Long-term Patterns of Shifts between Clear and Turbid States in Lake Krankesjön and Lake Tåkern

During the past century, Lake Tåkern and Lake Krankesjön, southern Sweden, have shifted repeatedly between a state of clear water and abundant submerged vegetation, and a state of turbid water and sparse vegetation. Long-term empirical data on such apparently alternative stable state dynamics are valuable as complements to modeling and experiments, although the causal mechanisms behind shifts are often difficult to identify in hindsight. Here, we summarize previous studies and discuss possible mechanisms behind the shifts. The most detailed information comes from monitoring of two recent shifts, one in each lake. In the 1980s, L. Krankesjön shifted to clear water following an expansion of sago pondweed, Potamogeton pectinatus. Water clarity increased when the pondweed was replaced by characeans. Zooplankton biomass in summer declined and the concentration of total phosphorus (TP) was reduced to half the previous level. The fish community changed over several years, including an increasing recruitment of piscivorous perch (Perca fluviatilis). An opposite directed shift to turbid water occurred in Lake Tåkern in 1995, when biomass of phytoplankton increased in spring, at the expense of submerged vegetation. Consistent with the findings in L. Krankesjön, phyto- and zooplankton biomass increased and the average concentration of TP doubled. After the shift to clear water in L. Krankesjön, TP concentration has increased during the latest decade, supporting the idea that accumulation of nutrients may lead to a long-term destabilization of the clear water state. In L. Tåkern, data on TP are inconclusive, but organic nitrogen concentrations oscillated during a 25-year period of clear water. These observations indicate that intrinsic processes cause gradual or periodic changes in system stability, although we cannot exclude the possibility that external forces are also involved. During such phases of destabilization of the clear water state, even small disturbances could possibly trigger a shift, which may explain why causes behind shifts are hard to identify even when they occur during periods of extensive monitoring.     

Foraging tactics in alternative heterochronic salamander morphs: trophic quality of ponds matters more than water permanency

1. In lentic freshwater habitats, the composition of animal assemblages shifts along a gradient from temporary to permanent basins. When habitats with different degrees of permanence are at the scale of the home range of species, they constitute alternatives in terms of energy acquisition through feeding. 2. In this context, previous studies showed an advantage of metamorphic over paedomorphic tiger salamanders (Ambystoma tigrinum) in temporary ponds which are only available to metamorphs. The aim of this study was to establish whether salamanders obtain similar benefits in ponds that do not differ in water permanence and whether salamanders shifted from detrimental to advantageous ponds. To this end, we determined the feeding habits, body condition and movement patterns of the two morphs in a complex of four permanent and four temporary ponds. 3. Consistent with previous studies, metamorphs consumed higher‐quality diets than paedomorphs in term of energy intake. However, these differences occurred because metamorphs consumed fairy shrimp in a single temporary pond. Individual movement patterns confirmed that most of the metamorphs used different aquatic habitats both within and between years and that most of them moved from permanent ponds for breeding towards the most profitable temporary pond in terms of foraging. 4. These results indicate that habitat selection by salamanders is optimal in term of energy intake in metamorphs that use high quality ponds independently of hydroperiod. It seems that both spatial and temporal variation can influence the relative foraging success of each morph.     

Migratory benthic fishes may induce regime shifts in a tropical floodplain pond

1. Alternative states are a widely recorded phenomenon in shallow lakes, which may shift between turbid‐ and clear‐water conditions. Here, we investigate whether such shifts in a tropical floodplain pond may be related to the effect of the flood pulse regime on the community structures of fish and macrophytes. 2. Using a long‐term data set, we demonstrate how benthic fish migration together with colonisation by submerged plants affected the transition from a turbid to a macrophyte‐dominated state in a floodplain pond without top‐down control. 3. In our study, the turbid state occurred mostly during low water phases and was largely characterised by high values for the biomass of benthic fish, chlorophyll‐a and total phosphorous. 4. During the period of rising water levels, the migration of benthic fish out of the pond occurs simultaneously with the establishment of submerged plants, while water turbidity decreases along with phytoplankton and nutrient concentrations, inducing a clear‐water phase. However, when submerged plants are absent and fish migration is low, a transient state is generated. 5. We suggest that, in contrast to temperate ponds and shallow lakes, where the main driving mechanisms establishing alternative states are related to cascading effects via the food chain, in tropical ponds and shallow lakes it is resuspension of sediments by benthic fish that plays the most significant role in establishing alternative states. However, the effect of the flood pulse regime plays an important role in the temporal dynamics of fish community structure by controlling benthic fish migration.     

小鼠Cidea蛋白N端缺失异构体的鉴定和研究

Cidea蛋白调节脂肪代谢,在机体能量平衡过程中起重要作用,在转录和翻译后水平受到严格调控,但在翻译水平的调节还不清楚．通过对CIDEA基因敲除小鼠模型研究,鉴定了小鼠棕色脂肪组织内源性表达Cidea蛋白N端缺失异构体mCidea-22．定点突变等研究表明其产生机制为选择性起始翻译．并且,在异位表达时,N端缺失异构体和全长异构体的比例呈现细胞系特异性．此外,蛋白质稳定性实验表明mCidea-22半衰期很短．亚细胞定位研究显示mCidea-22是内质网和脂滴定位蛋白．为深入理解Cidea蛋白的功能和精细调节提供了新的思路和方向．     

Solution Structure of the HIV-1 Intron Splicing Silencer and Its Interactions with the UP1 Domain of Heterogeneous Nuclear Ribonucleoprotein (hnRNP) A1

Splicing patterns in human immunodeficiency virus type 1 (HIV-1) are maintained through cis regulatory elements that recruit antagonistic host RNA-binding proteins. The activity of the 3′ acceptor site A7 is tightly regulated through a complex network of an intronic splicing silencer (ISS), a bipartite exonic splicing silencer (ESS3a/b), and an exonic splicing enhancer (ESE3). Because HIV-1 splicing depends on protein-RNA interactions, it is important to know the tertiary structures surrounding the splice sites. Herein, we present the NMR solution structure of the phylogenetically conserved ISS stem loop. ISS adopts a stable structure consisting of conserved UG wobble pairs, a folded 2X2 (GU/UA) internal loop, a UU bulge, and a flexible AGUGA apical loop. Calorimetric and biochemical titrations indicate that the UP1 domain of heterogeneous nuclear ribonucleoprotein A1 binds the ISS apical loop site-specifically and with nanomolar affinity. Collectively, this work provides additional insights into how HIV-1 uses a conserved RNA structure to commandeer a host RNA-binding protein.     

Mitochondrial Respiratory Chain Complex Patterns from Acanthamoeba castellanii and Lycopersicon esculentum: Comparative Analysis by BN-PAGE and Evidence of Protein–Protein Interaction Between Alternative Oxidase and Complex III

We have previously shown that a kinetic interplay exists between the cytochrome pathway and the alternative oxidase in mitochondria from amoeba Acanthamoeba castellanii . Native interaction analyses using blue native gel electrophoresis coupled to denaturating electrophoresis and immunodetection have indicated associations between alternative oxidase and oxidative phosphorylation complexes in both amoeba and tomato mitochondria. These associations are dependent on the expression level of alternative oxidase according to the physiological state in both organisms. Alternative oxidase associates broadly with large complexes of the respiratory chain when it is expressed in large amount, i.e., in ripe tomato and exponentially growing amoeba. On the contrary, alternative oxidase interacts specifically with complex III even if expression of the oxidase is low, i.e., in green tomato and stationary phase amoeba. This specific interaction represents a higher level of regulation driven by protein-protein interactions leading to a direct kinetic interplay between the cytochrome pathway and alternative oxidase in both plant and amoeba mitochondria.     

Tissue Specificity of Alternative Splicing of Transcripts Encoding Hampin,a New Mouse Protein Homologous to the <Emphasis Type="Italic">Drosophila</Emphasis> MSL-1 Protein

A number of mammalian genomes have one gene copy encoding the protein that we named hampin. A search in a number of databases revealed a distant homologue, the well-known Drosophila protein MSL-1 (male-specific lethal 1). An alternative splicing of mRNA led to a significant diversity of structural hampin variants with different domain compositions. We analyzed the tissue-specific expression of five mouse hampin variants using RT-PCR. Two variants encoding hampin proteins with truncated N termini were shown to have a restricted tissue specificity: they are exclusively expressed in the testes. The mRNAs of other hampin variants were detected in all the tested tissues at comparable levels. We obtained polyclonal antibodies to the recombinant hampin and used them to demonstrate that at least one of the variants is predominantly localized in the nucleus. The specific features of the hampin primary structure and its possible functions as a member of the hampin/MSL-1 family of proteins are discussed.__________Translated from Bioorganicheskaya Khimiya, Vol. 31, No. 4, 2005, pp. 363–371.Original Russian Text Copyright © 2005 by Dmitriev, Pestov, Korneenko, Gerasimova, Zhao, Modyanov, Kostina, Shakhparonov.The article was translated by the authors.     

光对绿豆种子和叶片分离线粒体耗氧的影响

实验结果表明:照光时绿豆叶片分离线粒体通过细胞色素氧化酶途径的NADH氧化部分受阻,电子转向交替途径。不产生能量,不受能荷控制的NADH氧化途径有利于绿色细胞线粒体在光合作用时执行其提供碳架的功能。看来绿色细胞线粒体本身具有对光的敏感性,在照光时调节呼吸途径以适应其功能的转换。呼吸途径的转换机制目前还不清楚。绿豆种子线粒体与叶片线粒体不同,没有上述的这种对光的反应。     

生态系统稳态转换检测研究进展

在气候变化、人类活动等影响下,生态系统结构和功能可能发生大规模的突变,导致生态系统从一个相对稳定的状态进入另一个稳定状态,这种现象称为稳态转换。由于生态系统的复杂性,准确刻画生态系统多稳态并界定其临界点尚存在挑战,提升对生态系统稳态转换的检测和预测能力依旧是生态学领域研究的热点和难题。基于多稳态理论和稳态转换经典概念框架,阐释了稳态转换检测的理论基础;归纳总结出四种稳态转换检测方法的原理和优劣势;鉴于稳态转换的尺度依赖性,梳理了单一生态系统、区域综合生态系统和全球生态系统不同尺度下的稳态转换检测方法、研究思路和应用案例。基于研究进展和问题现状,提出在未来研究中,亟待发展适应复杂系统的综合检测方法;创新稳态转换多尺度分析的技术方法体系;深化生态系统稳态转换驱动机制研究,构建多元耦合机理模型;进而深化稳态转换检测结果链接生态系统管理的实践研究;解析生态系统服务和可持续发展机制。