Wasp-waist interactions in the North Sea ecosystem

Background

In a “wasp-waist” ecosystem, an intermediate trophic level is expected to control the abundance of predators through a bottom-up interaction and the abundance of prey through a top-down interaction. Previous studies suggest that the North Sea is mainly governed by bottom-up interactions driven by climate perturbations. However, few studies have investigated the importance of the intermediate trophic level occupied by small pelagic fishes.

Methodology/Principal Findings

We investigated the numeric interactions among 10 species of seabirds, two species of pelagic fish and four groups of zooplankton in the North Sea using decadal-scale databases. Linear models were used to relate the time series of zooplankton and seabirds to the time series of pelagic fish. Seabirds were positively related to herring (Clupea harengus), suggesting a bottom-up interaction. Two groups of zooplankton; Calanus helgolandicus and krill were negatively related to sprat (Sprattus sprattus) and herring respectively, suggesting top-down interactions. In addition, we found positive relationships among the zooplankton groups. Para/pseudocalanus was positively related to C. helgolandicus and C. finmarchicus was positively related to krill.

Conclusion/Significance

Our results indicate that herring was important in regulating the abundance of seabirds through a bottom-up interaction and that herring and sprat were important in regulating zooplankton through top-down interactions. We suggest that the positive relationships among zooplankton groups were due to selective foraging and switching in the two clupeid fishes. Our results suggest that “wasp-waist” interactions might be more important in the North Sea than previously anticipated. Fluctuations in the populations of pelagic fish due to harvesting and depletion of their predators might accordingly have profound consequences for ecosystem dynamics through trophic cascades.     

Nephrogenic Systemic Fibrosis in Denmark– A Nationwide Investigation

Background

Nephrogenic systemic fibrosis is a debilitating and painful disorder with an increased stimulation of the connective tissue in the skin and systemic tissues. The disease is associated with exposure to gadolinium-based contrast agent used in magnetic resonance imaging in patients with renal impairment.

Methods

The prevalence of nephrogenic systemic fibrosis has so far never been determined at a national level. In 2009, Denmark was the first country to design a guideline for the tracing of nephrogenic systemic fibrosis patients. The aim of this paper is to communicate the main findings of this quest.

Results

The outcome of the nationwide investigation revealed that Denmark had 65 patients with nephrogenic systemic fibrosis and thereby the highest prevalence of nephrogenic systemic fibrosis worldwide with 65 per 5.6 million inhabitants, or 12 per million.

Conclusions

The nationwide investigation in Denmark revealed the highest prevalence of NSF worldwide. This may be rooted in a high level of awareness of NSF both among doctors, politicians and, not least, the media, combined with the fact that a nationwide NSF investigation was initiated.     

The Nordic Aortic Valve Intervention (NOTION) trial comparing transcatheter versus surgical valve implantation: study protocol for a randomised controlled trial

Background

Degenerative aortic valve (AV) stenosis is the most prevalent heart valve disease in the western world. Surgical aortic valve replacement (SAVR) has until recently been the standard of treatment for patients with severe AV stenosis. Whether transcatheter aortic valve implantation (TAVI) can be offered with improved safety and similar effectiveness in a population including low-risk patients has yet to be examined in a randomised setting.

Methods/Design

This randomised clinical trial will evaluate the benefits and risks of TAVI using the transarterial CoreValve System (Medtronic Inc., Minneapolis, MN, USA) (intervention group) compared with SAVR (control group) in patients with severe degenerative AV stenosis. Randomisation ratio is 1:1, enrolling a total of 280 patients aged 70 years or older without significant coronary artery disease and with a low, moderate, or high surgical risk profile. Trial outcomes include a primary composite outcome of myocardial infarction, stroke, or all-cause mortality within the first year after intervention (expected rates 5% for TAVI, 15% for SAVR). Exploratory safety outcomes include procedure complications, valve re-intervention, and cardiovascular death, as well as cardiac, cerebral, pulmonary, renal, and vascular complications. Exploratory efficacy outcomes include New York Heart Association functional status, quality of life, and valve prosthesis and cardiac performance. Enrolment began in December 2009, and 269 patients have been enrolled up to December 2012.

Discussion

The trial is designed to evaluate the performance of TAVI in comparison with SAVR. The trial results may influence the choice of treatment modality for patients with severe degenerative AV stenosis.

Trial registration

ClinicalTrials.gov: NCT01057173     

Treatment of Mycoplasma genitalium. Observations from a Swedish STD Clinic

Objectives

To evaluate therapy for Mycoplasma genitalium infection with doxycycline or azithromycin 1 g compared to five days of azithromycin (total dose 1.5 g).

Methods

A retrospective case study was performed among patients attending the STD-clinic in Falun, Sweden 1998–2005. All patients with a positive PCR test for M. genitalium were routinely offered a test of cure (toc). Response to doxycycline for 9 days, azithromycin 1 g single dose and extended azithromycin (500 mg on day 1 followed by 250 mg o.d. for 4 days) was determined. In patients with treatment failure after azithromycin, macrolide resistance was monitored before and after treatment. Furthermore, the rate of macrolide resistance was monitored for positive specimens available from 2006–2011.

Results

The eradication rate after doxycycline was 43% (48% for women and 38% for men), for azithromycin 1 g 91% (96% for women and 88% for men) and for extended azithromycin 99% (100% for women and 93% for men). Macrolide resistance developed in 7/7 examined (100%) of those testing positive after azithromycin 1 g, but in none of those treated with extended azithromycin. Macrolide resistance before treatment increased from 0% in 2006 and 2007 to 18% in 2011.

Conclusions

These findings confirm the results from other studies showing that doxycycline is inefficient in eradicating M. genitalium. Although azithromycin 1 g was not significantly less efficient than extended dosage, it was associated with selection of macrolide resistant M. genitalium strains and should not be used as first line therapy for M. genitalium. Monitoring of M. genitalium macrolide resistance should be encouraged.     

Postglacial migration supplements climate in determining plant species ranges in Europe

The influence of dispersal limitation on species ranges remains controversial. Considering the dramatic impacts of the last glaciation in Europe, species might not have tracked climate changes through time and, as a consequence, their present-day ranges might be in disequilibrium with current climate. For 1016 European plant species, we assessed the relative importance of current climate and limited postglacial migration in determining species ranges using regression modelling and explanatory variables representing climate, and a novel species-specific hind-casting-based measure of accessibility to postglacial colonization. Climate was important for all species, while postglacial colonization also constrained the ranges of more than 50 per cent of the species. On average, climate explained five times more variation in species ranges than accessibility, but accessibility was the strongest determinant for one-sixth of the species. Accessibility was particularly important for species with limited long-distance dispersal ability, with southern glacial ranges, seed plants compared with ferns, and small-range species in southern Europe. In addition, accessibility explained one-third of the variation in species' disequilibrium with climate as measured by the realized/potential range size ratio computed with niche modelling. In conclusion, we show that although climate is the dominant broad-scale determinant of European plant species ranges, constrained dispersal plays an important supplementary role.     

Deconstructing the mammal species richness pattern in Europe – towards an understanding of the relative importance of climate,biogeographic history,habitat heterogeneity and humans

Aim We deconstructed the mammal species richness pattern in Europe to assess the importance of large‐scale gradients in current macroclimate relative to biogeographic history, habitat heterogeneity and human influence (HHH variables) as richness determinants for total species, and for widespread and endemic species separately. Location Europe, west of 30° E. Methods We deconstructed total species richness (50‐km resolution) into its widespread and endemic species richness components. We used simultaneous autoregressive modelling (SAR) with information‐theoretic model selection and variation partitioning to assess the importance of macroclimate and HHH variables. The HHH variables included two historical factors, estimated by novel methodologies: (1) ice‐age‐driven dynamics, represented by accessibility to recolonization from hindcasting‐estimated glacial refugia, and (2) biogeographic peninsular dynamics, represented by distance to the entry region for the main European faunal source in western Asia. Results A large fraction of explained variation was shared between macroclimate and HHH in the SAR models. For total species richness, more variation could be uniquely attributed to macroclimate than to HHH, whereas for the deconstructed patterns (widespread and endemic species) the opposite was the case. Considering the individual factors, there was a strong peninsula effect on both widespread and endemic species richness but not on total richness. Main conclusions Both macroclimate and HHH variables (history, habitat heterogeneity and human influence) proved important predictors of species richness, but also difficult to disentangle. Notably, biogeographic history, in particular peninsular dynamics, is an important determinant of widespread and endemic species richness.     

Formation of Dynamic Soluble Surfactant-induced Amyloid β Peptide Aggregation Intermediates

Intermediate amyloidogenic states along the amyloid β peptide (Aβ) aggregation pathway have been shown to be linked to neurotoxicity. To shed more light on the different structures that may arise during Aβ aggregation, we here investigate surfactant-induced Aβ aggregation. This process leads to co-aggregates featuring a β-structure motif that is characteristic for mature amyloid-like structures. Surfactants induce secondary structure in Aβ in a concentration-dependent manner, from predominantly random coil at low surfactant concentration, via β-structure to the fully formed α-helical state at high surfactant concentration. The β-rich state is the most aggregation-prone as monitored by thioflavin T fluorescence. Small angle x-ray scattering reveals initial globular structures of surfactant-Aβ co-aggregated oligomers and formation of elongated fibrils during a slow aggregation process. Alongside this slow (minutes to hours time scale) fibrillation process, much faster dynamic exchange (k_ex ∼1100 s⁻¹) takes place between free and co-aggregate-bound peptide. The two hydrophobic segments of the peptide are directly involved in the chemical exchange and interact with the hydrophobic part of the co-aggregates. Our findings suggest a model for surfactant-induced aggregation where free peptide and surfactant initially co-aggregate to dynamic globular oligomers and eventually form elongated fibrils. When interacting with β-structure promoting substances, such as surfactants, Aβ is kinetically driven toward an aggregation-prone state.     

Rational and Combinatorial Engineering of the Glucan Synthesizing Enzyme Amylosucrase

Rational engineering of amylosucrase required detailed investigations of the molecular basis of catalysis. Biochemical characterization of the enzyme coupled to structural analyses enabled the polymerization mechanism to be elucidated. This provided key information for successfully changing amylosucrase to a hydrolase or an improved polymerase using site-directed mutagenesis. In parallel, a combinatorial approach was developed to further improve the catalyst. The method, based on random mutagenesis and recombination of parent sequences, has generated libraries of variants. These were searched for improved polymer formation using a first step of selection followed by a screening test including a double detection method. Several mutants with desired properties have been isolated, their sequences revealed that they could not have been designed following a rational approach.     

Activity and food choice of piscivorous perch (Perca fluviatilis) in a eutrophic shallow lake: a radio-telemetry study

SUMMARY 1. Radio transmitters were implanted in large perch (27–37 cm) in a shallow lake in Denmark. Between 6 and 13 perch were tracked every 3 h for 24‐h periods twice (summer) or once a month (winter) from August 1997 to July 1998. Activity levels were recorded as minimum distance moved per hour. 2. No significant differences in activity levels of individual fish were observed. 3. Highest activities were observed at daytime with peaks at dawn and dusk or midday. This diel pattern was most pronounced from October to April, whereas diel variations were less in the summer months, with no peaks occurring in midsummer. The general lack of activity at night supports the idea that perch is a visually oriented forager. 4. There was no significant relationship between daytime activity during the year and temperature or day length, but nighttime activity was correlated with temperature. In contrast with previous findings, activity levels varied little seasonally, except for high activity levels that occurred concomitantly with high temperatures in August. Instead, we found a significant relationship between the total distances moved per day and temperature, indicating that perch moved at the same average speed in the wintertime, but did so for shorter periods than in summer because of shorter day lengths. 5. Diet of the tagged perch shifted from fish dominance between August and January to invertebrates from February to June. There was no correlation between the diet shift and activity levels, indicating that feeding on invertebrate requires similar activity levels as predation on fish. 6. The results of this telemetry study throughout a year suggest that perch are more active during the winter than previously inferred from gill‐net catches. This observation underscores the importance of perch as a predator of 0+ planktivorous fish in lakes and has potential implications for pelagic food web structure and lake management by biomanipulation.