Breaking the routine: individual Cory's shearwaters shift winter destinations between hemispheres and across ocean basins

There is growing evidence that migratory species are particularly vulnerable to rapid environmental changes arising from human activity. Species are expected to vary in their capacity to respond to these changes: long-distance migrants and those lacking variability in migratory traits are probably at considerable disadvantage. The few studies that have assessed the degree of plasticity in behaviour of marine animals suggest that fidelity to non-breeding destinations is usually high. In the present study, we evaluated individual flexibility in migration strategy of a highly pelagic seabird, the Cory's shearwater Calonectris diomedea. Geolocation data from 72 different migrations, including 14 birds that were tracked for more than one non-breeding season, showed a remarkable capacity to change winter destinations between years. Although some birds exhibited high site fidelity, others shifted from the South to North Atlantic, from the western to eastern South Atlantic, and from the Atlantic to Indian Ocean. Individuals also showed flexibility in stopover behaviour and migratory schedule. Although their K-selected life-history strategy has the disadvantage that the chances of microevolution are slight if circumstances alter rapidly, these results suggest that Cory's shearwaters may be in a better position than many other long-distance migrants to face the consequences of a changing environment.     

基于微观空间单元的景观城市化水平对土地利用变化的影响

以深圳为研究案例,综合利用遥感数据、土地利用详查数据、政府部门资料和实地调查资料等多种数据源,引入GIS格网分析、空间分析和栅格数据分析等方法科学地绘制了基于微观空间单元的深圳景观城市化水平分布图,从定量角度揭示了建设用地增长、土地转移分布及速度和土地利用整体变化速度在景观城市化水平梯度上的分布规律,并归纳出了景观城市化水平梯度上土地利用变化速度的一般数学模型,拓展和丰富了城市化对土地利用变化的影响研究内容.     

不同刺激形式在成年大鼠海马CAl区诱导长时程压抑的谷氨酸受体机制

前期研究显示低频率多串刺激能够在成年大鼠海马CAl区诱发稳定的长时程压抑(long-term depression,LTD),而这种LTD的受体机制目前还不清楚.本研究采用成年大鼠海马脑片标本,电刺激Schaffer侧枝传入纤维,在CAl区锥体细胞层记录群体锋电位(population spikes,PS),并分别应用N-甲基-D-天冬氨酸(N-methyl-D-aspartate,NMDA)受体和代谢型谷氨酸(metabotropic glutamate,mGlu)受体的拮抗剂AP5和MCPG,观察两组低频率(2-Hz和5-Hz)多串刺激能否诱导LTD,以揭示不同刺激形式诱导成年大鼠LTD的可能受体机制.结果显示,AP5和MCPG都能抑制由2-Hz多串刺激诱导的LTD:强直刺激后20 min时PS幅度分别为基础值的(96.0±3.5)%(n=10)和(95.7±4.1)%(n=8).MCPG能够抑制5-Hz多串刺激诱导的LTD的产生,而AP5不能:分别应用AP5和MCPG后,强直刺激后35 min时PS的幅度分别为基础值的(73.6±4.4)%(n=10)和(98.2±8.9)%(n=8).以上结果提示,2-Hz多串刺激诱导的LTD可能依赖于NMDA受体与mGlu受体的共同活化,而5-Hz多串刺激诱导的LTD只与mGlu受体有关.因此,不同频率的多串刺激诱导的LTD涉及不同的谷氮酸受体机制.     

Fast cultural evolution of Crossbill (Loxia spp.) calls in the Palaearctic

Learned vocal signals of birds provide one of the most comprehensive sources of evidence for culture in animals. Such vocal signals often vary spatially and temporally. Signal variation can be driven by direct factors such as cultural drift and selection or by indirect factors such as changes in the environment, which may affect morphology and therefore acoustic capability. In this study we analysed flight and excitement calls of several call types of the Red Crossbill Loxia curvirostra and other crossbill species. Calls were recorded between 1962 and 2019 across the Palaearctic region. We measured acoustic similarity within flight and excitement calls and modelled the size of the effect attributed to temporal and geographical distance. Geographical distance between different sampling locations explained less call variation compared with temporal distance, and temporal variation within the excitement calls was smaller than in the flight calls. We conclude that calls of most call types of Red, Scottish and Parrot Crossbill are an example of cultural evolution. We suggest that excitement calls are less modifiable because they can serve better in dangerous situations when they are stable in time and space. In addition, we found no clear support for increasing or decreasing flight call similarity of call types while or after being in contact, as found in another study from North America. The reasons for the cultural evolution in calls of Palaearctic crossbills remain unclear.     

Downstream changes in phytoplankton composition and biomass in a lowland river–lake system (Warnow River, Germany)

To determine longitudinal changes in phytoplankton composition and biomass in the Warnow River (Germany), single water parcels were followed during their downstream transport in August and October 1996 and April 1997. In summer, the phytoplankton assemblage was dominated by centric diatom and cyanobacteria species. Stephanodiscus hantzschii, Pseudanabaena limnetica, Planktothrix agardhii and Aulacoseira granulata var. angustissima were the most frequent species. In autumn, small centric diatoms dominated the whole river course. Irrespective of the season, in the fluvial lakes of the upper river, a substantial increase of phytoplankton biomass was observed. Shallow upstream river stretches were associated with large biomass losses. In the deep, slow flowing lower regions, total biomass remained constant. Longitudinal changes in biomass reflected downstream variations in flow velocity and river morphology. Cyanobacteria, cryptophytes and diatom species were subjected to large biomass losses along fast flowing, shallow river sections, whereas chlorophytes were favoured. Diatoms and cryptophytes benefited from low flow velocity and increased water depth in the downstream river. Changes in water depth and flow velocity have been found as key factors that cause the longitudinal differences in phytoplankton composition and biomass in small rivers.     

Interaction of Brain-Type Creatine Kinase with its Transition State Analog: Kinetics of Inhibition and Conformational Changes

Abstract

The effects of components of the transition state analog (creatine, MgADP, planar anion) on the kinetics and conformation of creatine kinase isozyme BB from monkey brain was studied. From analysis of the reaction time course using the pH stat assay, it was shown that during accumulation of the reaction products (ADP and creatine phosphate), among several anions added, nitrate proved the most effective in inhibiting catalytic activity. Maximum inhibition (77%) was achieved with 50 mM nitrate. The K_m for ATP was 0.48 mM and in the presence of 2.5 mM nitrate, 2.2 mM; for ATP in the presence of the dead-end complex, creatine and ADP, the apparent Km was 2.0 mM and theK wasO.16mM; in the presence of the transition state analog, MgADP + NO₃” + creatine, the K was estimated to be 0.04 mM.

Ultraviolet difference spectra of creatine kinase revealed significant differences only in the presence of the complete mixture of the components of the transition state analog. Comparison of gel nitration elution profiles for creatine kinase in the absence and presence of the complete mixture of components of the transition state analog did not reveal any differences in elution volume. Addition of components of the transition state analog to creatine kinase resulted in only a marginal change in intrinsic fluorescence. The presence of the components of the transition state analog increased the rate of reactivity of the enzyme with trinitrobenzenesulfonic acid from k = 6.06 ±0.05M^?1min to 6.96 ± 0.11 M^?1min^?1.

This study provides evidence that, like the muscle isozyme of creatine kinase, the brain form is effectively inhibited by the transition state analog. However, the inhibition is accompanied by small changes in the overall conformation of the protein. This adds to the evidence that the functional differences of the isozymic forms of creatine kinase cannot be attributed to differences in kinetic properties.     

NMDA receptor activation results in PKA- and ERK-dependent Mnk1 activation and increased eIF4E phosphorylation in hippocampal area CA1

Protein synthesis is essential for the stabilization of glutamate receptor-dependent forms of long-lasting hippocampal synaptic plasticity and for the consolidation of memory, but the signal transduction mechanisms that regulate translation factors during these processes are not well understood. As a first step towards understanding how translation is activated during synaptic plasticity, we investigated how the eukaryotic initiation factor 4E (eIF4E), a rate-limiting mRNA cap-binding protein, and its kinase, Mnk1, are regulated by protein kinase C (PKC), cAMP-dependent protein kinase (PKA) and N-methyl-D-aspartate (NMDA) receptor activation in hippocampal area CA1. We found that treatment of mouse hippocampal slices with either phorbol ester, to activate PKC, or forskolin, to activate PKA, resulted in activation of Mnk1 and increased eIF4E phosphorylation that was dependent on extracellular signal-regulated kinase (ERK). Similarly, brief treatment of hippocampal slices with NMDA resulted in activation of Mnk1 and increased phosphorylation of eIF4E. The NMDA-induced activation of Mnk1 and increased phosphorylation of eIF4E were dependent on PKA and ERK, but not PKC, and were present in synaptoneurosome preparations. Immunohistochemical analysis revealed that the PKA- and ERK-dependent increases in Mnk1 activation induced by NMDA also occurred in dendrites. These findings identify a specific regulatory pathway that can couple NMDA receptor activation to translation initiation factors in the hippocampus, and may represent a mechanism for triggering dendritic protein synthesis during long-term potentiation and long-term memory formation.     

Oligochaete communities at the mouth of the Neva and their relationship to anthropogenic impact

Changes in the oligochaete community of the Neva Mouth for the period 1982–1993 are discussed in relation to anthropogenic impacts. A number of community parameters such as species composition, biomass and diversity were generally stable, although local changes were noted. Predominance of eutrophic species, i.e. L. hoffmeisteri, T. tubifex, P. hammoniensis was enhanced, whereas mesotrophic and oligotrophic species — L. isoporus, S. heringianus, T. newaensis disappeared or became less numerous at some stations. The reverse trend was observed at other stations. These phenomena were accompanied by a sharp increase in the variability of biomass and/or diversity, which is regarded as exceeding normal annual fluctuations. The oligochaete community is recognized as a promising indicator of the ecological situation in the Neva Mouth.     

Influence of proteolytic enzymes and calcium-binding agents on nuclear and cell surface topography

Summary Transmission electron microscopy was used to study the effects of proteolytic enzymes (collagenase, trypsin, clostripain), the calcium chelator ethyleneglycol-bis-(-aminoethyl ether) N,N,N',N'-tetraacetic acid (EGTA), and the calcium ionophore A 23187 on substrate adhesion and fine structure of chondrocytes and fibroblasts. Monolayer cultured cells responded to treatment with the proteolytic enzymes followed by EGTA or A 23187 by rounding and detaching from the substrate. This was accompanied by the formation of a microvillous surface, deep nuclear folds, and numerous cytoplasmic vacuoles. Labeling experiments with colloidal thorium dioxide indicated that the vacuoles were formed by endocytosis and fusion of endocytic vesicles with preexisting lysosomes. To a variable extent, similar changes were produced by trypsin or EGTA alone. The cells regained their normal fine structure after withdrawal of the reagents and when seeded onto a substrate. In suspension culture, recovery was incomplete; the cells retained a rounded shape and an increased number of cytoplasmic vacuoles.The results suggest that changes in plasma membrane composition and its permeability to calcium represent the primary signal for cell rounding and detachment. The cellular mechanisms responsible for the associated folding of the nuclear envelope and the cell surface remain unidentified. Nevertheless, this is believed to represent a means of handling of excess membrane during sudden transition from a flattened to a rounded shape. Membrane stored in folds and vacuoles is reutilized when the cells reattach and spread out on a substrate.Expert technical assistance was provided by Karin Blomgren and Anne-Marie Motakefi. Financial support was obtained from the Swedish Medical Research Council (06537), the King Gustaf V 80th Birthday Fund and from the Funds of Leiden University     

Seasonal changes in alkaline phosphatase activity of bacteria and microalgae in Lake Pavin (Massif Central,France)

Seasonal changes in alkalinephosphatase activity of bacteria and microalgae werestudied in the dimictic Lake Pavin (Massif Central,France), to test whetherthis activity is primarily algal or bacterial andwhether the APA presents seasonal variations coupledwith abiotic and biotic variables. Samples werecollected at different depths from May 1992 to May1993. The specific phosphatase activities wereanalysed spectrophotometrically with p-NitrophenylPhosphate (p-NPP) as substrate and were related to theprotein concentrations. No correlation was foundbetween alkaline phosphatase activity and solublereactive phosphorus (SRP) concentrations across anannual cycle. The specific activities of the smallclass (0.2–1.2 m) were the highest and thecontribution of this picoplanktonic size class(0.2–1.2 m) increased with depth. In addition, thelinear correlations between alkaline phosphataseactivity and protein concentration seemed to indicatethat most of these enzymes are constitutive. However,it cannot be excluded that the high phosphorusconcentrations repress APA.Finally, the measure of APA does not seem to be avalid quantitative test of the deficiency ofphosphorus for aquatic microorganisms.