NOR Position Research Articles

Physical chromosomal mapping of major ribosomal genes in 15 ant species with a review of hypotheses regarding evolution of the number and position of NORs in ants.

Recently, hypotheses regarding the evolutionary patterns of ribosomal genes in ant chromosomes have been under discussion. One of these hypotheses proposes a relationship between chromosomal location and the number of rDNA sites, suggesting that terminal locations facilitate the dispersion of rDNA clusters through ectopic recombination during meiosis, while intrachromosomal locations restrict them to a single chromosome pair. Another hypothesis suggests that the multiplication of rDNA sites could be associated with an increase in the chromosome number in Hymenoptera due to chromosomal fissions. In this study, we physically mapped rDNA sites in 15 new ant species and also reviewed data on rDNA available since the revision by Teixeira et al. (2021a). Our objectives were to investigate whether the new data confirm the relationship between chromosomal location and the number of rDNA sites, and whether the increase in the chromosome number is significant in the dispersion of rDNA clusters in ant karyotypes. Combining our new data with all information on ant cytogenetics published after 2021, 40 new species and nine new genera were assembled. Most species exhibited intrachromosomal rDNA sites on a single chromosome pair, while three species showed these genes in terminal regions of multiple chromosome pairs. On one hand, the hypothesis that the chromosomal location of rDNA clusters may facilitate the dispersion of rDNA sites in the ant genome, as previously discussed, was strengthened, but, on the other hand, the hypothesis of chromosomal fission as the main mechanism for dispersion of ribosomal genes in ants is likely to be refuted. Furthermore, in certain genera, the location of rDNA sites remained similar among the species studied, whereas in others, the distribution of these genes showed significant variation between species, suggesting a more dynamic chromosomal evolution.

Intraspecific divergence of diploid grass Aegilopscomosa is associated with structural chromosome changes.

Aegilopscomosa Smith in Sibthorp et Smith, 1806 is diploid grass with MM genome constitution occurring mainly in Greece. Two morphologically distinct subspecies - Ae.c.comosa Chennaveeraiah, 1960 and Ae.c.heldreichii (Holzmann ex Boissier) Eig, 1929 are discriminated within Ae.comosa, however, genetic and karyotypic bases of their divergence are not fully understood. We used Fluorescence in situ hybridization (FISH) with repetitive DNA probes and electrophoretic analysis of gliadins to characterize the genome and karyotype of Ae.comosa to assess the level of their genetic diversity and uncover mechanisms leading to radiation of subspecies. We show that two subspecies differ in size and morphology of chromosomes 3M and 6M, which can be due to reciprocal translocation. Subspecies also differ in the amount and distribution of microsatellite and satellite DNA sequences, the number and position of minor NORs, especially on 3M and 6M, and gliadin spectra mainly in the a-zone. Frequent occurrence of hybrids can be caused by open pollination, which, along with genetic heterogeneity of accessions and, probably, the lack of geographic or genetic barrier between the subspecies, may contribute to extremely broad intraspecific variation of GAAn and gliadin patterns in Ae.comosa, which are usually not observed in endemic plant species.

Chromosome Evolution of the Liolaemus monticola (Liolaemidae) Complex: Chromosomal and Molecular Aspects.

Chromosomal rearrangements can directly influence population differentiation and speciation. The Liolaemus monticola complex in Chile is a unique model consisting of several chromosome races arranged in a latitudinal sequence of increasing karyotype complexity from south to north. Here, we compared chromosomal and mitochondrial cytochrome b data from 15 localities across the northern geographic distribution of L. monticola. We expanded the distribution of the previously described Multiple Fissions race (re-described as MF2), in the Coastal range between the Aconcagua River and the Petorca River, and described a new Multiple Fissions 1 (MF1) race in the Andean range. Both races present centric fissions in pairs 1 and 2, as well as a pericentric inversion in one fission product of pair 2 that changes the NOR position. Additionally, we detected a new chromosomal race north of the Petorca River, the Northern Modified 2 (NM2) race, which is polymorphic for novel centric fissions in pairs 3 and 4. Our results increase the number of chromosomal races in L. monticola to seven, suggesting a complex evolutionary history of chromosomal rearrangements, population isolation by barriers, and hybridization. These results show the relevant role of chromosome mutations in evolution, especially for highly speciose groups such as Liolaemus lizards.

Chromosome evolution in Lophyohylini (Amphibia, Anura, Hylinae).

The hyline tribe Lophyohylini includes 87 species of treefrogs, of which cytogenetics aspects have been studied in less than 20% of them. In order to evaluate the evolution of some of its chromosome characters (NOR position, C-bands, and DAPI/CMA3 bands), we studied the karyotypes of 21 lophyohylines, 16 of them for the first time, and analyzed them in a phylogenetic context. Most species showed similar karyotypes regarding chromosome number (2n = 24) and morphology (FN = 48), excepting Phyllodytes edelmoi and Osteocephalus buckleyi with 2n = 22 (FN = 44) and 2n = 28 (FN = 50), respectively. The NOR location was variable among species and provided valuable phylogenetic information. This marker was located in pair 11 in all species of Trachycephalus, Itapotihyla langsdorffii, and Nyctimantis arapapa, representing the plesiomorphic condition of Lophyohylini. Besides, other apomorphic states were recovered for the clades comprising N. rugiceps and N. siemersi (NOR in pair 5), and Dryaderces pearsoni, Osteocephalus, and Osteopilus (NOR in pair 9). Phyllodytes presented variation for NORs position; they were in pair 2 in P. edelmoi, pair 7 in P. melanomystax, and pair 8 in P. gyrinaethes and P. praeceptor. Polymorphisms in size, number, and activity of this marker were observed for N. siemersi, Osteocephalus fuscifacies, and some species of Trachycephalus. Remarkably, in N. siemersi NORs were detected on a single chromosome in the two specimens studied by this technique, raising the question of how this complex polymorphism is maintained. Interstitial telomeric sequences were found in P. edelmoi, P. melanomystax, and Osteocephalus buckleyi, and their presence seems to be not related to the chromosome reorganization events. Finally, some species showed spontaneous rearrangements, possibly as a consequence of an uncommon phenomenon in anuran cytogenetics: the presence of fragile sites or secondary constrictions not associated with NORs. We propose that this rare feature would have played an important role in the evolution of this group of frogs. From the evidence obtained in this and previous studies, we conclude that Lophyohylini presents a complex chromosome evolution.

Anadolu’da Yaşayan Endemik Üç Pseudophoxinus Bleeker, 1860 (Teleostei: Leuciscidae) Türünün CMA3 ve DAPI Boyalı Kromozomları

The karyotypes and other chromosomal markers of representatives of the genus Pseudophoxinus have been little studied. Therefore, this study documents chromosomal NOR phenotypes as revealed using Chromomycin A3 (CMA3) and DAPI chromosomal stainings in three species Pseudophoxinus elizavetae Bogutskaya, Küçük & Atalay, 2007, P. firati Bogutskaya, Küçük & Atalay, 2007 and P. hittitorum Freyhof & Özuluğ, 2010, endemic in Anatolia. Simple NOR phenotype with only two CMA3 positive signals were observed in the karyotype of P. firati whereas derived NOR phenotype with four CMA3 positive signals were observed in those of P. elizavetae and P. hittitorum, respectively. No DAPI positive signal was detected in karyotypes in all three species. This study described new NOR phenotypes, i.e. number and position of major rDNA genes, in genomes of three Pseudophoxinus species contributing thus to known diversity of NOR phenotypes in otherwise karyotypically highly conservative leuciscid fishes.

Chromosome evolution in Cophomantini (Amphibia, Anura, Hylinae).

The hylid tribe Cophomantini is a diverse clade of Neotropical treefrogs composed of the genera Aplastodiscus, Boana, Bokermannohyla, Hyloscirtus, and Myersiohyla. The phylogenetic relationships of Cophomantini have been comprehensively reviewed in the literature, providing a suitable framework for the study of chromosome evolution. Employing different banding techniques, we studied the chromosomes of 25 species of Boana and 3 of Hyloscirtus; thus providing, for the first time, data for Hyloscirtus and for 15 species of Boana. Most species showed karyotypes with 2n = 2x = 24 chromosomes; some species of the B. albopunctata group have 2n = 2x = 22, and H. alytolylax has 2n = 2x = 20. Karyotypes are all bi-armed in most species presented, with the exception of H. larinopygion (FN = 46) and H. alytolylax (FN = 38), with karyotypes that have a single pair of small telocentric chromosomes. In most species of Boana, NORs are observed in a single pair of chromosomes, mostly in the small chromosomes, although in some species of the B. albopunctata, B. pulchella, and B. semilineata groups, this marker occurs on the larger pairs 8, 1, and 7, respectively. In Hyloscirtus, NOR position differs in the three studied species: H. alytolylax (4p), H. palmeri (4q), and H. larinopygion (1p). Heterochromatin is a variable marker that could provide valuable evidence, but it would be necesserary to understand the molecular composition of the C-bands that are observed in different species in order to test its putative homology. In H. alytolylax, a centromeric DAPI+ band was observed on one homologue of chromosome pair 2. The band was present in males but absent in females, providing evidence for an XX/XY sex determining system in this species. We review and discuss the importance of the different chromosome markers (NOR position, C-bands, and DAPI/CMA3 patterns) for their impact on the taxonomy and karyotype evolution in Cophomantini.

Nuclear Architecture of Mouse Spermatocytes: Chromosome Topology, Heterochromatin, and Nucleolus

The nuclear organization of spermatocytes in meiotic prophase I is primarily determined by the synaptic organization of the bivalents that are bound by their telomeres to the nuclear envelope and described as arc-shaped trajectories through the 3D nuclear space. However, over this basic meiotic organization, a spermatocyte nuclear architecture arises that is based on higher-ordered patterns of spatial associations among chromosomal domains from different bivalents that are conditioned by the individual characteristics of chromosomes and the opportunity for interactions between their domains. Consequently, the nuclear architecture is species-specific and prone to modification by chromosomal rearrangements. This model is valid for the localization of any chromosomal domain in the meiotic prophase nucleus. However, constitutive heterochromatin plays a leading role in shaping nuclear territories. Thus, the nuclear localization of nucleoli depends on the position of NORs in nucleolar bivalents, but the association among nucleolar chromosomes mainly depends on the presence of constitutive heterochromatin that does not affect the expression of the ribosomal genes. Constitutive heterochromatin and nucleoli form complex nuclear territories whose distribution in the nuclear space is nonrandom, supporting the hypothesis regarding the existence of a species-specific nuclear architecture in first meiotic prophase spermatocytes.

Relationships of the Moorish GeckoTarentola mauritanicaSensu Lato (Reptilia, Phyllodactylidae) Populations in Tunisia: Morphometric and Karyological Assessment

Morphometric and karyological variations were analysed within the Moorish gecko Tarentola mauritanica sensu lato from Tunisia, and compared with already published data. The results show high levels of interspecific variability, indicative of the existence of two distinct lineages: the larger one T. fascicularis, widespread in the south, nearly identical to specimens from Libya and Egypt and the other one, T. m. mauritanica, confined to the northern and central regions, belonging to the common “European” and “North African” morphotype. The observed morphological variation appears to be related to microevolutionary events (phylogenetic variation) derived from a speciation event between the two taxa. We observed that these two lineages also differed in karyotype, such as the shape of some chromosomes and position of NORs. This study highlights the importance of Tunisia as a transition area between eastern and western lineages of Moorish gecko. However, additional genetic studies seem to be essential to infer evolutionary relationships among T. mauritanica populations' across North Africa.

Conserved Karyotypes in Cophomantini: Cytogenetic Analysis of 12 Species from 3 Species Groups of Bokermannohyla (Amphibia: Anura: Hylidae)

Bokermannohyla is one of the five genera included in the recently recognized tribe Cophomantini, of the hylid frog subfamily Hylinae. Although karyotypic diversity is relatively well known in two genera of Cophomantini, Aplastodiscus and Hypsiboas, in Bokermannohyla chromosome data are restricted to only two of its 28 species. In this paper, we describe the karyotypes of 12 species of Bokermannohyla using standard staining, Ag-NOR, C-banding, DAPI, CMA3, and BrdU incorporation. The 12 species share a similar diploid karyotype with 2n = 24 biarmed chromosomes; most observed differences involved the NOR-bearing chromosomes (and the NOR position within these chromosomes) and C-banding patterns. The overall similarity of these karyotypes with those of Aplastodiscus and Hypsiboas widens the notion of remarkable morphological homogeneity among Cophomantini karyotypes. The results obtained thus far are promising for comparative studies on the genus Bokermannohyla and, in a wider sense, will allow a better understanding of karyotype differentiation and chromosomal evolution in Cophomantini.

The karyotype of three Brazilian Terrarana frogs (Amphibia, Anura) with evidence of a new Barycholos species

A recent substantial rearrangement of the 882 described eleutherodactyline frog species has considerably improved the understanding of their systematics. Nevertheless, many taxonomic aspects of the South American eleutherodactyline species remain unknown and require further investigation using morphological, cytogenetic and molecular approaches. In this work, the karyotypes of the Brazilian species Ischnocnema juipoca (Atibaia and Campos do Jordão, SP), Barycholos cf. ternetzi (Uberlândia, MG, and Porto Nacional, TO), and Pristimantis crepitans (Chapada dos Guimarães and São Vicente, MT) were analyzed using Giemsa staining, Ag-NOR labeling, and C-banding techniques. All individuals had a diploid number of 22 chromosomes, but the Fundamental Numbers were different among species. The herein described low chromosome number of Pristimantis crepitans is unique within this genus, suggesting that cytogenetically this species is not closely related either to its congeneric species or to Ischnocnema. In addition, karyotype differences, mainly in the NOR position, clearly distinguished the two Barycholos populations, besides indicating the existence of a so far undescribed species in this genus. A taxonomic review could clarify the systematic position of P. crepitans and verify the hypothetic new Barycholos species.

Chromosomal analysis of three Brazilian "eleutherodactyline" frogs (Anura: Terrarana), with suggestion of a new species

The karyotypes of four Brazilian “eleutherodactyline” samples were analyzed aiming to provide additional cytogenetic data for future understanding of the evolutionary and systematic relationships of this large anuran group. The populations consisted of Pristimantis dundeei (Chapada dos Guimarães and Rondonópolis, Mato Grosso), Pristimantis aff. dundeei (Aripuanã, Mato Grosso) and Ischnocnema paulodutrai (Ilhéus, Bahia). The data revealed that P. dundeei and P. aff. dundeei have 2n=28 chromosomes, whereas I. paulodutrai has 2n=30. All pairs of chromosomes were telocentric, except for the subtelocentric pair 4 in I. paulodutrai. Differences in Ag-NOR pattern and interstitial heterochromatin positions clearly distinguished P. aff. dundeei from P. dundeei, and differentiated them from I. paulodutrai. The specimens of I. paulodutrai showed two distinct color patterns, but they did not differ in their cytogenetic characteristics. Karyotypes with 2n=28 and 2n=30 chromosomes have not been previously described for Brazilian “eleutherodactylines” which, to date, had been characterized as 2n=20, 2n=22 and 2n=34. The NOR position differences identified between P. dundeei and P. aff. dundeei, allied to their known distinct behavior and ecological data, suggested that the P. aff. dundeei from the Aripuanã sampling location is a new species. Similarities between I. paulodutrai and species currently assigned to Pristimantis are herein discussed on the basis of chromosome number and morphological characteristics.

A new frog of the genus Mantidactylus from the rainforests of north-eastern Madagascar, and its karyological affinities

AbstractWe describe a new species of the genus Mantidactylus found during field inventories in the north-eastern rainforests of Madagascar. Mantidactylus salegy sp. n. reaches a snout-vent length of 45-50 mm, has evident dorsolateral ridges and whitish spots on the upper jaws (mainly in females). The vocal sacs in males are distinctly visible and paired subgular, without strongly inflatable areas recognizable between the blackish lateral skin flaps on the throat. This frog exhibits a mosaic of characters previously thought to be typical for either the subgenera Gephyromantis or Phylacomantis. Therefore, it is a crucial discovery towards better understanding of the relationships between the taxa included in these two subgenera, supporting previous molecular results which indicated their paraphyly. The call of M. salegy consists of a rapid series of 8-11 rattling notes emitted at 1000-3500 Hz. We also provide karyological data for M. salegy, and for several related species, M. granulatus, M. leucomaculatus, M. moseri, M. redimitus, M. zavona, and M. pseudoasper (attributed to the subgenus Phylacomantis) and M. luteus (subgenus Gephyromantis). In terms of general chromosome morphology and structure, NOR localisation and heterochromatin characteristics, M. salegy shows similarities to M. redimitus, M. zavona and M. leucomaculatus, all included within Phylacomantis. Our data confirm that NOR position is a phylogenetically informative character.

Further cytogenetic analyses of the Croatian triploid shallot “Ljutika” (Allium cepa var.viviparum, Alliaceae) and its comparison with the Indian triploid “Pran”

Feulgen and silver-stained karyotypes and meiosis of two triploid viviparous onion forms (Allium cepa var.viviparum), the Croatian “Ljutika” and the Indian “Pran”, were comparatively analyzed. The results of chromosome measurements show that “Ljutika” and “Pran” are karyologically not identical, although significant similarities were found in the morphology of their chromosomes. Five geographically distant clones of “Ljutika” showed good agreement in the number and gross morphology of the chromosomes and in the number and position of NORs and interphase nucleoli. Heterotrivalents were predominant in meiosis of “Ljutika” but a relatively high frequency of higher multivalents together with univalents and bivalents were also observed. The relationship between “Ljutika” and “Pran” and their possible origin are discussed.

Analysis of active nucleolus organizing regions inCapsicum (Solanaceae) by silver staining

Nucleolar activity of 22 samples belonging to nine diploid species of Capsicum was analyzed in somatic metaphases and interphase nuclei. They are: C, chacoënse, C. parvifolium, C. frutescens, C. chinense, C. annuum var. annuum, C. baccatum var. pendulum, C. pubescens, all with 2n = 24, and C. mirabile var. mirabile and C. campylopodium with 2n = 26. Silver staining was applied for the first time in Capsicum, providing useful markers for chromosome identification in combination with other banding techniques already employed in the genus. From two to eight AgNORs (silver‐stained nucleolus organizing regions) were found in the diploid complement of the taxa studied. Nucleolar organizers are located at secondary constrictions of chromosomes which are conventionally stained or banded (C‐banding or fluorochrome banding). Polymorphism of AgNORs and attached satellites often occurs. Nucleoli are usually fused to a variable extent. Number and position of active rDNA loci are variable not only between but also within species and populations. Homologies in position of NORs between species were established. The data obtained are related to previous conclusions on phylogenetic relationships in Capsicum. Possible trends of karyotype evolution concerning nucleolar organizers are discussed, and four NORs in the diploid complement (on chromosome pairs #1 [m] and #12 [st]) are regarded as the plesiomorphic condition.

Analysis of Active Nucleolus Organizing Regions in Capsicum (Solanaceae) by Silver Staining

Nucleolar activity of 22 samples belonging to nine diploid species of Capsicum was analyzed in somatic metaphases and interphase nuclei. They are: C, chacoënse, C. parvifolium, C. frutescens, C. chinense, C. annuum var. annuum, C. baccatum var. pendulum, C. pubescens, all with 2n = 24, and C. mirabile var. mirabile and C. campylopodium with 2n = 26. Silver staining was applied for the first time in Capsicum, providing useful markers for chromosome identification in combination with other banding techniques already employed in the genus. From two to eight AgNORs (silver-stained nucleolus organizing regions) were found in the diploid complement of the taxa studied. Nucleolar organizers are located at secondary constrictions of chromosomes which are conventionally stained or banded (C-banding or fluorochrome banding). Polymorphism of AgNORs and attached satellites often occurs. Nucleoli are usually fused to a variable extent. Number and position of active rDNA loci are variable not only between but also within species and populations. Homologies in position of NORs between species were established. The data obtained are related to previous conclusions on phylogenetic relationships in Capsicum. Possible trends of karyotype evolution concerning nucleolar organizers are discussed, and four NORs in the diploid complement (on chromosome pairs #1 [m] and #12 [st]) are regarded as the plesiomorphic condition.

Cytogenetic studies on the subfamily Hypoptopomatinae (Pisces, Siluriformes, Loricariidae). III. Analysis of seven species

SUMMARYCytogenetic studies carried out on nine species belonging to five genera of the subfamily Hypoptopomatinae showed that this group has a relatively constant diploid number, 2n = 54, with only one species having 2n = 72 chromosomes. Nevertheless, the karyotypic formulae, NOR position and C-band pattern are very different among species and sometimes among local populations, with species having undifferentiated sex chromosomes and species having the XX/XY or the ZZ/ZW mechanisms. The population structure of species belonging to the subfamily Hypoptopomatinae suggests that many chromosome rearrangements have been fixed in the different species and populations due to their geographic isolation and these karyotypic differences may be very important today for species definition.

Conservative nature of the Nucleolus Organizer Region in three species of Mediterranean Mugilids

SUMMARYWe have studied the distribution of the Nucleolus Organizer Regions on the chromosome complements of three species of Mediterranean Mugilids: Liza aurata, Liza ramada and Chelon labrosus, by means of the silver nitrate staining method. Only one representative pair of NOR-chromosomes was detected in each species, the submetacentric or metacentric number 24, common to all of them. The terminal NOR position on the short arm as well as the lack of variation in size indicate the conservative nature of the NORs in the Family Mugilidae. A certain variation of the nucleoli number (1 to 4) in interphasic nuclei was detected. This may be explained by the selectivity of the silver staining for the transcriptionally active NORs. Associations involving the NOR-chromosomes reveal a slight deleting of argirofilic proteins attached to them.

Nucleolar meiotic cycle in orthoptera

The evolution of nucleolar material was analyzed during spermatogenesis of two grasshopper species by using “in vivo” visualization and the silver staining method. Both nucleoli and nucleolar remnants are detectable during prophase I and absent from metaphase I until telophase I. During telophase I a great number of small silver positive masses which correspond to prenucleolar bodies (PBs) are observed covering the chromatin surface. At interkinesis these PBs coalesce to form nucleoli, which are dispersed at prophase II. Silver dots at NOR position were observed on metaphase II chromosomes. PBs reappear at telophase II and give rise to the nucleoli detected in early spermatids. This cycle is compared with those reported in plants and in some other animal species.

Taxonomic Implications of NOR-Localization in Lacertid Lizards

AbstractNucleolar organizer position was studied by means of AgNOR technique in 11 species of the Lacerta-complex. NOR position is the same in species within a subgenus, but it is different in different subgenera. This observation supports Arnold's (1973) and Guillaume and Lanza's (1982) suggestion that the different subgenera of Lacerta (Gallotia, Lacerta part I, Lacerta part II and Podarcir) are distinct genera. The results of this study also support the hypothesis that the evolution of lacertid karyotypes is characterized by progressive translocation of microchromosomes to macrochromosomes.

Mobile nucleolus organizing regions (NORs) inAllium (Liliaceae s. lat.)? ? Inferences from the specifity of silver staining

NORs and interphase nucleoli have been silver stained inAllium cepa, A. fistulosum, reciprocal crosses between both species, and in different strains of top onions which originated from hybridization betweenA. cepa andA. fistulosum. The variability observed in size, number, and position of active NORs and correspondingly in number (and size) of interphase nucleoli is at least in part strain-specific. These data are taken to indicate that NORs inAllium behave like movable genetic elements.—With respect to the staining specifity of silver nitrate, it was found that AgNO3 labels (1) nucleoli, (2) NORs (i.e., actively transcribed “ribosomal genes”) inside the achromatic secondary constrictions, and (3) sometimes (but less pronounced) centromeres; Giemsa banding labels heterochromatin surrounding the NOR but not the nucleolus organizing secondary constriction.