Viral Properties of Scrapie

ALTHOUGH scrapie agent has many unusual features^1–4, some aspects of its behaviour are analogous to viral properties⁵. The manner in which the agent invades the nervous system after peripheral inoculation immediately recalls such typically neurotropic viruses as poliomyelitis or rabies. After inoculation into the fore-limb changes occur first in the cervical cord; following injection into the leg they appear first in the lumbar cord⁶. We now report another way in which scrapie behaves as a classical virus.     

Population studies of the beech leaf mining weevil (Rhynchaenus fagi) in Ireland and Scotland

Abstract. 1. Population budgets for Rhynchaenus fagi, based for the most part on samples of beech leaves taken in June, were constructed for a 10-year period (Northern Ireland) and a 3-year period (Scottish borders).
2. There were years of sustained population growth and sustained decline, but not enough evidence to suggest a cycle. Similar population levels were found at both sites in all but one year.
3. Key factors were associated with the adult stage, although egg mortality may also make a significant contribution to population change.
4. Unknown sources of mortality embodied in the residual mortality were also suspected of acting in a density dependent manner, compensating for variation in parasitism.
5. Death rate of larvae within mines was related to May temperature in Northern Ireland, but not so clearly in Scotland.     

Historical and Ecological Factors in the Biogeography of Aposematic Neotropical Butterflies

SYNOPSIS. Quantitative analysis of low-level (mostly subspecific)geographic differentiation of aposematic color patterns in threegroups of forest butterflies (Heliconiini, Ithomiinae, and Troidini),in 1,550 half-degree quadrants throughout the Neotropics, indicatesfour principal species-endemicity regions, 44 principal subspecies-endemicitycenters, and 300 quadrants of subspecies hybridization. Theendemism centers are different in outline but nearly identicalin position for each of the three ecologically different groups.Basic data on present and past physical environments (climate,soils, geomorphology, and vegetation structures), when integratedinto maps, show 1) regions of favorable ecological conditionsfor forest organisms in the present, 2) regions of environmentalconformities and rapid transitions in the present, and 3) regionsof high probability for humid forest persistence during themajor landscape changes at the end of the last glacial period,13,000–20,000 yr ago. Species diversity (a local phenomenon)is readily related to favorable modern ecological conditionsand environmental microheterogeneity, promoted by unpredictablemild disturbance. Biogeographical patterns of evolution at thelevel of regional subspecies correlate very well with presumedpaleoecological conditions. The biogeographical data also supportan hypothesis of differentiation resulting from areas of rapidenvironmental change; most of the hybridization quadrants fallwithin transition zones. There is lower correlation betweencenters of endemism and zones of en vironmental conformity,but some individual cases of differentiation in the butterfliesmay be adequately explained by modern ecological factors. Speciespresently undergoing differentiation in isolated habitat islands(Amazonian savannas and high-altitude Andean forests and paramos)may offer the best opportunities for observation of evolutionaryprocesses in the present.     

Reintroducing capercaillie (Tetrao urogallus) into southern Scotland: identification of minimum viable populations at potential release sites

Capercaillie (Tetrao urogallus) populations are declining in western parts of their range, including Scotland. It has been proposed that their numbers, and the extent of their range in Scotland be increased to reduce the risk of a second extinction in the UK. The feasibility of a reintroduction of capercaillie to coniferous plantations in southern Scotland was assessed by undertaking a population viability analysis. Following a review of capercaillie ecology and habitat requirements, VORTEX population simulation software was used to identify a minimum viable population (MVP). From this the minimum dynamic area of suitable habitat required in order to support such a MVP was then calculated. It was estimated that a minimum of 60 individuals would be required in approximately 5000ha of habitat in order for the population to have a >0.95 probability of surviving for 50 years. Supplementation of populations with two unrelated individuals every five years reduced the MVP to ten individuals. Further simulations were run in order to establish the sensitivity of the model to changes in three key parameters. Assessment of areas of suitable habitat identified two potential release sites, Wauchope and Newcastleton forests, in southern Scotland. Some practical considerations relating to management of a release population are outlined. It was concluded that an appropriately planned and resourced reintroduction was feasible.     

Elevated volatile concentrations in high‐nutrient plants: do insect herbivores pay a high price for good food?

1. A tritrophic perspective is fundamental for understanding the drivers of insect–plant interactions. While host plant traits can directly affect insect herbivore performance by either inhibiting or altering the nutritional benefits of consumption, they can also have an indirect effect on herbivores by influencing rates of predation or parasitism. 2. Enhancing soil nutrients available to trees of the genus Eucalyptus consistently modifies plant traits, typically improving the nutritional quality of the foliage for insect herbivores. We hypothesised that resulting increases in volatile essential oils could have an indirect negative effect on eucalypt‐feeding herbivores by providing their natural enemies with stronger host/prey location cues. 3. Eucalyptus tereticornis Smith seedlings were grown under low‐ and high‐nutrient conditions and the consequences for the release of volatile cues from damaged plants were examined. The influence of 1,8‐cineole (the major volatile terpene in many Eucalyptus species) on rates of predation on model caterpillars in the field was then examined. 4. It was found that the emission of cineole increased significantly after damage (artificial or herbivore), but continued only when damage was sustained by herbivore feeding. Importantly, more cineole was emitted from high‐ than low‐nutrient seedlings given an equivalent amount of damage. In the field, predation was significantly greater on model caterpillars baited with cineole than on unbaited models. 5. These findings are consistent with the hypothesis that any performance benefits insect herbivores derive from feeding on high‐nutrient eucalypt foliage could be at least partially offset by an increased risk of predation or parasitism via increased emission of attractive volatiles.     

A comparison of daphnid gut particles with the sestonic particles present in two Thames Valley reservoirs throughout 1970 and 1971

The numerically most abundant component of the seston in two of the Thames Valley storage reservoirs of the Metropolitan Water Board consisted of flocculent organic material which, together with the hyaline, transparent and blackened particles, formed the non-living sestonic fraction. The abundance of bacterio-plankton was estimated from plate counts which are known to provide an under-estimate of the bacteria present. The phytoplankton consisted of the larger flagellates present throughout the year together with a seasonal succession of algae in much greater numbers, namely the smaller flagellates, diatoms, colonial greens, Tribonema and Anabaena. A seasonal analysis of the gut contents of Daphnia magna, D. pulex and D. hyalina (occurring as important grazers in the reservoirs), revealed the presence of organic particles throughout the year plus cells or filaments of the prevailing alga at different seasons. During the summer, there were periods when the guts contained recognizable animal and plant debris. Flagellate and bacterial remains were never seen intact in the guts although these were abundant in the seston during early spring. The filamentous Tribonema was ingested when large crops of it were present. The most frequent size of ingested particle was between 1–2 μm and up to 60% of the animals examined contained particles which were neither longer nor wider than 20μm. Most of these animals ranged between 0·5–1·9 mm in length. A limiting factor for ingestion was thought to be width rather than length of particle and most very large particles found in the gut were long narrow and pliant filaments like Tribonema, or gelatinous colonial green algae, or flexible, foldable crustacean filtering limbs. There appeared to be no difference in the nature or size of particle ingested by the three different species of daphnids and any difference in maximal particle width observed was more likely to be related to body size than to species of consumer.     

Phagocytosis in Dictyostelium: Nibbling, Eating and Cannibalism

ABSTRACT. Phagocytosis is a highly conserved biological process that serves numerous functions in a wide variety of organisms. Over the past few decades Dictyostelium has proven to be an excellent organism for investigations in cell biology and this is certainly no less the case for a study of phagocytosis. This review examines three distinct phagocytic activities which have been characterized in Dictyostelium. The first, "vegetative phagocytosis," represents the classical eukaryotic microbial uptake of food particles (bacteria). The second, a predatory form of phagocytosis, arises when one species such as Dictyostelium caveatum attacks another species of slime mold, engulfing small pieces of the target prey. This has been termed "cell nibbling." The third phagocytic process is "sexual cannibalistic phagocytosis." In this situation a zygote giant cell, having arisen from the fusion of gametic amoebae, attracts unfused nonzygotic amoebae of the same species and engulfs them as a food source. While cell nibbling has not been actively studied, vegetative and sexual cannibalistic phagocytosis have received varying amounts of attention leading to the idea that some of the elements (e.g., glycoprotein receptors and a G_αs subunit) involved in certain of these phagocytic events may be the same. On the other hand, some unique events (e.g., filopodial induction in prey by D. caveatum ) are also worthy of further investigation. Among other things, the presence of self-nonself recognition, the existence of opsonin-like substances and the presence of signal transduction elements (e.g., an A2-like receptor that negatively modulates sexual phagocytosis) once considered to be extant only in higher organisms suggest that much can be learned about phagocytosis in general by further studies in the classic, eukaryotic microbe Dictyostelium discoideum and related species.     

Feeding behaviour of Red Deer (Cervus elaphus) offered Sitka Spruce saplings (Picea sitchensis) grown under different light and nutrient regimes

1. In addition to exhibiting preferences for particular plant species, vertebrate herbivores select particular individuals of these species whilst leaving others undamaged. This pattern of diet selection may reflect differences in the chemical composition (and hence nutritional quality) between individual plants, and/or variability in the physical constraints on intake rate, such as plant structure.
2. An experiment was conducted to test the effects of environmental manipulations on the morphology and chemical composition of Sitka Spruce saplings, and to evaluate the consequences for herbivory by Red Deer. Fertilizing the trees increased tree height, branch span and leader length, twig width and needle width, and decreased the concentrations of total phenolics, condensed tannins, fibre and lignin but monoterpene content was not altered. Shading also reduced phenolic and tannin concentrations.
3. When the fertilized and shaded trees were offered to deer in feeding trials, the probability of a tree being visited by a deer and the biomass removed were influenced by tree morphological variables, as were the bite rate and intake rate of the deer. More biomass was removed from larger trees.
4. Once the effects of tree morphology had been taken into account, there was no effect of the fertilizer and shade treatments on deer browsing behaviour that could be attributed to changes in chemical composition of the trees. The relationship between intake rate and bite size at each tree varied between individual deer, but the functional response relationship between intake rate and bite size was not influenced by the treatments applied to the trees.
5. Tree morphology may have a larger influence on deer feeding behaviour than tree chemical composition.     

Growth and provisioning strategies of Northern Fulmars Fulmarus glacialis

Growth and foraging strategies in procellariiforms show a great deal of variation, but the fulmarine petrels are notable in that chicks are fed frequently and develop unusually rapidly. This study examined age-related and daily variation in provisioning of the Northern Fulmar Fulmarus glacialis throughout the chick-rearing period at Fair Isle in 1997. In common with many other petrels, meal mass showed an initial rise with age, probably because of a gradual increase in chick gut capacity, but then levelled off. By comparison, feeding frequency showed little age-specific variation until chicks reached the oldest age-class, when the number of meals declined to less than a third of the previous level as chicks underwent mass recession prior to fledging. Compared with the limited day-to-day variation in mean provisioning rates for the whole sample, food delivery to particular chicks was much more variable, suggesting that differences in feeding rates were determined by stochastic factors influencing the feeding success of individual parents. The caloric density of feeds and their size in relation to adult mass were lower in Northern Fulmars than in most other Procellariiformes. This implies that adults are not heavily dependent on stomach oil formation to raise the energy content of the payload, but rely on a high feeding frequency to maintain adequate rates of energy transfer to chicks.     

Temporal response of stream benthic macroinvertebrate communities to the synergistic effects of anthropogenic acidification and natural drought events

1. We evaluated whether the surprisingly weak biological recovery associated with declines in acid deposition were related to drought‐induced re‐acidification of streams. We used test site analysis (TSA) to characterise temporal changes (1995–2003) in the degree and nature of impairments to stream benthic macroinvertebrate (BMI) communities influenced by acid deposition and drought. 2. The BMI communities in four historically impacted test streams were compared with communities in 30 minimally impacted reference streams. Six multivariate (e.g. ordination axes scores) and four traditional (e.g. % Diptera) summary metrics were used to describe BMI communities. Using all metrics simultaneously (i.e. Mahalanobis or generalised distance), the TSA provided a single probability that a test community was impaired. If a test community was significantly impaired, a further analysis was done to identify the metric(s) important in distinguishing the test community from reference condition. 3. Results of the TSAs indicated that the generalised distances between test communities and the reference condition were inversely related to stream water pH (n = 36). The TSAs also indicated ordination metrics based on BMI abundance were important in distinguishing significantly impaired communities from reference conditions. Temporal trends indicated that there has been short‐term recovery of these BMI communities, but that overall improvements have been hampered by acid or metal toxicity associated with drought‐induced re‐acidification of the streams. 4. Our use of a variety of summary metrics to obtain a single statistical test of significance within the context of the reference‐condition approach provided a simple and unambiguous framework for evaluating the biological condition of test sites.