Short Arm Of Pair Research Articles

Comparative molecular and conventional cytogenetic analyses of three species of Rhinella (Anura; Bufonidae).

The genus Rhinella corresponds to a group of anurans characterized by numerous taxonomic and systemic challenges, leading to their organization into species complexes. Cytogenetic data for this genus thus far are limited to the diploid number and chromosome morphology, which remain highly conserved among the species. In this study, we analyse the karyotypes of three species of the genus Rhinella (Rhinella granulosa, Rhinella margaritifera, and Rhinella marina) using both classical (conventional staining and C-banding) and molecular (FISH-fluorescence in situ hybridization with 18S rDNA, telomeric sequences, and microsatellite probes) cytogenetic approaches. The aim of this study is to provide data that can reveal variations in the distribution of repetitive sequences that can contribute to understanding karyotypic diversification in these species. The results revealed a conserved karyotype across the species, with 2n = 22 and FN = 44, with metacentric and submetacentric chromosomes. C-banding revealed heterochromatic blocks in the pericentromeric region for all species, with a proximal block on the long arms of pairs 3 and 6 in R. marina and on the short arms of pairs 4 and 6 in R. margaritifera. Additionally, 18S rDNA probes hybridized to pair 5 in R. granulosa, to pair 7 in R. marina, and to pair 10 in R. margaritifera. Telomeric sequence probes displayed signals exclusively in the distal region of the chromosomes, while microsatellite DNA probes showed species-specific patterns. These findings indicate that despite a conserved karyotypical macrostructure, chromosomal differences exist among the species due to the accumulation of repetitive sequences. This variation may be attributed to chromosome rearrangements or differential accumulation of these sequences, highlighting the dynamic role of repetitive sequences in the chromosomal evolution of Rhinella species. Ultimately, this study emphasizes the importance of the role of repetitive DNAs in chromosomal rearrangements to elucidate the evolutionary mechanisms leading to independent diversification in the distinct phylogenetic groups of Rhinella.

Cytogenetic analysis in Tetragonopterus franciscoensis (Characiformes): another piece to the karyoevolutionary puzzle of tetra fishes

Tetragonopterus is a taxonomically complex genus in Characidae, being currently represented by nine species according to integrative approaches. One of them, T. franciscoensis was recently validated in rivers from northeastern Brazil. Even though molecular and morphological data have been collected in Tetragonopterus, the cytogenetic analyses in this group are scarce despite of the role of chromosomal variation in speciation. Herein, we present the first detailed karyotypic study in T. franciscoensis along with a comparative analysis with published cytogenetic data in characin fish. All specimens shared 2n=52 distributed in 12 metacentric (m), 12 submetacentric (sm), and 28 subtelocentric/acrocentric (st/a) chromosomes for both sexes as well as single nucleolus organizer regions on short arms of pair 8 and several GC-rich sites. The mapping of telomeric sequences (TTAGGG)n revealed no telomeric interstitial signals. While subtle cytogenetic differences were observed between samples from northeastern basins in Brazil, corroborating a recent genetic divergence, distinct karyotypes were detected in relation to congeneric taxa from other Brazilian regions. Therefore, the origin of large biarmed pairs in species with low 2n values should be related to occurrence of centric fusions.

Cytomolecular investigations using repetitive DNA probes contribute to the identification and characterization of Characidium sp. aff. C. vidali (Teleostei: Characiformes)

Abstract Characidium sp. aff. C. vidali is a species found in coastal streams in southeastern Brazil, which has karyotypic explanatory elements as the occurrence of microstructural variations, keeping the chromosomal macrostructure of the genus. The objective of this study was to apply cytomolecular tools in the chromosomes of Characidium sp. aff. C. vidali to identify characteristics in their karyotype contributing to cytogenetic definition of this species, adding information about the evolution of the chromosomal structure of the group. The species showed 2n = 50 chromosomes and from 1 to 4 additional B microchromosomes. FISH technique showed histone H3 and H4 genes in the short arm of pair 10, and microsatellites (CA)15, (CG)15, (GA)15 and (TTA)10 clustered in the subtelomeric portions of all A chromosomes, with total accumulation by supernumerary. The telomeric probe marked terminal regions of all chromosomes, in addition to the interstitial portion of four pairs, called ITS sites, with these markings being duplicated in two pairs, hence the double-ITS classification. C-banding revealed that supernumerary chromosomes are completely heterochromatic, that ITS sites are C-banding positive, but double-ITS sites are C-banding negative. So, throughout the evolution to Characidium, genomic events are occurring and restructuring chromosomes in populations.

ESTUDIO CARIOLÓGICO EN EL PACUL CHILENO Krameria cistoidea HOOK. & ARN.(KRAMERIACEAE)

The karyotype of the plant species Krameria cistoidea Hook. & Arn. was studied by assessing chromosome characters such as morphology, size, and C-banding pattern. The karyotype of K. cistoidea was composed only by metacentric chromosomes in the two populations studied. The haploid set length was 51.9±2.3 µm and the mean chromosome size was 8.68±0.78 µm. Some similarities in chromosome morphology and size can be observed among K. cistoidea and K. triandra, in addition to the chromosome number 2n=12 which is conserved within the genus. K. cistoidea exhibited a symmetric banding pattern with large C-bands in the telomeres of the short and long arms of all chromosomes, except the short arm of pair 1. The relative length of the C-bands was 23.5% of the total haploid set length. These cytological results on K. cistoidea are the first data on quantitative karyotype morphology and C-banding patterns in the genus Krameria. Key words: Krameria, karyotype, C-banding

The Karyotype of Microsternarchus aff. bilineatus: A First Case of Y Chromosome Degeneration in Gymnotiformes.

Various species and lineages that until recently were identified as Microsternarchus bilineatus (Hypopomidae, Gymnotiformes) have a widespread distribution in the Amazon and Orinoco River basins and across the Guiana shield. Recent molecular studies show five distinct lineages for Microsternarchus from different localities. These results suggest that this previously monotypic genus actually consists of more than one species. Here, we describe the karyotype of M. aff. bilineatus from the Cururutuia River (Bragança, Pará, Brazil). The diploid number of 48 chromosomes (14 meta-submetacentric/34 subtelo-acrocentric) is found for males and females, with an XX/XY sex chromosome system. The nucleolar organizer region is found in the short arm of pair 9. Constitutive heterochromatin occurs in the pericentromeric region of all chromosomes, in the distal region of 3p, 5p, 7p, 8q, 9q, 16q, and Xq, in the interstitial region in 2p, 10q, 11q, and 12q and all along 4p, and in a large block of the Y chromosome. These results indicate extensive karyotype divergence between this population and samples from Igarapé Tarumã Grande (Negro River, Amazonas, Brazil) studied by other researchers. Moreover, despite the diversity of sex chromosome systems found in Gymnotiformes, the XX/XY sex chromosome system of M. aff. bilineatus is the first case of Y chromosome degeneration in this order. The present data are valuable to help understand karyotype evolution in Hypopomidae.

Caracterização Citogenética de uma Espécie de Spatuloricaria (Siluriformes, Loricariidae) do Rio Xingu, (Pará, Amazônia, Brasil)

Genus Spatuloricaria (Loricariinae, Loricariidae) comprises 12 species which are not very precisely characterized, because morphological data are incipient and no karyotype information is available. In this work, was made the first cytogenetic characterization of a Spatuloricaria species of the Xingu River. Chromosomes were analyzed with conventional staining techniques, C banding, CMA3, DAPI, fluorescent in situ hybridization (FISH) with telomeric probes and rDNA18S. The results show that Spatuloricaria sp . has 2n=66 (6st/7sm/4m/16a) and a fundamental number (FN) of 92. The C-banding pattern revealed a distribution of heterochromatin in the centromeric and pericentromeric regions of the chromosomes and on the short arm of pair 15, coinciding with the DAPI labeling. FISH with rDNA 18S probes painted the terminal portion of chromosome pair eigth, corresponding to the CMA3 labeling, and a heteromorphism between the genomic blocks of this region was observed. The data obtained shall serve as cytotaxonomic markers for a better understanding of this group and its relationships within family Loricariidae, allowing inferences about the chromosomal evolution of the genus and its relations with other loricarids. Keywords: Loricariinae; cytotaxonomy; FISH; rDNA and telomeric probes.

Karyotype Patterns ofHypsolebias antenori(Cyprinodontiformes: Rivulidae): An Endangered Killifish of the Semiarid Region of Brazil

Annual fish which belong to the order Cyprinodontiformes constitute an excellent model for evolutionary studies. their short life cycle, distribution in ecologically dynamic environments, and low agility make them favorable for genetic analyses. The species Hypsolebias antenori (Rivulidae), encountered in seasonal pools located in the semiarid region of Northeastern Brazil, has been the object of surveys with a view to study its ecological and behavioral aspects. This study reports on the karyotype patterns of this species, which represents the first contribution to the cytogenetics of this genus. The karyotype of this species is composed of 2n = 48 chromosomes (6m + 4sm + 36st; NF = 96); the heterochromatic regions are located in centromeric or pericentromeric position and are more pronounced in the nucleolar organizer regions. Two sites Ag-NORs/CMA+/DAPI were identified in the short arms of pairs 2 (metacentric) and 21 (subtelocentric). Unlike the other species of this family which show an evolution modulated by events of centric fusions, H. antenori shows the maintenance of a basal diploid number and the large number of bibrachial elements indicates karyotypic diversification derived by pericentric inversions. Cytogenetic analyzes in this species will provide new taxonomic markers capable of being utilized in conservation issues and systematics.

Intra- and interspecific chromosome polymorphisms in cultivated Cichorium L. species (Asteraceae)

Endive (Cichorium endivia L.) and chicory (C. intybus L.) both have 2n = 18, but until now, there has been no detailed karyomorphological characterization. The present work evaluated five accessions of each species using FISH with rDNA probes and fluorochrome staining with CMA and DAPI. Both species presented distinct banding patterns after fluorochrome staining: while endive had proximal CMA++/DAPI− bands in the short arms of pairs 1, 2 and 3, chicory had proximal CMA-positive bands in chromosomes 1 and 3 and interstitial in the short arm of chromosome 8. Among endive accessions, FISH procedures revealed conserved position and number of 5S and 45S rDNA sites (two and three pairs, respectively), associated with the CMA-positive bands. Notwithstanding, polymorphisms were detected within chicory accessions regarding the number and the distribution of rDNA sites in relation to the most frequent karyotype (two pairs with 45S and one with 5S rDNA). The karyological markers developed allowed karyotypic differentiation between both species, uncovering peculiarities in the number and position of rDNA sites, which suggest chromosome rearrangements, such as translocations in chicory cultivars. The interspecific and intraspecific polymorphisms observed emphasize the potential of karyomorphological evaluations, helping our understanding of the relationships and evolution of the group.

Considerations on karyotype evolution in the genera Imparfinis Eigenmann and Norris 1900 and Pimelodella Eigenmann and Eigenmann 1888 (Siluriformes: Heptapteridae)

Heptapteridae is one of the fish families of the order Siluriformes with a wide distribution throughout the basins of the Neotropical region. The genera Imparfinis and Pimelodella comprise few species and/or populations with some chromosome information. Specimens of Imparfinis schubarti, Imparfinis mirini, and Pimelodella meeki from different sites located in the Paranapanema River Basin/PR/Brazil were cytogenetically analyzed. The two species of the genus Imparfinis exhibited 2n = 58 and FN = 116: I. schubarti, with a karyotypic formula of 30m + 28sm and I. mirini with a karyotype formula of 36m + 22sm. P. meeki presented a karyotype of 2n = 46 characterized by 26m + 14sm + 6st and FN = 92, confirming a variability in the 2n of the Heptapteridae family. Both Imparfinis species exhibited interstitial NORs in pair 1, coincident with a secondary constriction; P. meeki presented NORs located in the terminal position on the short arm of pair 17. All AgNORs were coincident with 18S rDNA probe and CMA3 positive. P. meeki showed a small amount of heterochromatin rich in AT and GC bases. The heterochromatin in I. schubarti was CMA3 positive. In I. mirini the heterochromatin was DAPI-positive. Furthermore, the long arm of one of the chromosomes of pair 19 revealed the presence of heterochromatic heteromorphism only in male individuals. After meiotic analyses, this heteromorphism could be easily identified in the pachytene and metaphase I stages, and was heteropyknotic and DAPI positive. This feature may be an indication of initial differentiation of sex chromosomes in I. mirini, increasing the great karyotypic variability within this family of fish.

Chromosomal and electric signal diversity in three sympatric electric knifefish species (Gymnotus, Gymnotidae) from the Central Amazon Floodplain

We describe chromosomal and electric signal diversity in three sympatric species of Gymnotus (Gymnotidae) fish from the Central Amazon Floodplain. Gymnotus arapaima presents a karyotype of 2n = 44 (24 m-sm + 20st-a), G. mamiraua 2n = 54 (42 m-sm + 12st-a), and G. jonasi 2n = 52 (12 m-sm + 40st-a). No evidence for a chromosomal sexual system was observed in two species for which both males and females were analyzed (G. mamiraua and G. arapaima). In all three species the constitutive heterochromatin is located primarily in pericentromeric regions, but also at some other sites. G. arapaima and G. mamiraua exhibit simple nucleolar organizing regions (NORs) on short arms of chromosome pairs 19 and 24, respectively. Gymnotus jonasi exhibits a multiple interstitial NOR on the long arm of pairs 9 and 10, and on the short arm of pair 11. G. arapaima and G. mamiraua exhibit several additional similarities in their karyotypic formulas—reflecting the phylogenetic proximity of these species within a G. carapo group clade (based on molecular phylogenetic evidence). The chromosomal differences among these three sympatric species imply complete post-zygotic reproductive isolation. A prominent pattern of partitioning of the peak power frequency of the electric organ discharge of these three species indicates pre-zygotic reproductive isolation of mate attraction signals. We conclude by discussing the evolutionary events that may have promoted signal divergence and reproductive isolation in Gymnotus of the Central Amazon, and the role that chromosomal rearrangements may place in diversification.

A diploid surrounded by polyploids: tadpole description, natural history and cytogenetics of Odontophrynus maisuma Rosset from Uruguay (Anura: Cycloramphidae)

Odontophrynus maisuma is a recently described diploid species of the diploid-tetraploid O. americanus complex. It inhabits coastal regions of Uruguay and southern Brazil. Tadpoles of O. maisuma at stages 33–36 are about 47 mm of total length, and similarly to that of other Odontophrynus are typical pond dwelling anuran larvae; the oral disc is small and laterally emarginated, bearing a single row of marginal papillae interrupted by a large dorsal gap. The labial tooth row formula is 2(2)/3(1); sometimes A2 and P1 are not divided. The advertisement call consists of notes that last 570– 785 ms, composed of 43–57 pulses, and with a dominant frequency between 1124–1211 Hz. The chromosome complement is composed by 11 biarmed chromosome pairs (2n = 2x = 22; NF = 44), with evident positive C-bands in the centromeric regions of all chromosome pairs, in the short arms of pairs 2 and 4, and in the long arms of pair 6 and 9. Nucleolar Organizer Regions (Ag-NORs) are located interstitially in the short arms of both chromosomes of pair 4. Preliminary data suggests that erythrocyte morphology could be used to discriminate between diploid and tetraploid tadpoles of Odontophrynus.

Cytogenetic analysis of orange-spotted grouper, Epinephelus coioides, using chromosome banding and fluorescence in situ hybridization

The orange-spotted grouper, Epinephelus coioides, is one of the most important commercial fish species in Southeast Asia. Although it has been widely cultured in China, basic cytogenetic information on this species is limited. In this study, we used Giemsa-staining, C-banding, argyrophilic nucleolar organizer regions (Ag-NORs), and repetitive sequencing (including 5S, 18S, and (TTAGGG)n) techniques to analyze the cytogenetics of the orange-spotted grouper. Our results showed that the karyotypic formula of the orange-spotted grouper was 2n = 2SM + 46A, NF = 50. C-banding patterns indicated that centromeric regions of all chromosomes were C-band positive except in pair no. 12. Heterochromatin was detected at the subcentromeric regions of both pair no. 5 and no. 12. In the smallest chromosome pair, no. 24, either the entire short arm or the end of the short arm was C-band positive. After Ag-NORs staining, one pair of nucleolar organizer regions was observed on the short arm of pair no. 24. FISH results showed that 5S rDNA was located at a pair of A-type chromosomes, while 18S rDNA appeared at the same location in the short arm of pair no. 24 where Ag-NORs were detected. The telomeric sequence (TTAGGG)n detected by FISH was located at both ends of each chromosome. Some of these chromosomal markers showed species-specific variations. Thus, despite the apparent karyotype stability (2n = 48), several microstructural chromosome changes must have occurred during chromosomal evolution, resulting in significant changes in the karyotype structure during the evolutionary diversification of the genus Epinephelus.

Discrimination of 2n = 60 Spalax leucodon cytotypes (Spalacidae, Rodentia) in Turkey by means of classical and molecular cytogenetic techniques

Comparative studies among seven populations of 2n = 60 S. leucodon employing classic cytogenetics (G- bands, C-bands, AgNOR-staining), fluorochrome staining, and fluorescence in situ hybridization of telomeric and rDNA probes are reported here for the first time. The studied specimens were assigned to two cytotypes: 2n = 60W and 2n = 60R. The basic karyotype of both cytotypes consisted of eight pairs of subtelocentric and 21 pairs of acrocentric autosomes, subtelocentric X and acrocentric Y chromosomes. Both cytotypes had variable numbers of B-chromosomes (1–3) and variable numbers of autosomal arms (NFa = 74–76) caused by amplification (deletion) of heterochromatin short arms in the second pair. The short arms of subtelocentric chromosomes were comprised of heterochromatin in both cytotypes. Nucleolar organizer regions (NORs) and rDNA clusters were detected at telomeric sites of the short arms in pairs Nos. 3, 5, 6, 9, and 13 in cytotype W, and in the short arms of pair No. 6, 8, 12, 13, and 16 in cytotype R. Different locations of rDNA clusters allowed unambiguous discrimination between two S. leucodon cytotypes possessing the same 2n = 60 and similar NFa (74–76) variability. Our findings suggest a high level of chromosomal divergence, which means that it is possible to consider these cytotypes as a well-differentiated, chromosomal lineage within the leucodon group.

Karyotypes and fluorescent chromosome banding in Pyrrhocactus (Cactaceae)

Karyotypes of the seven Pyrrhocactus species were studied for the first time with Feulgen staining and CMA/DAPI banding. All showed 2n = 22 (x = 11). The karyotypes were symmetrical with 9m + 2sm pairs, excepting P. catamarcensis with 8m + 2sm + 1st pairs. They had a terminal microsatellite on short arms of pair #1. Pyrrhocactus bulbocalyx possessed a second satellited pair (#2) exclusively detected with Feulgen. Increasing asymmetry was associated with a decline in karyotype size. Fluorochrome banding, applied for the first time in Cactaceae, revealed that nucleolar chromosome pair #1 had one CMA+/DAPI− terminal band in all species related to the nucleolar organizing region; additional pericentromeric bands were found. A pattern of homogeneous sized chromosomes with median and submedian centromeres is conserved in the genus. However, karyotypes can be distinguished by a combination of cytogenetic features. Species diversification in Pyrrhocactus has not been associated with large chromosome rearrangements or polyploidy, but with cumulative small and cryptic structural changes.

Differential staining and microchromosomal variation in karyotypes of four Brazilian species of Tupinambinae lizards (Squamata: Teiidae)

Kayotypes of four neotropical teiid lizard species (Tupinambinae) were herein studied after conventional as well as silver staining and CBG-banding: Crocodilurus amazonicus (2n = 34), Tupinambis teguixin (2n = 36), Tupinambis merianae and Tupinambis quadrilineatus (2n = 38). The karyological data for T. quadrilineatus as well as those obtained using differential staining for all species were unknown until now. The karyotypes of all species presented 12 macrochromosomes identical in morphology, but differed in the number of microchromosomes: 22 in C. amazonicus, 24 in T. teguixin and 26 in T. quadrilineatus and T. merianae. The Ag-NOR located at the secondary constriction at the distal end of pair 2 is shared by all species, contrasting with the variability observed for this character in species of the related Teiinae. CBG-banding revealed a species-specific pattern in T. quadrilineatus with conspicuous interstitial C-blocks at the proximal region of the long arm of pair 4 and the whole heterochromatic short arm of pair 6. The karyological data reported here corroborates the relationship hypothesis obtained for Tupinambis based on molecular characters. T. teguixin presents the putative ancestral karyotype for the genus with 2n = 36 whereas T. merianae and T. quadrilineatus exhibit 2n = 38, due to an additional pair of microchromosomes.

Chromosomal studies in four species of genus Chaunus (Bufonidae, Anura): localization of telomeric and ribosomal sequences after fluorescence in situ hybridization (FISH)

Fluorescence in situ hybridization (FISH) using telomeric and ribosomal sequences was performed in four species of toad genus Chaunus: C. ictericus, C. jimi, C. rubescens and C. schneideri. Analyses based on conventional, C-banding and Ag-NOR staining were also carried out. The four species present a 2n = 22 karyotype, composed by metacentric and submetacentric chromosomes, which were indistinguishable either after conventional staining or banding techniques. Constitutive heterochromatin was predominantly located at pericentromeric regions, and telomeric sequences (TTAGGG)(n) were restricted to the end of all chromosomes. Silver staining revealed Ag-NORs located at the short arm of pair 7, and heteromorphism in size of NOR signals was also observed. By contrast, FISH with ribosomal probes clearly demonstrated absence of any heteromorphism in size of rDNA sequences, suggesting that the difference observed after Ag-staining should be attributed to differences in chromosomal condensation and/or gene activity rather than to the number of ribosomal cistrons.

Unusual primitive heteromorphic ZZ/ZW sex chromosomes in Proceratophrys boiei (Anura, Cycloramphidae, Alsodinae), with description of C-Band interpopulational polymorphism

We performed cytogenetic analyses on specimens from three population samples of Proceratophrys boiei from southeastern and northeastern Brazil. We stained chromosomes of mitotic and meiotic cells with Giemsa, C-banding and Ag-NOR methods. All specimens of P. boiei presented a karyotype with a full chromosome complement of 2n=22, metacentric and submetacentric. We observed the secondary constriction within the short arm of pair 8, which was in the same position of the nucleolus organizer region (NOR). NOR heteromorphism was observed within two specimens from the municipality of Mata de São João (northeastern Bahia State). The C-banding evidenced an unusual heterochromatic pattern in the genome of P. boiei. In the southern most population samples (São Paulo State), we observed large blocks of heterochromatin in the centromeric regions of all chromosomes, whereas the northernmost samples (Bahia State) presented a small amount of constitutive heterochromatin. We suppose that this geographic variation in heterochromatin quantities could be due to heterochromatinization of some chromosome regions in the genome of the São Paulo samples. Furthermore, females from São Paulo presented, within chromosome pair 1 from C-banded karyotypes, one homologous chromosome almost heterochromatic, whereas males had heterochromatin restricted to the centromeric region. This unusual heterochromatic arrangement led us to assume that P. boiei owns a ZZ/ZW type of sexual determination system. This finding is very important, as this is the first record of ZZ/ZW sex chromosomes within Cycloramphidae. We believe that the cytogenetic differences found between southeastern and northeastern Brazilian population samples of P. boiei strongly supports the existence of a species complex under the name P. boiei, and the requirement of taxonomic and systematic reviews by morphological, bioacoustical, molecular, and cytogenetic data could define this taxonomic issue in the future.

Differences in karyotype between two sympatric species of Gymnotus (Gymnotiformes: Gymnotidae) from the eastern amazon of Brazil

In this paper we describe the karyotypes of two sympatric species of Gymnotus from Marajó Island, Pará, in the Eastern Amazon basin of Brazil. One of these species, G. mamiraua, has not previously been identified from this area. Karyotype studies demonstrate that G. cf. carapo Linnaeus, has 2n=42 (30M/SM+12ST/A) and G. mamiraua Albert & Crampton, 2n=54 (50M/SM+4ST). The Nucleolar Organizer Region (NOR) was found in the distal region of the short arm of pair 20 in G. cf. carapo and in the interstitial region of pair 1 of G. mamiraua. Both species have centromeric constitutive heterochromatin (CH) in all chromosomes and some in interstitial or distal regions. In both species, 4´6-Diamidino-2- phenylindole (DAPI) staining has shown banding concordant with C-banding, whereas the Chromomycin A3 (CMA3) staining in both species agrees with the NOR location. The new data and review of cytogenetic data in Gymnotus presented here is concordant with a hypothesis that G. carapo is either a complex of populations, or a complex of morphologically similar cryptic species with distinct karyotypes. These taxa may be reproductively isolated by prezygotic reproductive isolation barriers (such as the structure of the Electric Organ Discharge), or by post-zygotic barriers (such as karyotypic formula). The understanding of the cytogenetic structure of G. carapo, combined with associated studies of signal diversity, will yield insight into the mechanisms underlying the origins and maintenance of high species diversity in Gymnotus.

Differences in karyotype between two sympatric species of Gymnotus (Gymnotiformes: Gymnotidae) from the eastern amazon of Brazil

In this paper we describe the karyotypes of two sympatric species of Gymnotus from Marajó Island, Pará, in the Eastern Amazon basin of Brazil. One of these species, G. mamiraua, has not previously been identified from this area. Karyotype studies demonstrate that G. cf. carapo Linnaeus, has 2n=42 (30M/SM+12ST/A) and G. mamiraua Albert & Crampton, 2n=54 (50M/SM+4ST). The Nucleolar Organizer Region (NOR) was found in the distal region of the short arm of pair 20 in G. cf. carapo and in the interstitial region of pair 1 of G. mamiraua. Both species have centromeric constitutive heterochromatin (CH) in all chromosomes and some in interstitial or distal regions. In both species, 4´6-Diamidino-2- phenylindole (DAPI) staining has shown banding concordant with C-banding, whereas the Chromomycin A3 (CMA3) staining in both species agrees with the NOR location. The new data and review of cytogenetic data in Gymnotus presented here is concordant with a hypothesis that G. carapo is either a complex of populations, or a complex of morphologically similar cryptic species with distinct karyotypes. These taxa may be reproductively isolated by prezygotic reproductive isolation barriers (such as the structure of the Electric Organ Discharge), or by post-zygotic barriers (such as karyotypic formula). The understanding of the cytogenetic structure of G. carapo, combined with associated studies of signal diversity, will yield insight into the mechanisms underlying the origins and maintenance of high species diversity in Gymnotus.

Colocalization of the ribosomal gene families in Conger conger (Anguilliformes, Congridae)

The location of the major and minor ribosomal gene families in the conger eel (Conger conger) was investigated by in situ hybridization and CMA3 staining. The two gene families were localized in only one chromosome pair, on the short arm of pair 19, in an entirely CMA3‐positive region. Among the Anguilliformes, C. conger is the only species that shows the presence of the two gene families in the same chromosomal region.