.
Reviews in Fish Biology and Fisheries 04/2012; 20(1):1-8. · 2.27 Impact Factor
[show abstract][hide abstract] ABSTRACT: Karyotype and other chromosomal markers of Characidium cf. gomesi were analyzed using conventional (Giemsa-staining, Ag-NOR and C-banding) and molecular (Fluorescent insitu hybridization
(FISH) with 18S and 5S rDNA biotinylated probes) techniques. Both sexes had invariably diploid chromosome number 2n=50 while
karyotypes of males and females differed. That of male consisted of 32 metacentric+18 submetacentric chromosomes and that
of female consisted 31 metacentric+18 submetacentric+1 subtelocentric chromosomes. The Z chromosome was medium-sized metacentric,
while W was highly heterochromatinized subtelocentric element. NORs as revealed by Ag-staining were situated at 2–7 telomeric
regions while FISH with 18S probes showed consistently 10 signals at telomeric regions. FISH with 5S rDNA probe showed constantly
signals at one metacentric pair. Distribution of centromeric heterochromatin was mostly in all chromosome pairs, besides some
telomeric sites. The common origin of the sex chromosome system of ZZ/ZW type in the karyotypes of other representatives of
the genus analyzed so far might be hypothesized based on biogeography and partial phylogeny of the group.