Unimodal response of fish yield to dissolved organic carbon

Here, we demonstrate a contrasting effect of terrestrial coloured dissolved organic material on the secondary production of boreal nutrient poor lakes. Using fish yield from standardised brown trout gill‐net catches as a proxy, we show a unimodal response of lake secondary productivity to dissolved organic carbon (DOC). This suggests a trade‐off between positive and negative effects, where the initial increase may hinge upon several factors such as energy subsidising, screening of UV‐radiation or P and N load being associated with organic carbon. The subsequent decline in production with further increase in DOC is likely associated with light limitations of primary production. We also show that shallow lakes switch from positive to negative effects at higher carbon loads than deeper lakes. These results underpin the major role of organic carbon for structuring productivity of boreal lake ecosystems.     

Increased Inflammatory Response in Cytomegalovirus Seropositive Patients with Alzheimer’s Disease

Alzheimer’s disease (AD) has been associated with increased local inflammation in the affected brain regions, and in some studies also with elevated levels of proinflammatory cytokines in peripheral blood. Cytomegalovirus (CMV) is known to promote a more effector-oriented phenotype in the T-cell compartment, increasing with age. The aim of this study was to investigate the inflammatory response of peripheral blood mononuclear cells (PBMCs) from AD patients and non-demented (ND) controls. Using a multiplex Luminex xMAP assay targeting GM-CSF, IFN-γ, IL-1β, IL-2, IL-4, IL-5, IL-6, IL-8, IP-10 and TNF-α, cytokine profiles from PBMCs were analysed after stimulation with anti-CD3/CD28 beads, CMV pp65 peptide mix or amyloid β (Aβ) protofibrils, respectively. CMV seropositive AD subjects presented with higher IFN-γ levels after anti-CD3/CD28 and CMV pp65 but not after Aβ stimulation, compared to CMV seropositive ND controls. When analysing IFN-γ response to anti-CD3/CD28 stimulation on a subgroup level, CMV seropositive AD subjects presented with higher levels compared to both CMV seronegative AD and CMV seropositive ND subjects. Taken together, our data from patients with clinically manifest AD suggest a possible role of CMV as an inflammatory promoter in AD immunology. Further studies of AD patients at earlier stages of disease, could provide better insight into the pathophysiology.     

Attempted Suicide in Bipolar Disorder: Risk Factors in a Cohort of 6086 Patients

Objective

Bipolar disorder is associated with high risk of self-harm and suicide. We wanted to investigate risk factors for attempted suicide in bipolar patients.

Method

This was a cohort study of 6086 bipolar patients (60% women) registered in the Swedish National Quality Register for Bipolar Disorder 2004–2011 and followed-up annually 2005–2012. Logistic regression was used to calculate adjusted odds ratios for fatal or non-fatal attempted suicide during follow-up.

Results

Recent affective episodes predicted attempted suicide during follow-up (men: odds ratio = 3.63, 95% CI = 1.76–7.51; women: odds ratio = 2.81, 95% CI = 1.78–4.44), as did previous suicide attempts (men: odds ratio = 3.93, 95% CI = 2.48–6.24; women: odds ratio = 4.24, 95% CI = 3.06–5.88) and recent psychiatric inpatient care (men: odds ratio = 3.57, 95% CI = 1.59–8,01; women: odds ratio = 2.68, 95% CI = 1.60–4.50). Further, those with many lifetime depressive episodes were more likely to attempt suicide. Comorbid substance use disorder was a predictor in men; many lifetime mixed episodes, early onset of mental disorder, personality disorder, and social problems related to the primary group were predictors in women.

Conclusion

The principal clinical implication of the present study is to pay attention to the risk of suicidal behaviour in bipolar patients with depressive features and more severe or unstable forms of the disorder.     

Grey Matter Changes in Cognitively Impaired Parkinson's Disease Patients

Background

Cortical changes associated with cognitive decline in Parkinson''s disease (PD) are not fully explored and require investigations with established diagnostic classification criteria.

Objective

We used MRI source-based morphometry to evaluate specific differences in grey matter volume patterns across 4 groups of subjects: healthy controls (HC), PD with normal cognition (PD-NC), PD with mild cognitive impairment (MCI-PD) and PD with dementia (PDD).

Methods

We examined 151 consecutive subjects: 25 HC, 75 PD-NC, 29 MCI-PD, and 22 PDD at an Italian and Czech movement disorder centre. Operational diagnostic criteria were applied to classify MCI-PD and PDD. All structural MRI images were processed together in the Czech centre. The spatial independent component analysis was used to assess group differences of local grey matter volume.

Results

We identified two independent patterns of grey matter volume deviations: a) Reductions in the hippocampus and temporal lobes; b) Decreases in fronto-parietal regions and increases in the midbrain/cerebellum. Both patterns differentiated PDD from all other groups and correlated with visuospatial deficits and letter verbal fluency, respectively. Only the second pattern additionally differentiated PD-NC from HC.

Conclusion

Grey matter changes in PDD involve areas associated with Alzheimer-like pathology while fronto-parietal abnormalities are possibly an early marker of PD cognitive decline. These findings are consistent with a non-linear cognitive progression in PD.     

Host-Specificity and Dynamics in Bacterial Communities Associated with Bloom-Forming Freshwater Phytoplankton

Many freshwater phytoplankton species have the potential to form transient nuisance blooms that affect water quality and other aquatic biota. Heterotrophic bacteria can influence such blooms via nutrient regeneration but also via antagonism and other biotic interactions. We studied the composition of bacterial communities associated with three bloom-forming freshwater phytoplankton species, the diatom Aulacoseira granulata and the cyanobacteria Microcystis aeruginosa and Cylindrospermopsis raciborskii. Experimental cultures incubated with and without lake bacteria were sampled in three different growth phases and bacterial community composition was assessed by 454-Pyrosequencing of 16S rRNA gene amplicons. Betaproteobacteria were dominant in all cultures inoculated with lake bacteria, but decreased during the experiment. In contrast, Alphaproteobacteria, which made up the second most abundant class of bacteria, increased overall during the course of the experiment. Other bacterial classes responded in contrasting ways to the experimental incubations causing significantly different bacterial communities to develop in response to host phytoplankton species, growth phase and between attached and free-living fractions. Differences in bacterial community composition between cyanobacteria and diatom cultures were greater than between the two cyanobacteria. Despite the significance, major differences between phytoplankton cultures were in the proportion of the OTUs rather than in the absence or presence of specific taxa. Different phytoplankton species favoring different bacterial communities may have important consequences for the fate of organic matter in systems where these bloom forming species occur. The dynamics and development of transient blooms may also be affected as bacterial communities seem to influence phytoplankton species growth in contrasting ways.     

Global change‐driven effects on dissolved organic matter composition: Implications for food webs of northern lakes

Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial–aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)—the messenger between terrestrial and lake ecosystems—with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change‐driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice‐out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans.     

Timing and abundance as key mechanisms affecting trophic interactions in variable environments

Climatic changes are disrupting otherwise tight trophic interactions between predator and prey. Most of the earlier studies have primarily focused on the temporal dimension of the relationship in the framework of the match–mismatch hypothesis. This hypothesis predicts that predator's recruitment will be high if the peak of the prey availability temporally matches the most energy‐demanding period of the predators breeding phenology. However, the match–mismatch hypothesis ignores the level of food abundance while this can compensate small mismatches. Using a novel time‐series model explicitly quantifying both the timing and the abundance component for trophic relationships, we here show that timing and abundance of food affect recruitment differently in a marine (cod/zooplankton), a marine–terrestrial (puffin/herring) and a terrestrial (sheep/vegetation) ecosystem. The quantification of the combined effect of abundance and timing of prey on predator dynamics enables us to come closer to the mechanisms by which environment variability may affect ecological systems.     

UV-B induced mortality and antioxidant enzyme activities in Daphnia magna at different oxygen concentrations and temperatures

Survival of adult Daphnia magna was assessed after acute (<96h) exposure to UV₃₁₂ under various temperatures (6, 12 and 18°C)or oxygen concentrations (5.6, 8.5 and 14.1 mg O₂ l^–1)in the laboratory. The surviving animals were screened for theenzymes catalase (CAT) and glutathione transferase (GST), whichmay protect against UV-induced oxidative damage. In addition,the same two enzymes were assayed in separate experiments afteracute exposure to UV₃₁₂ (6 h, 0.014 mW cm^–2) and the differentlevels of temperature and oxygen. No differences were observedin either CAT or GST activity after exposure to the three levelsof oxygen, but there was a tendency for decreasing specificactivity with decreasing temperature for both enzymes. CAT activitywas not influenced by UV radiation, whereas GST activity displayeda slight increase. Oxygen concentration did not influence survivalduring UV exposure but, contrary to expectations, survival testsat different temperatures clearly showed that reduced temperatureincreased survival. The results indicate that temperature effectsmust be considered when comparing dose effect relationshipsin situ, and suggest that low temperature is not a major causeof UV susceptibility in cold-adapted alpine and Arctic populationsof Daphnia.     

Filtering structures and particle size selection in coexisting Cladocera

Summary Five commonly co-occurring cladocerans, Holopedium gibberum, Daphnia longispina, Ceriodaphnia quadrangula, Bosmina longispina, Diaphanosoma brachyurum and the calanoid copepod Eudiaptomus gracilis were fed monodisperse fluorescent latex beads (0.5, 1,5 m) to reveal clearance rates and particle size selection. The results were compared to those obtained with labelled bacteria and yeast. All cladoceran species ingested the beads, and particle size selection varied from a strong predominance of the largest particles in Holopedium, to an almost non selective particle retention in Diaphanosoma. The results indicated a strong correlation between morphology of the filtering combs, measured by Scanning electron microscopy, and ability to retain the smallest particles.