Showing papers in "Science in 1974"

Resource Partitioning in Ecological Communities

Abstract: To understand resource partitioning, essentially a community phenomenon, we require a holistic theory that draws upon models at the individual and population level. Yet some investigators are still content mainly to document differences between species, a procedure of only limited interest. Therefore, it may be useful to conclude with a list of questions appropriate for studies of resource partitioning, questions this article has related to the theory in a preliminary way. 1) What is the mechanism of competition? What is the relative importance of predation? Are differences likely to be caused by pressures toward reproductive isolation? 2) Are niches (utilizations) regularly spaced along a single dimension? 3) How many dimensions are important, and is there a tendency for more dimensions to be added as species number increases? 4) Is dimensional separation complementary? 5) Which dimensions are utilized, how do they rank in importance, and why? How do particular dimensions change in rank as species nuimber increases? 6) What is the relation of dimensional separation to difference in phenotypic indicators? To what extent does the functional relation of phenotype to resource characteristics constrain partitioning? 7) What is the distance between mean position of niches, what is the niche standard deviation, and what is the ratio of the two? What is the niche shape?

Chromatin structure: a repeating unit of histones and DNA.

Abstract: ciations of the histones in chromatin but says nothing of details, such as whether the F2A1 and F3 pair, which occurs as an (F2Al)2(F3)2 tetramer in solution, also occurs as a tetramer in chromatin. The most direct evidence for an (F2Al)2(F3)2 tetramer in chromatin is that a complex formed from tetramers, F2A2-F2B oligomers, and DNA gives the same x-ray pattern as chromatin (Fig. 4, upper two traces). Tetramers and F2A2-F2B oligomers are both required to give the x-ray pattern (Fig. 4, lower two traces), but Fl is not-in keeping with previous observations (3, 23 ) that removing Fl from chromatin does not affect the x-ray pattern. Further implications of these results are discussed in the accompanying article (24). We are currently studying associations of the histones in chromatin by cross-linking. There are two difficulties that do not arise in experiments on the histones in solution: the amino side chains are involved in salt linkages with the phosphate groups of DNA and are thus less available for chemical modification; and the presence of five rather than two histones complicates identification of products from molecular weights. -Preliminary results do show less cross-linking of histones in chromatin than in solution, but crosslinked products up to pentamers are readily observed and call for further investigation.

Amino Acid Difference Formula to Help Explain Protein Evolution

Abstract: A formula for diference between amino acids combines properties that correlate best with protein residue substitution frequencies: composition, polarity, and molecular volume. Substitution frequencies agree much better with overall chemical difference between exchanging residues than with minimum base changes between their codons. Correlation coefficients show that fixation of mutations between dissimilar amino acids is generally rare.

Genetic Control of the Cell Division Cycle in Yeast

Abstract: Mitotic cell division in eukaryotes is accomplished through a highly reproducible temporal sequence of events that is common to almost all higher organisms. An interval of time, Gl, separates the previous cell division from the initiation of DNA synthesis. Ohromosome replication is acco’mplished during the DNA synthetic period, S, which typically occupies about a third of the cell cycle. Another interval of time, G2, separates the completion of DNA synthesis from prophase, the beginning of mitosis, M. A dramatic sequence of changes in chromosome structure and of chromosome ,movement characterizes the brief mitotic period that results in the precise separation of sister chromatids to daughter nuclei. Mitosis is followed by cytokinesis, the partitioning of the cytoplasm into two daughter cells with separate plasma membranes. In some organisms the cycle is completed by cell wall separation. Each of these events occurs during the cell division cycle of the yeast, Saccharomyces cerevisiae (I) (Fig. 1) . However, two features which distinguish the cell cycle of S. cerevisiae from most other eukaryotes are particularly useful for an analysis of the gene functions that control the cell division cycle. First, the fact that both haploid and diploid cells undergo mitosis permits the isolation of recessive mutations in haploids and their analysis by complementation in diploids. Second, the daughter cell is recognizable at an early stage of the cell cycle as a bud on the surface of the parent cell. Since the ratio of bud size to parent cell size increases progressively during the cycle, this ratio pro-

Biological Populations with Nonoverlapping Generations: Stable Points, Stable Cycles, and Chaos

Abstract: Some of the simplest nonlinear difference equations describing the growth of biological populations with nonoverlapping generations can exhibit a remarkable spectrum of dynamical behavior, from stable equilibrium points, to stable cyclic oscillations between 2 population points, to stable cycles with 4, 8, 16, . . . points, through to a chaotic regime in which (depending on the initial population value) cycles of any period, or even totally aperiodic but boundedpopulation fluctuations, can occur. This rich dynamical structure is overlooked in conventional linearized analyses; its existence in such fully deterministic nonlinear difference equations is a fact of considerable mathematical and ecological interest.

Menstrual cycles: fatness as a determinant of minimum weight for height necessary for their maintenance or onset.

Abstract: Weight loss causes loss of menstrual function (amenorrhea) and weight gain restores menstrual cycles. A minimal weight for height necessary for the onset of or the restoration of menstrual cycles in cases of primary or secondary amenorrhea due to undernutrition is indicated by an index of fatness of normal girls at menarche and at age 18 years, respectively. Amenorrheic patients of ages 16 years and over resume menstrual cycles after weight gain at a heavier weight for a particular height than is found at menarche. Girls become relatively and absolutely fatter from menarche to age 18 years. The data suggest that a minimum level of stored, easily mobilized energy is necessary for ovulation and menstrual cycles in the human female.

Spheroid Chromatin Units (ν Bodies)

Abstract: Linear arrays of spherical chromatin particles (nu bodies) about 70 angstroms in diameter have been observed in preparations of isolated eukaryotic nuclei swollen in water, centrifuged onto carbon films, and positively or negatively stained. These bodies have been found in isolated rat thymus, rat liver, and chicken erythrocyte nuclei. Favorable views also reveal connecting strands about 15 angstroms wide between adjacent particles.

Steroid 5α-Reductase Deficiency in Man: An Inherited Form of Male Pseudohermaphroditism

Abstract: In male pseudohermaphrodites born with ambiguity of the external genitalia but with marked virilization at puberty, biochemical evaluation reveals a marked decrease in plasma dihydrotestosterone secondary to a decrease in steroid 5alpha-reductase activity. In utero the decrease in dihydrotestosterone results in incomplete masculinization of the external genitalia. Inheritance is autosomal recessive.

Neurons in Rhesus Monkey Visual Cortex: Systematic Relation between Time of Origin and Eventual Disposition

Abstract: Autoradiographic evidence after injection of tritiated thymidine indicates that cell position in the laminae of the monkey visual cortex is systematically related to time of cell orgin. The earliest-formed neurons, destined for the deepest stratum, arise at about embryonic day 45, and the last ones, destined for the outermost cell stratum, form at about day 102; cells of intervening layers are generated at intervening times. No neocortical neurons are produced in the last two prenatal months or after birth. Compared to cortical neurons in rodents, those in the monkey arise earlier, and the "inside-out" relation of cell position to time of origin is more rigid.

Sea Otters: Their Role in Structuring Nearshore Communities

Abstract: A comparison of western Aleutian Islands with and without sea otter populations shows that this species is important in determining littoral and sublittoral community structure. Sea otters control herbivorous invertebrate populations. Removal of sea otters causes increased herbivory and ultimately results in the destruction of macrophyte associations. The observations suggest that sea otter reestablishment indirectly affects island fauna associated with macrophyte primary productivity.

Behavioral Regulation of the Milieu Interne in Man and Rat

Abstract: In regulating the internal homeostatic environment mammals, by necessity, employ behavioral strategies that differ from the tactics used in coping with contingencies in the external environment. When an animal consumes a meal, the palatability of that meal is automatically adjusted in accordance with the ultimate internal effects of that meal. If the meal causes toxicosis, the animal acquires an aversion for the taste of the meal; conversely, if recuperation follows ingestion of the meal, the taste of that meal is enhanced. Unlike the learning that occurs when externally referred visual and auditory signals are followed by punishment in the form of peripheral pain or reward in the form of food in the mouth, conditioning to the homeostatic effects of food can occur in a single trial and rarely requires more than three to five trials, even though the ultimate effects of the meal are delayed for hours. Paradoxically, the animal need not be aware of the ultimate internal effect in the same sense that it is aware of external contingencies. For example, an aversion can be acquired even if the animal is unconscious when the agent of illness is administered. Thus, the way in which food-effects are stored in memory may be fundamentally different from the way in which memories of specific time-space strategies devised for external contingencies are stored. This separation of function is indicated by limbic lesions which disrupt conditioning to a buzzer that is followed by shock and facilitate conditioning to a taste that is followed by illness. Operationally speaking, one can describe both aversion conditioning and buzzer-shock conditioning in the spacetime associationistic terms of classical conditioning. However, psychologically speaking, one must realize that in aversion conditioning the animal does not act as if it were acquiring an "if-then" strategy. It acts as if a hedonic shift, or a change in the incentive value of the flavor were taking place. Such hedonic shifts are critical in regulation of the internal milieu. When an animal is in need of calories, food tends to be more palatable; as the caloric deficit is restored, food becomes less palatable. If the animal's body temperature is below optimum, a warm stimulus applied to the skin is pleasant. When body temperature is too high, the converse is true. In this way, homeostatic states monitored by internal receptors produce changes in the incentive values of external stimuli sensed by the peripheral receptors, and guide feeding behavior. In mammals at least, the gustatory system, which provides sensory control of feeding, sends fibers to the nucleus solitarius. This brainstem relay station also receives fibers from the viscera and the internal monitors of the area postrema. Ascending fibers bifurcate at the level of the pons and project toward the feeding areas of the hypothalamus and the cortex. The olfactory system which primarily projects to the limbic system does not play a primary role in adjusting food incentives. Rather, it plays a secondary role in the activation of feeding, as do other external sensory systems. This specialized conditioning mechanism, which specifically adjusts gustatory hedonic values through delayed visceral feedback, is widespread among animals, including man and rat. These two species are remarkably similar in their thresholds and preferences for gustatory stimuli. The behavioral similarities are based on the animals' having similar gustatory systems, similar convergence of gustatory and internal afferents to the nucleus solitarius, and similar midbrain regulatory mechanisms. Thus, it is not surprising that the feeding of obese rats with internal hypothalamic damage resembles the feeding of obese human beings insensitive to the internal signs of this caloric state. Obviously, man has a highly specialized form of symbolic communication and the rat does not, yet man's cognitive specialization does not prevent him from developing aversions to food consumed before illness even when he knows that his illness was not caused by food (43).

Free radicals and inflammation: protection of synovial fluid by superoxide dismutase.

Abstract: Enzymatically genierated superoxide radical. by reactitng with hydrogen peroxide to prduce the hydroxyl radical, depolymerized puirified hyaluronic acid and bovine synovial flulid. Since phagocytizing polymorphonuclear leukocytes produce superoxide radicals, this reac-tion is sutggested and shown to be quantitatively feasible as the ini vivo mechanism of synovial fluid degradation in anl inflamed joint. Superoxide dismutase, and catalase protect synaovial fluid against such degradation in vitro.

Eutrophication and Recovery in Experimental Lakes: Implications for Lake Management

Abstract: Combinations of phosphorus, nitrogen, and carbon were added to several small lakes in northwestern Ontario, Canada, at rates similar to those in many culturally eutrophied lakes. Phosphate and nitrate caused rapid eutrophication. A similar result was obtained with phosphate, ammonia, and sucrose, but recovery was almost immediate when phosphate additions only were discontinued. When two basins of one lake were fertilized with equal amounts of nitrate and sucrose, and phosphorus was also added to one of the basins, the phosphateenriched basin quickly became highly eutrophic, while the basin receiving only nitrogen and carbon remained at prefertilization conditions. These results, and the high affinity of sediments for phosphorus indicate that rapid abatement of eutrophication may be expected to follow phosphorus control measures.

How Big Is a Chunk?: By combining data from several experiments, a basic human memory unit can be identified and measured

Abstract: I have explored some of the interactions between research on higher mental processes over the past decade or two and laboratory experiments on simpler cognitive processes. I have shown that, by viewing experimentation in a parameter-estimating paradigm instead of a hypothesis-testing paradigm, one can obtain much more information from experiments-information that, combined with contemporary theoretical models of the cognitive processes, has implications for human performance on tasks quite different from those of the original experiments. The work of identifying and measuring the basic parameters of the human information processing system has just begun, but already important information has been gained. The psychological reality of the chunk has been fairly well demonstrated, and the chunk capacity of short-term memory has been shown to be in the range of five to seven. Fixation of information in longterm memory has been shown to take about 5 or 10 seconds per chunk. Some other "magical numbers" have been estimated-for example, visual scanning speeds and times required for simple grammatical transformations-and no doubt others remain to be discovered. But even the two basic constants discussed in this article-short-term memory capacity and rate of fixation in long-term memory-organize, systematize, and explain a wide range of findings, about both simple tasks and more complex cognitive performances that have been reported in the psychological literature over the past 50 years or more.

Female steroid hormones and target cell nuclei.

Abstract: The data discussed herein demonstrate the great variation in target-tissue response that can occur after administration of steroid hormones. The female sex steroids can exert regulatory effects on the synthesis, activity, and possibly even the degradation of tissue enzymes and structural proteins. Each response, nevertheless, appears to be dependent on the synthesis of nuclear RNA. In many instances, the steroid actually promotes a qualitative change in the base composition and sequence of the RNA synthesized by the target cell, implying a specific effect on gene transcription. Most important is our direct quantitative evidence that sex steroids cause a net increase in the intracellular amounts of specific mRNA molecules in target tissues. It thus appears that we are discovering a pattern of steroid hormone action which includes (Fig. 1): (i) uptake of the hormone by the target cell and binding to a specific cytoplasmic receptor protein; (ii) transport of the steroid-receptor complex to the nucleus; (iii) binding of this "active" complex to specific "acceptor" sites on the genome (chromatin DNA and acidic protein); (iv) activation of the transcriptional apparatus resulting in the appearance of new RNA species which includes specific mRNA's; (v) transport of the hormone-induced RNA to the cytoplasm resulting in synthesis of new proteins on cytoplasmic ribosomes; and (vi) the occurrence of the specific steroid-mediated "functional response" characteristic of that particular target tissue. To elucidate fully the mechanism of steroid hormone action we must study the biochemistry of the process by which information held by the steroid hormone-receptor complex is transferred to the nuclear transcription apparatus. If our assumptions are correct, we should ultimately be able to discover how this hormone-receptor complex exerts a specific regulatory effect on nuclear RNA metabolism. Such regulation might be achieved (i) by direct effects on chromatin template leading to increased gene transcription and thus RNA synthesis; (ii) by activation of the polymerase complex itself; (iii) by inhibition of RNA breakdown; or (iv) by intranuclear processing of large precursor molecules so that smaller biologically active sequences are produced, and (v) by transport of RNA from the nucleus to the cytoplasmic sites of cellular protein synthesis.

The pineal gland: a neurochemical transducer.

Abstract: In this article, Axelrod applied signal transduction theory to his research on the metabolic function of serotonin, even describing the pineal gland as a "neurochemical transducer."

Three-dimensional tertiary structure of yeast phenylalanine transfer RNA.

Abstract: Results of an analysis and interpretation of a 3-A electron density map of yeast phenylalanine transfer RNA. Some earlier detailed assignments of nucleotide residues to electron density peaks are found to be in error, even though the overall tracing of the backbone conformation of yeast phenylalanine transfer RNA was generally correct. A new, more comprehensive interpretation is made which makes it possible to define the tertiary interactions in the molecule. The new interpretation makes it possible to visualize a number of tertiary interactions which not only explain the structural role of most of the bases which are constant in transfer RNAs, but also makes it possible to understand in a direct and simple fashion the chemical modification data on transfer RNA. In addition, this pattern of tertiary interactions provides a basis for understanding the general three-dimensional folding of all transfer RNA molecules.

Cerebral Dominance in Musicians and Nonmusicians

Abstract: Musically experienced listeners recognize simple melodies better in the right ear than the left, while the reverse is true for naive listeners. Hence, contrary to previous reports, music perception supports the hypothesis that the left hemisphere is dominant for analytic processing and the right hemisphere for holistic processing.

Neonate Movement Is Synchronized with Adult Speech: Interactional Participation and Language Acquisition

Abstract: As early as the first day of life, the human neonate moves in precise and sustained segments of movement that are synchronous with the articulated structure of adult speech. These observations suggest a view of development of the infant as a participant at the outset in multiple forms of interactional organization, rather than as an isolate.

Innovation in Industry and the Diffusion of Technology

Abstract: The varied definitions used in the sources that have been discussed make any aggregate analysis difficult. A simple three-stage analysis of flows to, from, and within the firm was used to facilitate comparisons. Even so, each of the generalizations is drawn from relatively small and unrepresentative samples. Case studies may continue to be a source of ideas and hypotheses for further research, but do not appear to offer a means for deeper understanding of the innovation process. The retrospective nature of nearly all of the sources discussed probably means that the process has been viewed as much more rational and well-ordered than it is in fact. This failing is partially overcome in firsthand accounts such as those of Suites and Bueche (63) and Frey and Goldman (64). Each of these accounts involves a successful innovation according to technical or commercial criteria, or both. However, many of the characteristics of innovations that have failed commercially (10) appear to be similar to those of successful cases. The few longitudinal studies, and studies comparing more and less successful cases, do support the main conclusions drawn above (10, 32, 38). More serious problems are raised by the distinctly nonrepresentative nature of the samples used. There are few cases (17, 33, 65) in which the contributions of more than one organization, or details of interactions over a significant period of time, are discussed. There is a wide variation in the importance of the innovations included, ranging from those affecting the economy as a whole to cases involving production in a single firm, albeit with significant commercial results (66). In addition to questions of comparability and sampling, a central problem for further research on innovation will be to devise an operational model to account for interfirm and interindustry differences. Polar definitions used in past studies, "high technology" and "mature industry," for example, are insufficient. One possibility is to use the strategy for growth or competition evident in a firm or an industry, such as sales maximization (automotive), cost minimization (transportation, communications), performance maximization (aircraft, chemicals), or control of materials resources (mining, petroleum), as a basis for drawing distinctions (67). For example, in an industry that seeks to maximize sales, one would expect innovations that would be highly visible to consumers to be developed rapidly (68). In a cost-minimizing situation, production, as opposed to product technology, would be a major source of uncertainty, while the reverse might be the case in a performance-maximizing situation. Greater uncertainty arising from technical sources would imply greater sophistication in effective firms' product planning approaches, while a more stable technology would imply greater sophistication in market research and market-oriented strategies for innovation, and so forth. Much more work is needed along these lines if outcomes of interventions in the innovative process are to be predicted with any accuracy. Some implications for providing incentives and reducing barriers do seem clear from the work to date. Effective directions for federal action lie in strategies such as creating new markets through purchases or procurement policies; aggregating or focusing markets through regulation and other means; providing for market entry by contracts to smaller firms, venture capital, stronger patent protection, and so on; and providing for mobility and informal contacts within the technical community. Technology "push" strategies (such as tax incentives) to increase most research spending, prizes for new technology, and documentation and information retrieval systems would probably be less important in stimulating innovation. Definitive answers will require the most difficult kind of research-experiments in the field. Since the interventions required are difficult and expensive in most cases, they will not be under the researcher's control. Nor will the effect of policy changes be visible over a short period. Thus it seems imperative to take advantage of interventions that occur fortuitously to construct "quasi-experiments" (69) with as great a degree of control over other factors as possible. For example, have recent changes in policy regarding federally held patents increased the commercial use of these patents? Have changes in the capital gains laws retarded the development and growth of "spin-off" enterprises? Has the identification of technology gaps (3) and competitive opportunities stimulated innovation? The effects of such actions on technical innovation could be carefully observed with a modest but sustained research effort, which promises to yield valuable information beyond that available from largely historical sources.

Atmospheric concentrations and sources of trace metals at the South pole.

Abstract: The chemical composition of atmospheric particulate material collected at the geographic South Pole indicates that Al, Sc, Th, Sm, V, Mn, Eu, Fe, La, Ce, Co, Cr, Na, K, Mg, and Ca are derived from either crustal weathering or the ocean. The relatively volatile elements Zn, Cu, Sb, Se, Pb, and Br are apparently derived from other sources. Because of their volatility, vapor-phase condensation or a high-temperature dispersion source is suspected for these elements or their compounds.

Biological cycles for toxic elements in the environment

Abstract: Some of the chemical and biochemical transformations of toxic elements in the environment are discussed with special emphasis on the role played by microorganisms. When confronted with a toxic substance, microorganisms frequently adapt to detoxify it. However, the detoxification of a substance by microorganisms can yield a product that is either more or less toxic to higher organisms. The detoxification mechanisms of mercury are used as examples to demonstrate that there are biological cycles for the synthesis and degradation of toxic compounds. It is also shown that our present knowledge of the biologial cycles of toxic elements enables us to predict the behavior of other toxic elements in the environment.

DNA Ligase: Structure, Mechanism, and Function

Abstract: DNA ligase of E. coli is a polypeptide of molecular weight 75,000. The comparable T4-induced enzyme is somewhat smaller (63,000 to 68,000). Both enzymes catalyze the synthesis of phosphodiester bonds between adjacent 5'-phosphoryl and 3'-hydroxyl groups in nicked duplex DNA, coupled to the cleavage of the pyrophosphate bond of DPN (E. coli) or ATP (T4). Phosphodiester bond synthesis catalyzed by both enzymes occurs in a series of these discrete steps and involves the participation of two covalent intermediates (Fig. 1). A steady state kinetic analysis of the reaction-catalyzed E. coli ligase supports this mechanism, and further demonstrates that enzyme-adenylate and DNA-adenylate are kinetically significant intermediates on the direct path of phosphodiester bond synthesis. A strain of E. coli with a mutation in the structural gene for DNA ligase which results in the synthesis of an abnormally thermolabile enzyme is inviable at 42 degrees C. Although able to grow at 30 degrees C, the mutant is still defective at this temperature in its ability to repair damage to its DNA caused by ultraviolet irradiation and by alkylating agents. At 42 degrees C, all the newly replicated DNA is in the form of short 10S "Okazaki fragments," an indication that the reason for the mutant's failure to survive under these conditions is its inability to sustain the ligation step that is essential for the discontinuous synthesis of the E. coli chromosome. DNA ligase is therefore an essential enzyme required for normal DNA replication and repair in E. coli. Purified DNA ligases have proved to be useful reagents in the construction in vitro of recombinant DNA molecules.

Acid Rain: A Serious Regional Environmental Problem

Abstract: At present, acid rain or snow is falling on most of the northeastern United States. The annual acidity value averages about pH 4, but values between pH 2.1 and 5 have been recorded for individual storms. The acidity of precipitation in this region apparently increased about 20 years ago, and the increase may have been associated with the augmented use of natural gas and with the installation of particle-removal devices in tall smokestacks. Only some of the ecological and economic effects of this widespread introduction of strong acids into natural systems are known at present, but clearly they must be considered in proposals for new energy sources and in the development of air quality emission standards.

What Happened at Hawthorne?: New evidence suggests the Hawthorne effect resulted from operant reinforcement contingencies.

Abstract: The Hawthorne effect in experimental research is the unwanted effect of the experimental operations themselves. Following the Hawthorne studies, various explanations have been proposed to account for rising rates of production. Although in the Relay Assembly Test Room experiment the experimental operations may have produced other extraneous variables, a reexamination based on new and neglected evidence has yielded a new interpretation. The new variable, made more plausible because research in other contexts has shown it to have similar effects, is a combination of information feedback and financial reward. It is an example of the control of behavior by its consequences. Although several approaches may be taken to explain the effects of response-consequence contingencies, I have favored operant conditioning because it seems to account for progressive increases in response rate—the Hawthorne phenomenon. Generalizing from the particular situation at Hawthorne, I would define the Hawthorne effect as the confounding that occurs if experimenters fail to realize how the consequences of subjects9 performance affect what subjects do. But the Hawthorne effect need not be viewed solely as a problem in conducting experiments. The phenomenon that created it should be studied in its own right, as Sommer (67) suggested with a different phenomenon in mind. The study of response-consequence contingencies might well be extended to the examination of motivation in industrial workers.