Selection-induced mutations.

Some spontaneous mutations are specifically 'adaptive' in two ways: in that they occur more often when they are useful than when they are irrelevant to the survival of the cell; and in that they occur as specific responses to selective pressures. These 'selection-induced mutations' occur both in bacteria and in the eukaryotic microorganism, yeast.     

Mouse osteoblasts synthesize collagenase in response to bone resorbing agents

Bone cells isolated from mouse calvariae by a sequential digestion procedure have many osteoblast characteristics: they respond to PTH and prostaglandin E2 by activation of adenylate cyclase but not to calcitonin, they stain for alkaline phosphatase and they make only type I collagen. In confluent monolayer culture, they do not secrete collagenase in appreciable quantities, unless stimulated with resorptive substances such as PTH, prostaglandin E2, 1,25(OH)2 vitamin D-3 and monocyte-conditioned medium. This suggests they play a direct role in bone resorption.     

The case for studying tadpole autecology,with comments on strategies to study other small,fast-moving animals in nature

Two of the most fundamental questions in tadpole biology, also applicable to most small, under-studied organisms are: (1) ‘Why are they built the way they are?’ and (2) ‘Why do they live where they do?’ Regrettably, despite significant progress in most aspects of tadpole biology, the answers to these questions are not much better now than they were in the last century. We propose that an autecological approach, that is the careful observation of individuals and how they interact with the environment, is a potential path towards a fuller understanding of tadpole ecomorphology and evolution. We also discuss why more attention should be given to studying atypical tadpoles from atypical environments, such as torrential streams, water-filled cavities of terrestrial plants and wet rock surfaces neighbouring streams. Granted, tadpoles are rare in these settings, but in those unusual habitats the physical environments can be well described and characterized. In contrast, the more common ponds where tadpoles are found are typically too structurally complex to be easily delineated. This makes it difficult to know exactly what individual tadpoles are doing and what environmental parameters they are responding to. Our overall thesis is that to understand tadpoles we must see exactly what they are doing, where they are doing it, and how they are doing it. This takes work, but we suggest it is feasible and could greatly advance our understanding of how anuran larvae have evolved. The same strategies for studying tadpoles that we encourage here can be applied to the study of many other small and fast-moving animals.     

Doin' what comes natur'lly

Behavior affects evolution in many ways. Organisms are adapted for what they do, but they also do what they are adapted for.     

Responses of Hebeloma radicosum fruit-bodies to light and gravity: negatively gravitropic and nonphototropic growth

Responses of the long-rooting agaric Hebeloma radicosum fruit-bodies to light and gravity were studied. In light from below or obliquely below, fruit-bodies grew straight downward with gills tilted and cap swollen and waved if they had emerged downward from the culture medium, or bent upward from the beginning if they had emerged obliquely downward. In light from above or obliquely above, they grew upward if they had emerged upward. Thus, they did not grow toward unilateral light from obliquely below or obliquely above, and hence their growth was nonphototropic and negatively gravitropic from the beginning of development. Even the straight downward growth seems to be latently negative-gravitropic. In the dark, fruit-bodies grew upward, forming pseudorhizas, but they remained immature; they matured only in the light. These characteristics may be related to the growth habits of the fungus colonizing deep in the ground, forming primordia there, and developing mature fruit-bodies on the ground. Received: March 26, 2001 / Accepted: July 12, 2001     

Animal memory: episodic-like memory in rats

Recent experiments with rats on a radial maze indicate that they can remember what foods they encountered, and when and where they encountered them. These findings, and others with food-storing birds, challenge the idea that only humans have episodic memory.     

Animal cognition: multimodal tactics of orangutan communication

Orangutans select different tactics for repairing failed communication, depending upon how well they are understood: they repeat signals if they are partially understood and switch tactics entirely if completely misunderstood.     

Platelet-activating factor mediates procoagulant activity on the surface of endothelial cells by promoting leukocyte adhesion

Endothelial cells co-express platelet-activating factor and P-selectin on their surfaces after activation by certain receptor-mediated agonists. Together they mediate the adhesion of leukocytes to the endothelial cell surface. P-selectin tethers leukocytes to the endothelial cells surface allowing leukocyte activation by platelet-activating factor. Adhesion and activation are specific for leukocytes because they are the only cells known to express the ligand for P-selectin. Leukocytes adherent to the endothelial cell surface may promote thrombosis by three mechanisms: (1) they secrete factors that damage the underlying endothelium, (2) they secrete factors that directly initiate the coagulation cascade, and (3) they bind and activate platelets.     

Some Implications of Medical Beliefs and Practices for Social Anthropology

A people's medical beliefs and practices persist because they answer instrumental and moral imperatives, and they are empirically effective. This is not the same thing as saying that they are effective from the standpoint of Western medical notions or that they always bring the results for which people hope. The empirical effectiveness of these practices has important ontological consequences, since it enables sickness episodes to communicate and confirm ideas about the real world.     

Dependence receptors: Mechanisms of an announced death

Dependence receptors form a family of functionally related receptors which are all able to induce two completely opposite intracellular signals depending on the availability of their ligand. Indeed, in its presence, they mediate a positive, classical signal transduction of survival, differentiation or migration but without it, they trigger a negative signal which leads to cell death. The molecular mechanisms involved in triggering cell death in the absence of ligand are starting to be unravelled: dependence receptors are recruited at well-defined domains at the plasma membrane, they trigger cell death through a monomeric form, they are cleaved by caspases and they recruit a caspase activating complex.     

Appointment systems: evaluation of a flexible system offering patients limited choice

To test the efficiency of a flexible appointments system patients seeing one of the partners in a semirural dispensing practice were asked to choose whether they wanted appointments lasting five, 10, or 15 minutes. After seeing the doctor they were asked to fill in a questionnaire that asked, among other questions, how long an appointment they had booked, whether they had felt rushed, whether the doctor had seemed hurried, whether they had seen the doctor on the day they wanted, how long they had had to wait in the surgery, and whether they liked the system. Five minute appointments had been chosen by 124 of the 309 patients who returned completed questionnaires, 10 minute appointments by 155, and 15 minute appointments by 30. Mean consultation times were 6·1, 9·2, and 12·9 minutes, respectively. Altogether 298 patients liked the system.An appointment system that was flexible while remaining practical and efficient resulted from letting patients choose the length of their appointment. Such a system encourages patients to share in the responsibility of organising a practice efficiently.     

Five-Year Olds,but Not Chimpanzees,Attempt to Manage Their Reputations

Virtually all theories of the evolution of cooperation require that cooperators find ways to interact with one another selectively, to the exclusion of cheaters. This means that individuals must make reputational judgments about others as cooperators, based on either direct or indirect evidence. Humans, and possibly other species, add another component to the process: they know that they are being judged by others, and so they adjust their behavior in order to affect those judgments – so-called impression management. Here, we show for the first time that already preschool children engage in such behavior. In an experimental study, 5-year-old human children share more and steal less when they are being watched by a peer than when they are alone. In contrast, chimpanzees behave the same whether they are being watched by a groupmate or not. This species difference suggests that humans'' concern for their own self-reputation, and their tendency to manage the impression they are making on others, may be unique to humans among primates.     

How do RNA folding algorithms work?

Programs such as MFOLD and ViennaRNA are widely used to predict RNA secondary structures. How do these algorithms work? Why can't they predict RNA pseudoknots? How accurate are they, and will they get better?     

Feeding of ducks and their effects on water quality

Birds possess fast metabolism, and therefore they ingest and egest relatively large quantities of organic materials. Effects on the eutrophication depend on the site where they release their excrements. Mallards were studied as model animal to evaluate this process. Mallards of different ages have different ecological roles. In the beginning of their individual life they reduce the trophic level but later they contribute to the eutrophication processes.     

The natural history of visiting: responses to Charles Waterton and Walton Hall

Natural history collections are typically studied in terms of how they were formed rather than how they were received. This gives us only half the picture. Visiting accounts can increase our historical understanding of collections because they can tell us how people in the past understood them. This essay examines the responses of visitors to Walton Hall in West Yorkshire, home of the traveller-naturalist Charles Waterton and his famous taxidermic collection. Waterton’s specimens were not interpreted in isolation. Firstly, they were experienced as components of a larger visiting experience, in which travelling to the Hall, being admitted to the grounds, viewing the park, and meeting the owner, were all just as significant as seeing the specimens themselves. Secondly, they were interpreted in conjunction with familiar stories and images relating to Waterton’s adventurous collecting activities. Visiting accounts can help us begin to recover what people thought about Waterton and his collection in the nineteenth century. Furthermore, in so far as they were responsible for a large part of his subsequent reputation, they can help us better understand our own, present-day conceptions of Charles Waterton and Walton Hall.     

河南小秦岭自然保护区蕨类植物区系研究

小秦岭自然保护区共计有蕨类植物23科46属107种.其区系基本特征是:地理成分多样,区系联系广泛并具有一定的古老性;以温带性质为主,但有较明显的热带残遗性和亲缘性;特有现象明显,是东亚成分分布中心的一部分;隶属于华北区系,兼有强烈的西北和西南区系特色.     

The control of nest depth in a digger wasp (Sphex ichneumoneus L.)

Golden digger wasps, Sphex ichneumoneus L. (Sphecidae), are a solitary, ground-nesting species that dig burrows to particular depths in the soil. I develop and evaluate alternative hypeses about the mechanisms controlling digging behaviour. By altering the wasps' burrows as thare digging, I show that they are not digging for some prescribed length of time nor are they diggingtil they reach some suitable environmental characteristic deep in the soil. Rather, they appear be digging until they reach a particular tunnel length, making corrections if the tunnel is too shallor too deep. This distance can be altered somewhat by surface environmental conditions.     

Patterns of preventive practice in New Brunswick

A survey of active general practitioners was conducted in New Brunswick to ascertain their patterns of preventive practice with respect to cancer of four anatomic sites: the breast, the cervix, the colon and rectum, and the lung. Ninety-two percent of the physicians reported that they taught breast self-examination to their female patients, 98% that they performed breast examinations, 98% that they did Papanicolaou smears routinely, and 97% that they provided counselling against smoking. Few of the physicians reported that they submitted women aged 50 to 59 years to annual mammography (3%) or examined stool samples from asymptomatic patients over 44 years of age for occult blood (20%). Many (77%) said they still routinely performed chest roentgenography for early detection of lung cancer; an estimated 49% of the physicians said they performed cytologic screening of sputum samples for the same purpose. Preventive practices, when used, were usually carried out during major encounters with patients, such as general check-ups. The potential for prevention through this clinically based approach is still largely unrealized.     

The consultation and the therapeutic illusion.

At 45 general-practice surgery sessions 200 patients in whom no definite diagnosis could be made were randomly selected for one of two procedures. Either they were given a symptomatic diagnosis and medications, or they were told that they had no evidence of disease and therefore they required no treatment. No difference in outcome was found between these two methods as judged by the return or not of the patient within one month and his statement that he did or did not get better.     

Na channels and two types of Ca channels in rat pancreatic B cells identified with the reverse hemolytic plaque assay

The reverse hemolytic plaque assay (RHPA) was used to study the secretory properties of single rat pancreatic B cells, and to identify insulin-secreting cells for patch-clamp experiments. In secretion studies using the RHPA, we find that the percentage of secreting B cells and the amount of insulin secreted per B cell increase as the glucose concentration is raised from 0 to 20 mM. Using the whole-cell variation of the patch-clamp technique, we find that identified B cells have three types of channels capable of carrying inward current: (a) tetrodotoxin-sensitive, voltage-dependent Na channels, which are nearly completely inactivated at -40 mV, (b) fast deactivating (FD) Ca channels, and (c) slowly deactivating (SD) Ca channels. We have shown that Na channels are functionally significant to the B cell, because tetrodotoxin partially inhibits glucose-induced insulin secretion. The properties of FD and SD Ca channels differ in several respects. FD channels deactivate at -80 mV, with a time constant of 129 microseconds, they are half-maximally activated near +15 mV, they do not inactivate during 100 ms, they conduct Ba2+ better than Ca2+, and they are very sensitive to washout during intracellular dialysis. SD channels, on the other hand, deactivate with a time constant of 2.8 ms, they are half-maximally activated near -5 mV, they inactivate rapidly, they conduct Ba2+ and Ca2+ equally well, and they are insensitive to washout.