How the social parasitic bumblebee <Emphasis Type="Italic">Bombus bohemicus</Emphasis> sneaks into power of reproduction

Social parasitism is widespread in many groups of social living hymenopteran species and has also evolved in the genus Bombus. Cuckoo bumblebees (subgenus Psithyrus) are obligate brood parasites in nests of other bumblebee species. After nest usurpation and the killing of the host queen, the parasite female has to control worker reproduction in order to accomplish and maintain reproductive dominance and to ensure her reproductive success. The aim of our study was to examine whether the generalist parasitic bumblebee Bombus bohemicus monopolizes and prevents worker reproduction by physical or chemical means and to identify possible odor compounds involved therein. We performed bioassays with callow workers of the host Bombus terrestris and have shown that B. bohemicus females are able to suppress host worker ovarian development, when these host workers are under the direct influence of the parasite female. Furthermore, by chemical analyses, we have demonstrated that the parasite females adjust to the odor profiles of their host queens in order to maintain the level of fertility signaling inside the host colony although the host queen is absent. We also found that host workers change their odor profile after nest usurpation by the parasite female and consequently, we suggest that the host and parasite are caught up in a chemical arms race.     

Suppressing antagonistic bioengineering feedbacks doubles restoration success

In a seagrass restoration project, we explored the potential for enhancing the restoration process by excluding antagonistic engineering interactions (i.e., biomechanical warfare) between two ecosystem engineers: the bioturbating lugworm Arenicola marina and the sediment-stabilizing seagrass Zostera noltii Hornem. Applying a shell layer underneath half of our seagrass transplants successfully reduced adult lugworm density by over 80% and reduced lugworm-induced microtopography (a proxy for lugworm disturbance) at the wave-sheltered site. At the wave-exposed site adult lugworm densities and microtopography were already lower than at the sheltered site but were further reduced in the shell-treated units. Excluding lugworms and their bioengineering effects corresponded well with a strongly enhanced seagrass growth at the wave-sheltered site, which was absent at the exposed site. Enhanced seagrass growth in the present study was fully assigned to the removal of lugworms' negative engineering effects and not to any (indirect) evolving effects such as an altered biogeochemistry or sediment-stabilizing effects by the shell layer. The context-dependency implies that seagrass establishment at the exposed site is not constrained by negative ecosystem-engineering interactions only, but also by overriding physical stresses causing poor growth conditions. Present findings underline that, in addition to recent emphasis on considering positive (facilitating) interactions in ecological theory and practice, it is equally important to consider negative engineering interactions between ecosystem-engineering species. Removal of such negative interactions between ecosystem-engineering species can give a head start to the target species at the initial establishment phase, when positive engineering feedbacks by the target species on itself are still lacking. Though our study was carried out in a marine environment with variable levels of wave disturbance, similar principles may be expected to apply to other ecosystems that are inhabited by ecosystem engineers.     

Trophic cascade induced by molluscivore predator alters pore-water biogeochemistry via competitive release of prey

Effects of predation may cascade down the food web. By alleviating interspecific competition among prey, predators may promote biodiversity, but the precise mechanisms of how predators alter competition have remained elusive. Here we report on a predator-exclosure experiment carried out in a tropical intertidal ecosystem, providing evidence for a three-level trophic cascade induced by predation by molluscivore Red Knots (Calidris canutus) that affects pore water biogeochemistry. In the exclosures the knots' favorite prey (Dosinia isocardia) became dominant and reduced the individual growth rate in an alternative prey (Loripes lucinalis). Dosinia, a suspension feeder, consumes suspended particulate organic matter (POM), whereas Loripes is a facultative mixotroph, partly living on metabolites produced by sulfur-oxidizing chemoautotrophic bacteria, but also consuming suspended POM. Reduced sulfide concentrations in the exclosures suggest that, without predation on Dosinia, stronger competition for suspended POM forces Loripes to rely on energy produced by endosymbiotic bacteria, thus leading to an enhanced uptake of sulfide from the surrounding pore water. As sulfide is toxic to most organisms, this competition-induced diet shift by Loripes may detoxify the environment, which in turn may facilitate other species. The inference that predators affect the toxicity of their environment via a multi-level trophic cascade is novel, but we believe it may be a general phenomenon in detritus-based ecosystems.     

Robustness of variance and autocorrelation as indicators of critical slowing down

Ecosystems close to a critical threshold lose resilience, in the sense that perturbations can more easily push them into an alternative state. Recently, it has been proposed that such loss of resilience may be detected from elevated autocorrelation and variance in the fluctuations of the state of an ecosystem due to critical slowing down; the underlying generic phenomenon that occurs at critical thresholds. Here we explore the robustness of autocorrelation and variance as indicators of imminent critical transitions. We show both analytically and in simulations that variance may sometimes decrease close to a transition. This can happen when environmental factors fluctuate stochastically and the ecosystem becomes less sensitive to these factors near the threshold, or when critical slowing down reduces the ecosystem's capacity to follow high-frequency fluctuations in the environment. In addition, when available data is limited, variance can be systematically underestimated due to the prevalence of low frequencies close to a transition. By contrast, autocorrelation always increases toward critical transitions in our analyses. To exemplify this point, we provide cases of rising autocorrelation and increasing or decreasing variance in time series prior to past climate transitions.     

Trait similarity patterns within grass and grasshopper communities: multitrophic community assembly at work

Trait-based community assembly theory suggests that trait variation among co-occurring species is shaped by two main processes: abiotic filtering, important in stressful environments and promoting similarity, and competition, more important in productive environments and promoting dissimilarity. Previous studies have indeed found trait similarity to decline along productivity gradients. However, these studies have always been done on single trophic levels. Here, we investigated how interactions between trophic levels affect trait similarity patterns along environmental gradients. We propose three hypotheses for the main drivers of trait similarity patterns of plants and herbivores along environmental gradients: (1) environmental control of both, (2) bottom-up control of herbivore trait variation, and (3) top-down control of grass trait variation. To test this, we collected data on the community composition and trait variation of grasses (41 species) and grasshoppers (53 species) in 50 plots in a South African savanna. Structural equation models were used to investigate how the range and spacing of within-community functional trait values of both grasses and their insect herbivores (grasshoppers; Acrididae) respond to (1) rainfall and fire frequency gradients and (2) the trait similarity patterns of the other trophic level. The analyses revealed that traits of co-occurring grasses became more similar toward lower rainfall and higher fire frequency (environmental control), while showing little evidence for top-down control. Grasshopper trait range patterns, on the other hand, were mostly directly driven by vegetation structure and grass trait range patterns (bottom-up control), while environmental factors had mostly indirect effects via plant traits. Our study shows the potential to expand trait-based community assembly theory to include trophic interactions.     

Environmental federalism and environmental liability

Environmental federalism considers what level of government should optimally regulate pollution. This paper addresses this question for accidental pollution, which government regulates through the ex post liability regimes of either negligence or strict liability. We find that decentralizing the choice between these regimes does not, in general, induce the socially optimal outcome. When firms can pay all damages, all regions may choose negligence and impose an overly strict standard of due care. When firms may be bankrupted by damages, all regions may choose strict liability, which induces too little care. In addition, asymmetric equilibria are possible in which some regions choose negligence, others strict liability. Combining negligence with a Pigovian tax, or strict liability with a bonding requirement can align regional authorities' incentives with those of a central government.     

Small-scale entrainment in inclined gravity currents

We investigate the effect of buoyancy on the small-scale aspects of turbulent entrainment by performing direct numerical simulation of a gravity current and a wall jet. In both flows, we detect the turbulent/nonturbulent interface separating turbulent from irrotational ambient flow regions using a range of enstrophy iso-levels spanning many orders of magnitude. Conform to expectation, the relative enstrophy isosurface velocity \(v_n\) in the viscous superlayer scales with the Kolmogorov velocity for both flow cases. We connect the integral entrainment coefficient E to the small-scale entrainment and observe excellent agreement between the two estimates throughout the viscous superlayer. The contribution of baroclinic torque to \(v_n\) is negligible, and we show that the primary reason for reduced entrainment in the gravity current as compared to the wall-jet are 1) the reduction of \(v_n\) relative to the integral velocity scale \(u_T\); and 2) the reduction in the surface area of the isosurfaces.     

Fast and complete removal of the 5-fluorouracil drug from water by electro-Fenton oxidation

Cytostatic drugs are a troublesome class of emerging pollutants in water owing to their potential effects on DNA. Here we studied the removal of 5-fluorouracil from water using the electro-Fenton process. Galvanostatic electrolyses were performed with an undivided laboratory-scale cell equipped with a boron-doped diamond anode and a carbon felt cathode. Results show that the fastest degradation and almost complete mineralization was obtained at a Fe²⁺ catalyst concentration of 0.2 mM. The absolute rate constant for oxidation of 5-fluorouracil by hydroxyl radicals was 1.52 × 10⁹ M^?1 s^?1. Oxalic and acetic acids were initially formed as main short-chain aliphatic by-products, then were completely degraded. After 6 h the final solution mainly contained inorganic ions (NH₄ ⁺, NO₃ ^? and F^?) and less than 10% of residual organic carbon. Hence, electro-Fenton constitutes an interesting alternative to degrade biorefractory drugs.     

Monitoring and reporting attacks on education in the Democratic Republic of the Congo and Somalia

The United Nations' Monitoring and Reporting Mechanism is charged with documenting six grave violations against children in a time of conflict, including attacks on schools. Many of these incidents, however, remain unreported across the globe. This study explores whether or not a local knowledge base of education and child protection actors in North and South Kivu Provinces, Democratic Republic of the Congo, and in Mogadishu, Somalia, could contribute to a more complete record of attacks on education in those areas. Hundreds of semi‐structured interviews were conducted with key informants across the three settings, and in total 432 attacks on education were documented. Purposive samples of these reports were verified and a large majority was confirmed. Local non‐governmental organisations and education institutions were most knowledgeable about these incidents, but most never reported them to a monitoring authority. The study concludes that attack surveillance and response were largely insufficient, and recommends investing in mechanisms that utilise local knowledge to address these shortcomings.