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.     

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.     

“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.     

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.     

Is cyclin Zeuthen's “division protein”?

Biochemical evidence is presented for the presence of cyclin in Tetrahymena. Zeuthen previously postulated the existence of a heat-labile “division protein” to explain heat-shock-induced division synchrony in Tetrahymena [(1964) Synchrony in Cell Division and Growth (Zeuthen, E., Ed.), pp. 99–158, Interscience, New York]. We show that cyclin is heat-labile in Tetrahymena and suggest that cyclin may be Zeuthen's division protein. Cyclin and cell cycle control is of interest in Tetrahymena because the division mechanism drives macronuclear amitosis, closed and acentric micronuclear mitosis, and cortical differentiation in this cell type.     

Do “heavy” eaters live longer?

A new hypothesis is put forward, linking cellular endurance with dietary consumption of stable heavy isotopes. Due to the isotope effect, biomolecules that incorporate heavier isotopes give rise to more stable molecular structures with increased resistance to damages associated with aging and age-related disease. The inclusion of heavy isotopes might be either active (selection for heavier isotopes) or passive (incorporation reflecting the existing abundance). The hypothesis links consumption of foods relatively rich in heavy isotopes (such as (13)C and D, derived from C4-plants), especially at the early stages of the organism's development, with enhanced longevity. Implications of diets and intestinal microflora are also discussed.     

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.     

Can paleopathology provide evidence for “compassion”?

Paleopathological analyses of skeletal remains have provided significant information about diet and health in prehistoric populations. A number of individuals have been recovered whose remains show evidence of impairments that would have precluded "normal" functioning, resulting in a disability. The most famous example is Shanidar I; more recent discoveries include the Romito 2 dwarf from Italy and a boy with spina bifida from the Windover site in Florida. These finds have been interpreted by some writers as evidence for compassion and "moral decency" among the other members of the community, who would have had to support these nonproductive individuals. However, these interpretations are based on a number of implicit assumptions: about the number of nonproductive members normally present in any population, about the abilities of disabled individuals to contribute to society, about the treatment of disabled individuals by other members of the group, and about the "moral rightness" of facilitating the survival of a disabled individual under all circumstances. These assumptions are not justified by the evidence from the archeological record or by reference to ethnographic analogy. A tendency to focus on physical traits as the sole measure of productive ability, images of Rousseau's "noble savage" transported to the past, and unexamined beliefs about the disabled in modern societies have influenced these archeological interpretations. We are not justified in drawing conclusions either about the quality of life for disabled individuals in the past or about the motives or attitudes of the rest of the community from skeletal evidence of physical impairment.     

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.     

Gibt es einen „Duft der MHC‐Gene“?

MHC‐Genes: Do they influence the choice of partners via olfactory signals? Behavioral experiments in mice and humans suggest that genes of the major histocompatibilty complex (MHC) may be important for the differentiation of self and non‐self during mate choice. While this correlation is well documented for certain mouse strains, it is controversial for humans. Signal transfer between potential partners is considered to occur via the production of MHC‐dependent olfactory cues by a sender and their recognition by olfaction in the recipient. It is shown that in mice and humans the overall bouquet of volatiles is not and the pattern of peptides in mice is only marginally influenced by the MHC genes. However, in mice, olfactory cues without MHC contribution appear to play a role in mate choice, in that the profile learned from the parents during rearing is compared with the distinct profile of a potential partner, which is in turn selected for mating. Such olfactory differentiation between close relatives and potential mates without MHC‐contribution may also operate unconsciously in humans.     

“How pendulum‐like are siamangs? energy exchange during brachiation”

Hylobatidae (gibbons and siamangs) are known for their brachiation skills. The comparison of brachiation with a pendulum is made several times in the literature, and the costs and benefits of being pendulum-like are well described. However, the amount of energy exchange during brachiation of gibbons has rarely been determined. In this study, the amount of energy recovery (ER) during brachiation is assessed for three siamangs in a seminatural environment. The animals were recorded by four cameras while voluntarily brachiating on three different setups. The effects of locomotion speed, brachiation type, and setup on ER as well as on the external mechanical work during brachiation are determined. It is hypothesized that the amount of ER decreases with an increasing setup complexity while the external mechanical work increases. Additionally, we expect that support arm kinematics will be adjusted according to spatial complexity in order to maintain high recovery percentages. Our results show that ER is mainly determined by brachiation speed. Regardless of type of brachiation or setup, brachiation is done with a lower ER when brachiating faster. Within our limited range of setup variation, the expected effect of increasing complexity is not found. Although there is significant variation in support arm joint angles, no clear relation with speed, brachiation type, or setup is observed.     

How do plants “notice” attack by herbivorous arthropods?

Precise and deep comprehension of plant responses to herbivorous arthropods requires detailed knowledge of how a plant “notices” the attack. Herbivore attack is not restricted to plant wounding by feeding, but instead different phases of attack that elicit a plant response need to be distinguished: touch, oviposition and feeding. Touch, secretions released with eggs and regurgitate delivered during feeding may act in concert as elicitors of plant defence. Here, we discuss the current knowledge of what a plant “notices” during the different phases of herbivore attack and how it responds at the molecular, physiological and ecological level. Understanding the mechanisms of plant responses to the different phases of herbivore attack will be a key challenge in unravelling the complex communication pathways between plants and herbivores.     

Does hydrogen peroxide exist “free” in biological systems?

Hydrogen peroxide (H₂O₂) can diffuse far from the site of production to intracellular locations where biological effects may be greater. The diffusion range is extended by H₂O₂ carriers formed spontaneously by hydrogen bonding with monomeric and polymeric compounds, including amino and dicarboxylic acids, peptides, proteins, nucleic acid bases, and nucleosides. Hydrogen peroxide adducts (HPAs) are readily synthesized, e.g., crystalline histidine (His)-H₂O₂ adducts. An equilibrium exists between an adduct-forming compound and H₂O₂. The detection and relative stabilities of HPAs are measured by the degree of decomposition of H₂O₂ as influenced by test compounds in buffered solution competing with glucose or fructose for H₂O₂. The HPAs delay decomposition of H₂O₂ up to several hundredfold. The overall charge on an HPA, i.e., its ability to penetrate cell membranes, influences the cytotoxic and clastogenic effects of H₂O₂. Growth inhibition of Salmonella typhimurium LT₂ by H₂O₂ is enhanced by neutral HPAs but decreased by anionic HPAs. Addition of catalase 1, 10, or 30 min after inoculation of S. typhimurium LT₂ reduces or nearly eliminates partial growth inhibition by H₂O₂, but a neutral HPA, expecially his-H₂O₂, transported H₂O₂ into the cells within 1 min, and in about 10 min completely inhibited growth. The stability of HPAs decreases with increasing pH or increasing temperature, while added Fe(II) in the presence and absence of EDTA accelerates H₂O₂ and HPA decomposition. Calculations indicate H₂O₂ hydrogen bonds with nucleic acid-base pairs with no apparent bond strain and energy stabilization comparable to normal hydrogen bonding.     

Are tanning beds “safe”? Human studies of melanoma

Controversy continues over the carcinogenic properties of tanning beds. The tanning industry “sells” tanning beds as a safe alternative to UV exposure for both tanning as well as vitamin D biosynthesis. But, how safe are tanning beds? Epidemiologic data – incomplete and unsatisfactory – suggests that tanning beds are not safer than solar ultraviolet radiation and that they may have independent effects from solar exposure that increase risk for melanoma.