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The taxonomic identification of Lonchothrix emiliae (Rodentia, Echimyidae, Eumysopinae) is problematic because of the overlap of morphological characters with its sister clade represented by species in the genus Mesomys which, like L. emiliae, is distributed throughout the Amazonian biome. Cytogenetic studies reported the karyotype of L. emiliae as 2n = 60/FN = 116, but this karyotype and samples were later designated as M. hispidus. To evaluate the karyotype diversity of Lonchothrix and Mesomys, and to provide data useful as karyological diagnostic characters, in the present study we made a comparative analysis of specimens of L. emiliae and M. stimulax collected from two Brazilian Amazonian localities, using C-banding, G-banding, FISH using rDNA 45S and telomeric probes, and Cytochrome-b (Cytb) sequences. The results indicate that L. emiliae has 2n = 64♀, 65♂/FN = 124 and a multiple sexual system (XX/XY1Y2), while M. stimulax has 2n = 60/FN = 116. The Neo-X system found in L. emiliae also occurs in two Proechimys species, but cytogenetic analysis indicated an independent origin for these systems. The rDNA 45S analysis showed interstitial signals at one autosomal pair for each species, while an ITS found in L. emiliae was not coincident with the NOR. The molecular analysis confirmed Lonchothrix and Mesomys are sister genera, and the high level of intraspecific genetic divergence (7.1%) in M. stimulax suggests that it may be a species complex., Competing Interests: The authors have declared that no competing interests exist.

Loricariidae is a diverse group of fish from the neotropical region, occupying a wide variety of freshwater environments. Cytogenetic data have brought important insights into Loricariidae diversity because they help validate undescribed species as well as our understanding of inter- and intraspecific diversity. However, conventional cytogenetic approaches are limited in their ability to detect variability in some lineages, as seen in the Peckoltia clade, owing to their apparent conserved karyotype. Thus, the aim of this work was to map 5S and 18S ribosomal (rDNA) sites in five species of Peckoltia and one species of Ancistomus from the Amazon basin, and discusses the mechanisms of organization and diversification of these clusters. The species analyzed were found to have 2n = 52 and share KF = 38 m-sm +14st-a chromosomes, except Peckoltia vittata with KF = 34 m-sm +18st-a. Extensive variations in the number and location of 5S and 18S rDNA sites were observed among species. These data indicate that inversions are not the most important events in karyotype evolution in this group, and should prove useful in identifying the species studied here. In addition to inversions, transpositions are important evolutionary events that are involved at least in rDNA clusters spreading in Peckoltia and probably in other species of Hypostominae.

Gymnotus coatesi is a small and rare species of banded knife fish that was originally described by LaMonte in 1935, found along the main stretch of the Amazon River. There is no described cytogenetic data on this species. We analyzed the karyotype of five specimens of G. coatesi collected from Cururutuia Stream in Bragança, Pará, Brazil. The obtained diploid number is 50 and the karyotypic formula is 24 m/sm +26 st/a. The constitutive heterochromatin is DAPI positive and distributed mainly in the centromeric and pericentromeric regions of the chromosomes. Ag-nucleolus organizer regions staining showed nine active sites. The 5S rDNA probe hybridized chromosome pair 17 in the interstitial part of the long arm. Fluorescence in situ hybridization (FISH) with telomeric probes revealed signals only at terminal regions of the chromosomes. The 18S rDNA probe hybridized to 21 sites, and these signals colocalized with the telomeric sequences. This relatively high number of 18S rDNA sites may reflect gene duplication mediated by transposable elements. These results indicate that although the diploid number of G. coatesi is within the range previously observed for other members of the genus, various karyotypic characteristics distinguish G. coatesi from the other species of the genus and members of the Gymnotiform order.

Neacomys (Sigmodontinae) comprises 8 species mainly found in the Amazonian region. We describe 5 new karyotypes from Brazilian Amazonia: 2 cytotypes for N. paracou (2n = 56/FNa = 62-66), 1 for N. dubosti (2n = 64/FNa = 68), and 2 for Neacomys sp. (2n = 58/FNa = 64-70), with differences in the 18S rDNA. Telomeric probes did not show ITS. We provide a phylogeny using Cytb, and the analysis suggests that 2n = 56 with a high FNa is ancestral for the genus, as found in N. paracou, being retained by the ancestral forms of the other species, with an increase in 2n occurring independently in N. spinosus and N. dubosti. Alternatively, an increase in 2n may have occurred in the ancestral taxon of the other species, followed by independent 2n-reduction events in Neacomys sp. and in the ancestral species of N. tenuipes, N. guianae, N. musseri, and N. minutus. Finally, a drastic reduction event in the diploid number occurred in the ancestral species of N. musseri and N. minutus which exhibit the lowest 2n of the genus. The karyotypic variations found in both intra- and interspecific samples, associated with the molecular phylogeny, suggest a chromosomal evolution with amplification/deletion of constitutive heterochromatin and rearrangements including fusions, fissions, and pericentric inversions., (© 2015 S. Karger AG, Basel.)

Rodentia comprises 42 % of living mammalian species. The taxonomic identification can be difficult, the number of species currently known probably being underestimated, since many species show only slight morphological variations. Few studies surveyed the biodiversity of species, especially in the Amazon region. Cytogenetic studies show great chromosomal variability in rodents, with diploid numbers ranging from 10 to 102, making it difficult to find chromosomal homologies by comparative G banding. Chromosome painting is useful, but only a few species of rodents have been studied by this technique. In this study, we sorted whole chromosome probes by fluorescence-activated cell sorting from two Hylaeamys megacephalus individuals, an adult female (2n = 54) and a fetus (2n = 50). We made reciprocal chromosome painting between these karyotypes and cross-species hybridization on Cerradomys langguthi (2n = 46). Both species belong to the tribe Oryzomyini (Sigmodontinae), which is restricted to South America and were collected in the Amazon region. Twenty-four chromosome-specific probes from the female and 25 from the fetus were sorted. Reciprocal chromosome painting shows that the karyotype of the fetus does not represent a new cytotype, but an unbalanced karyotype with multiple rearrangements. Cross-species hybridization of H. megacephalus probes on metaphases of C. langguthi shows that 11 chromosomes of H. megacephalus revealed conserved synteny, 10 H. megacephalus probes hybridized to two chromosomal regions and three hybridized to three regions. Associations were observed on chromosomes pairs 1-4 and 11. Fluorescence in situ hybridization with a telomeric probe revealed interstitial regions in three pairs (1, 3, and 4) of C. langguthi chromosomes. We discuss the genomic reorganization of the C. langguthi karyotype.

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., Results: 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., Conclusions: 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.

Metaphases of Saguinas fuscicollis fuscicollis and Saguinas mystax were subjected to restriction enzyme banding (Alu I, Hae III, Hin fI, Rsa I, Dde I, Mbo I and Msp I) and sequenced C-banding, together with fluorochrome staining (CMA3 and DAPI). Both species showed large C-bands in the pericentromeric regions. S. f. fuscicollis also manifested distal C-bands in both arms of pair 5 and in the short arms of pairs 8-15. In each species the heterochromatin revealed different reactions to the restriction enzymes and fluorochromes. This was related to its location in the genome (centromeric, pericentromeric, distal), making possible the identification of distinct categories of constitutive heterochromatin. In S. f. fuscicollis there were at least five types, namely centromeric in bi-armed chromosomes, centromeric in acrocentrics, pericentromeric, distal, and cryptic bands, detected only with the Alu I. There were three types in S. mystax, viz centromeric in bi-armed chromosomes, centromeric in acrocentric, and pericentromeric chromosomes. Several aspects of their constitution and origin are discussed.

We describe a new karyotype of Callicebus torquatus using conventional staining, G-banding with Wright Stain, CBG, Ag-NOR staining and fluorescence in situ hybridization (FISH) with human telomere probes and comparative analysis with the previously reported karyotype of C. torquatus torquatus (2n = 20). We studied a female specimen maintained in captivity at the Centro Nacional de Primatas (Para, Brazil). This titi monkey presented 2n = 22, with four large biarmed and six acrocentric autosome pairs; the X chromosome is a medium submetacentric. C-bands were revealed at the centromeric region of all acrocentrics and X chromosome; punctual C-bands also are visualized at the centromeric region in the large biarmed pairs. The NOR site was located at the long arm of pair 4, at the position of a conspicuous secondary constriction. Hybridization signals were detected exclusively at the terminal region of all chromosomes. The karyotype described here has one acrocentric pair more than that found in the literature and also differs by amount and distribution of constitutive heterochromatin. Our data support the notion that the torquatus group may be composed of distinct species, each with its own karyotype.

The karyotype of Cebuella pygmaea (2n = 44) obtained by G-, C-banding, and NOR-staining is described. This species presents a heteromorphic C band in the intersticial region of the short arm of chromosome 2. The data obtained were compared with those previously described for the karyotypes of Callithrix jacchus and Callithrix emiliae. The three species differ in the amount and distribution of non-centromeric constitutive heterochromatin. The importance of the variation in constitutive heterochromatin for the phylogeny of the group is discussed. Comparison of the karyotypes in terms of G-banding patterns showed that C. pygmaea and C. emiliae differ from C. jacchus by a Robertsonian translocation and a paracentric inversion, whereas C. pygmaea and C. emiliae differ from each other by a reciprocal translocation between an acrocentric autosome and the short arm of the submetacentric chromosomes that distinguishes their karyotypes from that of C. jacchus. The possible evolutionary paths followed by the karyotypes of the three species are discussed.