Reduction of chromosome number in Eleocharis subarticulata (Cyperaceae) by multiple translocations

Eleocharis subarticulata is recorded as the third species of Cyperaceae with a reduced chromosome number ( n  = 3), following reports on Rhynchospora tenuis ( n  = 2) and Fimbristylis umbellaris ( n  = 3). For Eleocharis, the numbers recorded to date vary from 2 n  = 10 to 2 n  = c. 196, with x  = 5 as the possible basic number. The karyotype of E. subarticulata was studied using conventional staining (mitosis and meiosis), C-CMA₃/DAPI banding, and FISH with 45S rDNA and telomere probes. The chromosomes showed no primary constrictions, as expected in the holocentric chromosomes of Cyperaceae. The meiotic behaviour was abnormal, with a single multivalent ring of six chromosomes at metaphase I, resulting from multiple translocations. At anaphase I six chromatids migrated to each pole, evidencing the inverted meiosis, and these groups were also visible at metaphase II. The C-CMA₃/DAPI banding technique showed only four terminal GC-rich blocks. FISH with 45S rDNA probes revealed four terminal signals, probably associated with GC-rich blocks. The telomeric probe located terminal signals in all the chromosomes, besides a hybridization site in the middle of the large pair. The occurrence of ectopic telomeric sites has not been described previously for plants with holokinetic karyotypes and with reduced chromosome numbers. These data reinforce the hypothesis of the reduction in chromosome number by multiple translocations.  © 2005 The Linnean Society of London, Botanical Journal of the Linnean Society , 2005, 149 , 457–464.     

四十五种叶蝉的染色体研究（同翅目：叶蝉总科）

研究观察了45种中国雄性叶蝉的减数分裂,其中44种的核型为首次报道,染色体数目变化在2n=12～26之间,性别决定均为XO型。从叶蝉总科的组型图来看,该科染色体数目变化在2n=8～28之间,峰值为2n=18(16+XO),另外几种类型2n=16,20,22也有较高的出现频率。科内染色体数目的进化不具有明显的方向性,2n=22(20+XO)是该科的原始核型,易位导致的不均等互换可能是染色体数目进化的主要机制。从精子发生来看叶蝉总科与角蝉总科的关系较为密切,两者的共同特点是：①精母细胞体积较大,显著不同于沫蝉和蝉科;②减数分裂行为及精子变态过程相似;③染色体数目较少,染色体体积较大;④减数分裂前期具有典型的花束期,没有弥散期,因而不同于蜡蝉。但是由于叶蝉总科的染色体变异范围明显大于角蝉总科,而角蝉总科的核型相对较为保守,从核型上来说角蝉总科是比叶蝉总科较为原始的类群。     

Karyotypes of Bembidion quadrimaculatum (L.) and Clivina fossor (L.) (Coleoptera: Carabidae)

Bembidion quadrimaculatum possesses 24 chromosomes: 2n male = 22 + XY, 2n female = 22 + XX; their structure is meta- and submetacentric and differences in length between them are slight. Achiasmatic meiosis has been identified in spermatogenesis. The diploid chromosome number in Clivina fossor is 44; 2n male = 42 + XY, 2n female = 42 + XX. The chromosome structure is meta-, submeta-, and subtelocentric and X is the longest element in the set. 1 to 2 chiasmata per bivalent occur in meiosis.     

Cytogenetic studies in Pentatomidae (Heteroptera): A review

The suborder Heteroptera constitutes one of the most important insect groups because most species are plants feeders and cause damage on many plants of economic importance. One of the most important cytogenetic characteristics of Heteroptera is the holokinetic nature of the chromosomes. One particular feature of some species of Pentatomidae is the regular presence of an abnormal meiosis in one testicular lobe (harlequin lobe). From the 28 species cytogenetically analysed from Argentine material, 21 present the diploid number 2 n  = 14, four species present a reduced number (2 n  = 12) and another three species possess an increased diploid number (2 n  = 16); among all these only three present an harlequin lobe. In the present work, a bibliographic review of the chromosome number and sex determining system of 294 species and subspecies belonging to 121 genera within the subfamilies Asopinae, Discocephalinae, Edessinae, Pentatominae, Phyllocephalinae and Podopinae is presented. The male diploid numbers range from six to 27 with a mode in 14 chromosomes; this last diploid number is present in 85% of the species. The sex chromosome determining system is XY/XX except in three species: Macropygium reticulare (Fabricius, 1803), Rhytidolomia senilis (Say, 1832) and Thyanta calceata (Say, 1832) which present derived sex chromosome systems. Furthermore, the cytogenetic relationships with the other families of Pentatomoidea are discussed.     

Automictic and apomictic parthenogenesis in psocids (Insecta: Psocoptera)

Karyotypes and meiosis patterns in three obligatory thelytokous Psocoptera species have been studied for the first time. Females of Aaroniella badonneli (Danks) display 9 chiasmatic bivalents in oocyte metaphase I (2n = 18), hence meiosis is of the automictic type. Females of Ectopsocus meridionalis Ribaga and Valenzuela sp. display 3n = 27, and 27 univalent chromosomes are present in oocyte metaphase I. Thus, meiosis in these species is of the apomictic type.     

The cytology of oxalis dispar (brown)

Summary The chromosome complement ofOxalis dispar 2n = 12 consists of a pair of submedian (SM) chromosomes, three subterminal (ST) and seven telocentric (TE) chromosomes. At mitosis and meiosis the TE chromosomes are as efficient and stable as the other chromosomes of the complement. Chromosome breakage at the centromere in the metacentric chromosomes may give rise to new TE chromosomes. It is suggested that all the TE chromosomes may have arisen from metacentric chromosomes in this way. They may have been favoured because of the deleterious nature of the discarded chromosome arms.     

Male and female meiosis in diploid and colchitetraploid Phlox drummondii Hook. (Polemoniaceae)

Comparative studies on male and female meiosis in diploid (2n = 2x = 14) and colchitetraploid (2N = 4x = 28) ornamental Phlox drummondii reveal higher chiasma frequency in embryo-sac mother cells as compared with pollen mother cells in the diploid, and significant differences in the pairing properties of chromosomes in the pollen mother cells and embryo-sac mother cells of the colchitetraploid. Male meiosis in the colchicine-induced autotetraploid was abnormal with 51.70% of chromosomes associated in quadrivalents and tridents in 96% of the cells. This was followed by discordant anaphase I disjunction. In the female meiocytes the chromosomes formed 14 bivalents in 86.66% of the cells. Quadrivalents (1–3) appeared only in 13.34% of the cells. It is concluded that meiosis in male and female cells of the colchitetraploid is governed and regulated by different controlling systems of gene(s).     

Nonrandom chromosome segregation in Neocurtilla (Gryllotalpa) hexadactyla: an ultrastructural study

During meiosis I in males of the mole cricket Neocurtilla (Gryllotalpa) hexadactyla, the univalent X1 chromosome and the heteromorphic X2Y chromosome pair segregate nonrandomly; the X1 and X2 chromosomes move to the same pole in anaphase. By means of ultrastructural analysis of serial sections of cells in several stages of meiosis I, metaphase of meiosis II, and mitosis, we found that the kinetochore region of two of the three nonrandomly segregating chromosomes differ from autosomal kinetochores only during meiosis I. The distinction is most pronounced at metaphase I when massive aggregates of electron-dense substance mark the kinetochores of X1 and Y chromosomes. The lateral position of the kinetochores of X1 and Y chromosomes and the association of these chromosomes with microtubules running toward both poles are also characteristic of meiosis I and further distinguish X1 and Y from the autosomes. Nonrandomly segregating chromosomes are typically positioned within the spindle so that the kinetochoric sides of the X2Y pair and the X1 chromosome are both turned toward the same interpolar spindle axis. This spatial relationship may be a result of a linkage of X1 and Y chromosomes lying in opposite half spindles via a small bundle of microtubules that runs between their unusual kinetochores. Thus, nonrandom segregation in Neocurtilla hexadactyla involves a unique modification at the kinetochores of particular chromosomes, which presumably affects the manner in which these chromosomes are integrated within the spindle.     

Karyotype and male pre-reductional meiosis of the sharpshooter Tapajosa rubromarginata (Hemiptera: Cicadellidae)

Cicadellidae in one of the best represented families in the Neotropical Region, and the tribe Proconiini comprises most of the xylem-feeding insects, including the majority of the known vectors of xylem-born phytopathogenic organisms. The cytogenetics of the Proconiini remains largely unexplored. We studied males of Tapajosa rubromarginata (Signoret) collected at El Manantial (Tucumán, Argentina) on native spontaneous vegetation where Sorghum halepense predominates. Conventional cytogenetic techniques were used in order to describe the karyotype and male meiosis of this sharpshooter. T. rubromarginata has a male karyological formula of 2n = 21 and a sex chromosome system XO:XX (male:female). The chromosomes do not have a primary constriction, being holokinetic and the meiosis is pre-reductional, showing similar behavior both for autosomes and sex chromosomes during anaphase I. For this stage, chromosomes are parallel to the acromatic spindle with kinetic activities in the telomeres. They segregate reductionally in the anaphase I, and towards the equator during the second division of the meiosis. This is the first contribution to cytogenetic aspects on proconines sharpshooters, particularly on this economic relevant Auchenorrhyncha species.     

Meiotic behavior and pollen morphology variation in Centaurium pulchellum (Gentianaceae)

Centaurium pulchellum is an annual herb native to Europe, but introduced in South America, where it is widely used in the preparation of digestive infusions and bitter drinks. In this species, a wide variation in the aperture pattern of pollen grains was reported and has been attributed to environmental factors or irregularities at meiosis. For this reason, cytological and palynological studies have been undertaken on two different populations. The pollen grain analysis showed that some types are more frequent within each population, but the most common forms were the typical 3-colporate and 4-colporate. The cytological analysis revealed that the analyzed populations of C. pulchellum have chromosome number 2n = 36. The presence of tetravalents at meiosis strongly suggests that these populations are autotetraploid based on x = 9. The meiotic behavior showed a significant percentage of irregularities in different phases: off-plate bivalents, precocious segregation, laggard chromosomes, bridges, and cytomixis. However these irregularities are not related to the variation in the aperture pattern of pollen grains. The heteromorphism in the pollen grains observed in C. pulchellum could be a normal condition to which the species is well adapted.     

C-heterochromatin and extra (B) chromosome distribution in six species of the Nabis (Heteroptera, Nabidae) with the modal male karyotype 2n = 16 + XY

The basic male karyotype of the six Nabis species (Heteroptera, Nabidae) is confirmed as being 2n=16+XY. The chromosomes are holokinetic while male meiosis is achiasmatic. The sex chromosomes undergo postreduction and in second metaphase show distance pairing, registered in all nabid species examined so far. Using C-banding technique for the first time in the family Nabidae, the heterochromatin was revealed on chromosomes of six species. The species showed different amount and distribution of C-heterochromatin. Only in Nabis (Dolichonabis) limbatus did the C-bands distribution make possible the identification of every chromosome pair in the karyotype. In other species, C-bands were found in some of the autosomes and the X, localized either interstitially or at telomeres. Only the Y usually showed relative stability ofthe C-banding pattern. In four of six species, extra (B) chromosomes were observed and their behaviour in meiosis described.     

二十五种中国角蝉的染色体(英文)

本文记载了中国25种角蝉的染色体,研究表明染色体的数目、大小及其在减数分裂过程中的行为具有种或属一级的分类特征。该科昆虫染色体的数目变异在n＝5到12之间,众数为n＝11,另外,n＝10的类型也较为普遍。绝大多数种类的性别决定机制为XO型,仅个别种类具有新XY性染色体系统。     

First evidence of sex chromosome pre-reduction in male meiosis in the Miridae bugs (Heteroptera)

The karyotype and male meiosis of Macrolophus costalis Fieber (Insecta, Heteroptera, Miridae) were studied using C-banding, AgNOR-banding and DNA sequence specific fluorochrome staining. The chromosome formula of the species is 2n = 28(24+X1X2X3Y). Male meiotic prophase is characterized by a prominent condensation stage. At this stage, two sex chromosomes, "X" and Y are positively heteropycnotic and always appeared together, while in autosomal bivalents homologous chromosomes were aligned side by side along their entire length, that is, meiosis is achiasmatic. At metaphase I, "X" and Y form a pseudobivalent and orient to the opposite poles. At early anaphase I, the "X" chromosome disintegrates into three separate small chromosomes, X1, X2, and X3. Hence both the autosomes and sex chromosomes segregate reductionally in the first anaphase, and separate equationally in the second anaphase. This is the first evidence of sex chromosome pre-reduction in the family Miridae. Data on C-heterochromatin distribution and its composition in the chromosomes of this species are discussed.     

The spermatogenesis of Dictyocaulus filaria (Nematoda, Trichostrongyloidea)

A cytological study was carried out, using male Dictyocaulus filaria, that revealed the diploid number of chromosomes was 2n = 11 and the sex determining mechanism was XO. The behaviour of the chromosomes in the different stages of meiosis was also investigated. Cross, open ring and rod bivalents were observed in diakinesis. The chromosomes appeared to be acrocentric since they acquired a radial disposition in Metaphase-II. The chiasma frequency was 1 and the nucleolus-organizing region was located at the ends of the chromosomes.     

Nucleolus organizing regions and semi-persistent nucleolus during meiosis in Spartocera fusca (Thunberg) (Coreidae, Heteroptera)

The Coreidae are cytogenetically characterized by possessing holokinetic chromosomes and a pre-reductional type of meiosis. The modal diploid chromosome number of the family is 21, with a pair of m chromosomes and an XO/XX sex chromosome determining system. Spartocera fusca presents 2n=23/24=20+2m+XO/20+2m+XX (male/female). Meiosis follows the general pattern described for heteropterans, with a diffuse stage after pachytene and a particular chromosome arrangement at both metaphase plates. S. fusca presents some cytogenetic peculiarities: the X chromosome shows a secondary constriction in a medial position, which is not a nucleolus organizing region. It has been revealed by in situ hybridization with a rDNA probe that the NOR is localized at the telomeric region of one autosomal pair. Furthermore, during the meiosis of three specimens of S. fusca a semi-persistent nucleolus was detected from early meiotic prophase until telophase II; the presence of this semi-persistent nucleolus together with the long diffuse stage detected in the specimens suggest that a continuous biosynthetic activity is required for spermiogenesis. These observations could be related to differences in the environmental, and therefore, physiological conditions of the analyzed individuals.     

The chromosomes of Hemimerus bouvieri chopard (Dermaptera)

The parasitic insect Hemimerus bouvieri, of rather uncertain systematic position but probably an aberrant member of the order Dermaptera, shows 2n =7, 2n =8. The chromosomes appear to be holocentric. There is an X₁X₂Y sex chromosome mechanism in the male, and a sex-trivalent is formed at meiosis. The two autosomal bivalents seem to be chiasmate and the members of the sex-trivalent may also be held together by chiasmata, but this is uncertain. In general, these cytological features are similar to those of true earwigs (Forficulina).Supported by Public Health Service Grant GM-07212 from the Division of General Medical Seiendes, U.S. National Institutes of Health and by a grant from the Australian Research Grants Committee.     

Aberrant spermatogenesis and the peculiar mechanism of sex determination in Symphypleonan Collembola (Insecta)

Light and electron microscopy evidence have been obtained to describe the peculiar spermatogenesis in the collembolan species Sminthurus viridis and Allacma fusca (Sminthuridae). In these two species, the two sexes differ for the lack of two chromosomes (the sex chromosomes) in males (males, 2n = 10; females, 2n = 12). While oogenesis seems to proceed normally, spermatogenesis is peculiar because the two daughter cells of the first meiotic division have different chromosome numbers (six and four). The cell receiving four chromosomes degenerates, while the cell receiving six chromosomes completes meiosis and produces identical spermatozoa (n = 6). At fertilization, pronuclei with six chromosomes fuse together to form zygotes with 2n = 12. Male embryos must lose two sex chromosomes during the first zygotic mitosis, as all male cells have 2n = 10 chromosomes. The sex chromosome system of these species can be identified as X1X1X2X2:X1X20. Electron microscopy observations show that the same peculiar spermatogenesis occurs also in two others species of the same family, Caprainea marginata and Lipothrix lubbocki. The peculiar sex determination system described is similar but not identical to what is observed in other insect orders, and it may represent an evolutionary step toward parthenogenesis. It is suggested that this peculiar spermatogenesis is common to all Symphypleona.     

Cytology of higher polysomics in Coix gigantea (Poaceae): Pentasomy and hexasomy

Among a natural population of Coix gigantea a pentasomic (2n+3; 2n=23) and a hexasomic (2n+4; 2n=24) were isolated and studied cytologically for the first time. The extra homologous chromosomes in the pentasomic plant did not disturb the behaviour of the rest of the bivalents through meiosis except for the rare occurrence of a few univalents. The majority of PMCs at diakinesis showed nine bivalents and a pentavalent. The various anaphase segregations led to the formation of sub- and super-haploid male gametes with from n–1 (n=9) to n+4 (n=14) chromosomal constitutions. The four extra homologous chromosomes in the hexasomic plant, however, disturbed meiosis leading to sticky chromosomal configurations and sterility. At diakinesis, the majority of the PMCs showed nine bivalents and a hexavalent.The origin of these higher polysomics is considered to be through fusion of male and female super-haploid gametes produced by the trisomics that occurred in large numbers in the population. The occurrence and dominance of nullisomics together with other aneuploids in the diploid population of C. gigantea make it quite certain that the 2n=20 form of the species is at a tetraploid level.     

Cytological evidence of natural hybridization in Brachiaria brizantha Stapf (Gramineae)

Two accessions of Brachiaria brizantha under cytological analysis showed 2 n  = 5x = 45 chromosomes. Pentaploidy probably resulted from natural hybridization between two species that were not closely related: an apomictic tetraploid male (2 n  = 4x = 36), and a sexual diploid female (2 n  = 2x = 18). The lack of affinity between genomes was clearly indicated by asynchrony during meiosis. The haploid genome ( n  = 9) showed unique behaviour, remaining univalent during prophase I and metaphase I, and undergoing sister-chromatid segregation and lagging at anaphase I. The laggard genome did not always reach the poles in time to be included in the telophase nucleus. However, when the inclusion was effective, this genome was distributed peripherally, changing the otherwise spherical nucleus shape. In the second division, the haploid genome behaved similarly, but as there was sister-chromatid segregation during the first division, the chromatids were slow to reach the poles, forming several micronuclei at telophase II. The two accessions were characterized as allo-autopentaploids, with the tetraploid genome (2 n  = 4x = 36) designated as B (from B. brizantha ) and the haploid genome as X, representing a species with a distinct genome having little affinity with the B genome. Thus, the hybrids' genome composition is represented by BBBBX. By comparing their meiotic behaviour with that observed in synthetic hybrids between B. brizantha and B. ruziziensis analysed previously, B. ruziziensis is the putative diploid sexual parent species in these pentaploid accessions.  © 2006 The Linnean Society of London , Botanical Journal of the Linnean Society , 2006, 150 , 441–446.