Lichen species richness is highest in non-intensively used grasslands promoting suitable microhabitats and low vascular plant competition

Lichens are very sensitive to habitat changes and their species richness is likely to decline under intensive land use. Currently, a comprehensive study analyzing lichen species richness in relation to land-use types, extending over different regions and including information on habitat variables, is missing for temperate grasslands. In three German regions we studied lichen species richness in 490 plots of 16 m2 representing different land-use types, livestock types, and habitat variables. Due to the absence of low-intensity pastures and substrates such as woody plants, deadwood and stones, there were no lichens in the 78 plots in Schorfheide-Chorin. In the two other regions, the richness of lichen species was 45 % higher in pastures than in meadows, and 77 % higher than in mown pastures, respectively. Among the pastures, the richness of all lichen species was on average 10 times higher in sheep-grazed pastures than in the ones grazed by cattle or horses. On average, the richness of all lichen species increased by 3.3 species per additional microhabitat. Furthermore, the richness of corticolous lichens increased by 1.2 species with 10 % higher cover of woody plants, lignicolous lichen species richness increased by 4.8 species with 1 % higher cover of deadwood, and saxicolous lichen species richness increased by 1.0 species with 1 % higher cover of stones. Our findings highlight the importance of low-intensity land use for lichen conservation. In particular, the degradation of grasslands rich in microhabitats and the destruction of lichen substrates by intensification, and conversion of unfertilized pastures formerly grazed at low intensity to meadows should be avoided to maintain lichen diversity.

How to be in a good shape? The influence of clone morphology on cell competition

Cell competition is a conserved mechanism where slow proliferating cells (so called losers) are eliminated by faster proliferating neighbors (so called winners) through apoptosis.(1) It is an important process which prevents developmental malformations and maintains tissue fitness in aging adults.(2) Recently, we have shown that the probability of elimination of loser cells correlates with the surface of contact between losers and winners in Myc-induced competition.(3) Moreover, we have characterized an active mechanism that increases the surface of contact between losers and winners, hence accelerating the elimination of loser cells. This is the first indication that cell shape and mechanics can influence cell competition. Here, we will discuss the consequence of the relationship between shape and competition, as well as the relevance of this model for other modes of competition.

Tissue Crowding Induces Caspase-Dependent Competition for Space.

Regulation of tissue size requires fine tuning at the single-cell level of proliferation rate, cell volume, and cell death. Whereas the adjustment of proliferation and growth has been widely studied [1, 2, 3, 4 and 5], the contribution of cell death and its adjustment to tissue-scale parameters have been so far much less explored. Recently, it was shown that epithelial cells could be eliminated by live-cell delamination in response to an increase of cell density [6]. Cell delamination was supposed to occur independently of caspase activation and was suggested to be based on a gradual and spontaneous disappearance of junctions in the delaminating cells [6]. Studying the elimination of cells in the midline region of the Drosophila pupal notum, we found that, contrary to what was suggested before, Caspase 3 activation precedes and is required for cell delamination. Yet, using particle image velocimetry, genetics, and laser-induced perturbations, we confirmed [ 6] that local tissue crowding is necessary and sufficient to drive cell elimination and that cell elimination is independent of known fitness-dependent competition pathways [ 7, 8 and 9]. Accordingly, activation of the oncogene Ras in clones was sufficient to compress the neighboring tissue and eliminate cells up to several cell diameters away from the clones. Mechanical stress has been previously proposed to contribute to cell competition [ 10 and 11]. These results provide the first experimental evidences that crowding-induced death could be an alternative mode of super-competition, namely mechanical super-competition, independent of known fitness markers [ 7, 8 and 9], that could promote tumor growth.

Cell Competition During Growth and Regeneration

Tissue growth and regeneration are autonomous, stem-cell-mediated processes in which stem cells within the organ self-renew and differentiate to create new cells, leading to new tissue. The processes of growth and regeneration require communication and interplay between neighboring cells. In particular, cell competition, which is a process in which viable cells are actively eliminated by more competitive cells, has been increasingly implicated to play an important role. Here, we discuss the existing literature regarding the current landscape of cell competition, including classical pathways and models, fitness fingerprint mechanisms, and immune system mechanisms of cell competition. We further discuss the clinical relevance of cell competition in the physiological processes of tissue growth and regeneration, highlighting studies in clinically important disease models, including oncological, neurological, and cardiovascular diseases.

Active JNK-dependent secretion of Drosophila Tyrosyl-tRNA synthetase by loser cells recruits haemocytes during cell competition

Cell competition is a process by which the slow dividing cells (losers) are recognized and eliminated from growing tissues. Loser cells are extruded from the epithelium and engulfed by the haemocytes, the Drosophila macrophages. However, how macrophages identify the dying loser cells is unclear. Here we show that apoptotic loser cells secrete Tyrosyl-tRNA synthetase (TyrRS), which is best known as a core component of the translational machinery. Secreted TyrRS is cleaved by matrix metalloproteinases generating MiniTyr and EMAP fragments. EMAP acts as a guiding cue for macrophage migration in the Drosophila larvae, as it attracts the haemocytes to the apoptotic loser cells. JNK signalling and Kish, a component of the secretory pathway, are autonomously required for the active secretion of TyrRS by the loser cells. Altogether, this mechanism guarantees effective removal of unfit cells from the growing tissue.

Histoire de la littérature Judéo-allemande [Rezension]

Nathan Birnbaum

Strategy and Circumstance: the Response of American Firms to Japanese Competition in Semiconductors, 1980-1995

The transistor was an American invention, and American firms led the world in semiconductor production and innovation for the first three decades of that industry's existence. In the 1980s, however, Japanese producers began to challenge American dominance. Shrill cries arose from the literature of public policy, warning that the American semiconductor industry would soon share the fate of the lamented American consumer electronics business. Few dissented from the implications: the only hope for salvation would be to adopt Japanese-style public policies and imitate the kinds of capabilities Japanese firms possessed. But the predicted extinction never occurred. Instead, American firms surged back during the 1990s, and it now seems the Japanese who are embattled. This striking American turnaround has gone largely unremarked upon in the public policy literature. And even scholarship in strategic management, which thrives on stories of success instead of stories of failure, has been comparatively silent. Drawing on a more thorough economic history of the worldwide semiconductor industry (Langlois and Steinmueller 1999), this essay attempts to collect some of the lessons for strategy research of the American resurgence. We argue that, although some of the American response did consist in changing or augmenting capabilities, most of the renewed American success is in fact the result not of imitating superior Japanese capabilities but rather of taking good advantage of a set of capabilities developed in the heyday of American dominance. Serendipity played at least as important a role as did strategy.

Cooperation & Competition Between Navigation Systems in the Rat Brain: The Role of the Hippocampus and Striatum During a Dissociative Maze Task

While many tend to think of memory systems in the brain as a single process, in reality several experiments have supported multiple dissociations of different forms of learning, such as spatial learning and response learning. In both humans and rats, the hippocampus has long been shown to be specialized in the storage of spatial and contextual memory whereas the striatum is associated with motor responses and habitual behaviors. Previous studies have examined how damage to hippocampus or striatum has affected the acquisition of either a spatial or response navigation task. However even in a very familiar environment organisms must continuously switch between place and response strategies depending upon circumstances. The current research investigates how these two brain systems interact under normal conditions to produce navigational behavior. Rats were tested using a task developed by Jacobson and colleagues (2006) in which the two types of navigation could be controlled and studied simultaneously. Rats were trained to solve a plus maze using both a spatial and a response strategy. A cue (flashing light) was employed to indicate the correct strategy on a given trial. When no light was present, the animals were rewarded for making a 90º right turn (motor response). When the light was on, the animals were rewarded for going to a specific goal location (place strategy). After learning the task, animals had a sham surgery or dorsal striatum or hippocampus damaged. In order to investigate the individual role of each brain system and evaluate whether these brain regions compete or cooperate for control over strategy, we utilized a within-animal comparisons. The configuration of the maze allowed for the comparison of behavior in individual animals before and after specific brain areas were damaged. Animals with hippocampal lesions showed selective deficits on place trials after surgery and learned the reversal of the motor response more rapidly than striatal lesioned or sham rats. Unlike previous findings regarding maze learning, animals with striatal lesions showed deficits in both place and response trials and had difficulty learning the reversal of motor response. Therefore, the effects of lesions on the ability to switch back and forth between strategies were more complex than previously suggested. This work may reveal important new insight on the integration of hippocampal and striatal learning systems, and facilitate a better understanding of the brain dynamics underlying similar navigational processes in humans.

Competition and the Legal Environment: Intellectual Property Rights in the Early American Film Industry

No abstract available.

Le Jargon ou judéo-allemand : courte étude philologique suivie d'une chrestomathie

par H. Bourgeois

Histoire de la littérature judéo-allemande

par M. Pinès. Avec une préf. de Charles Andler

Langue des hommes et langue des femmes en judèo-allemand

Aus: Mélanges offerts à M. Charles Andler ... 1924