Derived cytogenetic traits, multiple NORs and B chromosomes in the compact karyotype of Canthigaster figueiredoi (Tetraodontiformes)

The Tetraodontiformes are one of the main irradiation lineages of Teleosts representing a highly specialized group. Among its families, Tetraodontidae has the lowest DNA/cell content of the vertebrates, and for this reason has been used as a model group for genomic evolution studies. Seeking to widen the cytogenetic database of this family, we performed a chromosomal analysis of the species Canthigaster figueiredoi using conventional staining, Ag-NORs, C-banding, base-specific fluorochromes DAPI-CMA(3), and in situ hybridization with 18S rDNA probe. This species has 2n=36 (10 m+6sm+20a; FN=52). Multiple Ag-NORs (CMA(3)(+)) sites were detected on the four chromosome pairs. Heterochromatic blocks (CMA(3)(+)) were present in the centromeric regions of most of the pairs, extending on the short arm of some chromosomes. A GC-positive polymorphic heterochromatic region was identified in some of the individuals, in one or both of the homologs of the 6th pair. The presence of heteromorphic B microchromosomes was detected in the karyotype of one female, exhibiting intra-individual variation of 0-3 Bs. The occurrence of heterochromatic polymorphisms, multiple NORs, and B chromosomes in C. figueiredoi are very infrequent events in marine fish. They are probably associated to the accentuated restructuring and genomic reduction suffered by this family.     

The karyotypes of the thorny catfishes <Emphasis Type="Italic">Wertheimeria maculata</Emphasis> Steindachner, 1877 and <Emphasis Type="Italic">Hassar wilderi</Emphasis> Kindle, 1895 (Siluriformes: Doradidae) and their relevance in doradids chromosomal evolution

We studied the karyotypes of two doradids, the rare and endangered Wertheimeria maculata and a derived Amazonian species, Hassar wilderi. Cytogenetic characterization was assessed using conventional staining (Giemsa), C-banding, and NOR banding. Both species had 2n = 58 chromosomes but differed in their chromosome formulae, 24 m + 14sm + 8st + 12a for W. maculata and 32 m + 16sm + 10st for H. wilderi. In W. maculata heterochromatin was mainly telomeric, and three chromosomes had a fully heterochromatic arm; in H. wilderi heterochromatin was also predominantly telomeric and evident in many more chromosomes. Hassar wilderi also presented one pair of homologues with a fully heterochromatic arm. In both species, nucleolar organizer regions were restricted to one pair of subtelocentric chromosomes. Assuming a basal position for W. maculata, we hypothesized that underlying conserved diploid and NOR-bearing chromosome numbers, chromosomal evolution in doradids has involved pericentric inversions and an increase of heterochromatic blocks.     

Diversified chromosomal characteristics in Centropyge fishes (Pomacanthidae, Perciformes)

We studied karyotypes and other chromosomal markers such as C-banded heterochromatin and Ag-stained nucleolus organizer regions (Ag-NORs), in seven Centropyge fishes (Pomacanthidae, Perciformes). These results revealed diversified chromosomal characteristics in Centropyge species. Three species had 2n = 48 chromosomes, whereas four species had 2n = 52 chromosomes. Fundamental numbers showed a large variation from 48 to 82, particularly in the species with 2n = 52 chromosomes. In all the species, Ag-NORs were located in a single chromosome pair and C-bands were mainly distributed in the centromeric regions of most chromosomes, as commonly seen in teleostean fishes. However, these chromosomal markers showed species-specific variations and provided us with useful information that could help us in understanding chromosomal evolution. On the basis of these chromosomal characteristics, we infer the process of chromosomal evolution, which according to us involves an increase in chromosome number from 2n = 48 to 2n = 52 through centric fission or other mechanisms, and in fundamental number through pericentric inversion. In particular, karyotypic evolution involving the increase in chromosome number is an unusual event in the evolution of higher teleostean groups. Handling editor: K. Martens     

Karyotypes of the most primitive catfishes (Teleostei: Siluriformas: Diplomystidae)

Karyotypes of Diplomystes composensis and Diplomystes nahuelbutaensis were the same diploid number (n= 56).The chromosome formula for D. composensis was 16 metacentric + 24 submetacentric + 8 subtelocentric + 8 telocentric chromosomes and for D. nahuelbutaensis was 14 metacentric + 26 submetacentric + 8 subtelocentric +8 telocentric chromosomes. In contrast, the differences in the chromosomal C-banding patterns between these species was large. For instance, chromosome pairs 5,6, and 7 of D. nahuelbutaensis showed heterochromatic centromeres and pairs 23, 24, 27, and 28 were entirely heterochromotic. Diplomystes composensis showed conspicuous C-banded blocks in pairs 7, 24, and 25 (chromosome pair 7 had one heterochromatic arm, chromosome pair 24 was entirely heterochromatic, and chromosome pair 25 had heterochromatin close to centromere). Comparison with other ostariophysan karyotypes (e.g. gymnotiforms, characiforms, and cypriniforms), does not allow any conclusions about the ploesiomorphic catfish condition, because the karyotypes of the outgroups are too variable. A synapomorphy shared by characiforms, gymnotiforms, and diplomystid catfishes is the presence of more metacentric to submetacentric than substelocentric to telocentric chromosomes. Cypriniforms are more primitive because they have more subtelocentric to telocentric than metacentric to submetacentric chromosomes.     

Karyotype of Callithrix mauesi (Callitrichidae,Primates) and its relations with those of C. emiliae and C. jacchus

A study was conducted on the most recently described marmoset species, Callithrix mauesi, and the results obtained were compared to those previously reported for the karyotypes of C. jacchus and C. emiliae. No mechanism of chromosome rearrangement differentiates the karyotypes of C. mauesi (2n = 44) and C. emiliae (2n = 44), which diverge from C. jacchus (2n = 46) by a Robertsonian translocation and a paracentric inversion. C. mauesi, like C. emiliae, presents telomeric constitutive heterochromatin in various chromosomes, forming large heterochromatic blocks in some. This does not occur in C. jacchus, which basically presents centromeric constitutive heterochromatin. The karyotype of C. mauesi differs from that of C. emiliae only by the amount and distribution of this telomeric constitutive heterochromatin. One of the chromosomes presenting a heterochromatic block in C. mauesi is chromosome X, a fact not previously reported in the Order Primates. The present chromosome data show that C. mauesi is closer to C. emiliae than to C. jacchus, in agreement with its inclusion in the C. argentata group. In the present paper, we describe for the first time, at the chromosome level, chimerism between fraternal twins of the same sex (XY/XY), with the heterochromatic block of pair 2 being the marker. © 1994 Wiley-Liss, Inc.     

The Giemsa banding patterns of the standard and four reconstructed karyotypes of Vicia faba

The Giemsa banding patterns of the standard karyotype of Vicia faba and of four new karyotypes with easily interdistinguishable chromosomes due to interchanges and inversions are described and compared with the data of other authors on preferential Giemsa staining in Vicia faba. All karyotypes contain 14 easily reproducible marker bands which characterize chromosome segments known to be heterochromatic. It is shown that the preferential Giemsa staining of chromosome regions is a valuable tool for the localization of translocation and inversion points in the chromosomes of the reconstructed Vicia karyotypes. A close correlation exists between banding patterns, segment extension by incorporation into chromosomal DNA of azacytidine and mutagen-specific clustering of induced chromatid aberrations in the new karyotypes.     

Chromosomal relationships of the tortoises (family Testudinidae)

Banded chromosomes of five species of testudinid turtles (Geochelone pardalis, G. elongata, G. elephantopus, Gopherus berlandieri, and G. polyphemus) reveal little variation within either genus, although there are differences in amount and distribution of heterochromatin between Geochelone pardalis and G. elongata. The chromosomal position and size of the nucleolar-organizer region differs between species of the two genera.Comparisons of standard karyotypes of these species and Malacochersus tornieri with data in the literature on other tortoises show a diploid number of 52 characterizes the family. These data are consistent with those for other families which show turtles are karyotypically conservative. G-banded chromosomes of Geochelone are identical to those of Chinemys reevesi, a karyotypically primitive batagurine emydid, supporting a derivation of the tortoises from a batagurine ancestor.     

Comparative chromosomal study of five taxa of genus Callithrix,group Jacchus (Platyrrhini,primates)

The karyotypes of four marmoset species of the Callithrix jacchus group (C. aurita, C. kuhlii, C. geoffroyi, and C. penicillata) were investigated. The patterns of G-, C-, and NOR-bands of these karyotypes were compared with those of C. jacchus, previously described, in order to clarify the taxonomic relationships of this species group. All species present 2n = 46, 14 uni- and 30 biarmed autosomes, a median size submetacentric X chromosome, and the same NOR-band patterns. No rearrangement or constitutive heterochromatic variation differentiate these species, which differ only in the morphology of the Y chromosome. The data obtained indicate that, from the chromosomal point stand, the marmoset species of C. jacchus group constitute a homogeneous clade. Am J Primatol 41:53–60, 1997. © 1997 Wiley-Liss, Inc.     

Chromosomal divergence and evolutionary inferences in Rhodniini based on the chromosomal location of ribosomal genes

In this study, we used fluorescence in situ hybridisation to determine the chromosomal location of 45S rDNA clusters in 10 species of the tribe Rhodniini (Hemiptera: Reduviidae: Triatominae). The results showed striking inter and intraspecific variability, with the location of the rDNA clusters restricted to sex chromosomes with two patterns: either on one (X chromosome) or both sex chromosomes (X and Y chromosomes). This variation occurs within a genus that has an unchanging diploid chromosome number (2n = 22, including 20 autosomes and 2 sex chromosomes) and a similar chromosome size and genomic DNA content, reflecting a genome dynamic not revealed by these chromosome traits. The rDNA variation in closely related species and the intraspecific polymorphism in Rhodnius ecuadoriensis suggested that the chromosomal position of rDNA clusters might be a useful marker to identify recently diverged species or populations. We discuss the ancestral position of ribosomal genes in the tribe Rhodniini and the possible mechanisms involved in the variation of the rDNA clusters, including the loss of rDNA loci on the Y chromosome, transposition and ectopic pairing. The last two processes involve chromosomal exchanges between both sex chromosomes, in contrast to the widely accepted idea that the achiasmatic sex chromosomes of Heteroptera do not interchange sequences.     

Karyotype analysis of Eucinostomus argenteus, E. gula, E. harengulus, and Eugerres plumieri (Teleostei, Gerreidae) from Florida and Puerto Rico

The karyotypes of four gerreids of the western Atlantic Ocean are documented. A diploid chromosome complement of 48 telocentric chromosomes was found in the four species (2N=48t, fundamental number FN=48). No differences were detected either in the number of chromosomes of the standard karyotype, in their karyotype size, or between the karyotypes derived from male or female specimens of any of the species. Chromosome length decreased progressively and slightly from pair 1 to pair 24. The Ag–NOR karyotypes of E. argenteus and E. harengulus were characterized by the position of the nucleolar organizer regions next to the centromere in chromosome pair 1, whereas in E. gula and E. plumieri Ag–NORs were detected in pair 4. The other 46 chromosomes showed a light staining of the centromere with no terminal or intermediate heterochromatic blocks. All Eucinostomus species showed Ag–NORs of similar size, while Eugerres plumieri showed Ag–NORs 10–20% larger than Eucinostomus species. A combination of size and position of the Ag–NORs identified E. gula, while size alone identified E. plumieri. However, the ancestral state for size and position of Ag–NORs could not be established. There was no differential staining of the chromosomes by G-banding. The karyotype of the gerreids appears similar to the hypothetical ancestral karyotype of fish. The phylogenetic relationships among these species could not be established because of the lack of chromosome G-bands. Most likely this indicates a homogeneous distribution of GC nucleotides in the chromosomes.     

Karyotype variation in 11 species of the Vernonieae Cass. tribe (Asteraceae Bercht. & J. Presl)

The Vernonieae tribe presents strong taxonomic delimitation problems as it is considered one of the most complex groups of the Asteraceae family, comprising approximately 1100 species distributed across 129 genera. In this study, a comparative analysis of the Vernonieae species was performed to understand the events involved in the chromosome evolution of these species and to further deduce their taxonomy. The representatives were cytogenetically characterized via analyses of morphology, karyotype asymmetry and differential staining with fluorochromes CMA and DAPI as well as FISH. According to morphometric data, all species showed symmetrical karyotypes with prevailing metacentric chromosomes, even in species belonging to different genera. Variability in diploid chromosome number was detected (2n = 18 to 2n = 60), and chromosome sizes were observed to be between 1.00 and 4.09 μm. Additionally, variation in the pattern of heterochromatin was observed mainly in relation to CMA⁺ bands, in which the number varied from 4 to 16 heterochromatic regions. Only one species, Vernonia scorpioides, presented positive DAPI bands, which were located in the terminal position in most of the chromosomes. The differences in the sizes and quantities of heterochromatic bands may be related to small structural rearrangements during karyotype evolution of the Vernonieae tribe.     

Molecular cytogenetic characterization of <Emphasis Type="Italic">Rumex papillaris</Emphasis>, a dioecious plant with an XX/XY<Subscript>1</Subscript>Y<Subscript>2</Subscript> sex chromosome system

Rumex papillaris Boiss, & Reut., an Iberian endemic, belongs to the section Acetosa of the genus Rumex whose main representative is R. acetosa L., a species intensively studied in relation to sex-chromosome evolution. Here, we characterize cytogenetically the chromosomal complement of R. papillaris in an effort to enhance future comparative genomic approaches and to better our understanding of sex chromosome structure in plants. Rumex papillaris, as is common in this group, is a dioecious species characterized by the presence of a multiple sex chromosome system (with females 2n = 12 + XX and males 2n = 12 + XY₁Y₂). Except for the X chromosome both Y chromosomes are the longest in the karyotype and appear heterochromatic due to the accumulation of at least two satellite DNA families, RAE180 and RAYSI. Each chromosome of pair VI has an additional major heterochromatin block at the distal region of the short arm. These supernumerary heterochromatic blocks are occupied by RAE730 satellite DNA family. The Y-related RAE180 family is also present in an additional minor autosomal locus. Our comparative study of the chromosomal organization of the different satellite-DNA sequences in XX/XY and XX/XY₁Y₂ Rumex species demonstrates that of active mechanisms of heterochromatin amplification occurred and were accompanied by chromosomal rearrangements giving rise to the multiple XX/XY₁Y₂ chromosome systems observed in Rumex. Additionally, Y₁ and Y₂ chromosomes have undergone further rearrangements leading to differential patterns of Y-heterochromatin distribution between Rumex species with multiple sex chromosome systems.     

Chromosome plasticity in Ctenomys (Rodentia Octodontidae): chromosome 1 evolution and heterochromatin variation

A chromosome 1 (Cr1) pericentric inversion is described in six of seven species in the genus Ctenomys (tuco-tucos) from Uruguay. The inversion was inferred from G-band analyses of subtelocentric Cr1 hypothesised to be derived from the ancestral metacentric condition. Cr1 varies across species in heterochromatin amount and localisation including a metacentric chromosome without positive C-bands in C. torquatus, a subtelocentric chromosome with heterochromatic short arms in C. rionegrensis, and a subtelocentric chromosome negative after C-banding in five of the species analysed here. Pachytene chromosomes from C. rionegrensis, a species with the highest heterochromatin content, and C. torquatus, one of the species with the lowest heterochromatin content, were analysed in order to assess possible mechanisms of heterochromatin evolution. This analysis revealed the presence of three heterochromatic chromocenters in C. rionegrensis where bivalents converge, while in C. torquatus only one chromocenter was observed. In both species, highly repetitive DNA was observed, localised in chromocenters after “in situ” hybridisation. Heterochromatin associated protein M31 was localised in chromocenters of both species after immuno-detection. The spread of heterochromatin in Ctenomys chromosomes could be produced by chromatin exchanges at the chromocenter level. We propose the exchange of this DNA associated proteins between non-homologous chromosomes in pachytene to be the responsible for the spread of heterochromatin through the karyotypes of species like C. rionegrensis     

Chromosomal diversification of reef fishes from genus <Emphasis Type="Italic">Centropyge</Emphasis>(Perciformes,Pomacanthidae)

The genus Centropyge is remarkable for species richness, composing a highly specialized fish group amongst members from family Pomacanthidae. However, cytogenetical reports are nearly absent in these animals. New data are provided from karyotypical studies carried out on Centropyge aurantonotus from the Brazilian coast of the Atlantic Ocean and C. ferrugatus from the Philippines Sea of the Indo-Pacific Ocean. Both species present 2n=48 but karyotypes are differentiated by fundamental number. C. aurantonotus has a great number of biarmed chromosomes (4 m + 14 sm+16 st+4 a), while C. ferrugatus presents only acrocentric chromosomes. Single nucleolar organizer regions (NORs) are located at interstitial position of an acrocentric pair in C. ferrugatus and on short arms of a subtelocentric pair in C. aurantonotus, as confirmed by fluorescent in situ hybridization (FISH) with 18S rDNA probes. Heterochromatin is distributed over NOR and centromeric regions in both species, but additional GC-rich heterochromatic blocks on short arms of up to eight chromosomal pairs can be detected in C. aurantonotus. 5S rDNA segments were located interstitially on two chromosomal pairs in C. ferrugatus and on nine pairs in C. aurantonotus, mostly equivalent to heterochromatic blocks on short arms of biarmed chromosomes. C. ferrugatus can be considered a species in which basal chromosomal features proposed for modern Teleosteans were conserved. The derived karyotype pattern of C. aurantonotus seems to be determined by pericentric inversions and heterochromatin addition which probably determined the notorious dispersion of 5S rRNA (pseudo)genes. It is demonstrated that, even within a group generally characterized by cytogenetical homogeneity as the family Pomacanthidae, diversified karyotypes can be found.     

Chromosome number ofSaruma oliver (Aristolochiaceae)

Chromosome number ofSaruma henryi, the only species of the genus, was counted for the first time. The species has 2n=52 chromosomes, and its chromosomal complement is characteristically composed of very small chromosomes. Based on chromosome data available for the family, comparisons indicate an isolated position ofSaruma in Aristolochiaceae.     

The karyotype of Nodipecten nodosus (Bivalvia: Pectinidae)

Earlier karyotypical work on Nodipecten nodosus embryos indicated that this species has a diploid number of 38, with six pairs respectively of metacentric and submetacentric chromosomes and seven pairs of subtelocentric chromosomes, although there were some difficulties in obtaining complete metaphases. The present work provides additional results on specific regions of the chromosomes in N. nodosus and, by meiotic studies, confirms the chromosome number with more reliability. Active nucleolar organizer regions (NOR), detected in mitotic metaphases from embryos, can be characterized in N. nodosus by a high level of heteromorphism of NOR-sites, indicating that these regions are not appropriate as chromosomal markers in this species. The procedure for detecting constitutive heterochromatin of chromosomes allowed us to observe most of the heterochromatic blocks at a pericentromeric position and some at telomeric and interstitial positions. The analysis of meiotic chromosomes from gonad tissue revealed the presence of 19 bivalents during metaphase I, all homomorphic and isopicnotic, confirming the previously described diploid chromosomal number of 38 for N. nodosus. From these results, some evolutionary aspects of the Pectinidae are briefly discussed.     

Qualitative analysis of constitutive heterochromatin and primate evolution

The results of qualitative heterochromatin analysis in 16 species of primates: Homo sapiens , Pan troglodytes and Gorilla gorilla (F. Hominidae), Hylobates syndactilus (F. Hylobatidae), Macaca fascicularis , M. tibetana , Mandrillus sphinx , M. leucophaeus , Cercopithecus aethiops , C. sabaeus and C. albogularis (F. Cercopithecidae), Cebus apella , Ateles belzebuth hybridus , Aotus azarae , Saimiri sciureus and Lagothrix lagothricha (F. Cebidae) are presented in this work. We characterized heterochromatin using: (a) in situ digestion with restriction enzymes AluI, HaeIII, RsaI and Sau3A, and (b) chromosome staining with DA/DAPI on unbanded chromosomes, on C-banded chromosomes and on sequentially G-C-banded chromosomes. The aim of this work was to relate the qualitative characteristics of constitutive heterochromatin observed with the cytogenetic evolutive processes in the primate group. Results obtained show that (1) in the family Cercopithecidae, Papionini species do not present chromosomal rearrangements when their karyotypes are compared and the heterochromatin characteristics are uniform, while Cercopithecini species show a high number of chromosomal reorganizations, but they have the same heterochromatic characteristics; (2) the Platyrrhini species analysed show variability in their karyological and heterochromatic characteristics; (3) the Hominoidea present two different situations: Pan , Gorilla and Homo with few chromosomal reorganizations among their karyotypes but with a high variability in their heterochromatin characteristics, and Hylobates with low heterochromatin variability and a highly derived karyotype. Speciation processes related to chromosome changes and heterochromatin variations in different groups of primates are discussed.  © 2003 The Linnean Society of London, Biological Journal of the Linnean Society , 2003, 80 , 107–124.     

Comparative cytogenetics of the African elephant (Loxodonta africana) and Asiatic elephant (Elephas maximus)

G- and C-banded karyotypes of the two extant species of the mammalian order Proboscidea are presented for the first time. Chromosome complements were 2n = 56 in both Loxodonta africana and Elephas maximus. Comparisons between the species demonstrated a high level of chromosome band homology, with 26 conserved autosomal pairs. The normal diploid karyotype of L. africana had 25 acrocentric/telocentric and two metacentric/submetacentric autosomal pairs. E. maximus differed by having one less acrocentric and one additional submetacentric pair due to either a heterochromatic arm addition or deletion involving autosomal pair 27. Several acrocentric autosomes of L. africana exhibited small short arms that were absent in homologous chromosomes of E. maximus. The X chromosomes in both species were large submetacentric elements and were homologous. However, the small acrocentric Y chromosomes differed; in E. maximus it was slightly larger and had more distinct G-bands than its counterpart in L. africana. Extant Elephantidae appear to be relatively conservative in their rates of chromosomal change compared to some other mammalian families. The high-quality banded karyotypes presented here should prove useful as references in future chromosome analyses of elephant populations and in comparative cytogenetic studies with other ungulate orders.     

XX/XY sex chromosome system and chromosome markers in the snake eel Ophisurus serpens (Anguilliformes: Ophichtidae)

We report evidence of an XX/XY sex chromosome system in the snake eel Ophisurus serpens (Anguilliformes: Ophichthidae). We characterized the male and female karyotypes by C-, replication- and HaeIII-bandings. The 45S and 5S ribosomal gene families were located using dual fluorescence in situ hybridization, which showed that the 5S rDNA sites were present on the X chromosome, beside an autosome pair. FISH with a telomeric peptide nucleic acid probe enabled recognition of Interstitial Telomeric Sequences (ITSs), likely remnants of chromosomal rearrangements, in five chromosome pairs, including the rDNA-bearing ones. Possible mechanisms of the origin of sex chromosomes in this species are discussed, considering the presence of a sex-linked marker and ITSs.