Co‐occurrence patterns of trees along macro‐climatic gradients and their potential influence on the present and future distribution of Fagus sylvatica L.

Aim During recent and future climate change, shifts in large‐scale species ranges are expected due to the hypothesized major role of climatic factors in regulating species distributions. The stress‐gradient hypothesis suggests that biotic interactions may act as major constraints on species distributions under more favourable growing conditions, while climatic constraints may dominate under unfavourable conditions. We tested this hypothesis for one focal tree species having three major competitors using broad‐scale environmental data. We evaluated the variation of species co‐occurrence patterns in climate space and estimated the influence of these patterns on the distribution of the focal species for current and projected future climates. Location Europe. Methods We used ICP Forest Level 1 data as well as climatic, topographic and edaphic variables. First, correlations between the relative abundance of European beech (Fagus sylvatica) and three major competitor species (Picea abies, Pinus sylvestris and Quercus robur) were analysed in environmental space, and then projected to geographic space. Second, a sensitivity analysis was performed using generalized additive models (GAM) to evaluate where and how much the predicted F. sylvatica distribution varied under current and future climates if potential competitor species were included or excluded. We evaluated if these areas coincide with current species co‐occurrence patterns. Results Correlation analyses supported the stress‐gradient hypothesis: towards favourable growing conditions of F. sylvatica, its abundance was strongly linked to the abundance of its competitors, while this link weakened towards unfavourable growing conditions, with stronger correlations in the south and at low elevations than in the north and at high elevations. The sensitivity analysis showed a potential spatial segregation of species with changing climate and a pronounced shift of zones where co‐occurrence patterns may play a major role. Main conclusions Our results demonstrate the importance of species co‐occurrence patterns for calibrating improved species distribution models for use in projections of climate effects. The correlation approach is able to localize European areas where inclusion of biotic predictors is effective. The climate‐induced spatial segregation of the major tree species could have ecological and economic consequences.     

Ergatoid reproductives in Nasutitermes columbicus (Isoptera,Termitidae)

Numerous functional ergatoid replacement reproductives were found in one colony of Nasutitermes columbicus in Panama. Their morphology was mainly workerlike, although several imaginal characters such as the compound eyes and variable wing buds were more or less developed. The sex organs were fully mature and the fat body of the females, not of the males, was of the “royal” type. The development of the eyes was not accompanied by the differentiation of the optic lobes of the brain, nor was the presence of wing buds correlated with a development of the wing muscles.     

Plasmid replication stimulates DNA recombination in Bacillus subtilis

The effects of plasmid replication on the frequency of homologous recombination have been investigated. For that purpose Bacillus subtilis strains that carry in their chromosome directly repeated DNA sequences, and an integrated copy of plasmid pE194 either proximal or distal to the repeats, were constructed. The repeat consists either of 3.9 X 10(3) base pBR322 sequences or 2.1 X 10(3) base B. subtilis chromosomal sequences. As plasmid pE194 is naturally thermosensitive for replication, the activity of the replicon could be regulated. Recombination between the repeated sequences was infrequent (about 10(-4) per generation) when the integrated plasmid did not replicate. It was 20 to 450 times higher when the plasmid was allowed to replicate, provided that the repeats were in the proximity of the plasmid. These results show that plasmid replication stimulates DNA recombination.     

Induction of DNA amplification in the Bacillus subtilis chromosome.

A system allowing the induction of DNA amplification in Bacillus subtilis was developed, based on a thermosensitive plasmid, pE194, stably integrated in the bacterial chromosome. An amplification unit, comprising an antibiotic resistance marker flanked by directly repeated sequences, was placed next to the integrated plasmid. Activation of pE194 replication led to DNA amplification. Two different amplification processes appeared to take place: one increased the copy number of all sequences in the vicinity of the integrated plasmid and was possibly of the onion skin type, while the other increased the copy number of the amplification unit only and generated long arrays of amplification units. These arrays were purified and shown to consist mainly of directly repeated amplification units but to also contain non-linear regions, such as replication forks and recombination intermediates. They were attached to the chromosome at one end only, and were, in general, not stably inherited, which suggests that they are early amplification intermediates. Longer arrays were detected before the shorter ones during amplification. When the parental amplification unit contained repeats which differed by a restriction site the arrays which derived thereof contained in a majority of cases only a single type of repeat. We propose that the amplified DNA is generated by rolling circle replication, and that such a process might underlie a number of amplification events.     

Synthesis of sulfated proteoglycans throughout the cell cycle in smooth muscle cells from pig aorta

Cultured smooth muscle cells from pig aorta arrested in G0 phase by serum deprivation were stimulated to proliferate by replacing the medium with one containing 10% serum. Studies in DNA replication and proliferation of cells showed a relatively good synchrony: 90% of the cells were in G1 phase for 16 h after addition of serum; they entered S phase between 18 and 24 h, completed S phase and traversed G2 phase between 24 and 30–32 h; 75% of these cells multiplied after 30–32 h and the remainder were blocked at the end of G2 phase. The synthesis and secretion of sulfated proteoglycans were examined throughout a full cell cycle using metabolic labelling with [³⁵S]sulfate. Smooth muscle cells in G1 or G2 phase synthesized and secreted sulfated proteoglycans with a possible pause at the end of the G2 phase but at the beginning of the S phase and during mitosis the incorporation of [³⁵S]sulfate into these macromolecules stopped entirely. Structural characteristics of sulfated proteoglycans secreted into the medium during G1 phase and an entire cell cycle were investigated. The proportion of proteoglycan complexes and the relative hydrodynamic size of monomers and of constituent subunits of complexes were determined after chromatography on Sepharose CL-2B and CL-6B columns run under both associative and dissociative conditions. No significant differences were observed for the periods of the cell cycle that were studied:

1. 1. [³⁵S]Proteoglycan complexes represented at the end of G1 phase and of the cell cycle respectively 19 and 16% of the total [³⁵S]proteoglycans secreted into the medium.

2. 2. More than 90% of the subunits, obtained after dissociation of complexes, were characterized by a similar k_av after chromatography on Sepharose CL-2B columns eluted under dissociative conditions (k_av 0.68 at the end of G1 phase and 0.65 at the end of full cell cycle).

3. 3. About 95% of monomers synthesized at the two stages of the cell cycle were eluted at k_av 0.25 after chromatography on Sepharose CL-6B column run under associative conditions and were characterized by a similar glycosaminoglycan distribution. These results suggest that smooth muscle cells in culture liberate similar populations of proteoglycans into the medium during the G1 and G2 phases.

     

Etude des premiers stades de développement de la Coccidie Coelotropha durchoni

Summary This study considers the earlier growth stages of Coccidium Coelotropha durchoni in its host, Nereis diversicolor. Before evolving into free trophozoites and gamontes in coeliac fluid, the parasites remain in muscular and coeliac cells in microscopic intracellular form. Electron microscope reveals that these stages show an intermediary fine structure between that of a sporozoite — from which they keep some typical characteristics such as the conoid, the fibers and the involuted tubuli — and that of the future free trophozoites. The wall consisting in two clear membrans is provided with one or several micropores. The classical cytoplasmic organites clearly stand out: dictyosomes show constant relationship with ergastoplasm, the mitochondria contain short inner tubuli. Besides the paraglycogen granules and lipoid vacuoles, at least three types of vacuoles may be observed. Peculiar topographic relationship connects mitochondria and paraglycogen granules probably in formation. In the nucleus with classical membrane and heterogeneous structure, a rather voluminous nucleolus may be seen.     

Role respectif des males et des femelles dans la formation des sexués néoténiques chezCalotermes flavicollis

Résumé ChezCalotermes flavicollis, la formation des sexués néoténiques est plus facile, ou plus rapide, dans le sexe femelle que dans le sexe mâle.Les sexués femelles montrent un pouvoir inhibiteur à l'égard des individus femelles; les sexués mâles inhibent les mâles de façon moins complète; la stabilisation complète peut être obtenue dans les élevages unisexués, formés uniquement de mâles ou de femelles.La régulation du nombre des néoténiques ne se fait pas de la même façon dans les élevages et dans les élevages . Dans les premiers, 2 néoténiques subsistent, quelquefois 3; dans les seconds ne persiste qu'un seul néoténique , rarement deux.Ces résultats mettent en lumière le rôle différent joué par les mâles et les femelles dans les sociétés de Termites.     

SSR cross-amplification and variation within coffee trees (Coffea spp.).

Primer sets were developed from 85 Coffea arabica sequences in addition to 25 already published primer sets. They were subsequently used for amplification in six African Coffea species: Coffea canephora (CAN), Coffea eugenioides (EUG), Coffea heterocalyx (HET), Coffea liberica (LIB), Coffea sp. Moloundou (MOL) and Coffea pseudozanguebariae (PSE). The amplification percentages for these 110 primer pairs ranged from 72.7% for LIB to 86.4% for PSE. Good transferability was thus obtained within the Coffea genus. When focusing on the two species CAN and PSE, high genetic diversity, high polymorphic locus rates (above 80%) and a mean allele number per polymorphic locus of more than 3 were noted. The estimated null allele percentage was -11% for PSE and -9% for CAN. Sixty three percent (CAN) and 79.5% (PSE) of the fixation index (Fis) values were positive. The within-species polymorphism information content (PIC) distribution showed two modes for both species. Although the two species shared 30 polymorphic loci, no correlation between CAN and PSE PIC values was obtained. All of these data are discussed in relation to the polymorphism level and the potential use of these SSRs for subsequent analysis of genetic diversity or genetic mapping.     

Chemical composition and ultrastructure of cellular and extracellular Moraxella glucidolytica lipopolysaccharides

A cellular (LPS I) and extracellular (LPS II) lipopolysaccharide were isolated from Moraxella glucidolytica cells grown on ethanol and from the culture fluid, respectively. Both LPS were toxic when injected to mice and chick embryos. These LPS contained glucose, galactose, glucosamine, galactosamine, 2-keto-3-deoxyoctonate and lipids. By permethylation studies, glucose was found to be linked (16) and (13) in LPS I and only (16) in LPS II. Galactose was the terminal non-reducing sugar. Branching occurred at positions 3 and 4 of galactose residues. LPS I was rich in - and -hydroxylauric and -hydroxymyristic acids and LPS II contained mainly stearic and -hydroxymyristic acids. LPS I was detoxified by mild acid and alkaline treatments. It was also dissociated by sodium deoxycholate and chromatographed on Sephadex G-75. The main fraction was reassociated by removing the surfactant by dialysis. The morphology of LPS I and LPS II was examined by electron microscopy. LPS I (original and reassociated fractions) consisted exclusively of ribbons while LPS II contained ribbons and vesicles.Non-Standard Abbreviations KDO 2-Keto-3-deoxyoctonic acids - LPS Lipopolysaccharide - NaD Sodium deoxycholate