Division of labour and worker size polymorphism in ant colonies: the impact of social and genetic factors

Division of labour among workers is central to the organisation and ecological success of insect societies. If there is a genetic component to worker size, morphology or task preference, an increase in colony genetic diversity arising from the presence of multiple breeders per colony might improve division of labour. We studied the genetic basis of worker size and task preference in Formica selysi, an ant species that shows natural variation in the number of mates per queen and the number of queens per colony. Worker size had a heritable component in colonies headed by a doubly mated queen (h ²=0.26) and differed significantly among matrilines in multiple-queen colonies. However, higher levels of genetic diversity did not result in more polymorphic workers across single- or multiple-queen colonies. In addition, workers from multiple-queen colonies were consistently smaller and less polymorphic than workers from single-queen colonies. The relationship between task, body size and genetic lineage appeared to be complex. Foragers were significantly larger than brood-tenders, which may provide energetic or ergonomic advantages to the colony. Task specialisation was also often associated with genetic lineage. However, genetic lineage and body size were often correlated with task independently of each other, suggesting that the allocation of workers to tasks is modulated by multiple factors. Overall, these results indicate that an increase in colony genetic diversity does not increase worker size polymorphism but might improve colony homeostasis.     

Within-group spatial position and vigilance: a role also for competition? The case of impalas (<Emphasis Type="Italic">Aepyceros melampus</Emphasis>) with a controlled food supply

Theory predicts that individuals at the periphery of a group should be at higher risk than their more central conspecifics since they would be the first to be encountered by an approaching terrestrial predator. As a result, it is expected that peripheral individuals display higher vigilance levels. However, the role of conspecifics in this “edge effect” may have been previously overlooked, and taking into account the possible role of within-group competition is needed. Vigilance behavior in relation to within-group spatial position was studied in impalas (Aepyceros melampus) feeding on standardized patches. We also controlled for food distribution in order to accurately define a “central” as opposed to a “peripheral” position. Our data clearly supported an edge effect, with peripheral individuals spending more time vigilant than their central conspecifics. Data on social interactions suggest that it was easier for a foraging individual to defend its feeding patch with its head lowered, and that more interactions occurred at the center of the group. Together, these results indicate that central foragers may reduce their vigilance rates in response to increased competition. Disentangling how the effects of competition and predation risk contribute to the edge effect requires further investigations.     

A statistical model to forecast the profile of the index structure constant $${C_N^2}$$

A statistical study was performed over 145 profiles of meteorological balloons, equipped with microthermal sensors, from the ground to the midstratosphere. This study put into evidence the lognormal distribution of the fluctuations of the structure constant of temperature, the fluctuations of the buoyancy force and the vertical shear of the horizontal wind speed. We show that these quantities, computed over a large scale (100 m), are correlated up to the midstratosphere. A model is adjusted to estimate the optical turbulence strength from the macroscopic meteorological parameters. The model performances, to estimate and forecast the strength and the altitude of the optical turbulent layers, are quantified and compared with other already defined models. This model was shown to have the best performances and put into evidence a new relation to describe the turbulence on a large scale.     

Deep eutectic solvents as green absorbents of volatile organic pollutants

Volatile organic compounds are a major source of air pollutants. Absorption is an effective solution to treat polluted air loaded with volatile organic compounds, but most actual absorbents are often toxic and non-biodegradable. Here, we tested eutectic solvent mixtures for the absorption of volatile organic compounds for the first time. The affinity of solvent mixtures for toluene, acetaldehyde and dichloromethane was determined by measuring vapour–liquid partition coefficients and liquid phase absorption capacities. Results show that the vapour–liquid partition coefficients vary, at 30 °C, from close to zero for acetaldehyde in the mixtures choline chloride:urea, choline chloride:glycerol and tetrabutylphosphonium bromide:glycerol to 0.124 for dichloromethane in the choline chloride:urea eutectic mixture. These values are similar or even superior to those published for ionic liquids and organic solvents. Solvents based on choline chloride, a food additive, and urea, can solubilize up to 500 times more volatile organic compounds compare to water. Moreover, deep eutectic solvents are easier to prepare and more biodegradable than ionic liquids, which are also toxic. Deep eutectic solvents are more biodegradable than silicone oils, which are also expensive. Furthermore, in terms of recycling, the absorption capacities of the tested solvents remained unchanged during five absorption–desorption cycles. These findings are patented.     

The risk/no-risk rhetoric of environmental impact assessments (EIA): the case of offshore wind farms in Sweden

Risk is a key topic in the communication between developers of infrastructure projects, permit-granting authorities, and civil society. The nature of risk communication is contested among academics, however. Whereas some scholars conceive of risk communication as a matter of effectively communicating expert knowledge on factual matters to the public, others emphasise the role of symbolic construction and rhetoric. This article analyses how wind farm developers rhetorically construct risks in relation to the environmental impact assessment (EIA) for a large offshore wind farm project. Our analysis is inspired by the New Rhetoric, the theory of argumentation developed by Perelman and Olbrechts-Tyteca (Traité de l'argumentation – la nouvelle rhétorique, Brussels: Éditions des presses de l'université de Bruxelles, 1958). We suggest that the EIA adopt a dual argumentative strategy. The report associates numerous risks with the project by identifying and cataloguing them; however, these risks are also disconnected from the project by being described as nonexistent, negligible, or manageable. We discuss some implications of considering EIAs, not as accounts of reality, but as loci of production for this reality.     

Effect of potassium and phosphorus on the transport of radiocesium by arbuscular mycorrhizal fungi

Potassium, a chemical analogue of cesium, and phosphorus, an essential macronutrient transported by arbuscular mycorrhizal fungi (AMF), have been suggested to influence the transport of radiocesium by AMF. However, no study investigated the effects of increasing concentrations of both elements on the importance of this transport. Here, the arbuscular mycorrhizal-plant (AM-P) in vitro culture system associating Medicago truncatula plantlets with Glomus intraradices was used to evaluate this effect.Using three concentrations of K (0, 1, 10 mM) and two concentrations of P (30 and 3000 μM) added to a compartment only accessible to the AMF, we demonstrated that K and P individually and in combination significantly influenced radiocesium transport by AMF. Whilst increased concentration of K decreased the amount of radiocesium transported, the opposite was observed for P. Although the exact mechanisms involved need to be assessed, both elements were identified as important factors influencing the transport of radiocesium by AMF.     

Dynamics of copper and zinc sedimentation in a lagooning system receiving landfill leachate

This study characterises the sediment dredged from a lagooning system composed of a settling pond and three lagoons that receive leachates from a municipal solid waste (MSW) landfill in France. Organic carbon, carbonate, iron oxyhydroxides, copper (Cu) and zinc (Zn) concentrations were measured in the sediment collected from upstream to downstream in the lagooning system. In order to complete our investigation of sedimentation mechanisms, leachates were sampled in both dry (spring) and wet (winter) seasonal conditions. Precipitation of calcite and amorphous Fe-oxyhydroxides and sedimentation of organic matter occurred in the settling pond. Since different distributions of Zn and Cu concentrations are measured in sediment samples collected downstream in the lagooning system, it is suggested that these elements were not distributed in a similar way in the leachate fractions during the first stage of treatment in the settling pond, so that their sedimentation dynamics in the lagooning system differ. In the lagoons, it was found that organic carbon plays a major role in Cu and Zn mobility and trapping. The presence of macrophytes along the edges provided an input of organic matter that enhanced Cu and Zn scavenging. This edge effect resulted in a two-fold increase in Cu and Zn concentrations in the sediment deposited near the banks of the lagoons, thus confirming the importance of vegetation for the retention of Cu and Zn in lagooning systems.