Aggregation of Lepidostomatidae in small mesh size litter-bags: implication to the leaf litter decomposition process

Invertebrate colonization during leaf litter decomposition was studied at the 2nd order of Yanase River, Iruma city, Saitama, Japan from November 13, 2002 to May 20, 2003. Two different mesh sizes (1 and 5 mm) of litter-bags were used to evaluate the decomposition of leaf litter of Sakura (Prunus lannesiana), bags were placed equally in riffle (water flow velocity: 0.2–0.6 m s⁻¹) and pool (water flow velocity: 0.04–0.06 m s⁻¹). Mass loss and invertebrates in the litter-bags were monitored at interval between 1 and 3 weeks, and the invertebrates were classified based on their functional feeding group. Among the invertebrates found inside the litter-bags, the case-bearing shredder Lepidostomatidae was the most dominant invertebrates and they were the early colonizer that appeared about 3 months after the litter-bags immersion. In absence or low number of leaf-shredders, the decomposition rates in 1 and 5 mm litter mesh bags followed the exponential (or first-order) decay kinetic (R ²: 0.72–0.92). However, the presence of a large number of leaf-shredders in 1 mm litter-bags caused an acceleration of decomposition process; that even resulted faster mass loss than the loss from the 5 mm mesh bags placed in riffle area (0.030 day⁻¹ vs. 0.011 day⁻¹). Our results shows the importance of using different mesh sizes of litter-bags in decomposition study, which is applicable to the experiment in lotic or lentic ecosystem. Using smaller mesh size of litter-bags can provide information on how significant the effect of detritus feeders on the decomposition process, while the bigger mesh size can represent better the natural decomposition process when a large number detritus feeders is present in the smaller mesh size of litter-bags.     

Synthesis, cytotoxicity and human telomerase inhibition activities of a series of 1,2-heteroannelated anthraquinones and anthra[1,2-d]imidazole-6,11-dione homologues

A series of 1,2-heteroannelated anthraquinones and anthra[1,2-d]imidazole-6,11-dione tetracyclic analogues with different side chain were prepared using an various synthetic route via acylation, cyclization, condensation, and intramolecular heterocyclization. Tetracyclic system containing alkyl and aryl, aromatic and heterocyclic, linear and cyclic, polar and apolar, and basic and acids residues were incorporated. They were evaluated for their effects on telomerase activity, hTERT expression, cell proliferations, and in vitro cytotoxicity against NCI’s 60 cell line human tumor screen. Compounds 4, 11, 12, 14, 15, 16, 17, 19, 20, 23, 25, and 26 were selected by the NCI for one dose screening program and further studies on 4, 23 and 25 where the curves cross these lines represent the interpolated values to cause 50% growth inhibition (GI₅₀), total growth inhibition (TGI) and 50% cell killing (LC₅₀), respectively. Further studies did not reveal any compound that showed potent and significant on telomerase inhibitory activity and hTERT repressing ability. Comparative testing of these compounds in the NCI’s screen revealed varying levels of potency and differential cytotoxicity, apparently related to the unsaturation levels in and substitution patterns on the core ring system. It appeared that addition of a fourth planar aromatic system to a tricyclic chromophore might enhances potent cytotoxic agents, at a level equivalent to a second side chain in one of the tricyclic series. Although the exact mechanism of how this pharmacophore contributes to its activity is still unclear, however, the group in the extended arm of the tetracyclic system might contribute to proper binding to the residues within the grove of G-quadruplex structure.     

Horizontal gradient in fish assemblage structures in and around a seagrass habitat: some implications for seagrass habitat conservation

Horizontal gradients in fish assemblage structures in and around a seagrass habitat were evaluated by visual observations. The assemblage structures clearly differed between open microhabitats lacking seagrass, i.e., nearby sand and the area adjoining the outer margin of the seagrass bed (referred to as “outer gap”), and microhabitats with seagrass within the overall seagrass bed, although not differing among the latter microhabitats, including both edge and core portions. Such open microhabitats were found to be not always inferior, but nearly equal to or even sometimes greatly superior in fish species’ diversity and/or abundance to the microhabitats with seagrass. In particular, the outer gap was always ranked first in total species’ number and had outstanding abundance in spring. Similar open microhabitats adjoining seagrass walls facing the sand patch within the seagrass bed (referred to as “inner gap”) in spring were also characterized by higher fish species and individual numbers. The 11 most abundant fishes showed four discrete distribution patterns (three recognized herein and one implied by precedent studies), such contributing to a horizontal gradient in the fish assemblage structure. While no fishes showed a preference for the edge or core of the seagrass bed, group-forming juveniles of several species favored gap microhabitats, suggesting that, in addition to the traditionally recognized edge and core microhabitats, the concept of gap microhabitats should be included in seagrass conservation ecology.     

Impact of secondary forest management on ant assemblage composition in the temperate region in Japan

In Japan, the impacts of human disturbance on ant assemblages have been intensively studied mainly in suburban areas. In contrast, the impact on ant assemblages of long-term human management and abandonment of forests is not well studied even though forestry is viewed as a process that seriously impacts ant assemblages. Besides, the studies focused on the relationship between secondary forest management for producing the firewood and charcoal which is considered to be characteristic of Japan and ant assemblage is not well studied. Do the long-term impacts on the secondary forest alter the ant composition? The effects of forest management on ant assemblages were studied through comparisons of managed, unmanaged and clear cut forest plots in secondary tree stands that had been used previously for producing firewood and charcoal. Ant species richness did not differ among forest categories, but ant species composition varied among forest categories. The absence or presence of openland and woodland ant specialist species is considered a good indicator for secondary forest management.     

Paradoxical effect of l-arginine: Acceleration of endothelial cell senescence

We have recently shown that inhibition of nitric oxide (NO) synthesis by asymmetrical dimethylarginine (ADMA) accelerated endothelial cell (EC) senescence which was prevented by coincubation with l-arginine; however the effect of long-term treatment of l-arginine alone on senescence of ECs have not been investigated. Human ECs were cultured in medium containing different concentrations of l-arginine until senescence. l-Arginine paradoxically accelerated senescence indicated by inhibiting telomerase activity. Moreover, l-arginine decreased NO metabolites, increased peroxynitrite, and 8-iso-prostaglandin F_2α formation. In old cells, the mRNA expression of human amino acid transporter (hCAT)2B, the activity and protein expression of arginase II were upregulated indicated by enhanced urea, l-ornithine, and l-arginine consumption. Inhibition of arginase activity, or transfection with arginase II siRNA prevented l-arginine-accelerated senescence. The most possible explanation for the paradoxical acceleration of senescence by l-arginine so far may be the translational and posttranslational activation of arginase II.     

Effects of plant species richness and composition on epifaunal colonization in brackish water angiosperm communities

Studies conducted in terrestrial ecosystems have shown that increasing plant diversity enhances ecosystem processes such as primary production. In marine systems, knowledge of how plant diversity influences ecosystem processes and higher trophic levels is still limited. To examine how plant richness and composition influence recruitment and colonization processes, defaunated eelgrass (Zostera marina), sago pondweed (Potamogeton pectinatus) and perfoliate pondweed (Potamogeton perfoliatus) were planted on an unvegetated, sandy bottom in all possible combinations in July and August. Both field experiments lasted 1 week. Our results showed that in these plant assemblages plant richness had a negative effect on faunal diversity (H′) and evenness (J′), while total abundance showed strong temporal variation with weak, positive relationships with plant species richness in both August and July. Plant species composition had strong effects on amphipods (Gammarus spp.), thus both the abundance and biomass were higher in treatments containing P. perfoliatus. The colonization process was significantly influenced by the numerical dominance of a few faunal species, e.g. the settlement of lagoon cockles (Cerastoderma glaucum), and by the timing of the experiments. The results indicate that faunal colonization in these communities is rapid and significantly influenced by the traits of particular plant species.     

Seasonal variation of black fly (Diptera: Simuliidae) species diversity and community structure in tropical streams of Thailand

Seasonal variation of the physicochemical conditions of streams plays an important role in aquatic insect diversity and community structure. Asian tropical streams profoundly change between seasons due to the effects of monsoons. However, little is known about how these changes affect aquatic insect diversity and community structure. The objectives of this study are to examine seasonal variations of the physicochemical conditions in tropical streams in Thailand and to assess the effects of these changes on black fly community structure and diversity. Black flies were sampled and physicochemical conditions recorded at eight sites between December 2007 and December 2008. A total of 10 black fly species were found. Comparisons of the streams between seasons revealed that physical conditions related to rainfall rate were significantly different. Canonical correspondence analysis differentiated sampling sites from each season. Streams in the rainy season were faster and deeper, with higher discharge and conductivity than those of the cold and dry seasons. Species richness was significantly higher in the rainy season than in the cold and dry seasons ( F  = 6.23, P  = 0.004). Community structure profoundly changed between the low-flow season (cold and dry) and high-flow season. Black fly species found predominantly in the low-flow season ( Simulium siamense "cytoform A", S. aureohirtum ) decreased dramatically during the high-flow season. In contrast, species found at high frequency during the high-flow season ( S. nakhonense , S. angulistylum ) disappeared in the low-flow season. The study demonstrates the importance of seasonal variation of stream conditions on black fly community structure and diversity.     

龙感湖沉积物泥芯硅藻群落和营养状态的反演

The importance of aquatic vegetation to the ecologi-cal restoration has been recognized commonly bylimnolo-gists and lake managements[1—4].As to the ecologicalrestoration in eutrophicated lakes,it is of great signifi-cance to knowthe dynamic process of the ecosystemevo-lution in a macrophyte-dominated lake under the humanimpacts in historical period,to make it clear whether thecommunitystructure and ecological function would be af-fected bythe extension of the vegetation growth,tofind asolutionto remain ste...