Water-Proofing Properties of Cuticular Lipids

SYNOPSIS. Epicuticular lipids play a critical role in allowingarthropods to thrive in terrestrial environments, by reducingtranspiration of water through the cuticle. These lipids consistof a diverse array of compounds, especiaUy long-chain hydrocarbons.Rates of water loss are correlated with hydrocarbon structuralfeatures, including chain length, unsaturation and methyl-branching.The water-proofing abilities of cuticular lipids appear to dependlargely on their physical properties. In most arthropods, ratesof water loss increase rapidly above a "transition" temperature.A widely accepted model proposes that this transition is dueto melting of the surface lipids to a fluid, permeable state.Evidence for this hypothesis has primarily been correlative,due to experimental limitations. Recent technical advances inlipid biophysics and water loss measurements have made it possibleto test the lipid melting model more directly. Experiments usingmodel cuticles, in vitro preparations and intact arthropodssupport the idea that the phase behavior of cuticular lipidsis a major factor determining cuticular permeability.     

Effects of biological invasions on forest carbon sequestration

There has been a rapidly developing literature on the effects of some of the major drivers of global change on carbon (C) sequestration, particularly carbon dioxide (CO₂) enrichment, land use change, nitrogen (N) deposition and climate change. However, remarkably little attention has been given to one major global change driver, namely biological invasions. This is despite growing evidence that invasive species can dramatically alter a range of aboveground and belowground ecosystem processes, including those that affect C sequestration. In this review, we assess the evidence for the impacts of biological invaders on forest C stocks and C sequestration by biological invaders. We first present case studies that highlight a range of invader impacts on C sequestration in forest ecosystems, and draw on examples that involve invasive primary producers, decomposers, herbivores, plant pathogens, mutualists and predators. We then develop a conceptual framework for assessing the effects of invasive species on C sequestration impacts more generally, by identifying the features of biological invaders and invaded ecosystems that are thought to most strongly regulate C in forests. Finally we assess the implications of managing invasive species on C sequestration. An important principle that emerges from this review is that the direct effects of invaders on forest C are often smaller and shorter‐term than their indirect effects caused by altered nutrient availability, primary productivity or species composition, all of which regulate long‐term C pools and fluxes. This review provides a conceptual basis for improving our general understanding of biological invaders on ecosystem C, but also points to a paucity of primary data that are needed to determine the quantitative effects of invaders on ecosystem processes that drive C sequestration.     

Factors Controlling the Abundance and Size Distribution of the Phototrophic Ciliate Myrionecta rubra in Open Waters of the North Atlantic

ABSTRACT. Myrionecta rubra, a ubiquitous planktonic ciliate, has received much attention due to its wide distribution, occurrence as a red tide organism, and unusual cryptophyte endosymbiont. Although well studied in coastal waters, M. rubra is poorly examined in the open ocean. In the Irminger Basin, North Atlantic, the abundance of M. rubra was 0–5 cells/ml, which is low compared with that found in coastal areas. Distinct patchiness (100 km) was revealed by geostatistical analysis. Multiple regression indicated there was little relationship between M. rubra abundance and a number of environmental factors, with the exception of temperature and phytoplankton biomass, which influenced abundance in the spring. We also improve on studies that indicate distinct size classes of M. rubra; we statistically recognise four significantly distinct width classes (5–16, 12–23, 18–27, 21–33 μm), which decrease in abundance with increasing size. A multinomial logistic regression revealed the main variable correlated with this size distribution was ambient nitrate concentration. Finally, we propose a hypothesis for the distribution of sizes, involving nutrients, feeding, and dividing of the endosymbiont.     

Modification of native grasses for biofuel production may increase virus susceptibility

Bioenergy production is driving modifications to native plant species for use as novel biofuel crops. Key aims are to increase crop growth rates and to enhance conversion efficiency by reducing biomass recalcitrance to digestion. However, selection for these biofuel‐valuable traits has potential to compromise plant defenses and alter interactions with pests and pathogens. Insect‐vectored plant viruses are of particular concern because perennial crops have potential to serve as virus reservoirs that influence regional disease dynamics. In this study, we examined relationships between growth rates and biomass recalcitrance in five switchgrass (Panicum virgatum) populations, ranging from near‐wildtype to highly selected cultivars, in a common garden trial. We measured biomass accumulation rates and assayed foliage for acid detergent lignin, neutral detergent fiber, in vitro neutral detergent fiber digestibility and in vitro true dry matter digestibility. We then evaluated relationships between these traits and susceptibility to a widely distributed group of aphid‐transmitted Poaceae viruses (Luteoviridae: Barley and cereal yellow dwarf viruses, B/CYDVs). Virus infection rates and prevalence were assayed with RT‐PCR in the common garden, in greenhouse inoculation trials, and in previously established switchgrass stands across a 300‐km transect in Michigan, USA. Aphid host preferences were quantified in a series of arena host choice tests with field‐grown foliage. Contrary to expectations, biomass accumulation rates and foliar digestibility were not strongly linked in switchgrass populations we examined, and largely represented two different trait axes. Natural B/CYDV prevalence in established switchgrass stands ranged from 0% to 28%. In experiments, susceptibility varied notably among switchgrass populations and was more strongly predicted by potential biomass accumulation rates than by foliar digestibility; highly selected, productive cultivars were most virus‐susceptible and most preferred by aphids. Evaluation and mitigation of virus susceptibility of new biofuel crops is recommended to avert possible unintended consequences of biofuel production on regional pathogen dynamics.