Sprunghafter Anstieg von Brutst?rungen bei H?hlenbrütern

Summary From 1986 onwards increasing numbers of Great Tits (Parus major) and Blue Tits (Parus caeruleus) were registered breeding on empty nests. In 1987 and 1988 up to 4% of all found sitting on nests did not lay any egg. The rate of breeding failures might be considerably higher because many individuals breeding on empty nests could have been overlooked by weekly checks of the nest boxes.     

Chick integrin alpha V subunit molecular analysis reveals high conservation of structural domains and association with multiple beta subunits in embryo fibroblasts.

We have cloned and characterized a chick homologue of the human vitronectin receptor alpha subunit (alpha v) whose primary sequence is 83% identical with its human counterpart but less than 40% identical with any other known integrin alpha subunit. Comparison of the chick and human sequences reveals several highly conserved regions, including the cytoplasmic domain. The putative ligand binding domain contains alpha v-specific residues that may contribute to ligand binding specificity. These are concentrated in three regions that are located before and between the first three Ca2+ binding domains. Polyclonal antibodies raised against two peptides deduced from the putative cytoplasmic and extracellular domains of the chick alpha v sequence recognize specifically integrin heterodimers in chick embryo fibroblasts. At least three putative beta subunits coimmunoprecipitate with the chick alpha v subunit. In addition to a protein with the same molecular weight as beta 3 (94K), protein bands of Mr 84K and 110K are also coprecipitated. By successive immunodepletions, we demonstrate that this latter Mr 110K subunit is beta 1, which appears to be one of the alpha v-associated subunits in chick embryo fibroblasts.     

Sequence complexity of poly(A) RNA fromPhysarum polycephalum

Summary Poly(A) RNA from S phase, G₂ phase and starved macroplasmodia of Physarum contain mRNA sequences which when translated in vitro, yield similar patterns of polypeptides after fluorography.Reassociation of nick-translated DNA (Cot) allows the isolation of highly labeled single copy DNA which, after saturation hybridization with poly(A) RNA, gives values of 23% for growth and 17% for starvation.Homologous cDNA/poly(A) RNA hybridization reactions (Rot) indicate that 22–28% of the genome is transcribed during growth and 12% during starvation and that about half of the cDNA reacts with 0.1% of the genome and could represent 50–80 RNA species, each present in about 1,000 copies per nucleus. Up to 25,000 different RNA species, 1–5 copies each per nucleus, are estimated to be present during growth, and about 15,000 during starvation. Heterologous cDNA/poly(A) RNA hybridization reactions (Rot) indicate that the RNA sequences in S and G₂ phase of the cell cycle are similar, with RNA sequences being more abundant in G₂ phase.During starvation about 25% of the sequences present during growth cannot be detected and those sequences present during growth have become diluted during starvation.     

Specificity of Insertion by the Translocatable Tetracycline-Resistance Element Tn10

Genetic analysis of 131 independent transpositions of the tetracycline-resistance element Tn10 from a single site in phage P22 into the histidine operon of Salmonella typhimurium reveals that Tn10 insertions are not randomly distributed along this chromosomal target. The insertions occur in 22 different "clusters"; insertions within each cluster are very tightly linked in recombination tests. Tn10 insertions are not evenly distributed among the identified clusters. The existence of these clusters suggests that this chromosomal target contains particular genetic signals that guide Tn10 to particular preferred positions for insertion. Insertions within each cluster occur in both orientations with roughly equal frequency.--The relationship among different insertions within each cluster has been examined. The resolution of genetic mapping places an upper limit of about 50 basepairs on the distance between different insertions within a cluster. Different insertions within a cluster usually have the same reversion frequency; however, heterogeneity in reversion frequency has been detected in at least two clusters. For most clusters, the available data are consistent with the simple possibility that all insertions within a cluster are at identical positions; however, the data do not exclude other possibilities.     

Figure-ground discrimination by relative movement in the visual system of the fly

The visual system of the fly performs various computations on photoreceptor outputs. The detection and measurement of movement is based on simple nonlinear multiplication-like interactions between adjacent pairs and groups of photoreceptors. The position of a small contrasted object against a uniform background is measured, at least in part, by (formally) 1-input nonlinear flicker detectors. A fly can also detect and discriminate a figure that moves relative to a ground texture. This computation of relative movement relies on a more complex algorithm, one which detects discontinuities in the movement field. The experiments described in this paper indicate that the outputs of neighbouring movement detectors interact in a multiplication-like fashion and then in turn inhibit locally the flicker detectors. The following main characteristic properties (partly a direct consequence of the algorithm's structure) have been established experimentally: a) Coherent motion of figure and ground inhibit the position detectors whereas incoherent motion fails to produce inhibition near the edges of the moving figure (provided the textures of figure and ground are similar). b) The movement detectors underlying this particular computation are direction-insensitive at input frequencies (at the photoreceptor level) above 2.3 Hz. They become increasingly direction-sensitive for lower input frequencies. c) At higher input frequencies the fly cannot discriminate an object against a texture oscillating at the same frequency and amplitude at 0° and 180° phase, whereas 90° or 270° phase shift between figure and ground oscillations yields maximum discrimination. d) Under conditions of coherent movement, strong spatial incoherence is detected by the same mechanism. The algorithm underlying the relative movement computation is further discussed as an example of a coherence measuring process, operating on the outputs of an array of movement detectors. Possible neural correlates are also mentioned.     

A special class of nonlinear interactions in the visual system of the fly

Flies can detect a small object in front of a randomly contrasted background if the object undergoes small motions. The effect was investigated in fixed flying flies under open-loop conditions. The results suggest that nonlinear inhibitory interactions underly this elementary case of figure-ground discrimination.     

Visually induced height orientation of the fly Musca domestica

The visually controlled height orientation of fixed flying flies (Musca domestica) was investigated. The flight lift force measured by a transducer drives the vertical motion of a panorama. The dynamical conditions of the free flight are electronically simulated for the fly with respect to this degree of freedom of motion. In most of the experimentally investigated cases the panorama consists of a horizontally oriented narrow dark stripe on a bright background. The fly orientates with respect to the stripe, transporting it into a stable fixation position just below the equatorial plane of its compound eyes. It is experimentally demonstrated that the formalism of the linearized theory of the pattern induced flight orientation — Poggio and Reichardt (1973a) — can be applied to describe the height orientation of the fly. The experimental evidence concerning the simultaneous perception of stripes moving in a well defined manner in front of each of the two compound eyes is consistent with the hypothesis that the two halves of the visual system are perceptually additive.     

MOLECULAR DELINEATION OF SPECIES AND SYNGENS IN VOLVOCACEAN GREEN ALGAE (CHLOROPHYTA)1

Two species of the colonial green flagellate family Volvocaceae are worldwide in distribution yet exhibit contrasting species structure. Geographically disparate isolates of Gonium pectorale Mueller can interbreed while isolates of Pandorina morum Bory behave quite differently. More than 20 sexually isolated subpopulations occur within this species; these have been termed “syngens” (sensu Sonneborn). Because prezygotic barriers to mating cause intersyngen pairings to fail, breeding analyses cannot be used to estimate genetic relatedness among the syngens of P. morum. DNA comparisons provide an alternative method of assessing genetic relatedness. We compared the nucleotide sequence of the internal transcribed spacer (ITS) region of the nuclear ribosomal repeat among clones of P. morum and of G. pectorale. Members of syngens of P. morum with distribution restricted to one small geographical area show great similarity. Likewise, members of any syngen of worldwide distribution show near uniformity, even those from different continents. However, the ITS sequence of each syngen differs from that of other syngens. In contrast, G. pectorale, which has an ITS region that is remarkably uniform throughout the world, appears to consist of a single syngen within North America and Europe by mating tests. The molecular data are in complete conformity with previous syngen assignment. Because the latter is based on mating affinity, with two complementary mating types per syngen, the evolution of new mating type pairs appears to be the basis of microevolution in these algae. We infer that either P. morum is a more ancient species than G. pectorale or that P. morum has a less stable genome. In either case, the biogeographic distribution of certain syngens may reflect climatological changes of the past.     

The Burden of Research on Trauma for Respondents: A Prospective and Comparative Study on Respondents Evaluations and Predictors

The possible burden of participating in trauma research is an important topic for Ethical Committees (EC''s), Review Boards (RB''s) and researchers. However, to what extent research on trauma is more burdensome than non-trauma research is unknown. Little is known about which factors explain respondents evaluations on the burden: to what extent are they trauma-related or dependent on other factors such as personality and how respondents evaluate research in general? Data of a large probability based multi-wave internet panel, with surveys on politics and values, personality and health in 2009 and 2011, and a survey on trauma in 2012 provided the unique opportunity to address these questions. Results among respondents confronted with these events in the past 2 years (N = 950) showed that questions on trauma were significantly and systematically evaluated as less pleasant (enjoyed less), more difficult, but also stimulated respondents to think about things more than almost all previous non-trauma surveys. Yet, the computed effect sizes indicated that the differences were (very) small and often meaningless. No differences were found between users and non-users of mental services, in contrast to posttraumatic stress symptoms. Evaluations of the burden of previous surveys in 2011 on politics and values, personality and health most strongly, systematically and independently predicted the burden of questions on trauma, and not posttraumatic stress symptoms, event-related coping self-efficacy and personality factors. For instance, multiple linear regression analyses showed that 30% of the variance of how (un)pleasant questions on trauma and life-events were evaluated, was explained by how (un)pleasant the 3 surveys in 2011 were evaluated, in contrast to posttraumatic stress symptoms (not significant) and coping self-efficacy (5%). Findings question why EC''s, RB''s and researchers should be more critical of the possible burden of trauma research than of the possible burden of other non-trauma research.