Collembolan water relations and environmental change in the maritime Antarctic

The water status of the collembolan Cryptopygtus antarcticus (Willem) was investigated from April 1984 to December 1987 at Signy Island, maritime Antarctic, by monthly field sampling to determine body water content. Water content, expressed either as the weight of water per unit dry weight or as a proportion of fresh weight, exhibited both a seasonal cycle and an upward trend over the 44-month study, both of which were highly significant. On an annual basis, body water content was at a minimum (1.21 g g^?1) in July and maximal (1.98 g g^?1) in September, whilst over the entire study water contents increased from 1.3 to 2.0 g g^?1 (or 57-66% of fresh weight) calculated from the fitted linear regression line. Field water contents were below those found for this species in culture (2.9-5.9 g g^?1). Individual C. antarcticus survived experimental loss of 20% of their body water with a resultant significant rise in haemolymph osmolarity from 285 to 397 mOsm L^?1 and there was no evidence of osmoregulation under the experimental conditions of 20 °C and 35% relative humidity. The cuticular permeability (mean conductance) of individual Collembola in dry air increased exponentially with temperature over the range D-45 °C (Q₁₀= 2.0) showing no control of water loss. The physiological response of C. antarcticus suggests that it experiences water stress in its maritime Antarctic habitats with significant seasonal variations of body water content, which correlate with annual cycles of water availability. It is concluded that the significant rise in its mean body water content over the 44-month field study was associated with increased glacial ablation due to higher levels of irradiation and windspeed making available more liquid water. Analyses of climate records for Signy Island from 1947 to 1990 showed that mean monthly air temperature rose by 0.93 °C over this period and by 2.29 °C during the 1980s, both statistically significant increases. Mean monthly windspeeds also increased significantly during 1970–90, and it is suggested that this parameter is the primary climatic driving force behind the increase in glacial ablation during the last two decades. The field water status of species such as C. antarcticus may reflect changes in the patterns of atmospheric circulation, associated with the circumpolar vortex, through increased ozone depletion due to increased tropospheric concentrations of halocarbons.     

Gap junction structures: Analysis of the x-ray diffraction data

Models for the spatial distribution of protein, lipid and water in gap junction structures have been constructed from the results of the analysis of X-ray diffraction data described here and the electron microscope and chemical data presented in the preceding paper (Caspar, D. L. D., D. A. Goodenough, L. Makowski, and W.C. Phillips. 1977. 74:605-628). The continuous intensity distribution on the meridian of the X-ray diffraction pattern was measured, and corrected for the effects of the partially ordered stacking and partial orientation of the junctions in the X-ray specimens. The electron density distribution in the direction perpendicular to the plane of the junction was calculated from the meridional intensity data. Determination of the interference function for the stacking of the junctions improved the accuracy of the electron density profile. The pair-correlation function, which provides information about the packing of junctions in the specimen, was calculated from the interference function. The intensities of the hexagonal lattice reflections on the equator of the X-ray pattern were used in coordination with the electron microscope data to calculate to the two-dimensional electron density projection onto the plane of the membrane. Differences in the structure of the connexons as seen in the meridional profile and equatorial projections were shown to be correlated to changes in lattice constant. The parts of the junction structure which are variable have been distinguished from the invariant parts by comparison of the X-ray data from different specimens. The combination of these results with electron microscope and chemical data provides low resolution three- dimensional representations of the structures of gap junctions.     

Survival strategies in polar terrestrial arthropods

Three components of the survival strategy of a terrestrial Antarctic mite, Alaskozetes antarcticus (Acari: Cryptostigmata) are considered: overwintering survival, energetics and life history. Supercooling is an important feature of its cold tolerance, whilst elevation of standard metabolism allows activity at low temperatures, both of which contribute tcTa long development and maximum survival of individuals in the population. These are facets of the overall survival strategy evolved by such a species in response to the Antarctic terrestrial environment, but which may be widespread in polar invertebrates.     

Fuel-Reduction Treatment Effects on Avian Community Structure and Diversity

Abstract: We assessed responses of the breeding bird community to mechanical thinning and prescribed surface fire, alone and in combination, between 2000 and 2006 in ponderosa pine (Pinus ponderosa) forests in northern Arizona, USA. Fuel-reduction treatments did not affect species richness or evenness, and effects on density of 5 commonly detected species varied among species. Populations of some species, such as the western bluebird (Sialia mexicana), increased following burning treatments, whereas others, such as the mountain chickadee (Poecile gambeli), decreased in response to thinning treatments. Our results also identified a temporal response component, where avian community composition and structure changed synchronously on all treatments over time. Given the modest effects these small-scale fuel-reduction treatments had on avian composition and the specific density responses of particular species, our results suggest that land managers should consider implementing prescribed surface fire after thinning projects, where appropriate.     

The role of nitric oxide in cancer

Nitric oxide (NO) is a pleiotropic regulator, critical to numerous biological processes, including va-sodilatation, neurotransmission and macrophage-mediated immunity. The family of nitric oxide synthases (NOS) comprises inducible NOS (iNOS), endothelial NOS (eNOS), and neuronal NOS (nNOS). Interestingly, various studies have shown that all three isoforms can be involved in promoting or inhibiting the etiology of cancer. NOS activity has been detected in tumour cells of various histogenetic origins and has been associated with tumour grade, proliferation rate and expression of important signaling components associated with cancer development such as the oestrogen receptor. It appears that high levels of NOS expression (for example, generated by activated macrophages) may be cytostatic or cytotoxic for tumor cells, whereas low level activity can have the opposite effect and promote tumour growth. Paradoxically therefore, NO (and related reactive nitrogen species) may have both genotoxic and angiogenic pro