Resource availability and plant antiherbivore defense

The degree of herbivory and the effectiveness of defense varies widely among plant species. Resource availability in the environment is proposed as the major determinant of both the amount and type of plant defense. When resource are limited, plants with inherently slow growth are favored over those with fast growth rates; slow rates in turn favor large investments in antiherbivore defenses. Leaf lifetime, also determined by resource availability, affects the relative advantages of defenses with different turnover rates. Relative limitation of different resources also constrains the types of defenses. The proposals are compared with other theories on the evolution of plant defenses.     

Phytochemical deterrence of snowshoe hare browsing by adventitious shoots of four alaskan trees

After snowshoe hares have severely browsed deciduous trees and shrubs, these woody plants produce adventitious shoots that are extremely unpalatable to them. The adventitious shoots of four common boreal forest trees contain significantly higher concentrations of terpene and phenolic resins than the mature-growth-form twigs of the same species. These resins are experimentally shown to be repellent to snowshoe hares and appear to explain the avoidance of adventitious shoots by hares. The production of adventitious shoots after intense hare browsing and the avoidance of these shoots by hares may play an important role in the 10-year hare cycle.     

Perturbations in Perigee Height of Vanguard I

The effect of solar radiation pressure on the perigee height of satellite 1958ss(2) (Vanguard I) has been considered. Previous consideration of the effect of the third hairmonic and the lunar and solar gravitational perturbations left an unexplained discrepancy between the observed and calculated values of perigee height. The inclusion of the effect of radiation pressure leads to close agreement between the orbit data and the theoretical results for Vanguard I.     

Flake tools stratified below paleo-Indian artifacts

In northwest Missouri, Lithic stage flake tools struck from prepared cores have been excavated underlying a Paleo-Indian fluted point assemblage. These assemblages were in two different loesses of the last glaciation. Thermoluminescent analysis of stone tools dates the Paleo-Indian occupations at 8690 +/- 1000 B.C. and 12,855 +/- 1500 B.C.; the Lithic stage occupations must be older than 13,000 B.C. on the basis of geologic correlation, lithic analysis, and cultural stratigraphy.     

Oestrous behaviour in a herd of dairy cows.

A group of 60 housed Friesian cows were observed continuously for a period of 25 days, during which time all cows were recorded for incidence of mounting activity and 18 selected cows were recorded for various aspects of maintenance activity. All 60 cows were judged as showing oestrus. Average duration of oestrus (+/-SD) in 33 cows was 14-9 +/- 4-7 hours, and the cows were mounted 56-3 +/- 34-8 times. The greatest mounting activity was associated with the night hours. There was no diurnal pattern of onset of oestrus. The majority of mounting activity (79 per cent) occurred in the cubicle area of the building. Comparison of maintenance activities showed that oestrous cows spent, on average, less time standing in a cubicle (P less than 0-01), lying in a cubicle (P less than 0-001) and more time standing elsewhere (P less than 0-001) than non-oestrous cows. The results are discussed in relation to oestrus detection.     

Anthelmintic action—A metabolic approach (a review)

The effects of anthelmintic drugs on intermediary metabolism of parasites can be examined using techniques developed for the investigation of metabolic regulation. Most attention has been paid to the pathways of respiratory metabolism in parasites, since maintenance of high energy levels is essential to an organism's survival. Respiratory metabolism is thus a prime target for anthelmintic attack. Parasites differ from their hosts in a number of pathways of respiratory metabolism and they produce incompletely-oxidised organic acids as end products.A variety of anthelmintic drugs have been shown to inhibit some enzymes of these pathways, including phosphoenolpyruvate carboxykinase, malate dehydrogenase, and the fumarate reductase, ‘succinoxidase’ and succinate decarboxylase systems. Energy synthesis in mitochondria from parasites is also inhibited by many anthelmintics: this target is a particularly important one since its properties differ significantly from those of the host. This process requires considerable study and it may not necessarily be valid to equate ‘uncoupling’ in mammalian tissues with that in parasite tissues. Changes in ATP levels affect flux through the respiratory pathways; a complete assessment of effects of anthelminstics on the respiratory pathways of parasites would include measurement of the uptake and utilization of carbon sources (e.g., glucose and glycogen), of metabolic intermediates, including adenine nucleotides, and of excreted end products. Sites of change can then be identified and studied in greater detail.Comparison of the effect of mebendazole in vivo and in vitro on unrelated species, Moniezia expansa and Fasciola hepatica adults, sheds some light on the mechanism of its anthelmintic effects. This drug elicits similar changes in proportions and totals of adenine nucleotides in the two species, but it differs in the rapidly of its effect, its effect on glucose uptake and glycogen depletion, and in changes in respiratory end product. Consequently mebendazole may not act in the same way against these two species. It also affects a number of other systems in other parasites: the suggestion of a single ‘mode of action’ may be inappropriate for this compound.Respiratory metabolism is not the only system affected by anthelmintics: other parasite systems are also attacked, but the final effect of lethal anthelmintic is observed as changes in the respiratory metabolic pathways. Some anthelmintics, for example, levamisole, affect the respiratory pathway directly, but also affect other systems (the nervous system in the case of levamisole) and may be effective in vitro but not in vivo. In these cases it is necessary to distinguish between effects that may be subordinate to a primary effect, and to take host and permeability factors into account.