Parthenogenetic development of dwarf surf dam,Mulinia lateralis,oocytes treated with polar body suppressing agents

Summary

Parthenogenesis following oocyte activation has been observed in a number of marine invertebrates, but the fate of parthenogenesis in bivalve mollusc embryos is unclear. We used the dwarf surf clam, Mulinia lateralis, to examine parthenogenetic development of KC1-activated oocytes using the polar body suppressing agents caffeine and heat or cytochalasin B. Development was followed by epifluorescence microscopy and flow-cytometric analysis using the DNA-specific fluorochrome DAPI. All agents suppressed polar body formation to some degree, putatively increasing the ploidy level and retaining a meiotic centrosome in the zygote; but the zygotes failed to develop normally. Failure of the zygotes to develop suggests that the meiotic centrosome is incapable of participating in mitosis in bivalves.     

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.