About the possibility of hybridogenesis in the species origin of the midge Chironomus usenicus Loginova et Beljanina (Chironomidae,Diptera)

Hybridogenesis as a possible way of speciation in Chironomidae was considered with special reference to the species Chironomus usenicus resulting from hybridization between C. plumosus and C. behningi. The three species had 2n = 8 and belonged to the thummi cytocomplex with chromosome arm combinations AB, CD, EF, and G. Arm G had a marker chromosome disk sequence (CDS) and was used to demonstrate the hybrid origin of C. usenicus. Most C. usenicus larvae were heterozygous in CDS of arm G. CDS use G2 proved to be identical to CDS beh G1 of C. behningi and CDS use G1, to CDS plu G1 of C. plumosus. It was assumed that C. usenicus results from hybridization between eurybiont C. plumosus and stenobiont C. behnigni at the boundary of their species areas, in freshwater or brackish water bodies of the southern Saratov oblast and northern Kazakhstan. Morphologically and karyotypically, the hybrid was probably similar to C. plumosus. Crosses with C. plumosus eliminated virtually all C. behningi chromosome sequences from the karyotype of the hybrid. Further chromosome divergence resulting in C. usenicus involved a number of chromosome rearrangements, including duplication of pericentric heterochromatin and other chromosome regions; inversion, which occurred in arm F (regions 13-16) and was fixed in the karyotype; and other paracentric inversions and deletions accumulated in heterozygote in the karyotype pool of the species. Since C. behningi was eliminated from the introgression zone and its species are reduced, the assimilation character was assumed for introgressive hybridization of C. behningi and C. plumosus.     

Comparison of Chironomus usenicus and Chironomus curabilis with species of the group plumosus (Diptera) inferred from the mitochondrial DNA Gene COI and by the polytene chromosomes banding pattern

The sequence of a 595-bp fragment of the mitochondrial COI gene was determined for the species Chironomus usenicus and Chironomus curabilis of the genus Chironomus. Phylogenetic reconstructions based on the analysis of the COI gene sequence coincide on the whole with cytogenetic data, permitting Ch. usenicus and Ch. curabilis to be regarded as members of the group plumosus. Chironomus usenicus and Ch. plumosus have identical COI gene sequences. Two hypotheses explaining this identity are considered: inheritance of mtDNA from one of the parental species during hybridogenesis and horizontal transfer of mitochondrial genes.     

Cytogenetic characteristics of species of the Chironomus plumosus group (Chironomidae, Diptera) in Finland

The cytogenetic characteristics of species of the Chironomus plumosus group in Finland were examined. The species included C. balatonicus Devai, Wülker, Scholl, C. entis Shobanov, C. plumosus L., C. muratensis Ryser, Scholl, Wülker, and two karyotypes of unknown species. All belonged to the thummi complex having 2n = 8 chromosomes, with arm combinations of AB, CD, EF, G. In C. balatonicus arms A to G the band sequences corresponded with those of other populations. A new band sequence was found in arm B. In C. entis an arm A had a band sequence similar to those in C. agilis. A large pericentric inversion was observed in chromosome AB. The arms B to G had band sequences typical for C. entis. The chromosome arms A and B in C. plumosus from Lake Marsjon had band sequences corresponding to those of C. agilis and C. entis, respectively. C. plumosus from Helsinki may be a more divergent population with a large amount of centromere heterochromatin. C. muratensis was not distinguishable by band sequences from those of other Palaearctic populations. Two new karyotypes similar to those of species of the plumosus group have been described.     

Homology of Balbiani rings among chironomid species and localization of a new mobile element on the polytene chromosomes

The results ofin situ cross-hybridization of the cloned DNA fragments of BRa, BRb and BRc fromChironomus thummi to the polytene chromosomes of 14Chironomus species andCamptochironomus tentans are presented. BRs of the species studied were demonstrated to contain the homologus DNA sequences. The cloned fragment from the BRa ofC. thummi hybridized with the BRa ofC. piger and with a region on the arm G ofC. tentans andC. plumosus, the latter species had no extra BR. The clone 16 from the BRb ofC. thummi hybridized only with the developed BR on the arm G of all species studied. The sequence from the BRc ofC. thummi was located in the BRc ofC. piger and in the developed BR ofC. plumosus andC. nuditarsis, which were located at the most distal end of arm G. These clones can be used as markers of homologous BRs. The new mobile elements C6.10 fromC. thummi genome were localized on the polytene chromosomes of 10Chironomus species andCamptochironomus tentans. The species of the generaLipiniella, Cryptochironomus andGlyptotendipes did not contain the sequences homologous to ME C6.10.     

Speciation and chromosomal evolution of the Baikalian endemic chironomids of the genus Sergentia Kief. (Diptera, Chironomidae): Karyotype divergence and chromosomal polymorphism in the populations of deep-water species Sergentia nebulosa Linevitsh et al. and Sergentia assimilis Proviz V. et Proviz L.

Specific karyotype structure and chromosomal polymorphism was investigated in the populations of Sergentia nebulosa Linevitsh et al., 1984 and Sergentia assimilis Proviz V. et Proviz L., 1999, the deep-water endemic chironomid species (Diptera, Chironomidae) from the Baikal Lake. The distinguishing feature of the karyotypes of these species, compared to the other Baikalian Sergentia, is well-developed nucleolus in region 6 of arm C. Both species display the presence of interspecific population polymorphism, determined by the structure of this arm. In some populations, chromosome regions from 4 to 6 contain a homozygous inversion, which is absent in the other populations. The distinguishing karyotype feature of S. assimilis, which shares fluctuating homozygous inversions with the other species, is the presence of two species-specific homozygous inversions. These are the secondary overlapping inversion in arm A, regions 2 to 7, and the inversion in regions 4 to 10 of arm G. Both species of interest contain nucleolus organizer in region 10 of arm G. In populations of S. nebulosa, six heterozygous inversions localized in arms A, B, C, F, and G were discovered. The highest number of heterozygotes for inversions (71%) was observed in the population from Southern Baikal. In arm B of S. assimilis, one heterozygous inversion and heterozygosity for nucleolus organizer in the chromosome region 16 was detected. Chromosomal evolution of Baikalian Sergentia, and the role of inversion polymorphism in the population adaptation is discussed. Original Russian Text ? V.I. Proviz, 2008, published in Genetika, 2008, Vol. 44, No. 12, pp. 1627–1637.     

<Emphasis Type="Italic">Agropyron elongatum</Emphasis> chromatin localization on the wheat chromosomes in an introgression line

The introgressed small-chromosome segment of Agropyron elongatum (Host.) Neviski (Thinopyrum ponticum Podp.) in F₅ line II-1-3 of somatic hybrid between common wheat (Triticum aestivum L.) and A. elongatum was localized by sequential fluorescence in situ hybridization (FISH), genomic in situ hybridization (GISH) and karyotype data. Karyotype analysis offered basic data of arm ratios and relative lengths of 21 pairs of chromosomes in parent wheat Jinan177 and hybrid II-1–3. Using special high repetitive sequences pSc119.2 and pAs1 for FISH, the entire B- and D-genome chromosomes were detected. The FISH pattern of hybrid II-1-3 was the same as that of parent wheat. GISH using whole genomic DNA from A. elongatum as probe determined the alien chromatin. Sequential GISH and FISH, in combination with some of the karyotype data, localized the small chromosome segments of A. elongatum on the specific sites of wheat chromosomes 2AL, 1BL, 5BS, 1DL, 2DL and 6DS. FISH with probe OPF-03₁₂₉₆ from randomly amplified polymorphic DNA (RAPD) detected E-genome chromatin of A. elongatum, which existed in all of the small chromosome segments introgressed. Microsatellite primers characteristic for the chromosome arms above were used to check the localization and reveal the genetic identity. These methods are complementary and provide comprehensive information about the genomic constitution of the hybrid. The relationship between hybrid traits and alien chromatin was discussed.     

A simple chromosomal marker can reliably distinguishes <Emphasis Type="Italic">Poncirus</Emphasis> from <Emphasis Type="Italic">Citrus</Emphasis> species

Several chromosome types have been recognized in Citrus and related genera by chromomycin A₃ (CMA) banding patterns and fluorescent in situ hybridization (FISH). They can be used to characterize cultivars and species or as markers in hybridization and backcrossing experiments. In the present work, characterization of six cultivars of P. trifoliata (“Barnes”, “Fawcett”, “Flying Dragon”, “Pomeroy”, “Rubidoux”, “USDA”) and one P. trifoliata × C. limonia hybrid was performed by sequential analyses of CMA banding and FISH using 5S and 45S rDNA as probes. All six cultivars showed a similar CMA⁺ banding pattern with the karyotype formula 4B + 8D + 6F. The capital letters indicate chromosomal types: B, a chromosome with one telomeric and one proximal band; D, with only one telomeric band; F, without bands. In situ hybridization labeling was also similar among cultivars. Three chromosome pairs displayed a closely linked set of 5S and 45S rDNA sites, two of them co-located with the proximal band of the B type chromosomes (B/5S-45S) and the third one co-located with the terminal band of a D pair (D/5S-45S). The B/5S-45S chromosome has never been found in any citrus accessions investigated so far. Therefore, this B chromosome can be used as a marker to recognize the intergeneric Poncirus × Citrus hybrids. The intergeneric hybrid analyzed here displayed the karyotype formula 4B + 8D + 6F, with two chromosome types B/5S-45S and two D/5S-45S. The karyotype formula and the presence of two B/5S-45S chromosomes clearly indicate that the plant investigated is a symmetric hybrid. It also demonstrates the suitability of karyotype analyses to differentiate zygotic embryos or somatic cell fusions involving trifoliate orange germplasm. During the submission of this paper, we analyzed 25 other citrus cultivars with the same methodology and we found that the chromosome marker reported here can indeed distinguish Poncirus trifoliata from grapefruits, pummelos, and one variegated access of Citrus, besides the previously reported access of limes, limons, citrons, and sweet-oranges. However, among 14 mandarin cultivars, two of them displayed a single B/5S-45S chromosome, whereas in Citrus hystrix D.C., a far related species belonging to the Papeda subgenus, this chromosome type was found in homozygosis. Since these two mandarin cultivars are probably of hybrid origin, we assume that for almost all commercial cultivars and species of the subgenus Citrus this B type chromosome is a useful genetic marker.     

Succession of Chironomus Meigen Species (Diptera,Chironomidae) in Newly Filled Ponds

The colonization by Chironomus spp. of two ponds filled after a dry period was investigated. Field data were collected by means of quantitative benthic samples and emergence traps. C. melanescens. C. annularius, C. riparius, C. piger, C. luridus, C. obtusidens, C. plumosus, C. dorsalis and Camptochironomus tentans were determined cytotaxonomically in ponds investigated. C. melanescens and C. annularius appear to be the most characteristic species colonizing in high numbers in newly filled ponds. Larvae of C. annularius grew more slowly in ponds compared with the former one which resulted in a characteristic succession of both larval types. Most species mentioned disappeared completely from the ponds investigated after the metamorphosis of a single cohort. They were replaced by C. plumosus which was often attended by C. annularius in smaller ponds.     

A new species of Chironomus Meigen, 1803 (Diptera,Chironomidae) from the southeast of Brazil

The article describes the larva, pupa, adults and karyotype of Chironomus reissi, sp. n., which live on leaf detritus beds of small temporary waters in the southeast of Brazil. The species belongs to the pseudothummi cytocomplex with the chromosome arm combination AE, BF, CD, G.     

Influence of Cytokinins and Temperature on Development of Asparagus plumosus Shoot Tips in vitro

Lateral shoot tips from young shoots of Asparagus setaceus (Kunth) Jessop (syn. A. plumosus Baker) were grown on a modified Murashige and Skoog medium. PBA was the most effective cytokinin for growth and development of Asparagus plumosus shoot tips. The optimal range of PBA was between 0.02 and 2 mg/1. Zeatin was less effective, and kinetin, BA and 2iP were poor as cytokinins for A. plumosus. The optimal temperature for growth and development was 21°C. There was interaction between the temperature and the PBA concentration. With increasing temperature from 17 to 24°C the need for PBA increased from 0.2 to 2 mg/1.     

Chromosomal and genomic mutations in <Emphasis Type="Italic">Chironomus plumosus</Emphasis> (L.) (Diptera,Chironomidae) from Novozybkov raion of Bryansk oblast

The data on karyopool analysis of Chironomus plumosus from Novozybkov raion of Bryansk oblast, radioactively contaminated as a result of the Chernobyl accident, are presented. In the karyopool of this population, four types of heterozygous inversions (A1.2, B1.2, C1.2, D1.2) and a structurally small rearrangement in arm D, which is thought to be also associated with inversion, were identified. For inversions A1.2, C1.2, and structurally small rearrangement in arm D the cases of somatic mosaicism were described. The mean number of inversions per individual constituted 0.78. The number of genotypic combinations was 13. In 5% of the individuals chromosome B was identified, while 15.6% were polyploid (3n). In 1.8% of triploids somatic mosaicism for the level of polytene chromosomes was observed. Most of the larvae were characterized by partial asynapsis of the homologs in different regions of chromosome III. Specific features of the Chironomus plumosus karyopool from Novozybkov are thought to be associated with the habitation of a number of generations of this population on radioactively polluted territory.     

Cytogenetic analysis of a hybrid, Glyptotendipes pallens Mg. × Glyptotendipes glaucus Mg. (Diptera, Chironomidae): evolutionary considerations

The karyotype of experimentally obtained hybrids between the two closely related species Glyptotendipes pallens and Glyptotendipes glaucus is described. Hybridization was successful in one direction only ( G. pallens ♂ x G. glaucus ♀). The polytene chromosomes AB and EF of the hybrid show a more or less intimate pairing throughout their length. In the chromosomes CD in which an inversion occurs the characteristic loop is formed. The homologues of chromosome G are almost completely asynaptic. The localization of centromere heterochromatin was also studied. Centromere heterochromatin as well as intercalary heterochromatin could be observed in all chromosomes. By C banding analyses it could be shown that G. pallens has a telomeric chromosome G while in G. glaucus it is acrocentric. According to karyotype similarity it can be assumed that these two species have quite recently derived from a common ancestor since they still share much of their genomic organization. On the Black Sea coast (southeast part of Bulgaria) a natural hybridization zone between the sympatric species G. pallens and G. glaucus has been detected. The idea that hybridization between the two species might finally proceed to the formation of a new species by hybrid origin and introgression is discussed.     

Some remarks on the karyotype of an intergeneric hybrid,Salmo trutta × Salvelinus fontinalis (Pisces: Salmoniformes)

The karyotype of an intergeneric hybrid, Salmo trutta × Salvelinus fontinalis, was studied on metaphase plates from somatic cells. Detailed information was given on the karyotype morphology in the hybrid and both parental species. Findings were discussed in the light of an evaluation of the interrelationships between the two genera. Special attention was directed to Salmo trutta, a possible chromosome polymorphism being hypothesized to occur also in this species.     

Karyotyping of three Pinaceae species via fluorescent in situ hybridization and computer-aided chromosome analysis

The positions of 18/25S rRNA genes, 5S RNA genes and of Arabidopsis-type telomeric repeats were localized by fluorescent in situ hybridization (FISH) on the chromosomes of three coniferous species; Picea abies, Larix decidua and Pinus sylvestris, each with 2n=24 chromosomes. Computer-aided chromosome analysis was performed on the basis of the chromosome length, the arm length ratio and the position of the hybridization signals. This enabled the chromosomes of the Norway spruce, 4 chromosomes of the European larch and 3 of the karyotype of the Scots pine to be individually distinguished. With respect to the chromosomal positions of rDNA and 5S rDNA loci, chromosome pair I of P. sylvestris is suggested to be homoeologous to pair II of P. abies, while another chromosome pair of P. sylvestris might be homoeologous to chromosome pair III of L. decidua.     

Comparative cytogenetics of six Indo‐Pacific moray eels (Anguilliformes: Muraenidae) by chromosomal banding and fluorescence in situ hybridization

A comparative cytogenetic analysis, using both conventional staining techniques and fluorescence in situ hybridization, of six Indo‐Pacific moray eels from three different genera (Gymnothorax fimbriatus, Gymnothorax flavimarginatus, Gymnothorax javanicus, Gymnothorax undulatus, Echidna nebulosa and Gymnomuraena zebra), was carried out to investigate the chromosomal differentiation in the family Muraenidae. Four species displayed a diploid chromosome number 2n = 42, which is common among the Muraenidae. Two other species, G. javanicus and G. flavimarginatus, were characterized by different chromosome numbers (2n = 40 and 2n = 36). For most species, a large amount of constitutive heterochromatin was detected in the chromosomes, with species‐specific C‐banding patterns that enabled pairing of the homologous chromosomes. In all species, the major ribosomal genes were localized in the guanine‐cytosine‐rich region of one chromosome pair, but in different chromosomal locations. The (TTAGGG)_n telomeric sequences were mapped onto chromosomal ends in all muraenid species studied. The comparison of the results derived from this study with those available in the literature confirms a substantial conservation of the diploid chromosome number in the Muraenidae and supports the hypothesis that rearrangements have occurred that have diversified their karyotypes. Furthermore, the finding of two species with different diploid chromosome numbers suggests that additional chromosomal rearrangements, such as Robertsonian fusions, have occurred in the karyotype evolution of the Muraenidae.     

Major structural genomic alterations can be associated with hybrid speciation in Aegilops markgrafii (Triticeae)

During evolutionary history many grasses from the tribe Triticeae have undergone interspecific hybridization, resulting in allopolyploidy; whereas homoploid hybrid speciation was found only in rye. Homoeologous chromosomes within the Triticeae preserved cross‐species macrocolinearity, except for a few species with rearranged genomes. Aegilops markgrafii, a diploid wild relative of wheat (2n = 2x = 14), has a highly asymmetrical karyotype that is indicative of chromosome rearrangements. Molecular cytogenetics and next‐generation sequencing were used to explore the genome organization. Fluorescence in situ hybridization with a set of wheat cDNAs allowed the macrostructure and cross‐genome homoeology of the Ae. markgrafii chromosomes to be established. Two chromosomes maintained colinearity, whereas the remaining were highly rearranged as a result of inversions and inter‐ and intrachromosomal translocations. We used sets of barley and wheat orthologous gene sequences to compare discrete parts of the Ae. markgrafii genome involved in the rearrangements. Analysis of sequence identity profiles and phylogenic relationships grouped chromosome blocks into two distinct clusters. Chromosome painting revealed the distribution of transposable elements and differentiated chromosome blocks into two groups consistent with the sequence analyses. These data suggest that introgressive hybridization accompanied by gross chromosome rearrangements might have had an impact on karyotype evolution and homoploid speciation in Ae. markgrafii.     

Redescription of the karyotype of five species of the family Bufonidae (Amphibia: Anura) from central area of Argentina

In this study karyotypic features of the five species of the family Bufonidae from the central area of Argentina are described. The species are Rhinella achalensis, Rhinella arenarum, Rhinella fernandezae, Rhinella schneideri and Melanophryniscus stelzneri. The metaphases were obtained from intestinal and testis cells, using conventional techniques. Twenty metaphasic figures per individual were analyzed and the total length of each chromosome and the length of the four arms were measured. The obtained measurements were processed using Excel 2000 to obtain the average length of the arms p and q, the arm ratio, the centromeric index, the relative chromosome length and the relative arm length. All species showed karyotype 2n = 22, and karyotype formula of 6: 5. Pairs one to six were large, with a relative chromosome length between 18.64–7.59%; pairs seven to eleven were small, with a relative chromosome length between 7.18–2.42%. In all species the chromosome morphology was metacentric or submetacentric. Karyotype and ideograms were made for all species, based on morphometric parameters of the chromosome complement. Finally, discriminant analysis was used to separate the five species analyzed, with a highly significant classification rate of 80% and P < 0.0001. These results agree, in general, with those presented by other authors, however, in M. stelzneri detailed karyological studied have not been made so far, thus this work represents a significant contribution to the karyotypic decryption features of this species and the Rhinellla species from central area of Argentina.     

Polytene chromosome maps in four species of tsetse flies Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans (Diptera: Glossinidae): a comparative analysis

Photographic polytene chromosome maps from pupal trichogen cells of four tsetse species, Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans were constructed and compared. The homology of chromosomal elements between the species was achieved by comparing banding patterns. The telomeric and subtelomeric chromosome regions were found to be identical in all species. The pericentromeric regions were found to be similar in the X chromosome and the left arm of L1 chromosome (L1L) but different in L2 chromosome and the right arm of L1 chromosome (L1R). The L2 chromosome differs by a pericentric inversion that is fixed in the three species, G. pallidipes, G. morsitans morsitans and G. m. submorsitans. Moreover, the two morsitans subspecies appeared to be homosequential and differ only by two paracentric inversions on XL and L2L arm. Although a degree of similarity was observed across the homologous chromosomes in the four species, the relative position of specific chromosome regions was different due to chromosome inversions established during their phylogeny. However, there are regions that show no apparent homology between the species, an observation that may be attributed to the considerable intra—chromosomal rearrangements that have occurred following the species divergence. The results of this comparative analysis support the current phylogenetic relationships of the genus Glossina.     

Divergence of karyofunds in sibling species of the plumosus group (Diptera: Chironomidae)

Cytogenetic differentiation of eight sibling species of the plumosus group was examined. The karyofunds of these sibling species were shown to diverge incompletely. In each species karyofund, the banding sequences homologous to those of the remaining species of this group were revealed. The number of banding sequences that displayed interspecific homology varied from 3 to 13 per species karyofund. In a species karyotype, the homologous sequences were localized to chromosome arms 1-6. Both similar and contrasting frequencies of homologous banding sequences were observed in karyofunds of different sibling species. The average cytogenetic distance between sibling species of the plumosus group was 2.618 +/- 0.400. The presence of species-specific banding sequences, the absence of homologous banding sequences in some chromosome arms of the karyotype, and different frequencies of the homologous banding sequences determined the cytogenetic divergence of the sibling species.     

Cytotaxonomy of Chironomidae (Diptera) from Lake Shabla (Bulgaria): cytogenetic evidence for introgressive hydribization

Twenty-two chironomid species were found in Lake Shabla. Five species (Chironomus bonus, Dicrotendipes lobiger, Kiefferulus tendipediformis, Cricotopus suspiciosus and Cricotopus sp.) are new for Bulgaria. Their karytopes are described for the first time.Cytogenetic studies of two closely related chironomid species, Glyptotendipes glaucus and G. pallens, show that in one area of sympatry (Lake Shabla, Bulgaria) about 2.5% of the naturally occuring individuals are hybrids. In most cases, in this hybrid, 1st, IInd and IIIrd chromosomes correspond fully to the chromosomes of G. glaucus. The IVth chromosome is a hybrid, with one homologue of the species G. glaucus; the other homologue is derived from G. pallens. Introgressive hybridization is of particular importance to the production of these combinations. Despite hybridization, natural selection appears to maintain the essential integrity of each separate gene pool.