Tragedy of the commons in Melipona bees

In human society selfish use of common resources can lead to disaster, a situation known as the ‘tragedy of the commons’ (TOC). Although a TOC is usually prevented by coercion, theory predicts that close kinship ties can also favour reduced exploitation. We test this prediction using data on a TOC occurring in Melipona bee societies

When resistance is useless: policing and the evolution of reproductive acquiescence in insect societies

In social groups composed of kin, inclusive fitness benefits can favor greater cooperation. Alternatively, cooperation can be enforced through the policing of less cooperative individuals. Here, we show that the effect of policing can be twofold: not only can it directly suppress individual selfishness, it can also entirely remove the incentive for individuals to act selfishly in the first place. We term such individual restraint in response to socially imposed policing "acquiescence" and illustrate the concept using examples drawn from the social Hymenoptera (the ants, bees, and wasps). Inclusive fitness models confirm that when a policing system is in place, individuals should be less tempted to act selfishly. This is shown to have important consequences for the resolution of conflict within their societies. For example, it can explain why in many species very few workers attempt to reproduce and why immature females usually do not attempt to develop as queens rather than workers. Although our analyses are primarily focused on the social insects, our conclusions are likely to be general and to apply to other societies as well

The determinants of Foreign Direct Investments attraction in Portugal and Spain: A comparative analysis

Double Degree. A Work Project presented as part of the requirements for the Award of a Master Degree in Management from the NOVA – School of Business and Economics and a Master Degree in Business Engineering from Louvain School of ManagementThis paper analyzed the determinants of the net Foreign Direct Investments inflows in Portugal and Spain; two countries chosen for their historical and geographical closeness. The study included a large set of macroeconomic, institutional and locational variables. The dataset is composed by yearly data points covering the period 1984-2012. Using regressions in first differences, the paper concluded to the significance of unit labor costs, openness to trade, political stability and socioeconomic conditions for Portugal. As for Spain, market size and European Union GDP growth played a significant role.NSBE - UN

Vertical transmission of honey bee viruses in a Belgian queen breeding program

Background: The Member States of European Union are encouraged to improve the general conditions for the production and marketing of apicultural products. In Belgium, programmes on the restocking of honey bee hives have run for many years. Overall, the success ratio of this queen breeding programme has been only around 50%. To tackle this low efficacy, we organized sanitary controls of the breeding queens in 2012 and 2014. Results: We found a high quantity of viruses, with more than 75% of the egg samples being infected with at least one virus. The most abundant viruses were Deformed Wing Virus and Sacbrood Virus (>= 40%), although Lake Sinai Virus and Acute Bee Paralysis Virus were also occasionally detected (between 10-30%). In addition, Aphid Lethal Paralysis Virus strain Brookings, Black Queen Cell Virus, Chronic Bee Paralysis Virus and Varroa destructor Macula-like Virus occurred at very low prevalences (<= 5%). Remarkably, we found Apis mellifera carnica bees to be less infected with Deformed Wing Virus than Buckfast bees ( p < 0.01), and also found them to have a lower average total number of infecting viruses ( p < 0.001). This is a significant finding, given that Deformed Wing Virus has earlier been shown to be a contributory factor to winter mortality and Colony Collapse Disorder. Moreover, negative-strand detection of Sacbrood Virus in eggs was demonstrated for the first time. Conclusions: High pathogen loads were observed in this sanitary control program. We documented for the first time vertical transmission of some viruses, as well as significant differences between two honey bee races in being affected by Deformed Wing Virus. Nevertheless, we could not demonstrate a correlation between the presence of viruses and queen breeding efficacies

Comprehensive bee pathogen screening in Belgium reveals Crithidia mellificae as a new contributory factor to winter mortality

Since the last decade, unusually high honey bee colony losses have been reported mainly in North-America and Europe. Here, we report on a comprehensive bee pathogen screening in Belgium covering 363 bee colonies that were screened for 18 known disease-causing pathogens and correlate their incidence in summer with subsequent winter mortality. Our analyses demonstrate that, in addition to Varroa destructor, the presence of the trypanosomatid parasite Crithidia mellificae and the microsporidian parasite Nosema ceranae in summer are also predictive markers of winter mortality, with a negative synergy being observed between the two in terms of their effects on colony mortality. Furthermore, we document the first occurrence of a parasitizing phorid fly in Europe, identify a new fourth strain of Lake Sinai Virus (LSV), and confirm the presence of other little reported pathogens such as Apicystis bombi, Aphid Lethal Paralysis Virus (ALPV), Spiroplasma apis, Spiroplasma melliferum and Varroa destructor Macula-like Virus (VdMLV). Finally, we provide evidence that ALPV and VdMLV replicate in honey bees and show that viruses of the LSV complex and Black Queen Cell Virus tend to non-randomly co-occur together. We also noticed a significant correlation between the number of pathogen species and colony losses. Overall, our results contribute significantly to our understanding of honey bee diseases and the likely causes of their current decline in Europe

The effect of forager loss on honeybee workers temporal polyethism and social network structure

The western honeybee Apis mellifera is perhaps the best-known example of an advanced eusocial species displaying temporal polyethism, a process in which workers perform different tasks in the colony as they age. Previous studies demonstrated that this temporal division of labour is not only regulated by the age of the bees but also by the proportion of workers performing the required tasks in the colony. As we progress through the Anthropocene, the Intergovernmental Panel on Climate Change predicted that a significant increase in both the frequency and intensity of severe weather events can be expected in the coming decades. Here, we performed a controlled interrupted time series experiment with the objective of quantifying the possible effects that these weather events might have in the honeybee colony dynamics. By simulating a significant loss of foragers in the colony, we observed that honeybee workers quickly replaced the missing foragers by accelerating their transition to a subsequent task and, in some cases, completely skipped several of the natural task transitions with respect to their age. In addition, we analysed how the colony social network structure is affected by the sudden loss of foragers. Indeed, our data show that honeybee colonies increased their network cohesion with workers having a higher number of interactions as well as becoming more closely connected to one another soon after the disturbance. Overall, our data shows that even when faced with a substantial perturbation, honeybees can respond swiftly in order to maintain colony homeostasis and likely increase their resilience against future perturbations

Electronic band gaps of confined linear carbon chains ranging from polyyne to carbyne

Ultra long linear carbon chains of more than 6000 carbon atoms have recently been synthesized within double-walled carbon nanotubes, and they show a promising new route to one--atom--wide semiconductors with a direct band gap. Theoretical studies predicted that this band gap can be tuned by the length of the chains, the end groups, and their interactions with the environment. However, different density functionals lead to very different values of the band gap of infinitely long carbyne. In this work, we applied resonant Raman excitation spectroscopy with more than 50 laser wavelengths to determine for the first time the band gap of long carbon chains encapsulated inside DWCNTs. The experimentally determined band gaps ranging from 2.253 to 1.848 eV follow a linear relation with Raman frequency. This lower bound is the smallest band gap of linear carbon chains observed so far. The comparison with experimental data obtained for short chains in gas phase or in solution demonstrates the effect of the DWCNT encapsulation, leading to an essential downshift of the band gap. This is explained by the interaction between the carbon chain and the host tube, which greatly modifies the chain's bond length alternation.Comment: 7 pages, 5 figure

Contrasting indirect effects of an ant host on prey–predator interactions of symbiotic arthropods

Indirect interactions occur when a species affects another species by altering the density (density-mediated interactions) or influencing traits (trait-mediated interactions) of a third species. We studied variation in these two types of indirect interactions in a network of red wood ants and symbiotic arthropods living in their nests. We tested whether the ant workers indirectly affected survival of a symbiotic prey species (Cyphoderus albinus) by changing the density and/or traits of three symbiotic predators, i.e., Mastigusa arietina, Thyreosthenius biovatus and Stenus aterrimus, provoking, respectively, low, medium and high ant aggression. An ant nest is highly heterogeneous in ant worker density and the number of aggressive interactions towards symbionts increases with worker density. We, therefore, hypothesized that varying ant density could indirectly impact prey-predator interactions of the associated symbiont community. Ants caused trait-mediated indirect effects in all three prey-predator interactions, by affecting the prey capture rate of the symbiotic predators at different worker densities. Prey capture rate of the highly and moderately aggressed spider predators M. arietina and T. biovatus decreased with ant density, whereas the prey capture rate of the weakly aggressed beetle predator S. aterrimus increased. Ants also induced density-mediated indirect interactions as high worker densities decreased the survival rate of the two predatory spider species. These results demonstrate for the first time that a host can indirectly mediate the trophic interactions between associated symbionts. In addition, we show that a single host can induce opposing indirect effects depending on its degree of aggression towards the symbionts.status: publishe

Separation of specific single-enantiomer single-wall carbon nanotubes in the large-diameter regime

The enantiomer-level isolation of single-walled carbon nanotubes (SWCNTs) in high concentration and with high purity for nanotubes greater than 1.1 nm in diameter is demonstrated using a two-stage aqueous two-phase extraction (ATPE) technique. In total, five different nanotube species of ∼1.41 nm diameter are isolated, including both metallics and semiconductors. We characterize these populations by absorbance spectroscopy, circular dichroism spectroscopy, resonance Raman spectroscopy, and photoluminescence mapping, revealing and substantiating mod-dependent optical dependencies. Using knowledge of the competitive adsorption of surfactants to the SWCNTs that controls partitioning within the ATPE separation, we describe an advanced acid addition methodology that enables the fine control of the separation of these select nanotubes. Furthermore, we show that endohedral filling is a previously unrecognized but important factor to ensure a homogeneous starting material and further enhance the separation yield, with the best results for alkane-filled SWCNTs, followed by empty SWCNTs, with the intrinsic inhomogeneity of water-filled SWCNTs causing them to be worse for separations. Lastly, we demonstrate the potential use of these nanotubes in field-effect transistors