Chemical signals and habitat selection by three zooplankters in Andean Patagonian ponds

1. Zooplankton may react differently to chemical signals produced by macrophytes in shallow systems. They may be attracted by macrophytes, as the plants may be used as a refuge against predators, or the plants may have a repellent effect (e.g. when the plants are a habitat for numerous invertebrate predators or fish). In fishless Patagonian ponds, the structural complexity provided by macrophytes modulates the rate of predation on zooplankton by the invertebrate predator Mesostoma ehrenbergii (Turbellaria). 2. We performed a field study to analyse the coexistence of M. ehrenbergii and three of its prey (two copepods, the calanoid Boeckella gracilis and the cyclopoid Acanthocyclops robustus, and the cladoceran Ceriodaphnia dubia) in four ponds. In two of the ponds, we carried out day and night sampling to evaluate the influence of macrophytes on the distribution of these zooplankters. 3. In laboratory experiments, we analysed the response of the zooplankters to the chemical signals produced by macrophytes (the emergent Juncus pallescens and the submerged Myriophyllum quitense), the predator M. ehrenbergii and the ‘alarm signal’ provided by a homogenate of conspecifics. 4. Our field studies demonstrated the coexistence of M. ehrenbergii and the selected prey in different seasons and that A. robustus and C. dubia choose the vegetated area (a mixed bed of J. pallescens and M. quitense) over the non‐vegetated area. The habitat choice experiments indicated that the presence of M. ehrenbergii may directly affect the habitat selection of B. gracilis, because this zooplankter swam away from the predator. In addition, Mesostoma may indirectly affect the habitat selection of the cyclopoid copepod A. robustus and the cladoceran C. dubia as both zooplankters exhibited a negative response to the alarm signal produced by crushed conspecifics. 5. The presence of the submerged M. quitense did not affect the horizontal movements of any of the zooplankters studied. In contrast, the emergent macrophyte J. pallescens elicited a positive response of B. gracilis, suggesting that this aquatic plant may act as a predation refuge. 6. Our results suggest that predator avoidance behaviour can occur in fishless environments in response to a tactile invertebrate predator like Mesostoma. In addition, the refuge effect of emergent macrophytes, enhancing the survival of pelagic zooplankters, may act as a key factor in stabilizing predator–prey interactions in fishless Patagonian ponds, as has been widely recorded in northern temperate lakes with fish.     

Plant chemical defence allocation constrains evolution of local range

Many species of plants in the wild are distributed spatially in patches, the boundaries of which may occur and change because of a complicated interplay between myriad environmental stressors and limitations of, or constraints on, plant coping mechanisms. By examining genetic variation and co‐variation among marker‐inferred inbred lines and sib‐families of an upland wild mustard species within and just a few meters across a natural patch boundary, we show that the evolution of tolerance to the stressful environment outside the patch may be constrained by allocation to glucosinolate compounds (GS) that are defensive against generalist insect herbivores. Several potential stressors were associated with the patch boundary, but carbon isotope ratios indicated that sib‐families with smaller stomatal apertures maintained performance better in response to late season dry conditions, suggesting that drought was an important stressor. The presence of GS may help explain the characteristic patchy distribution of mustards, a relatively diverse and important plant family. This result challenges one end of the continuum of the long‐standing Plant Apparency hypothesis, which essentially states the opposite causation, that low molecular weight toxins like GS are evolutionary responses of patchy distributions and correlated life‐history traits.     

Synthetic cells and organelles: compartmentalization strategies

The recent development of RNA replicating protocells and capsules that enclose complex biosynthetic cascade reactions are encouraging signs that we are gradually getting better at mastering the complexity of biological systems. The road to truly cellular compartments is still very long, but concrete progress is being made. Compartmentalization is a crucial natural methodology to enable control over biological processes occurring within the living cell. In fact, compartmentalization has been considered by some theories to be instrumental in the creation of life. With the advancement of chemical biology, artificial compartments that can mimic the cell as a whole, or that can be regarded as cell organelles, have recently received much attention. The membrane between the inner and outer environment of the compartment has to meet specific requirements, such as semi‐permeability, to allow communication and molecular transport over the border. The membrane can either be built from natural constituents or from synthetic polymers, introducing robustness to the capsule.     

Hygroreception in olfactometer studies

Abstract In olfactometric studies, a technique used to measure insect behavioural bias towards airborne chemicals, many of the factors that could affect the bioassay outcome other than the volatiles themselves are carefully controlled (e.g. lighting conditions, temperature, spatial position, physiological state of the insects, time of day when the bioassay is performed) but one factor, namely humidity, is overlooked frequently when studying responses to plant volatiles. Many insect species respond positively and negatively to changes in humidity and, during bioassays, differences arising from odour choices with different water vapour release rates might have confounding effects versus the original intent of the behavioural study. The present study aims to assess the effect of different substrates on the water vapour content of air in an olfactometer‐like set‐up. The results show that airflow humidity is affected by the odour source used in the olfactometer air flow. In addition, the response of the aphid parasitoid Aphidius colemani Viereck (Hymenoptera: Aphidiidae) is studied towards different humidities and plant material in an olfactometer. The present study suggests that humidity needs to be controlled in olfactometric studies.     

Nonequilibrium Pathways during Electrochemical Phase Transformations in Single Crystals Revealed by Dynamic Chemical Imaging at Nanoscale Resolution

The energy density of current batteries is limited by the practical capacity of the positive electrode, which is determined by the properties of the active material and its concentration in the composite electrode architecture. The observation in dynamic conditions of electrochemical transformations creates the opportunity of identifying design rules toward reaching the theoretical limits of battery electrodes. But these observations must occur during operation and at multiple scales. They are particularly critical at the single‐particle level, where incomplete reactions and failure are prone to occur. Here, operando full‐field transmission X‐ray microscopy is coupled with X‐ray spectroscopy to follow the chemical and microstructural evolution at the nanoscale of single crystals of Li_1+xMn_2–xO₄, a technologically relevant Li‐ion battery electrode material. The onset and crystallographic directionality of a series of complex phase transitions are followed and correlated with particle fracture. The dynamic character of this study reveals the existence of nonequilibrium pathways where phases at substantially different potentials can coexist at short length scales. The results can be used to inform the engineering of particle morphologies and electrode architectures that bypass the issues observed here and lead to optimized battery electrode properties.