Pathways towards and away from Alzheimer's disease

Slowly but surely, Alzheimer's disease (AD) patients lose their memory and their cognitive abilities, and even their personalities may change dramatically. These changes are due to the progressive dysfunction and death of nerve cells that are responsible for the storage and processing of information. Although drugs can temporarily improve memory, at present there are no treatments that can stop or reverse the inexorable neurodegenerative process. But rapid progress towards understanding the cellular and molecular alterations that are responsible for the neuron's demise may soon help in developing effective preventative and therapeutic strategies.     

Indicators of red squirrel (Tamiasciurus hudsonicus) abundance in the whitebark pine zone

We investigated occupied squirrel middens and squirrel sightings and vocalizations as indicators of red squirrel ( Tamiasciurus hudsonicus ) abundance in high-elevation whitebark pine ( Pinus albicaulis ) zone. Data were collected 1984-1989 from line transects located on 2 study sites in the Yellowstone ecosystem. We evaluated the performance of each measure on the basis of precision and biological considerations. We concluded that, of the 3 measures, active middens were the best indicator of red squirrel abundance. We also observed that the density of active middens dropped by 48%-66% between 1987 and 1989, following a severe drought and extensive wildfires that burned one of the study sites during 1988.     

Foot loadings and pad and track widths of Yellowstone grizzly bears

I used measurements of grizzly bears ( Ursus arctos horribilis ) from the Yellowstone region, USA, to investigate relationships between widths of foot pads and widths of tracks, foot loading and pad size, incidence of tracks and type of activity, and widths of front-foot pads and gender and age-class. Track width was affected by substrates and increased relative to pad width as sizes of both pads and tracks increased. Foot loading (kg · cm -2 ) did not vary substantially with foot size and so did not explain the proportionately larger tracks of larger animals. Tracks were most commonly associated with feeding activity that entailed excavation of fossorial foods (roots and rodents); they were least common when bears were feeding in the forest, feeding on ungulates, or traveling. Adult males and females could be differentiated by the width of their front-foot pads. Virtually all pads > 14.5 cm wide belonged to adult or large subadult males. The pads of subadult females were most commonly < 12.5 cm wide, whereas those of adult females were most commonly 12.5--14.5 cm wide.     

Roost sites of the silver-haired bat ( Lasionycyeris noctivagans ) in the Black Hills, South Dakota

We investigated the roosting ecology of silver-haired bats ( Lasionycteris noctivagans ) in the Black Hills, of western South Dakota. Using radiotelemetry, we located 39 roosts, 10 of which were maternity aggregations containing 6 to 55 bats. The roosts were mostly in ponderosa pine ( Pinus ponderosa ) snags that averaged 39 cm diameter at breast height. Solitary bats preferred roosting under loose bark or in crevices in trees, regularly moving among trees. All maternity aggregations were found in tree cavities, primarily those created by woodpeckers. Roost trees were located in patches of forest with relatively high snag densities, about 21 snags/ha. This study suggests that snags play an important role in maintain silver-haired bat populations in ponderosa pine ecosystems.     

Earth-like sand fluxes on Mars

Strong and sustained winds on Mars have been considered rare, on the basis of surface meteorology measurements and global circulation models, raising the question of whether the abundant dunes and evidence for wind erosion seen on the planet are a current process. Recent studies showed sand activity, but could not determine whether entire dunes were moving--implying large sand fluxes--or whether more localized and surficial changes had occurred. Here we present measurements of the migration rate of sand ripples and dune lee fronts at the Nili Patera dune field. We show that the dunes are near steady state, with their entire volumes composed of mobile sand. The dunes have unexpectedly high sand fluxes, similar, for example, to those in Victoria Valley, Antarctica, implying that rates of landscape modification on Mars and Earth are similar.     

Effects of exotic species on Yellowstone's grizzly bears

Humans have affected grizzly bears ( Ursus arctos horribilis ) by direct mortality, competition for space and resources, and introduction of exotic species. Exotic organisms that have affected grizzly bears in the Greater Yellowstone Area include common dandelion ( Taraxacum officinale ), nonnative clovers ( Trifolium spp.), domesticated livestock, bovine brucellosis ( Brucella abortus ), lake trout ( Salvelinus namaycush ), and white pine blister rust ( Cronartium ribicola ). Some bears consume substantial amounts of dandelion and clover. However, these exotic foods provide little digested energy compared to higher-quality bear foods. Domestic livestock are of greater energetic value, but use of this food by bears often leads to conflicts with humans and subsequent increases in bear mortality. Lake trout, blister rust, and brucellosis diminish grizzly bears foods. Lake trout prey on native cutthroat trout ( Oncorhynchus clarkii ) in Yellowstone Lake; white pine blister rust has the potential to destroy native whitebark pine ( Pinus albicaulis ) stands; and management response to bovine brucellosis, a disease found in the Yellowstone bison ( Bison bison ) and elk ( Cervus elaphus ), could reduce populations of these 2 species. Exotic species will likely cause more harm than good for Yellowstone grizzly bears. Managers have few options to mitigate or contain the impacts of exotics on Yellowstones grizzly bears. Moreover, their potential negative impacts have only begun to unfold. Exotic species may lead to the loss of substantial highquality grizzly bear foods, including much of the bison, trout, and pine seeds that Yellowstone grizzly bears currently depend upon.     

Effects of simulated mountain lion caching on decomposition of ungulate carcasses

Caching of animal remains is common among carnivorous species of all sizes, yet the effects of caching on larger prey are unstudied. We conducted a summer field experiment designed to test the effects of simulated mountain lion ( Puma concolor ) caching on mass loss, relative temperature, and odor dissemination of 9 prey-like carcasses. We deployed all but one of the carcasses in pairs, with one of each pair exposed and the other shaded and shallowly buried (cached). Caching substantially reduced wastage during dry and hot (drought) but not wet and cool (monsoon) periods, and it also reduced temperature and discernable odor to some degree during both seasons. These results are consistent with the hypotheses that caching serves to both reduce competition from arthropods and microbes and reduce odds of detection by larger vertebrates such as bears ( Ursus spp.), wolves ( Canis lupus ), or other lions.     

IL-23 promotes tumour incidence and growth

Chronic inflammation has long been associated with increased incidence of malignancy and similarities in the regulatory mechanisms have been suggested for more than a century. Infiltration of innate immune cells, elevated activities of matrix metalloproteases and increased angiogenesis and vasculature density are a few examples of the similarities between chronic and tumour-associated inflammation. Conversely, the elimination of early malignant lesions by immune surveillance, which relies on the cytotoxic activity of tumour-infiltrating T cells or intra-epithelial lymphocytes, is thought to be rate-limiting for the risk to develop cancer. Here we show a molecular connection between the rise in tumour-associated inflammation and a lack of tumour immune surveillance. Expression of the heterodimeric cytokine interleukin (IL)-23, but not of its close relative IL-12, is increased in human tumours. Expression of these cytokines antagonistically regulates local inflammatory responses in the tumour microenvironment and infiltration of intra-epithelial lymphocytes. Whereas IL-12 promotes infiltration of cytotoxic T cells, IL-23 promotes inflammatory responses such as upregulation of the matrix metalloprotease MMP9, and increases angiogenesis but reduces CD8 T-cell infiltration. Genetic deletion or antibody-mediated elimination of IL-23 leads to increased infiltration of cytotoxic T cells into the transformed tissue, rendering a protective effect against chemically induced carcinogenesis. Finally, transplanted tumours are growth-restricted in hosts depleted for IL-23 or in IL-23-receptor-deficient mice. Although many strategies for immune therapy of cancer attempt to stimulate an immune response against solid tumours, infiltration of effector cells into the tumour tissue often appears to be a critical hurdle. We show that IL-23 is an important molecular link between tumour-promoting pro-inflammatory processes and the failure of the adaptive immune surveillance to infiltrate tumours.