A three-stage symbiosis forms the foundation of seagrass ecosystems     

van der Heide T  Govers LL  de Fouw J  Olff H  van der Geest M  van Katwijk MM  Piersma T  van de Koppel J  Silliman BR  Smolders AJ  van Gils JA 《Science (New York, N.Y.)》2012,336(6087):1432-1434

Seagrasses evolved from terrestrial plants into marine foundation species around 100 million years ago. Their ecological success, however, remains a mystery because natural organic matter accumulation within the beds should result in toxic sediment sulfide levels. Using a meta-analysis, a field study, and a laboratory experiment, we reveal how an ancient three-stage symbiosis between seagrass, lucinid bivalves, and their sulfide-oxidizing gill bacteria reduces sulfide stress for seagrasses. We found that the bivalve-sulfide-oxidizer symbiosis reduced sulfide levels and enhanced seagrass production as measured in biomass. In turn, the bivalves and their endosymbionts profit from organic matter accumulation and radial oxygen release from the seagrass roots. These findings elucidate the long-term success of seagrasses in warm waters and offer new prospects for seagrass ecosystem conservation.  相似文献   

Adenylate cyclases of Trypanosoma brucei inhibit the innate immune response of the host     

Salmon D  Vanwalleghem G  Morias Y  Denoeud J  Krumbholz C  Lhommé F  Bachmaier S  Kador M  Gossmann J  Dias FB  De Muylder G  Uzureau P  Magez S  Moser M  De Baetselier P  Van Den Abbeele J  Beschin A  Boshart M  Pays E 《Science (New York, N.Y.)》2012,337(6093):463-466

The parasite Trypanosoma brucei possesses a large family of transmembrane receptor-like adenylate cyclases. Activation of these enzymes requires the dimerization of the catalytic domain and typically occurs under stress. Using a dominant-negative strategy, we found that reducing adenylate cyclase activity by about 50% allowed trypanosome growth but reduced the parasite's ability to control the early innate immune defense of the host. Specifically, activation of trypanosome adenylate cyclase resulting from parasite phagocytosis by liver myeloid cells inhibited the synthesis of the trypanosome-controlling cytokine tumor necrosis factor-α through activation of protein kinase A in these cells. Thus, adenylate cyclase activity of lyzed trypanosomes favors early host colonization by live parasites. The role of adenylate cyclases at the host-parasite interface could explain the expansion and polymorphism of this gene family.  相似文献   

2.8 million years of Arctic climate change from Lake El'gygytgyn, NE Russia     

Melles M  Brigham-Grette J  Minyuk PS  Nowaczyk NR  Wennrich V  DeConto RM  Anderson PM  Andreev AA  Coletti A  Cook TL  Haltia-Hovi E  Kukkonen M  Lozhkin AV  Rosén P  Tarasov P  Vogel H  Wagner B 《Science (New York, N.Y.)》2012,337(6092):315-320

The reliability of Arctic climate predictions is currently hampered by insufficient knowledge of natural climate variability in the past. A sediment core from Lake El'gygytgyn in northeastern (NE) Russia provides a continuous, high-resolution record from the Arctic, spanning the past 2.8 million years. This core reveals numerous "super interglacials" during the Quaternary; for marine benthic isotope stages (MIS) 11c and 31, maximum summer temperatures and annual precipitation values are ~4° to 5°C and ~300 millimeters higher than those of MIS 1 and 5e. Climate simulations show that these extreme warm conditions are difficult to explain with greenhouse gas and astronomical forcing alone, implying the importance of amplifying feedbacks and far field influences. The timing of Arctic warming relative to West Antarctic Ice Sheet retreats implies strong interhemispheric climate connectivity.  相似文献   

Recent plant diversity changes on Europe's mountain summits   总被引：2，自引：0，他引：2  

Pauli H  Gottfried M  Dullinger S  Abdaladze O  Akhalkatsi M  Benito Alonso JL  Coldea G  Dick J  Erschbamer B  Fernández Calzado R  Ghosn D  Holten JI  Kanka R  Kazakis G  Kollár J  Larsson P  Moiseev P  Moiseev D  Molau U  Molero Mesa J  Nagy L  Pelino G  Puşcaş M  Rossi G  Stanisci A  Syverhuset AO  Theurillat JP  Tomaselli M  Unterluggauer P  Villar L  Vittoz P  Grabherr G 《Science (New York, N.Y.)》2012,336(6079):353-355

In mountainous regions, climate warming is expected to shift species' ranges to higher altitudes. Evidence for such shifts is still mostly from revisitations of historical sites. We present recent (2001 to 2008) changes in vascular plant species richness observed in a standardized monitoring network across Europe's major mountain ranges. Species have moved upslope on average. However, these shifts had opposite effects on the summit floras' species richness in boreal-temperate mountain regions (+3.9 species on average) and Mediterranean mountain regions (-1.4 species), probably because recent climatic trends have decreased the availability of water in the European south. Because Mediterranean mountains are particularly rich in endemic species, a continuation of these trends might shrink the European mountain flora, despite an average increase in summit species richness across the region.  相似文献   

Automated observation and analysis of earthworm surface behaviour under experimental habitat quality and availability conditions     

Jan Valckx  Toon Leroy  Gerard Govers  Bart Muys 《Pedobiologia》2010,53(4):259-263

Currently, the driving factors of active earthworm dispersal across the soil surface are not sufficiently understood, and distances traversed by individual earthworms have rarely been quantified. Research progress has been hampered by the lack of adequate observation methods as well as fast, objective and quantitative measurements of nocturnal earthworm behaviour.In this work, we report on the potential of a new, automated method using infrared-sensitive webcams and computer image analysis. Nightly surface activities of Lumbricus terrestris L. were monitored quantitatively while manipulating levels of disturbance, burrow availability and congener presence in standard observation units.The automated observation system proved to be simple and inexpensive to build, provided reliable quantitative measures of locomotive behaviour without animal disturbance, and considerably reduced human workload and bias.Waterlogging of the burrow zone stimulated surface activities around and away from the home burrow as compared to habitat disturbance by pesticide application and vibration. However, dispersing earthworms never settled in prefabricated burrows. Surface activity of individuals subjected to waterlogged conditions was influenced by the availability of alternative habitat. Minimal habitat disturbance (vibration) and the presence of conspecific individuals resulted in an increased amount of burrow-anchored, possibly sexually oriented, behaviour, but reciprocal burrow visits and mating were not observed. Pesticide application did not result in dispersal, increased foraging activities or sexual attraction attempts during this short-term study.The presence, extent and mechanisms of the remote assessment of important cues in the surroundings of the home burrow by L. terrestris need further research. Infrared monitoring opens new research avenues of earthworm surface behaviour studies (e.g. density-dependent dispersal, habitat selection, (re)colonization, invasion).  相似文献   

Flood Retention and Drinking Water Supply – Preventing Conflicts of Interest     

Matthias Maier  Dirk Kühlers  Heinz-Jürgen Brauch  Michael Fleig  Dietrich Maier  Gerhard H. Jirka  Ulf Mohrlok  Ekkehart Bethge  Hans Helmut Bernhart  Boris Lehmann  Gudrun Hillebrand  Jan Wölz  Henner Hollert 《Journal of Soils and Sediments》2006,6(2):113-114

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The mobilization of copper in sheep by chelating agents.     

Nils E. Sli  Arne Frslie  Jan Aaseth 《Acta veterinaria Scandinavica》1978,19(3):422-429

D-penicillamine and 2,3-dimercapto-propane-l-sulphonate (DMPS) were administered orally and disodium-calcium-ethylene-diamine-tetraacetate (Ca-EDTA) subcutaneously into copper loaded sheep. The results showed that D-penicillamine has a copper mobilizing effect, while DMPS and Ca-EDTA do not seem to have this effect to any significant degree. Penicillamine, 52 mg/kg of body weight daily for 6 days, increased the urinary excretion of copper by a factor of 10 to 20. The same dosage (on weight basis) of DMPS increased the excretion of copper in urine by 2 fold. Following Ca-EDTA treatment no increase in urinary excretion of copper was observed. Penicillamine could be used in prophylactic treatment of copper toxicosis in sheep, but it is still too expensive for practical use.  相似文献   

The Effect of Cyclic Adenosine 3', 5' Monophosphate,Methyl Xanthines and Nicotinic Acid on Plasma Nonesterified Fatty Acids in Sheep     

Jan Luthman  Gsta Jonson 《Acta veterinaria Scandinavica》1971,12(4):536

The intravenous injection of 3'', 5'' AMP, 10 mg/kg, caused an immediate rise in blood glucose in normal sheep. In sheep where liver glycogen was depleted by pretreatment with 100 mg/kg of nicotinic acid, the blood glucose response was greatly reduced. The glycogenolytic effect of 3'', 5'' AMP was thus easily demonstrated. The injection of 3'', 5'' AMP was followed by an immediate rise in NEFA, which was most pronounced in the pretreated animals. After the initial increase there was a fall in NEFA in both the normal and the pretreated animals. The role of hyperglycemia for the NEFA response to exogenous 3'', 5'' AMP was discussed. It seemed possible that hyperglycemia may modify the initial increase in NEFA. The later fall in NEFA was discussed as a complex response, which may be the result of the action of several hormones, which may be released by 3'', 5'' AMP injection. Nicotinic acid and pyridyl-3-acetic acid showed a potent antilipolytic activity. Nicotinic acid caused a rebound elevation of NEFA. No rebound was observed after pyridyl-3-acetic acid. Pyridyl-3-acetic acid, however, did not change NEFA when administered orally. Pyridyl-2-acetic acid had no antilipolytic effect. Of the methyl xanthines caffeine and theophylline showed about the same lipolytic activity. Theobromine was quite ineffective.  相似文献   

Das Leben des Waldes und seine Lebensunsicherheit     

Jan Kouba 《European Journal of Forest Research》2002,121(4):211-228

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Evidence for common genetic mechanisms controlling the tolerance of sudden salt stress in the tribe Triticeae     

Gan-Yuan  Zhong Jan  Dvo&#;ák 《Plant Breeding》1995,114(4):297-302

Previous studies in several Triticeae species have suggested that salt tolerance is a polygenic trait, but that genes on some chromosomes confer better tolerance to salt stress than others. This suggests an intriguing possibility that there may be a similar basis for salt tolerance in the species of the tribe Triticeae. In this study, chromosomal control of the tolerance to sudden salt stress, measured as the mean rate of leaf elongation in solution cultures with a single increment of 200 mM NaCl, was investigated in the genomes of cultivated barley (Hordeum vulgare L.), rye (Secale cereale L.), and Dasypyrum villosum (L.) Can-dargy by using disomic addition lines of individual pairs of chromosomes or chromosome arms of each of the three species in the ‘Chinese Spring’ wheat genetic background. It was observed that the chromosomes of homoeologous groups 3, 4, and 5 in barley, 5 and 7 in rye, and 4 and 6 in D. villosum carry loci with significant positive effects on salt tolerance. Increased doses of chromosomes of group 2, however, reduce or do not increase the tolerance to salt stress. These results are in agreement with a previous study of the tolerance of this salt stress regime in wheat and wheatgrass Lophopyrum elongatum. A ranking analysis of the chromosomal effects within each genome of the five Triticeae species investigated in this and previous studies revealed that the chromosomes of homoeologous groups 3 and 5 consistently confer large positive effects on the tolerance of sudden salt stress, while the chromosomes of homoeologous group 2 in increased dose have no or negative effects on the tolerance. This strongly suggests that species of the tribe Triticeae share some common genetic mechanisms of tolerance of sudden salt stress. The findings in this study give credence to the proposal that wild relatives can be exploited in the development of wheat cultivars with greater tolerance to salt stress.  相似文献