Karyotypes of 10 species of neotropical cichlids (Pisces, Perciformes)

Ten neotropical species of family Cichlidae (Pisces: Perciformes) were analyzed cytogenetically. The results obtained also support the indications that the chromosomal evolution of this group was more conservative than divergent from the numerical point of view. All species showed a chromosome number of 2n = 48, although differences in chromosome morphology were observed. The species Chaeto-branchopsis amtrale exhibited a karyotype consisting of 48 subtelo-acrocentric chromosomes, which is possibly of a more primitive type in relation to the karyotypes of the remaining species investigated. No chromosome differences were detected between males and females, indicating the absence of morphologically differentiated sex chromosomes. © 1985 Taylor & Francis Group, LLC

Chromosome mapping of repetitive sequences in four Serrasalmidae species (Characiformes)

The Serrasalmidae family is composed of a number of commercially interesting species, mainly in the Amazon region where most of these fishes occur. In the present study, we investigated the genomic organization of the 18S and 5S rDNA and telomeric sequences in mitotic chromosomes of four species from the basal clade of the Serrasalmidae family: Colossoma macropomum, Mylossoma aureum, M. duriventre, and Piaractus mesopotamicus, in order to understand the chromosomal evolution in the family. All the species studied had diploid numbers 2n = 54 and exclusively biarmed chromosomes, but variations of the karyotypic formulas were observed. C-banding resulted in similar patterns among the analyzed species, with heterochromatic blocks mainly present in centromeric regions. The 18S rDNA mapping of C. macropomum and P. mesopotamicus revealed multiple sites of this gene; 5S rDNA sites were detected in two chromosome pairs in all species, although not all of them were homeologs. Hybridization with a telomeric probe revealed signals in the terminal portions of chromosomes in all the species and an interstitial signal was observed in one pair of C. macropomum. © 2014, Sociedade Brasileira de Genética

Karyological analysis of Proechimys cuvieri and Proechimys guyannensis (Rodentia, Echimyidae) from central Amazon

The aim was to characterize the karyotype of rodents of the genus Proechimys from three localities in the central Brazilian Amazon, in the search for new markers that might shed light on our understanding of the taxonomy and evolutionary history of this taxon. Two karyotypes were found, viz., 2n = 28, FN = 46 in individuals from the NRSP (Cuieiras River) and REMAN (Manaus), and 2n = 46, FN = 50 in individuals from the Balbina Hydroelectric Plant. While individuals with the karyotype with 2n = 28 chromosomes were morphologically associated with Proechimys cuvieri, their karyotype shared similarities with those of the same diploid number in two other regions. Although three karyotypes are described for Proechimys cuvieri, no geographic distribution pattern that defined a cline could be identified. Based on the morphological examination of voucher specimens and additional results from molecular analysis, the karyotype with 2n = 46 and FN = 50 could be associated with P. guyannensis

Occurrence of two cytotypes in Serrasalmus spilopleura Kner, 1858 (characiformes, serrasalmidae) from the confluence region of the Negro and Solimões Rivers, Amazonas, Brazil

The karyotype of Serrasalmus spilopleura from the Central Amazon is reported here for the first time. All analized individuals showed 60 chromosomes, as observed in previously published karyotypes of this species from the Paraná-Paraguai basin. However, two different cytotypes were found in sites near the confluence of the Negro and Solimões rivers, where the specimens were collected. Such karyotypic differences were not related to sex differentiation. Moreover, the two amazon cytotypes are different from the three cytotypes described in animals from Paraná-Paraguai basin. The different karyotypes detected so far, in both simpatry and allopatry conditions, suggest that S. spilopleura may be either a cytogenetically heterogeneous species or a complex of sibling species.Descreve-se pela primeira vez o cariótipo de exemplares de S. spilopleura da Amazônia Central. Todos os indivíduos analisados apresentaram número diplóide igual a 60 cromossomos, em conformidade com os dados da espécie obtidos em indivíduos da bacia do Paraná-Paraguai. No entanto, dois citótipos foram encontrados em simpatria na região de confluência dos rios Negro e Solimões, os quais não estão relacionados a heteromorfismo sexual. Além disso, os dois citótipos da Amazônia diferem dos três anteriormente descritos em exemplares do Paraná-Paraguai. A presença de distintos citótipos encontrados em simpatria e alopatria para S. spilopleura nos leva a sugerir que, ou essa espécie apresenta uma ampla heterogeneidade cariotípica ou existe um complexo de espécies cuja morfologia é muito semelhante

Chromosomal variability in the wild ornamental species of Symphysodon (Perciformes: Cichlidae) from Amazon

Cytogenetic studies were conducted on three discus species which inhabit the Amazon in Brazil: Symphysodon haraldi from Manacapuru, S. aequifasciatus from Tefé and S. discus from Barcelos. All individuals showed 2n=60 chromosomes, most of them biarmed. No sexual chromosomal heteromorphism was verified. However, different karyotypic formulae, owing to the presence of subtelocentric chromosomes, were verified for S. aequifasciatus and S. discus. One of the karyotypic formulae from S. aequifasciatus (cytotype 2) differs from the others, due to one of the homologues in the first chromosome pair being significantly larger than the other. A large variability was observed toward the nucleolar organizer regions (NOR) of S. haraldi and S. aequifasciatus. Although the number of silver-stained blocks varied from 2 to 5, confirming different NOR patterns, at least seven homologue pairs were involved with NORs. In S. discus only two marks were observed, however two chromosome pairs were involved, characterizing a multiple NOR system for the three species. The heterochromatic blocks were mainly located in the pericentromeric region of all chromosomes but, in some of them, they are also located in the proximal regions, both in the short and long arms. Moreover, in the cytotype 2 from S. aequifasciatus, an interstitial heterochromatic block was observed on the long arm of the largest homologue of the first pair. A direct comparison of karyotypes from more related genera (Heros, Uaru, Mesonauta and Pterophyllum), makes it clear that a succession of chromosomal rearrangements, mainly pericentric inversions, translocations and fissions/fusions occurred resulting in the present diploid number and intraspecific karyological variability found in Symphysodon. Copyright © 2008 Sociedade Brasileira de Ictiologia

Mapping of ribosomal genes and chromosomal markers in three species of the genus Serrasalmus (Characidae, Serrasalminae) from the Amazon basin

Karyotypic characteristics of three species of the genus serrasalmus (S. altispinnis, S. gouldingi and S. Serrulatus) from the middle and lower Negro River, Amazon Basin, were investigated using different staining techniques and Fluorescent in situ hybridization with 5S and 18S rDNA probes. The diploid number was invariably 2n = 60 and the fundamental number was FN = 110. Nevertheless, the karyotypes differed from each other in composition: 24m, 20sm, 6st, 10a in S. altispinnis; 22m, 22sm, 6st, 10a in S. gouldingi and 20m, 22sm, 8st, 10a in S. serrulatus. The karyotype of S. altispinnis differed from the one previously described in a population from the Pitinga River. C-positive constitutive heterochromatin was mainly pericentromeric in the karyotypes of all species. Nucleolar organizer regions were multiple and preferentially located terminally on the short arms of the subtelocentric/acrocentric chromosomes, as evidenced by both silver nitrate staining and fluorescent in situ hybridization with the 18S rDNA probe. The maximum number of NORs varied among species, as did the NOR-bearing chromosomes. FISH with the 5S rDNA probe produced an interstitial signal on the long arms of the pair 7 in all species, coincident with a C-positive heterochromatic band. While some chromosome features were shared by the three species, some were species-specific and thus useful for cytotaxonomy. Copyright © 2008, Sociedade Brasileira de Genética

Karyological evidence for interspecific hybridization between Cichla monoculus and C. temensis (Perciformes, Cichlidae) in the Amazon

Cichla monoculus, Cichla temensis (peacock bass or tucunaré), and its presumed hybrids, were cytogenetically analyzed. The fish were collected at three distinct sites in the central Amazon basin, namely in the Uatumã (C. monoculus, C. temensis and their natural hybrid), Jaú (C. temensis), and Solimões rivers (C. monoculus). The two species and the natural hybrid showed the same diploid number, 2n=48 acrocentric chromosomes. Single NORs were detected in the distal region of the long arm in all three species. However, in C. monoculus, the NOR was found on the second pair of the complement, in C. temensis, on the third pair and in the hybrid two NOR patterns were found, one on the second pair and the other on the third pair of chromosomes. The two species and the hybrid have their constitutive heterochromatin located in the pericentromeric region of all chromosomes and an interstitial C-band located on the largest chromosome pair. The great similarity in the chromosome number and morphology, chromosome size class differences, the NOR patterns and C-banding suggested chromosomal stasis during speciation and hybridization of Cichla

Karyotype characterization and ZZ/ZW sex chromosome heteromorphism in two species of the catfish genus Ancistrus Kner, 1854 (Siluriformes: Loricariidae) from the Amazon basin

We present karyotypic characteristics and report on the occurrence of ZZ/ZW sex chromosomes in Ancistrus ranunculus (rio Xingu) and Ancistrus sp. "Piagaçu" (rio Purus), of the Brazilian Amazon. Ancistrus ranunculus has a modal number of 2n=48 chromosomes, a fundamental number (FN) of 82 for both sexes, and the karyotypic formula was 20m+8sm+6st+14a for males and 19m+9sm+6st+14a for females. Ancistrus sp. "Piagaçu" presented 2n=52 chromosomes, FN=78 for males and FN=79 for females. The karyotypic formula was 16m+8sm+2st+26a for males and 16m+9sm+2st+25a for females. The high number of acrocentric chromosomes in karyotype of Ancistrus sp. "Piagaçu" differs from the majority of Ancistrini genera studied so far, and may have resulted from pericentric inversions and translocations. The lower number of chromosomes in A. ranunculus indicates that centric fusions also occurred in the evolution of Ancistrus karyotypes. We conclude that karyotypic characteristics and the presence of sex chromosomes can constitute important cytotaxonomic markers to identify cryptic species of Ancistrus. However, sex chromosomes apparently arose independently within the genus and thus do not constitute a reliable character to analyze phylogenetic relations among Ancistrus species. Copyright © 2007 Sociedade Brasileira de Ictiologia

Comparative cytogenetics of spiny rats of the genus proechimys (Rodentia, Echimyidae) from the Amazon region

We made a comparative analysis of the cytogenetics of spiny rat species of the genus Proechimys collected from several sites of the Madeira River basin (Amazonas State, Brazil) and Jari River valley (Pará State, Brazil). Individuals were assigned to three groups based on diploid and fundamental numbers: 2n=28, FN=46 (P. cuvieri and P. gr. longicaudatus); 2n=38, FN=52 (Proechimys gr. guyannensis), and 2n=40, FN=54 (P. gardneri). The nucleolar organizer region (NOR) was interstitial on the long arm of one submetacentric pair, as seen in all species of Proechimys analyzed thus far. However, its position in the karyotype was variable. A duplication of the NOR in one of the homologues was detected in P. gr. longicaudatus from the Aripuanã basin along the mid Madeira. The C-band pattern varied between species and, together with the NOR, allowed the identification of two evolutionary units in P. gr. longicaudatus in the region of the mid Madeira River (cytotypes A and B). The morphology and banding of the sex chromosomes were species specific. A range extension is suggested for the geographic distribution of P. gardneri and P. gr. longicaudatus. Moreover, we suggest that species of Proechimys with 2n=38 chromosomes are restricted to east of the Negro River and north of the Amazon River. We also revised the published chromosome data available for Proechimys. © FUNPEC-RP