5S rDNA Clusters Research Articles

Cytogenetic studies on the social parasite Acromyrmex ameliae (Formicidae: Myrmicinae: Attini) and its hosts reveal chromosome fusion in Acromyrmex

The ant Acromyrmex ameliae is a social parasite of two leaf-cutting ant subspecies: Acromyrmex subterraneus subterraneus and A. subterraneus brunneus. Cytogenetic data are available for 14 species of Acromyrmex and all of them possess 2n = 38 chromosomes. In this study, chromosome number, heterochromatin detection, and detection of AT and GC-rich blocks of colonies of A. ameliae and its hosts were carried out. Additionally, the detection of nucleolus organizer regions and 18S rDNA clusters in chromosomes of the parasite and physical mapping of telomeres were undertaken. The same chromosome number and morphology were detected for the hosts 2n = 38 (10m + 14sm + 12st + 2a), while the females and males of the social parasite A. ameliae presented 2n = 36 (10m + 16sm + 8st + 2a) and n = 18 (5m + 8sm + 4st + 1a). In both A. ameliae and its hosts, the terminal region on the short arm of the largest subtelocentric pair is heterochromatic GC-rich, and this region corresponded to the 18S rDNA clusters in the parasite. The short arms of several chromosomes were heterochromatin-rich. The telomeric probe hybridized telomeres on all chromosomes of the parasite and was not detected in intrachromosomal regions. Through a comparative cytogenetic analysis, we hypothesize that the karyotype of A. ameliae (2n = 36) originated from a chromosomal rearrangement that reduced the number of chromosomes from 38 to 36; as available data on the genus Acromyrmex show that all other species possess 38 chromosomes, representing 45% of the 33 valid species in this genus. The mechanism of the chromosome rearrangement is discussed. Thus, the chromosome number observed in A. ameliae is a derivation from the genus. Our data show variation in the chromosomal number in Acromyrmex and suggest that analyses of the karyotypes of parasite species can yield novel insights with regards to the evolution of this genus.

Comparative study on the physical mapping of ribosomal genes and repetitive sequences in Friesella schrottkyi (Friese 1900) (Hymenoptera: Apidae, Meliponini)

Over the past several decades, stingless bee cytogenetic studies have focused on chromosome number and morphology of specific samples, with little emphasis on population variations. More recently, molecular techniques have facilitated analyses of the fine chromosomal structure, allowing the identification of interspecific variations and increasing our knowledge of the karyotype structure. Thus, the present study aimed to analyse the distribution of ribosomal genes and repetitive sequences in the genome of Friesella schrottkyi (Friese 1900), providing relevant information about its genomic organization. Two samples were obtained from Minas Gerais state (Rio Paranaíba and Viçosa) and one from Cunha/São Paulo state, Brazil, all of which showed 2n = 34 chromosomes, 2K: 10m + 12sm + 12st. Heterochromatin (C-banding) was detected mainly in the centromeric/pericentromeric region, but some specific patterns were verified in individuals from each location. An intense spreading of the microsatellite (GA)15 was observed, most commonly in the euchromatic areas of the chromosomes. The CMA3+ bands were found in two chromosomes in the samples from Cunha and Viçosa, while the sample from Rio Paranaíba contained three CMA3+ bands. There were also differences in the number and locations of the 18S rDNA clusters among the different samples. Although we found no differences between samples from the same location, the many intraspecific variations founded clearly demonstrate the potential of utilising molecular cytogenetics as a method of improving our understanding of the genetic variability in the Meliponini tribe.

Molecular Cytogenetics of Eurasian Species of the Genus Hedysarum L. (Fabaceae).

The systematic knowledge on the genus Hedysarum L. (Fabaceae: Hedysareae) is still incomplete. The species from the section Hedysarum are valuable forage and medicinal resources. For eight Hedysarum species, we constructed the integrated schematic map of their distribution within Eurasia based on currently available scattered data. For the first time, we performed cytogenomic characterization of twenty accessions covering eight species for evaluating genomic diversity and relationships within the section Hedysarum. Based on the intra- and interspecific variability of chromosomes bearing 45S and 5S rDNA clusters, four main karyotype groups were detected in the studied accessions: (1) H. arcticum, H. austrosibiricum, H. flavescens, H. hedysaroides, and H. theinum (one chromosome pair with 45S rDNA and one pair bearing 5S rDNA); (2) H. alpinum and one accession of H. hedysaroides (one chromosome pair with 45S rDNA and two pairs bearing 5S rDNA); (3) H. caucasicum (one chromosome pair with 45S rDNA and one chromosome pair bearing 5S rDNA and 45S rDNA); (4) H. neglectum (two pairs with 45S rDNA and one pair bearing 5S rDNA). The species-specific chromosomal markers detected in karyotypes of H. alpinum, H. caucasicum, and H. neglectum can be useful in taxonomic studies of this section.

Chromosome Mapping of 5S Ribosomal Genes in Indo-Pacific and Atlantic Muraenidae: Comparative Analysis by Dual Colour Fluorescence In Situ Hybridisation.

The Muraenidae is one of the largest and most complex anguilliform families. Despite their abundance and important ecological roles, morays are little studied, especially cytogenetically, and both their phylogenetic relationships and the taxonomy of their genera are controversial. With the aim of extending the karyology of this fish group, the chromosomal mapping of the 5S ribosomal gene family was performed on seven species belonging to the genera Muraena and Gymnothorax from both the Atlantic and Pacific oceans. Fluorescence in situ hybridisation (FISH) experiments were realized using species-specific 5S rDNA probes; in addition, two-colour FISH was performed to investigate the possible association with the 45S ribosomal gene family. Multiple 5S rDNA clusters, located either in species-specific or in possibly homoeologous chromosomes, were found. Either a syntenic or different chromosomal location of the two ribosomal genes was detected. Our results revealed variability in the number and location of 5S rDNA clusters and confirmed a substantial conservation of the number and location of the 45S rDNA.

Distribution of 18S rDNA clusters in Central European harvestmen of the suborder Eupnoi (Arachnida: Opiliones)

rDNA clusters are an important cytogenetic marker for studying karyotype evolution and chromosomal changes. The variability of this cytogenetic characteristic is, however, still almost unknown in the karyotypes of the entire class Arachnida (Arthropoda: Chelicerata). This situation is particularly evident in harvestmen (Arachnida: Opiliones), with 97 species studied cytogenetically, for which there is information on the number and position of rDNA clusters for only 13. Moreover, previous studies indicate that the number of rDNA loci is highly variable in the species analysed, ranging from one to five pairs of rDNA clusters. Based on this fragmentary information, which is for rare species mainly from the limits of the distribution of their families, it is still not possible to reconstruct the ancestral state for this important cytogenetic feature in this order. Building upon recent research in Central Europe, we analysed the number and position of 18S rDNA in 13 species belonging to the suborder Eupnoi. This revealed that their karyotypes were variable in terms of the diploid number (2n = 16-36) and number of 18S rDNA clusters (from one to seven pairs). For the first time, an 18S rDNA cluster was detected on B chromosomes in harvestmen. Our study sheds new light on the karyotype evolution and 18S rDNA distribution in harvestmen and provides an improved understanding of the ancestral state of karyotypes in the order Opiliones.

Cytogenetic and Molecular Characterization of Three Mimetic Species of the Genus Alagoasa Bechyné 1955 (Coleoptera: Alticinae) from the Neotropical Region

Coleoptera is a mega-diverse order, but only about 1% of its species have been analyzed cytogenetically. In this order, the subfamily Alticinae presents many identification problems, mainly due to the occurrence of mimicry. The objective of this work was to cytogenetically characterize 3 very similar species of the genus Alagoasa (A. pantina, A.areata, and A.scissa). We used classical and molecular cytogenetic as well as molecular genetic techniques. All 3 species showed a diploid chromosome number of 2n = 22 (20+X+y), but differences in the morphology of the chromosomes. All had a meiotic formula of 2n = 10II+X+y and an X+y sex determination system with giant, fully asynaptic sex chromosomes, concordant characteristics observed in the subtribe Oedionychina. FISH demonstrated the presence of 18S and 5S rDNA clusters in 1 pair of autosomes, syntenic and colocalizing in the 3 analyzed species. However, in A. areata, heteromorphism between the cistrons was observed. The telomeric (TTAGG)_n probe showed signals in all 3 species, with proximal signals in the X and dispersed signals in the y chromosome of A. areata, and 2 proximal signals in the X chromosome of A. scissa. Molecular analysis of the COI gene indicated that they are 3 distinct species, corroborating the observed cytogenetic characteristics.

Cytogenetics of entelegyne spiders (Arachnida, Araneae) from southern Africa.

Spiders represent one of the most studied arachnid orders. They are particularly intriguing from a cytogenetic point of view, due to their complex and dynamic sex chromosome determination systems. Despite intensive research on this group, cytogenetic data from African spiders are still mostly lacking. In this study, we describe the karyotypes of 38 species of spiders belonging to 16 entelegyne families from South Africa and Namibia. In the majority of analysed families, the observed chromosome numbers and morphology (mainly acrocentric) did not deviate from the family-level cytogenetic characteristics based on material from other continents: Tetragnathidae (2n♂ = 24), Ctenidae and Oxyopidae (2n♂ = 28), Sparassidae (2n♂ = 42), Gnaphosidae, Trachelidae and Trochanteriidae (2n♂ = 22), and Salticidae (2n♂ = 28). On the other hand, we identified interspecific variability within Hersiliidae (2n♂ = 33 and 35), Oecobiidae (2n♂ = 19 and 25), Selenopidae (2n♂ = 26 and 29) and Theridiidae (2n♂ = 21 and 22). We examined the karyotypes of Ammoxenidae and Gallieniellidae for the first time. Their diploid counts (2n♂ = 22) correspond to the superfamily Gnaphosoidea and support their placement in this lineage. On the other hand, the karyotypes of Prodidominae (2n♂ = 28 and 29) contrast with all other Gnaphosoidea. Similarly, the unusually high diploid number in Borboropactus sp. (2n♂ = 28) within the otherwise cytogenetically uniform family Thomisidae (mainly 2n♂ = 21–24) supports molecular data suggesting a basal position of the genus in the family. The implementation of FISH methods for visualisation of rDNA clusters facilitated the detection of complex dynamics of numbers of these loci. We identified up to five loci of the 18S rDNA clusters in our samples. Three different sex chromosome systems (X0, X1X20 and X1X2X30) were also detected among the studied taxa.

The Utility of Graph Clustering of 5S Ribosomal DNA Homoeologs in Plant Allopolyploids, Homoploid Hybrids, and Cryptic Introgressants.

IntroductionRibosomal DNA (rDNA) loci have been widely used for identification of allopolyploids and hybrids, although few of these studies employed high-throughput sequencing data. Here we use graph clustering implemented in the RepeatExplorer (RE) pipeline to analyze homoeologous 5S rDNA arrays at the genomic level searching for hybridogenic origin of species. Data were obtained from more than 80 plant species, including several well-defined allopolyploids and homoploid hybrids of different evolutionary ages and from widely dispersed taxonomic groups.Results(i) Diploids show simple circular-shaped graphs of their 5S rDNA clusters. In contrast, most allopolyploids and other interspecific hybrids exhibit more complex graphs composed of two or more interconnected loops representing intergenic spacers (IGS). (ii) There was a relationship between graph complexity and locus numbers. (iii) The sequences and lengths of the 5S rDNA units reconstituted in silico from k-mers were congruent with those experimentally determined. (iv) Three-genomic comparative cluster analysis of reads from allopolyploids and progenitor diploids allowed identification of homoeologous 5S rRNA gene families even in relatively ancient (c. 1 Myr) Gossypium and Brachypodium allopolyploids which already exhibit uniparental partial loss of rDNA repeats. (v) Finally, species harboring introgressed genomes exhibit exceptionally complex graph structures.ConclusionWe found that the cluster graph shapes and graph parameters (k-mer coverage scores and connected component index) well-reflect the organization and intragenomic homogeneity of 5S rDNA repeats. We propose that the analysis of 5S rDNA cluster graphs computed by the RE pipeline together with the cytogenetic analysis might be a reliable approach for the determination of the hybrid or allopolyploid plant species parentage and may also be useful for detecting historical introgression events.

Chromosomal mapping of repetitive sequences in Hyphessobrycon eques (Characiformes, Characidae): a special case of the spreading of 5S rDNA clusters in a genome.

Cytogenetic data showed a variation in diploid chromosome number in the genus Hyphessobrycon ranging from 2n = 46 to 52, and studies involving repetitive DNA sequences are scarce in representatives of this genus. The purpose of this paper was the chromosomal mapping of repetitive sequences (rDNA, histone genes, U snDNA and microsatellites) and investigation of the amplification of 5S rDNA clusters in the Hyphessobrycon eques genome. Two H. eques populations displayed 2n = 52 chromosomes, with the acrocentric pair No. 24 bearing Ag-NORs corresponding with CMA3+/DAPI-. FISH with a 18S rDNA probe identified the NORs on the short (p) arms of the acrocentric pairs Nos. 22 and 24. The 5S rDNA probe visualized signals on almost all chromosomes in genomes of individuals from both populations (40 signals); FISH with H3 histone probe identified two chromosome pairs, with the pericentromeric location of signals; FISH with a U2 snDNA probe identified one chromosome pair bearing signals, on the interstitial chromosomal region. The mononucleotide (A), dinucleotide (CA) and tetranucleotide (GATA) repeats were observed on the centromeric/pericentromeric and/or terminal positions of all chromosomes, while the trinucleotide (CAG) repeat showed signals on few chromosomes. Molecular analysis of 5S rDNA and non-transcribed spacers (NTS) showed microsatellites (GATA and A repeats) and a fragment of retrotransposon (SINE3/5S-Sauria) inside the sequences. This study expanded the available cytogenetic data for H. eques and demonstrated to the dispersion of the 5S rDNA sequences on almost all chromosomes.

Centric Fusions behind the Karyotype Evolution of Neotropical Nannostomus Pencilfishes (Characiforme, Lebiasinidae): First Insights from a Molecular Cytogenetic Perspective.

Lebiasinidae is a Neotropical freshwater family widely distributed throughout South and Central America. Due to their often very small body size, Lebiasinidae species are cytogenetically challenging and hence largely underexplored. However, the available but limited karyotype data already suggested a high interspecific variability in the diploid chromosome number (2n), which is pronounced in the speciose genus Nannostomus, a popular taxon in ornamental fish trade due to its remarkable body coloration. Aiming to more deeply examine the karyotype diversification in Nannostomus, we combined conventional cytogenetics (Giemsa-staining and C-banding) with the chromosomal mapping of tandemly repeated 5S and 18S rDNA clusters and with interspecific comparative genomic hybridization (CGH) to investigate genomes of four representative Nannostomus species: N. beckfordi, N. eques, N. marginatus, and N. unifasciatus. Our data showed a remarkable variability in 2n, ranging from 2n = 22 in N. unifasciatus (karyotype composed exclusively of metacentrics/submetacentrics) to 2n = 44 in N. beckfordi (karyotype composed entirely of acrocentrics). On the other hand, patterns of 18S and 5S rDNA distribution in the analyzed karyotypes remained rather conservative, with only two 18S and two to four 5S rDNA sites. In view of the mostly unchanged number of chromosome arms (FN = 44) in all but one species (N. eques; FN = 36), and with respect to the current phylogenetic hypothesis, we propose Robertsonian translocations to be a significant contributor to the karyotype differentiation in (at least herein studied) Nannostomus species. Interspecific comparative genome hybridization (CGH) using whole genomic DNAs mapped against the chromosome background of N. beckfordi found a moderate divergence in the repetitive DNA content among the species’ genomes. Collectively, our data suggest that the karyotype differentiation in Nannostomus has been largely driven by major structural rearrangements, accompanied by only low to moderate dynamics of repetitive DNA at the sub-chromosomal level. Possible mechanisms and factors behind the elevated tolerance to such a rate of karyotype change in Nannostomus are discussed.

Genomic Markers Associated with Cold-Hardiness in Brassica rapa L.

Brassica rapa L. is a valuable and widespread species, but its cultivation in risk farming areas requires high-quality cold-hardy varieties to be developed. Mechanisms of the cold stress response in plants involve expression of numerous genes, including ribosomal ones, and are related to plant chromosome variability. FISH- and PCR-based methods were used to study intraspecific chromosome variability in the number and localization of 45S and 5S rDNA clusters and also to examine a set of molecular markers associated with cold-hardiness in winter B. rapa cultivars from high-risk farming areas. Several SSR (Na10-CO3 and BrgMS5339-1) and SCAR (BoCCA1-F/BoCCA1-1R1 and BoCCA1-F/BoCCA1-2R1) markers were identified as suitable for diagnosing cold-resistant and cold-susceptible genotypes in B. rapa. Compared with fodder cultivars, oilseed and leaf cultivars were shown to have more molecular markers associated with cold-hardiness and a higher level of polymorphism for the chromosomal distribution of 45S and 5S rDNAs, including chromosome heteromorphism. Thus, the least cold-resistant genotypes were found to display the lowest level of chromosome variability in the distribution of the 45S and 5S rDNA clusters and vice versa. The findings could be useful for the development of new cold-tolerant B. rapa varieties.

The distribution of 45S rDNA sites in bird chromosomes suggests multiple evolutionary histories.

The distribution of 45S rDNA cluster in avian karyotypes varies in different aspects, such as position, number of bearer chromosomes, and bearers being macro- or microchromosomes. The present study investigated the patterns of variation in the 45S rDNA-bearer chromosomes of birds in order to understand the evolutionary dynamics of the cluster configuration and its contribution to the evolution of bird karyotypes. A total of 73 bird species were analyzed, including both published data and species for which rDNA-FISH was conducted for the first time. In most birds, the 45S rDNA clusters were located in a single pair of microchromosomes. Hence, the location of 45S rDNA in macrochromosomes, observed only in Neognathae species, seems to be a derived state, probably the result of chromosomal fusion between microchromosomes and distinct macrochromosomes. Additionally, the 45S rDNA was observed in multiple microchromosomes in different branches of the bird phylogeny, suggesting recurrence of dispersion processeses, such as duplications and translocations. Overall, this study indicated that the redistribution of the 45S rDNA sites in bird chromosomes followed different evolutionary trajectories with respect to each lineage of the class Aves.

Cytogenetics of the small-sized fish, Copeina guttata (Characiformes, Lebiasinidae): Novel insights into the karyotype differentiation of the family.

Lebiasinidae is a small fish family composed by miniature to small-sized fishes with few cytogenetic data (most of them limited to descriptions of diploid chromosome numbers), thus preventing any evolutionary comparative studies at the chromosomal level. In the present study, we are providing, the first cytogenetic data for the red spotted tetra, Copeina guttata, including the standard karyotype, C-banding, repetitive DNA mapping by fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH), providing chromosomal patterns and novel insights into the karyotype differentiation of the family. Males and females share diploid chromosome number 2n = 42 and karyotype composed of 2 metacentric (m), 4 submetacentric (sm) and 36 subtelocentric to acrocentric (st-a) chromosomes. Blocks of constitutive heterochromatin were observed in the centromeric and interstitial regions of several chromosomes, in addition to a remarkably large distal block, heteromorphic in size, which fully corresponded with the 18S rDNA sites in the fourth chromosomal pair. This overlap was confirmed by 5S/18S rDNA dual-color FISH. On the other hand, 5S rDNA clusters were situated in the long and short arms of the 2nd and 15th pairs, respectively. No sex-linked karyotype differences were revealed by male/female CGH experiments. The genomic probes from other two lebiasinid species, Lebiasina melanoguttata and Pyrrhulina brevis, showed positive hybridization signals only in the NOR region in the genome of C. guttata. We demonstrated that karyotype diversification in lebiasinids was accompanied by a series of structural and numeric chromosome rearrangements of different types, including particularly fusions and fissions.

Chromosomal dynamics in space and time: evolutionary history of Mycetophylax ants across past climatic changes in the Brazilian Atlantic coast

Fungus-farming ants of the genus Mycetophylax exhibit intra and interspecific chromosome variability, which makes them suitable for testing hypotheses about possible chromosomal rearrangements that endure lineage diversification. We combined cytogenetic and molecular data from Mycetophylax populations from coastal environments to trace the evolutionary history of the clade in light of chromosomal changes under a historical and geographic context. Our cytogenetic analyses revealed chromosomal differences within and among species. M. morschi exhibited three distinct karyotypes and considerable variability in the localization of 45S rDNA clusters. The molecular phylogeny was congruent with our cytogenetic findings. Biogeographical and divergence time dating analyses estimated that the most recent common ancestor of Mycetophylax would have originated at about 30 Ma in an area including the Amazon and Southern Grasslands, and several dispersion and vicariance events may have occurred before the colonization of the Brazilian Atlantic coast. Diversification of the psammophilous Mycetophylax first took place in the Middle Miocene (ca. 18–10 Ma) in the South Atlantic coast, while “M. morschi” lineages diversified during the Pliocene-Pleistocene transition (ca. 3–2 Ma) through founder-event dispersal for the Northern coastal regions. Psammophilous Mycetophylax diversification fits into the major global climatic events that have had a direct impact on the changes in sea level as well as deep ecological impact throughout South America. We assume therefore that putative chromosomal rearrangements correlated with increased ecological stress during the past climatic transitions could have intensified and/or accompanied the divergence of the psammophilous Mycetophylax. We further reiterate that “M. morschi” comprises a complex of at least three well-defined lineages, and we emphasize the role of this integrative approach for the identification and delimitation of evolutionary lineages.

Chromosomal study of Khawia abbottinae (Cestoda: Caryophyllidea): karyotype and localization of telomeric and ribosomal sequences after fluorescence in situ hybridization (FISH).

An original cytogenetic study combining classical karyotype analysis and modern fluorescence in situ hybridization using telomeric (TTAGGG)n and ribosomal sequences (18S rDNA) was performed in Khawia abbottinae (Cestoda, Caryophyllidea), a parasite of Chinese false gudgeon (Abbottina rivularis) from China. Analyses based on conventional Giemsa staining, DAPI, YOYO-1 dye, and silver (Ag) staining were also carried out. The karyotype is composed of eight pairs of metacentric and telocentric chromosomes (2n = 16, n=5m + 3t). Constitutive heterochromatin was mainly positioned at pericentromeric regions, and telomeric sequences (TTAGGG)n were restricted to the end of all chromosomes. In mitotic preparations stained with Giemsa, both homologues of chromosome pair 4 showed a distinct secondary constriction. FISH with rDNA probe confirmed that this secondary constriction contains a nucleolar organizer region (NOR). The process of spermatocyte meiosis and the dynamics of nucleolus degradation in dividing cell were scrutinized. The present study and its results enhance the limited knowledge on basic karyotype characteristics and 18S rDNA clusters location in caryophyllidean tapeworms.

Molecular Organization and Chromosomal Localization Analysis of 5S rDNA Clusters in Autotetraploids Derived From Carassius auratus Red Var. (♀) × Megalobrama amblycephala (♂).

The autotetraploid fish (4n = 200, RRRR) (abbreviated as 4nRR) resulted from the whole genome duplication of red crucian carp (Carassius auratus red var., 2n = 100, RR) (abbreviated as RCC). During investigation of the influence of polyploidization on organization and evolution of the multigene family of 5S rDNA, molecular organization and chromosomal localization of the 5S rDNA were characterized in autotetraploid fish. By sequence analysis of the coding region (5S) and adjacent non-transcribed spacer (NTS), three distinct 5S rDNA units (type I: 203 bp; type II: 340 bp; and type III: 477bp) were identified and characterized in 4nRR. These 5S rDNA units were inherited from their female parent (RCC), in which obvious base variations in NTS and array recombination of repeat units were found. Using fluorescence in situ hybridization employing different 5S rDNA units as probes, these 5S rDNA clusters were localized in chromosomes of 4nRR, respectively, and showed obvious loss of chromosomal loci (type I and type II). Our data revealed genetic variation of the 5S rDNA multigene family in the genome of autopolyploid fish. Furthermore, results provided new insights into the evolutionary patterns of this vertebrate multigene family.

Morphological and cytogenetic characteristics of Neobisium (Blothrus) slovacum Gulička, 1977 (Pseudoscorpiones, Neobisiidae), the northernmost troglobitic species of the subgenus Blothrus in Europe

A redescription is provided of the adult, tritonymph and deutonymph life stages of the troglobitic Neobisium (Blothrus) slovacum Gulička, 1977, which is known from Slovakia and Hungary. Material examined included 35 previously deposited museum specimens and 15 newly collected specimens. In addition, the karyotype and distribution of 18S rDNA clusters are described, using fluorescence in situ hybridization (FISH). The male karyotype of N.slovacum comprises 69 chromosomes, with a predominance of biarmed chromosomes, and an X0 sex chromosome system. Two pairs of signals for 18S rDNA on biarmed chromosomes (submetacentric and metacentric) of different sizes were identified. The present study provides the first information about the distribution of these clusters in the arachnid order Pseudoscorpiones. The geographic distribution of the species is summarized and mapped. Neobisiumslovacum is endemic to the Slovak and Aggtelek Karst area in southern Slovakia and north-western Hungary, where it has been recorded from 16 caves. One of these, Hačavská cave (in Slovakia), is the northernmost locality known for any species of the subgenus Blothrus.

Karyoevolution of Crenicichla heckel 1840 (Cichlidae, Perciformes): a process mediated by inversions.

ABSTRACTCrenicichla (Cichliformes, Cichlidae) present a highly conserved diploid number 2n=48 with fundamental numbers varying between 52 and 62. We analyzed four species in order to investigate the role of repetitive DNA in chromosome evolution in the genus. Crenicichla johanna, Crenicichla cf. saxatilis and Crenicichla cf. regani have 2n=48 (8 m/sm and 40st/a) and FN=56, while Crenicichla sp. ‘Xingu I’ has 2n=48 (48 st/a) and FN=48. Different patterns of constitutive heterochromatin distribution were observed including pericentric, interstitial and whole arm C bands. A single chromosome bears 18S rDNA clusters in most species, except C. johanna, where population variation exists in terms of the quantity and distribution of clusters and their association with interstitial telomeric sequences. All species showed hybridization of 5S rDNA sequences in an interstitial region on an acrocentric chromosome pair. The karyotypic differences and maintenance of the diploid number supports chromosome evolution mediated by inversions in Crenicichla. The telomeric and 18S rDNA sequence association in various chromosomes of C. johanna are proposed to represent hotspots for breakage, favoring intra-chromosomal rearrangements. The results suggest that repetitive sequences can contribute to microstructural cytogenetic diversity in Crenicichla.

New data on karyotypes of lace bugs (Tingidae, Cimicomorpha, Hemiptera) with analysis of the 18S rDNA clusters distribution.

The karyotypes of 10 species from 9 genera of the family Tingidae (Hemiptera, Heteroptera, Cimicomorpha) are described and illustrated for the first time. These species are: Agrammaatricapillum (Spinola, 1837), Catoplatuscarthusianus (Goeze, 1778), Dictylaplatyoma (Fieber, 1861), Lasiacanthahermani Vásárhelyi, 1977, Oncochilasimplex (Herrich-Schaeffer, 1830), Tingis (Neolasiotropis) pilosa Hummel, 1825, and T. (Tropidocheila) reticulata Herrich-Schaeffer, 1835, all with 2n = 12A + XY, as well as Acalyptamarginata (Wolff, 1804), Derephysia (Paraderephysia) longispina Golub, 1974, and Dictyonotastrichnocera Fieber, 1844, all with 2n = 12A + X(0). Moreover, genera Catoplatus Spinola, 1837, Derephysia Spinola, 1837, and Oncochila (Herrich-Schaeffer, 1830) were explored cytogenetically for the first time. Much as all other hitherto studied lace bugs, the species studied here have 12 autosomes but differ in their sex chromosome systems. The ribosomal clusters were localized on male meiotic cells of all ten species already mentioned and, additionally, in Acalyptacarinata Panzer, 1806 known to have 2n = 12A + X (Grozeva and Nokkala 2001) by fluorescence in situ hybridization (FISH) using a PCR amplified 18S rDNA fragment as a probe. In all cases, rDNA loci were located interstitially on a pair of autosomes. Furthermore, two species possessed some additional rDNA clusters. Thus, Acalyptamarginata showed clearly defined interstitial clusters on one more pair of autosomes, whereas Derephysialongispina had a terminal cluster on the X-chromosome. FISH performed with the telomeric (TTAGG)n probe did not reveal labelling in chromosomes of any species studied. Hence, the results obtained provide additional evidence for the karyotype conservatism, at least regarding the number of autosomes, for variation in chromosomal distribution of rDNA loci between species and for the lack of the ancestral insect telomeric sequence TTAGG in lace bugs. Preliminary taxonomic comments are made basing on some cytogenetic evidence.

The Karyotype of the Hoatzin (Opisthocomus hoazin) - A Phylogenetic Enigma of the Neornithes

The hoatzin (Opisthocomus hoazin Müller, 1776) is a folivorous bird, endemic to the Amazonian region. It presents some unique characteristics, including wing claws and foregut fermentation, which make its phylogenetic relationship to other birds difficult to determine. There have been various attempts to place it among the Galliformes, Gruiformes, Musophagiformes, Cuculiformes, and Charadriiformes, but phylogenetic analyses always show low supporting values. Nowadays, the hoatzin is included in the monotypic order Opisthocomiformes, but the relationship of this order to other groups of birds is still unclear. Although its karyotype resembles the typical avian model, fissions of the syntenic groups corresponding to chicken chromosomes 1 and 2 and 2 fusions were found. The presence of 18S rDNA clusters in 2 pairs of microchromosomes is another derived character. Hence, different rearrangements were detected in the karyotype of the hoatzin, indicating it has been derived from the putative ancestral karyotype by the occurrence of fissions and fusions. However, as these rearrangements are not exclusive to O. hoazin, they do not clarify the phylogenetic position of this enigmatic species.