Sur la structure des chromosomes salivaires de Bilobella massoudi Cassagnau (Collembola: Neanuridae)

This work is a study of the giant salivary chromosomes of a Collembolan species of the family Neanuridae, Bilobella massoudi, recently discovered in North Jugoslavia. The salivary glands of this species have a great number of nuclei (from 100 to 140) containing polytene chromosomes which are very short and easy to spread. Their number is diploid (2n=14), with sometimes partial pairing of the homologues and they are characterized by the presence of broad heterochromatic zones. Chromosomes VI and VII produce ringlike nucleoli. Differences of structure are observed in these chromosomes according to ecological conditions which influence the animal's life.

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Zusammenfassung Wir studieren in dieser Arbeit die Riesenchromosomen eines im Norden Yugoslaviens kürzlich entdeckten Collembolen der Neanuridae-Familie, Bilobella massoudi. Die Speicheldrüsen dieser Art besitzen zahlreiche Kerne (100–140), deren polytäne Chromosomen besonders kurz und leicht ausbreitbar sind. Ihre Zahl ist diploid (2n=14), und sie sind charakterisiert durch die Anwesenheit breiter, Scheiben- oder schärpenförmiger Zonen von negativem Heterochromatin. Zwei dieser Chromosomen (VI und VII) haben ringförmige Nukleolen.Strukturveränderungen wurden bei diesen Chromosomen bemerkt, je nach den ökologischen Bedingungen, denen diese Tiere unterworfen sind.

     

Studies on populations of Folsomia candida (Insecta: Collembola)

Summary Experiments are described that were designed to investigate the effects of food availability and rate of exploitation on the growth and production of populations of Folsomia candida (Willem). In an initial experiment in which there was excess food it was found that increasing the rate of exploitation resulted in increases in both the numerical and biomass productivity of the populations. In a second experiment it was shown that, when there is severe competition for food, the rate of exploitation does not affect either the biomass or the numerical production. It is concluded that the effect of overcrowding, in the form of competition for space, does contribute to the growth in numbers of populations, but that the supply of food plays a more important role in regulating the population. Anomalous results, showing that exploitation has a lesser effect when there is severe competition for food, are discussed.     

Dicyrtotnina and Ptenothrix (Insecta:Collembola) of the Solomon Islands

This paper deals primarily with the collembolan species of the subfamily Dicyrtominae collected during the Royal Society Expedition to the Solomon Islands of 1965 by P. N. Lawrence, supplemented by material from these islands collected by Dr and Mrs P. J. M. Greenslade, all of which is in the British Museum (Natural History). Additional supporting material described here has been derived from the Noona Dan Expedition of the Zoological Museum, Copenhagen and from the Bernice P. Bishop Museum, Hawaii. I should like to express my thanks to the individuals and Museum sconcerned.     

Das Doppelauge vonEntomobrya muscorum Nicolet (Insecta,Collembola)

Zusammenfassung Der bodenlebende CollembolaEntomobrya muscorum hat an jeder Kopfseite ein loses Aggregat von acht Ommatidien, von denen zwei einen deutlich kleineren Linsendurchmesser aufweisen. Die sechs großen Ommatidien werden als Haupt-, die zwei kleinen als Nebenaugen bezeichnet. Beide Ommatidientypen haben verschieden gebaute Rhabdome, so daß der Komplex ein Doppelauge darstellt. Es wird der Bau der Hauptaugen geschildert. Ihr sensibler Teil setzt sich aus acht Retinulazellen zusammen, die ein offenes Rhabdom in zwei Lagen bilden. Eine zentrale sechste Zelle in der distalen Schicht weicht in ihrer Feinstruktur deutlich von den übrigen ab. Die Rhabdome beider Ommatidientypen werden miteinander verglichen, und ihre funktionelle Bedeutung vor allem in Hinblick auf eine mögliche Arbeitsteilung für eine Polarisationswahrnehmung wird erörtert. Es wird kurz die phylogenetische Bedeutung dieser Augen für die Insekten und die Collembolen selbst angeschnitten.

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The double eye ofEntomobrya muscorum nicolet (Insecta, Collembola)

Summary The ground living CollembolaEntomobrya muscorum has on each side of the head eight circular ommatidia in an arrangement characteristic of the species. Of these two have a distinctly smaller lens. The six big ommatidia are called primary eyes, the two small ones accessory eyes. The two types of ommatidia have different rhabdom structures, so justifying the term double eye. The structure of the primary eyes is described. The photosensitive part is constructed of eight retinula cells which form an open rhabdom in two layers. The central sixth cell in the distal layer is quite different from the others. The rhabdoms of both types are compared. The possible function of the accessory eyes in perception of the e-vector is discussed. The phylogenetic significance of these eyes for the Insecta and the Collembola is considered.

     

A New Species of Halophilous Collembola (Insecta) from Korea

Three species of interstitial Collembola in Entomobryidae were identified from South Korean coast. One of them, Sinella (Coecobrya) maritima, is new to science. So far 21 halophilous species in 10 families of Collembola, including the new species in this paper, were reported from the Korean peninsula.     

B chromosomes in Sternorrhyncha (Hemiptera, Insecta)

In the hemipteroid insects of the suborder Sternorrhyncha, B chromosomes are relatively common in comparison with other suborders of Hemiptera. However, the occurrence of supernumerary chromosomes is restricted, in most cases, to several genera or closely related species. At least in some species of Psylloidea with the XY sex determination system, a mitotically stable B chromosome integrated into an achiasmatic segregation system with the X, and became fixed as a Y chromosome. In some Aphidoidea with a multiple X system of sex determination, B chromosomes appear to be in fact non-functional X chromosomes. Supernumerary chromosomes thus probably play an important role in the evolution of sex determination systems in Sternorrhyncha.     

A novel method of self-righting in the springtail Sminthurus viridis (Insecta: Collembola)

Photographic evidence shows that the ventral tube can be used as a tentacle-like mechanical aid for self-righting from an inverted position. It is proposed that the extraordinary length of the vesicles of the ventral tube in globular springtails has been evolved in order to combat postural instabilities resulting from spherical symmetry of body form.     

DNA replication in polytene chromosomes: Similarity of termination patterns in somatic and germ-line derived polytene chromosomes of Anopheles stephensi liston (Diptera: Culicidae)

DNA replication is initiated in the ovarian follicles of the anautogenous Culicid Anopheles stephensi in response to a blood meal. The chronology of nurse cell polytene chromosome³H-thymidine labelling patterns has been defined and the terminal labelling patterns of the nurse cell and larval salivary gland polytene X-chromosomes have been compared and found to be essentially similar.     

Interspecific comparisons of polytene chromosomes in the genus Parasarcophaga (Sarcophagidae: Diptera)

A comparison of the polytene chromosomes of Parasarcophaga argyrostoma, P. ruficornis, P. misera and P. knabi, is presented. There is close resemblance in the banding patterns of the four species. Two independent paracentric inversions in chromosome arm IIR, a small paracentric inversion in chromosome arm IIIR and a pericentric inversion in chromosome V were found to be fixed as interspecific differences.     

Ecology of Cryptopygus sverdrupi (Insecta: Collembola) from Dronning Maud Land,Antarctica

Summary Observations on the ecology of Cryptopygus sverdrupi Lawrence (Collembola, Isotomidae) were made with specimens from the Mühlig-Hofmannfjella, Dronning Maud Land, Antarctica. At an elevation of 1600 m a.s.l. the species was numerous in association with the green alga Prasiola on gravel fields and in crevices of large boulders. The distribution of size-classes in field samples suggested that the population comprised several overlapping generations. Growth and development is probably very slow due to long winters and daily periods of subzero temperatures in their microhabitat during the summer. Specimens collected in mid-January had a mean supercooling point of-24.6°C with small individual variations. The lack of high supercooling points in the summer suggests that the springtails feed on a nuleatorfree diet. The ability to supercool was increased during prolonged starvation and acclimation at 0,-4 and-8°C. Glycerol and other potential low molecular weight cryoprotective substances were demonstrated in specimens acclimated at-4 and-8°C. The species possessed a relatively high tolerance to desiccation.Publication No. 81 of the Norwegian Antarctic Research Expeditions (1984/85)     

Ultrastructure of the male accessory glands ofAllacma fusca(Insecta, Collembola)

The accessory glands ofAllacma fusca(L.) (Insecta, Collembola, Sminthuridae) consist of a series of secretory units that are arranged in parallel and open into the ejaculatory duct. Each unit is composed of microvillate cells stacked around a common cavity. Basal cells are involved in ion-control of fluids from the hemocoel to the cavity. The intermediate and apical cells, which have a laminar appearance and contain many microtubules, are involved in the structural integrity of the unit. Supporting cells ensheath the most apical cells. Large openings in the cuticle allow the gland secretion to flow into the ejaculatory duct lumen. These openings are protected by a porous cuticle different from that lining the epithelium of the ejaculatory duct. Conspicuous muscle fibers run along the lateroventral side of the ejaculatory duct beneath the insertion of the accessory glands. The fine structure of the accessory glands indicates that they are type I ectodermic glands as defined by Noirot & Quennedey (1974). Their function could be to control the fluidity of the material for spermatophore formation and to ensure the proper physiological conditions for spermatozoa stored in the ejaculatory duct lumen.     

High diversity and community permeability: the riparian Collembola (Insecta) of a Pyrenean massif

This work deals with the structure of Collembolan communities in riparian habitats. Sixty samples collected along running waters in a Pyrenean massif have been analysed. Diversity was much higher than for any comparable habitat studied in the literature. The proportion of rare species was particularly high, and explained a large part of the observed diversity. The contribution of specialized hydrophilous species to overall diversity was low: they were 5 times less numerous than non-hydrophilous species for a similar global abundance. Correspondence analysis showed that the riparian community was loosely structured, without any strong determining factor. Epigeomorphic species of hydrophilous Collembola were, however, clustered in a well-defined group. The forest type, of major importance for soil fauna diversity in the area, was a poor predictor of diversity in the riparian habitats. Conversely, richness was significantly related to distance from water, in spite of the samples having been all collected from permanently water-saturated substrates. The importance of non-hydrophilous species for the diversity of riparian habitats along running water is interpreted as reflecting the ecological permeability of the hydrophilous community, resulting from the spatial organisation of the habitat in narrow strips, and its frequent disturbance by flooding. Finally, the riparian habitat may act as a refuge for a significant proportion of the soil species affected by reafforestation, presently the most severe disturbance of Pyrenean ecosystems.     

Localization of phaseolin genes in the polytene chromosomes ofPhaseolus coccineus (Leguminosae)

The location of the genes for the major storage protein, phaseolin, was determined in the polytene chromosomes of the embryo-suspensor ofPhaseolus coccineus, cv. Hammond's Dwarf Scarlett, byin situ hybridization with a³⁵S-labelled cloned probe. The genes were adjoined to chromosome pair no. 3. The distribution of the label indicates a puffed state of the sites during embryogenesis of the legume studied. The location of the phaseolin genes was certified by hybridization of a ribosomal DNA probe to the polytene chromosomes, because their position is well known.     

Structural paradox of polytene chromosomes

The observation of thick chromatin fibers in interbands of Dipteran polytene chromosomes suggests that there should be 5 to 10 times more mass and DNA in interbands than is commonly thought to be present. To resolve this paradox, the chromatin content of interbands was estimated, using whole-mounted polytene chromosomes from Drosophila melanogster. Densitometry of high voltage electron microscopic negatives provides an estimate of less than 4:1 for the average ratio of cross-sectional dry mass (or mass per unit chromosome length) of bands relative to interbands. This ratio, combined with an estimate of the length of chromosome composed of interbands, indicates that at least 26% of chromosome mass is contributed by interband chromatin. Since DNA comprises a similar proportion of chromatin mass in bands and interbands (Laird et al., 1980b), these data imply that DNA sequences in interbands represent at least 26% of the euchromatic genome of D. melanogaster. This result calls for reinterpretation of some of the genetic and molecular data from Diptera. The discrepancy between this higher estimate of interband mass and DNA, and previous estimates of 3-5%, is discussed. One possibility is that previous measurements were made on prominent interbands, which are proposed here to be in regions that are delayed in DNA replication. Such interbands would be reduced in polyteny and DNA content compared with the average interband region. The concept of local variations in polyteny is also used here to explain major differences in the cross-sectional mass of bands. This leads to a revised model of polytene chromosomes in which at least three levels of polyteny, rather than one or two levels, can be present within one euchromatic region.     

Chromomeric organization of polytene chromosomes

This is a review summarizing work carried out at the Laboratory of Molecular Cytogenetics in recent years. Problems of genetic organization of bands, interbands and puffs as well as intercalary heterochromatin and position effect variegation are discussed from the point of view of the dynamic model of polytene chromosome organization.     

Malpighian tubule polytene chromosomes of Culex quinquefasciatus (Diptera,Culicinae)

Dipteran polytene chromosomes provide an excellent model for understanding in species complexes, as well as for structural and functional cytogenetics. The status of species in the Culex pipiens complex is controversial and the use of polytene chromosomes for cytogenetic analysis in the subfamily Culicinae has been difficult because of methodological problems. In this study, Malpighian tubule polytene chromosomes were obtained from young (0 to 12 h, 20 C) and old (20 to 42 h, 28 C) laboratory-bred C. pipiens quinquefasciatus pupae. The chromosome maps for this species were constructed and compared with published data for C. pipiens pipiens and C. p. quinquefasciatus. Although the banding patterns were conserved between subspecies, analysis of the structural variations in the bands and interbands revealed differences apparently related to the physiological stage and ecogeographical strain. The organization of the centromeric regions in larval and pupal chromosomes showed greater similarity to each other than did those of pupal and adult chromosomes. The use of pupal polytene chromosomes for in situ hybridization with vector competence probes is discussed.     

Studies on polytene chromosomes of Smittia parthenogenetica (Chironomidae,Diptera)

In polytene chromosome II of Smittia parthenogenetica a heterochromatin insertion has been studied which is derived from a germ-line limited chromosome section (Bauer, 1970). This insertion is C-banding positive, late replicating, inactive in RNA synthesis, fluoresces brightly with quinacrine and is polytenized. After N-banding a major part of the heterochromatin insertion is N-banding negative, whereas in the centre of the insertion a N-banding positive body is present. The properties of the N-positive and N-negative parts of the inserted heterochromatin section are compared with the properties of the heterochromatin of Chironomus melanotus and Drosophila melanogaster. It is concluded that the heterochromatin insertion consists of two different heterochromatin types and it is discussed whether the N-banding positive part within the insertion represents a heterochromatin type which is underreplicated during polytenization.Dedicated to Professor Dr. Hans Bauer in honour of his 75th birthday on September 27, 1979