Predicted warming and browning affect timing and magnitude of plankton phenological events in lakes: a mesocosm study

1. Aquatic ecosystems in Northern Europe are expected to face increases in temperature and water colour (TB) in future. While effects of these factors have been studied separately, it is unknown whether and how a combination of them might affect phenological events and trophic interactions. 2. In a mesocosm study, we combined both factors to create conditions expected to arise during the coming century. We focused on quantifying effects on timing and magnitude of plankton spring phenological events and identifying possible mismatches between resources (phytoplankton) and consumers (zooplankton). 3. We found that the increases in TB had important effects on timing and abundance of different plankton groups. While increased temperature led to an earlier peak in phytoplankton and zooplankton and a change in the relative timing of different zooplankton groups, increased water colour reduced chlorophyll‐a concentrations. 4. Increased TB together benefitted cladocerans and calanoid copepods and led to stronger top‐down control of algae by zooplankton. There was no sign of a mismatch between primary producers and grazers as reported from other studies. 5. Our results point towards an earlier onset of plankton spring growth in shallow lakes in future with a stronger top‐down control of phytoplankton by zooplankton grazers.     

Effects of brown and turbid water on piscivore–prey fish interactions along a visibility gradient

1. Environmental changes such as eutrophication and increasing inputs of humic matter (brownification) may have strong effects on predator–prey interactions in lakes through a reduction in the visual conditions affecting foraging behaviour of visually oriented predators. 2. In this experiment, we studied the effects of visual range (25–200 cm) in combination with optically deteriorating treatments (algae, clay or brown humic water) on predator–prey interactions between pike (Esox lucius) and roach (Rutilus rutilus). We measured effects on reaction distance and strike distance for pike and escape distance for roach, when pike individuals were exposed to free‐swimming roach as well as to roach held in a glass cylinder. 3. We found that reaction distance decreased with decreasing visual range caused by increasing levels of algae, clay or humic matter. The effect of reaction distance was stronger in turbid water (clay, algae) than in the brown water treatment. 4. Strike distance was neither affected by visual range nor by optical treatment, but we found shorter strike distances when pike attacked roach using visual cues only (roach held in a cylinder) compared to when pike could use multiple senses (free‐swimming roach). Escape distance for roach was longer in turbid than in brown water treatments. 5. Changes in environmental drivers, such as eutrophication and brownification, affecting the optical climate should thus have consequences for the strength of predator–prey interactions through changes in piscivore foraging efficiency and prey escape behaviour. This in turn may affect lake ecosystems through higher‐order interactions.     

Toxoplasma gondii actively inhibits neuronal function in chronically infected mice

Upon infection with the obligate intracellular parasite Toxoplasma gondii, fast replicating tachyzoites infect a broad spectrum of host cells including neurons. Under the pressure of the immune response, tachyzoites convert into slow-replicating bradyzoites, which persist as cysts in neurons. Currently, it is unclear whether T. gondii alters the functional activity of neurons, which may contribute to altered behaviour of T. gondii-infected mice and men. In the present study we demonstrate that upon oral infection with T. gondii cysts, chronically infected BALB/c mice lost over time their natural fear against cat urine which was paralleled by the persistence of the parasite in brain regions affecting behaviour and odor perception. Detailed immunohistochemistry showed that in infected neurons not only parasitic cysts but also the host cell cytoplasm and some axons stained positive for Toxoplasma antigen suggesting that parasitic proteins might directly interfere with neuronal function. In fact, in vitro live cell calcium (Ca(2+)) imaging studies revealed that tachyzoites actively manipulated Ca(2+) signalling upon glutamate stimulation leading either to hyper- or hypo-responsive neurons. Experiments with the endoplasmatic reticulum Ca(2+) uptake inhibitor thapsigargin indicate that tachyzoites deplete Ca(2+) stores in the endoplasmatic reticulum. Furthermore in vivo studies revealed that the activity-dependent uptake of the potassium analogue thallium was reduced in cyst harbouring neurons indicating their functional impairment. The percentage of non-functional neurons increased over time In conclusion, both bradyzoites and tachyzoites functionally silence infected neurons, which may significantly contribute to the altered behaviour of the host.     

Future climate change driven sea‐level rise: secondary consequences from human displacement for island biodiversity

Sea‐level rise (SLR) due to global warming will result in the loss of many coastal areas. The direct or primary effects due to inundation and erosion from SLR are currently being assessed; however, the indirect or secondary ecological effects, such as changes caused by the displacement of human populations, have not been previously evaluated. We examined the potential ecological consequences of future SLR on >1,200 islands in the Southeast Asian and the Pacific region. Using three SLR scenarios (1, 3, and 6 m elevation, where 1 m approximates most predictions by the end of this century), we assessed the consequences of primary and secondary SLR effects from human displacement on habitat availability and distributions of selected mammal species. We estimate that between 3–32% of the coastal zone of these islands could be lost from primary effects, and consequently 8–52 million people would become SLR refugees. Assuming that inundated urban and intensive agricultural areas will be relocated with an equal area of habitat loss in the hinterland, we project that secondary SLR effects can lead to an equal or even higher percent range loss than primary effects for at least 10–18% of the sample mammals in a moderate range loss scenario and for 22–46% in a maximum range loss scenario. In addition, we found some species to be more vulnerable to secondary than primary effects. Finally, we found high spatial variation in vulnerability: species on islands in Oceania are more vulnerable to primary SLR effects, whereas species on islands in Indo‐Malaysia, with potentially 7–48 million SLR refugees, are more vulnerable to secondary effects. Our findings show that primary and secondary SLR effects can have enormous consequences for human inhabitants and island biodiversity, and that both need to be incorporated into ecological risk assessment, conservation, and regional planning.     

Synaptic proteome changes in mouse brain regions upon auditory discrimination learning

Changes in synaptic efficacy underlying learning and memory processes are assumed to be associated with alterations of the protein composition of synapses. Here, we performed a quantitative proteomic screen to monitor changes in the synaptic proteome of four brain areas (auditory cortex, frontal cortex, hippocampus striatum) during auditory learning. Mice were trained in a shuttle box GO/NO-GO paradigm to discriminate between rising and falling frequency modulated tones to avoid mild electric foot shock. Control-treated mice received corresponding numbers of either the tones or the foot shocks. Six hours and 24 h later, the composition of a fraction enriched in synaptic cytomatrix-associated proteins was compared to that obtained from na?ve mice by quantitative mass spectrometry. In the synaptic protein fraction obtained from trained mice, the average percentage (±SEM) of downregulated proteins (59.9 ± 0.5%) exceeded that of upregulated proteins (23.5 ± 0.8%) in the brain regions studied. This effect was significantly smaller in foot shock (42.7 ± 0.6% down, 40.7 ± 1.0% up) and tone controls (43.9 ± 1.0% down, 39.7 ± 0.9% up). These data suggest that learning processes initially induce removal and/or degradation of proteins from presynaptic and postsynaptic cytoskeletal matrices before these structures can acquire a new, postlearning organisation. In silico analysis points to a general role of insulin-like signalling in this process.     

ATP occlusion by P-glycoprotein as a surrogate measure for drug coupling

The multidrug efflux pump P-glycoprotein (Pgp) couples drug transport to ATP hydrolysis. Previously, using a synthetic library of tetramethylrosamine ( TMR) analogues, we observed significant variation in ATPase stimulation ( V m (D)). Concentrations required for half-maximal ATPase stimulation ( K m (D)) correlated with ATP hydrolysis transition-state stabilization and ATP occlusion (EC 50 (D)) at a single site. Herein, we characterize several TMR analogues that elicit modest turnover ( k cat 相似文献   

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Modeling the microbial loop: An estuarine modeler's perspective

Contemporary models of the microbial loop should be critically evaluated relative to their compartmental structures, flow networks, and treatment of upper ocean physics (vertical and horizontal boundary conditions). The development of new models that include better representation of the autotrophic components and mixotrophy/competitive interactions is warranted. The mathematical structures should reflect contemporary knowledge of controls (e.g., multiple resource limitation), thresholds and limits, and be based on testable assumptions. Stochastic processes must at some point be included to evaluate known patterns of spatial and temporal variability.