Anna Maryańska-Nadachowska

Holocentric chromosomes in meiosis. I. Restriction of the number of chiasmata in bivalents

The number of chiasmata in bivalents and the behaviour of chiasmata during the meiotic divisions were studied in Psylla foersteri (Psylloidea, Homoptera). Two chiasmata with a frequency of 97% and one or three chiasmata with frequencies of 2% and 0.9%, respectively, were observed in the largest bivalent in male meiosis. Meiosis was normal for the largest bivalents with one or two chiasmata, whereas bivalents with three chiasmata were not capable of completing anaphase I because of their inability to resolve the chiasma located in the middle. Consequently, the bivalent was seen as a laggard joining together two metaphase II daughter plates. Apparently, cells of this kind are eliminated. Inability to resolve the chiasma situated in the middle is attributed to the condensation process, which is unable to change the spatial orientation of successive chiasma loops in holocentric bivalents so that chiasma loops would be arranged perpendicular to each other at metaphase I. Thus they retain their parallel orientation from diplotene to metaphase I. Consequently, sister chromatid cohesion is exposed for release only in the outermost chiasmata but the chiasma in the middle continues to interlock the chromosomes in the bivalent. The elimination of the cells carrying bivalents with more than two chiasmata creates a strong selection against the formation of more than two chiasmata in holocentric bivalents.

The origin of the achiasmatic XY sex chromosome system in Cacopsylla peregrina (Frst.) (Psylloidea, Homoptera)

The status of an extra univalent, if it is a B chromosome or an achiasmatic Y chromosome, associating with the X chromosome in male meiosis of Cacopsylla peregrina (Frst.) (Homoptera, Psylloidea) was analysed. One extra univalent was present in all males collected from three geographically well separated populations, it was mitotically stable, and showed precise segregation from the X chromosome. These findings led us to propose that the univalent represents in fact a Y chromosome. The behaviour of the X and Y chromosomes during meiotic prophase suggested that their regular segregation was based on an achiasmatic segregation mechanism characterised by a ‘touch and go’ pairing of segregating chromosomes at metaphase I. To explain the formation of the achiasmatic Y within an insect group with X0 sex chromosome system, it was suggested that the Y chromosome has evolved from a mitotically stable B chromosome that was first integrated into an achiasmatic segregation system with the X chromosome, and has later become fixed in the karyotype as a Y chromosome.

A comparative study of genome organization and inferences for the systematics of two large bushcricket genera of the tribe Barbitistini (Orthoptera: Tettigoniidae: Phaneropterinae)

BackgroundPoecilimon and Isophya are the largest genera of the tribe Barbitistini and among the most systematically complicated and evolutionarily intriguing groups of Palearctic tettigoniids. We examined the genomic organization of 79 taxa with a stable chromosome number using classical (C–banding, silver and fluorochrome staining) and molecular (fluorescence in situ hybridization with 18S rDNA and (TTAGG)n telomeric probes) cytogenetic techniques. These tools were employed to establish genetic organization and differences or similarities between genera or species within the same genus and determine if cytogenetic markers can be used for identifying some taxonomic groups of species.ResultsDifferences between the karyotypes of the studied genera include some general changes in the morphology of the X chromosome in Isophya (in contrast to Poecilimon). The number of major rDNA clusters per haploid genome divided Poecilimon into two main almost equal groups (with either one or two clusters), while two rDNA clusters predominated in Isophya. In both genera, rDNA loci were preferentially located in the paracentromeric region of the autosomes and rarely in the sex chromosomes. Our results demonstrate a coincidence between the location of rDNA loci and active NORs and GC-rich heterochromatin regions. The C/DAPI/CMA3 bands observed in most Poecilimon chromosomes suggest the presence of more families of repetitive DNA sequences as compared to the heterochromatin patterns in Isophya.ConclusionsThe results show both differences and similarities in genome organization among species of the same genus and between genera. Previous views on the systematics and phylogenetic grouping of certain lineages are discussed in light of the present cytogenetic results. In some cases, variation of chromosome markers was observed to correspond with variation in other evolutionary traits, which is related to the processes of ongoing speciation and hybridization in zones of secondary contact. It was concluded that the physical mapping of rDNA sequences and heterochromatin may be used as an additional marker for understanding interspecific relationships in these groups and their routes of speciation.

Achiasmate segregation of a B chromosome from the X chromosome in two species of psyllids (Psylloidea, Homoptera)

The segregation of a B chromosome from the X chromosome was studied in male meiosis in two psyllid species, Rhinocola aceris (L.) and Psylla foersteri (Flor.) (Psylloidea, Homoptera). The frequency of segregation was determined from cells at metaphase II. In R. aceris, the B chromosome was mitotically stable and segregated quite regularly from the X chromosome in four geographically distant populations, while it showed less regular, but preferential segregation in one population. This was attributed to the presence of B chromosome variants that differ in their ability to interact with the X chromosome in segregation. In P. foersteri, the B chromosome was mitotically unstable and segregated preferentially from the X chromosome in spermatocyte cysts, which displayed one B chromosome in every cell. Behaviour of the B chromosome and X chromosome univalents during meiotic prophase and at metaphase I in R. aceris, and during anaphase I in P. foersteri suggested that the regular segregation resulted from the incorporation of B chromosomes in achiasmate segregation mechanisms with the X chromosome in the place occupied by the Y chromosome in species with XY system. The regular segregation of a B chromosome from the X chromosome may obscure the distinction of a B chromosome and an achiasmate Y chromosome in some cases.

Holocentric chromosomes in meiosis. II. The modes of orientation and segregation of a trivalent

The modes of orientation and segregation of the sex chromosome trivalent X1X2Y in male meiosis of Cacopsylla mali (Psylloidea, Homoptera) were analysed. Males with an X1X2Y sex chromosome system coexist with males displaying a neo-XY system in populations of this species. The fusion chromosome resulting in the formation of a trivalent in meiosis originates from the fusion of an autosome with the neo-Y chromosome. In the majority of metaphase I cells (92.4%) the X1X2Y trivalent showed co-orientation; X1 and X2 chromosomes oriented towards one pole whereas the Y oriented towards the opposite pole. In the rest of the cells (7.6%) the trivalent with subterminal chiasmata was oriented parallel to the equatorial plane. From this orientation the trivalent produced triple chromatids joined together by undivided telomeric parts of chromosomes and hence by sister chromatid cohesion at anaphase I. In the majority of metaphase II cells the orientation of triple chromatids suggested the production of unbalanced gametes. However, in a small number of cells (1.7%) the trivalent showed co-orientation of X1X2 with Y. Both the first division and second division co-orientations, or 94.1% of divisions as a whole, were estimated to yield balanced gametes, containing either X1 and X2 chromosomes or Y chromosome. It was concluded that, since the triple chromatid contained undivided telomere regions at metaphase II, which divided at anaphase II, the orientation of the trivalent with its longitudinal axis parallel to the equatorial plane in metaphase I also represents co-orientation and results in pre-reduction. The existence of post-reductional behaviour of holocentric bivalents and multivalents is discussed.

Cytogenetic variability of European tettigoniinae (Orthoptera, Tettigoniidae); karyotypes, C- and Ag-NOR-banding.

Karyotypes, C-banding pattern and localization ofnucleolus organizer regions (NORs) in 34 European species and subspecies belonging to the subfamily Tettigoniinae are described (the karyotypes of 26 species for the first time). In the males chromosome numbers vary from 2n=33 to 2n=23 and Fundamental Numbers (FN) from 36 to 27. The highest number of chromosomes for this group, 2nmale=33 (FN=33), was found in Psorodonotus illyricus macedonicus. In species belonging to genera Decticus, Metrioptera, Anterastes, Bucephaloptera, Parapholidoptera, and Eupholidoptera, as well as in Pholidoptera frivaldskyi and Pholidoptera griseoaptera, a karyotype of2n=30+XO (FN=31) was found. Ph. macedonica and Ph. aptera aptera are characterized by 2n=28+X0 (FN=31). In species from genera Drymadusa (D. dorsalis limbata) 2n=26+X0: FN=30 and Gampsocleis (G. abbreviata), karyotypes of 2n=22+X0 (FN=36) were found. Ph. macedonica and Ph. aptera aptera as well as G. abbreviata differ in karyotypes from other representatives of these genera. New data confirmed that Robertsonian fusions and tandem fusions played the most important role in the evolution of the chromosome set in Tettigoniinae. Cytogenetic similarities and differences between particular species are discussed.

Mediterranean Species of the Spittlebug Genus Philaenus: Modes of Chromosome Evolution

Abstract The evolution of karyotypes and sex determination system of Philaenus Stål (Auchenorrhyncha: Aphrophoridae) species is studied here in detail. The most plausible scenario of chromosomal rearrangements accompanying phylogenetic differentiation in Philaenus is advanced. It is postulated that the ancestral karyotype of Philaenus was 2n = 24 + X0. Karyotype changes occurred several times independently in the genus. The karyotype of 2n = 22 + X0 (P. spumarius and P. tesselatus) originated from 2n = 24 + X0 by fusion between two autosomal pairs. The neo—XY system (P. arslani, P. loukasi, P. signatus, P. maghresignus, and P. tarifa) also originated from the 24 + X0 karyotype by means of independent fusions between autosomes and the original X chromosome. The neo—X1X2Y system (P. italosignus) evolved from the 2n = 22 + neo—XY karyotype by an additional fusion between the Y chromosome and one more autosomal pair. The neo—XnY system of P. italosignus is the first reported case of an evolutionarily fixed multiple sex chromosome system in Auchenorrhyncha.

Meiotic Karyotypes in Males of Nineteen Species of Psylloidea (Hemiptera) in the Families Psyllidae and Triozidae

Meiotic karyotypes in males of 16 species (assigned to 9 genera and 7 subfamilies) ofthe family Psyllidae and 3 species (assigned to 3 genera of the subfamily Triozinae) of the family Triozidae are described for the first time. The first data on the genus Ligustrinia are presented. All the species were shown to exhibit the modal karyotype for psyllids, 2n = 24 + X, except Bactericera nigricornis and Arytainilla spartiophila, in which 2n = 24 + XY and 2n = 22 + X were found, respectively. The karyotype of Ctenarytaina eucalypti (Psyllidae, Spondyliaspidinae) was reinvestigated, and the karyotype 2n = 10 + X, characteristic of Spondyliaspidinae, was revealed. The karyotypes ofStrophingia fallax, S. arborea, and Craspedolepta topicalis were studied using the C-banding technique.

Cytogenetic variability of the genus Saga Charp. (Orthoptera, Tettigoniidae, Saginae): heterochromatin differentiation

Abstract Chromosome complements of Saga hellenica, S. natoliae, and S. rhodiensis consist of 2n = 28 + XO in males and 2n = 28 + XX in females (FN = 32 and 34, respectively). Robertsonian fusions and tandem fusion play the most important role in the evolution of the chromosome set in Saginae. The chromosomes of three species of Saginae were analyzed by four different staining methods: C-banding, Ag-NOR, DAPI and CMA3. The studied species show a uniform karyotype with differences in constitutive heterochromatin content. C-banding patterns plus fluoro-chrome staining shows differences between paracentomeric, interstitial, and telomeric segments, as well as the heterochromatin associated with NORs.

New data on karyotypes and the number of testicular follicles in the psyllid families Aphalaridae, Psyllidae, Carsidaridae and Triozidae (Homoptera, Psylloidea)

SUMMARYKaryotypes of 13 species from Taiwan (9 species) and from Holland (4 species) belonging to the families Aphalaridae, Psyllidae, Homotomodae, Carsidaridae, and Triozidae are described for the first time. Karyotypes of Bactericera maura, Cacopsylla hippophaeus, Dynopsylla pinnativena, Leptynoptera sulfurea, Macrohomotoma gladiata, Paurocepbala chonchainensis, P. sauteri, P. trematos, Sympauropsylla triozoneura, and Tenaphalara acutipennis were 2n = 24 + X0. However, the karyotypes of three species are as follows: Cacopsylla sorbi 2n = 20 + XY, Heteropsylla cubana 2n = 24 + XY, and Trioza remota 2n= 14+ X0.