Does “supersaturated coexistence” resolve the “paradox of the plankton”?

In contradiction with field observations, theory predicts that the number of coexisting plankton species at equilibrium cannot exceed the number of limiting resources, which is called the "paradox of the plankton". Recently, Huisman & Weissing (1999 , 2000 ) showed, in a model study, that the number of coexisting species may exceed the number of limiting resources when internal system feedback induces oscillations or chaos. In this paper, we use the term "supersaturated coexistence" for this phenomenon. On the basis of these findings, they claimed that the paradox of the plankton is solved. We investigated the prerequisites for supersaturated coexistence in the same model. Our results indicate that supersaturated coexistence is a rare phenomenon in parameter space, requires a very precise parameterization of the community members and is sensitive to the introduction of new species and the removal of the present species. This raises the question of whether supersaturated coexistence is likely to occur in nature. We conclude that the claim by Huisman & Weissing (1999 , 2000 ) is premature.     

Are the Kow Swamp hominids “archaic”?

Initial reports of hominids recovered at Kow Swamp, in the Murray Valley of Victoria indicated that, on the basis of cranial analyses, there was a "survival of Homo erectus features in Australia until as recently as 10,000 years ago (Thorne and Macumber, 1972, p. 316). This claim was later refuted by others, who suggested that artificial cranial deformation may have been responsible for at least some of the distinctive and "primitive" traits seen in the Kow Swamp individuals. Previous research by this worker and others has indicated that taxonomic traits at both specific and subspecific levels are present in hominine femora. Therefore, it may be possible to evaluate the "primitiveness" of the Kow Swamp sample on the basis of their femoral anatomy. Morphometric analyses were undertaken, using as controls femora of Romano British, Tasmanian, and other Murray Valley populations. On the basis of bivariate and multivariate analyses it was found that, at least in this single element of the postcranium, no primitive features were present. The Kow Swamp sample, in fact, shows a very close morphometric relationship with all included Homo sapiens controls and is significantly distinct from Homo erectus.     

Survivin study: An update of “What is the next wave?”

Studies on survivin over the past 2-3 years have shown that survivin possesses multiple subcellular localizations and is a multifunctional molecule involved in many aspects of cellular processes and/or behaviors. The subcellular localization and function of the survivin splice variants, however, have not yet been well elucidated. We have, therefore, provided additional observations on several survivin splice variants for further exploration. This review article will update the role of survivin, and its splice variants in the mitosis/cell cycle, apoptosis, tumorigenesis, chemoprevention, drug/radiation resistance, and cancer therapeutics.     

Parrot claylick distribution in South America: do patterns of “where” help answer the question “why”?

Geophagy is well known among some Neotropical parrots. The clay apparently adsorbs dietary toxins and/or provides supplemental nutrients. We used location data and 23 environmental layers to develop a predictive model of claylick distribution using Maxent software. We related species characteristics to claylick use and examined how parrot assemblages using claylicks changed with distance from the centre of claylick distribution. Fifty‐two parrot claylicks were reported from an area of ca 4 million km² but over 50% were restricted to a 35 000 km² region of southeast Peru and northern Bolivia. Claylicks were strongly associated with moist forest on younger (<65 millions of yr) geological formations and exposed river banks. The predictive model of claylick distribution matched our reported range well, with precipitation of warmest quarter, land cover, temperature seasonality, and distance from the ocean being most important predictors of claylick presence. Twenty‐six of the region's 46 parrot species visited claylicks. Species differed greatly in their lick use, but body size, dietary breadth, abundance and other traits were poor predictors of lick use. We are confident that our survey identified the distribution of major parrot claylicks in South America, although less conspicuous parrot geophagy may occur elsewhere. We suggest that claylick distribution reflects both underlying geology (allowing claylick formation in only some regions) and the physiological need for geophagy among parrots in different parts of the continent. Data on the latter are inconclusive, but we argue that parrot claylick distribution supports the contention that geophagy is related more to sodium deficiencies than to protection from dietary toxins.     

“The” genetic code?

The DNA‐based code for protein through messenger and transfer RNA is widely regarded as the code of life. But genomes are littered with other kinds of coding elements as well, and all of them probably came after a supercode for the tRNA system itself.     

How “representative” is the Terry collection? Evidence from the proximal femur

The work reported here is the beginning of an attempt to determine whether data on skeletal aging changes derived from the Terry collection (Smithsonian Institution) can safely be applied to present-day clinical and forensic problems. Measurements made on radiographs of the proximal third of the right femur below the greater trochanter were compared in three groups of American white females: Terry collection “regulars,” Terry collection willed, and GW (George Washington University Medical Center) willed. Mean birth year for the Terry regulars was 1883, whereas the mean birth year for Terry and GW willed was 1910. Terry willed femora are longer than those of Terry regulars, but not more robust. The two groups show opposing secular trends in femoral length, and in this respect the Terry regulars appear closer to the general U.S. population. In two indices of relative medullary cavity size (which reflect changes in cortical thickness as well as internal and external diameters) all three groups agree in showing age-related increase of medullary diameters, greater increase in the anterior–posterior dimension, and greatest amount of increase at diaphyseal levels. The major difference between groups is in timing, with medullary cavity expansion becoming evident at least a decade earlier and leading to greater eventual loss of cortical thickness in the willed groups.     

What is the role of the second “structural” NADP+‐binding site in human glucose 6‐phosphate dehydrogenase?

Human glucose 6-phosphate dehydrogenase, purified after overexpression in E. coli, was shown to contain one molecule/subunit of acid-extractable "structural" NADP+ and no NADPH. This tightly bound NADP+ was reduced by G6P, presumably following migration to the catalytic site. Gel-filtration yielded apoenzyme, devoid of bound NADP+ but, surprisingly, still fully active. Mr of the main component of "stripped" enzyme by gel filtration was approximately 100,000, suggesting a dimeric apoenzyme (subunit Mr = 59,000). Holoenzyme also contained tetramer molecules and, at high protein concentration, a dynamic equilibrium gave an apparent intermediate Mr of 150 kDa. Fluorescence titration of the stripped enzyme gave the K d for structural NADP+ as 37 nM, 200-fold lower than for "catalytic" NADP+. Structural NADP+ quenches 91% of protein fluorescence. At 37 degrees C, stripped enzyme, much less stable than holoenzyme, inactivated irreversibly within 2 d. Inactivation at 4 degrees C was partially reversed at room temperature, especially with added NADP+. Apoenzyme was immediately active, without any visible lag, in rapid-reaction studies. Human G6PD thus forms active dimer without structural NADP+. Apparently, the true role of the second, tightly bound NADP+ is to secure long-term stability. This fits the clinical pattern, G6PD deficiency affecting the long-lived non-nucleate erythrocyte. The Kd values for two class I mutants, G488S and G488V, were 273 nM and 480 nM, respectively (seven- and 13-fold elevated), matching the structural prediction of weakened structural NADP+ binding, which would explain decreased stability and consequent disease. Preparation of native apoenzyme and measurement of Kd constant for structural NADP+ will now allow quantitative assessment of this defect in clinical G6PD mutations.     

Was heißt “lebendig”?

“Life” means “being alive” of special entities, which we call “organisms”. From a physical point of view, living entities are open systems, which exchange matter as well as energy with their surroundings. Against disruptive influences permanently present, they maintain actively and autonomously a steady state far from the thermodynamic equilibrium. This dynamic state of living beings represents a functional order, an internal “organization”. That means that the involved processes one and all must be correlated in such a way that they in sum prevent the breakdown of the living state. Organization implies functionality, which in turn requires structural relationships, and structures require information for their specification. Information in turn presupposes a source, which is constituted in living systems by the nucleic acids. Organisms are unique in having a capacity to use information, which is stored in the nucleic acid and yields the basis for their specific internal organization in its perpetuation: Living beings, and only they, show a self‐maintained organization.     

Is (9Z)‐“meso”‐zeaxanthin optically active?

The question raised in the title was answered. (3R, 3'S)-meso-Zeaxanthin was submitted to iodine catalyzed photochemical stereoisomerisation. The enantiomeric (9Z) and (9'Z) geometrical isomers were isolated by semipreparative HPLC and separated as diastereomeric dicarbamates on a chiral column only. Cleavage of the carbamate could not be effected. CD-Spectra of (1"S, 1"S)- and (1"R, 1"R)-dicarbamates of geometrical isomers of (3R, 3'R)- and (3R, 3'S)-meso-zeaxanthin were systematically studied and the contribution from the carbamate moieties revealed. It was concluded that (9Z, 3R, 3'S)-"meso"-zeaxanthin, in spite of having no symmetry elements, is optically inactive. The result has been rationalised in line with the current hypothesis on the origin of carotenoid CD spectra.     

“How Local Is Local?”—A Review of Practical and Conceptual Issues in the Genetics of Restoration

In plant conservation, restoration (the augmentation or reestablishment of an extinct population or community) is a valuable tool to mitigate the loss of habitat. However, restoration efforts can result in the introduction of novel genes and genotypes into populations when plant materials used are not of local origin. This movement is potentially important because many plant species are subdivided into populations that are adapted to local environmental conditions. Here we focus on genetic concerns arising from ongoing restoration efforts, where often little is known about “How local is local?” (i.e., the geographic or environmental scale over which plant species are adapted). We review the major issues regarding gene flow and local adaptation in the restoration of natural plant populations. Finally, we offer some practical, commonsense guidelines for the consideration of genetic structure when restoring natural plant populations.     

Revisiting “what do tadpoles really eat?” A 10‐year perspective

相似文献   

Was “Lucy” more human than her “child”? Observations on early hominid postcranial skeletons

Fully adult partial skeletons attributed to Australopithecus afarensis (AL 288-1, “Lucy”) and to Homo habilis (OH 62, “Lucy's child”), respectively, both include remains from upper and lower limbs. Relationships between various limb bone dimensions of these skeletons are compared to those of modern African apes and humans. Surprisingly, it emerges that OH 62 displays closer similarities to African apes than does AL 288-1. Yet A. afarensis, whose skeleton is dated more than 1 million years earlier, is commonly supposed to be the ancestor of Homo habilis. If OH 62, classified as Homo habilis by its discoverers, does indeed represent a stage intermediate between A. afarensis and later Homo, a revised interpretation of the course of human evolution would be necessary.