Do tastants have a smell?

The stimuli used in taste research are usually considered to be odourless. This was tested in two experiments with aqueous solutions of two representative compounds for each of the five taste qualities including umami. In the first experiment elderly and young subjects rated the intensity and pleasantness of three concentrations of the stimuli, while wearing or not wearing a noseclip. Saliva production was also measured. Blocking olfaction only influenced salivation for umami. It reduced taste intensity ratings, but as in an earlier experiment with the same compounds in food products, this effect was stronger in the young, who also liked the stimuli better wearing the noseclip. In the second experiment, another group of young people tried to detect the odours of the tastants dissolved in demineralized, double-distilled or Evian water. A considerable number of subjects could regularly detect seven of the ten tastants by olfaction and the extent to which they did correlated significantly with the reduction in taste intensity ratings for the different tastants found in the first experiment. We suggest that most tastants can be smelled and that this smell contributes to taste intensity ratings.     

Why do we not have a cure for rheumatoid arthritis?

There are currently unprecedented opportunities to treat rheumatoid arthritis using well-designed, highly effective, targeted therapies. This will result in a substantial improvement in the outcome of this disorder for most affected individuals, if they can afford these therapies. Yet our lack of understanding of the basic mechanisms that initiate and sustain this disease remains a major obstacle in the search for a definitive cure. It is possible, if not likely, that our best approach will be to identify individuals at risk and devise reliable, safe methods of preventing the disease before it occurs. The means to do this are currently unknown but should serve as a major focus of research.     

Do small animals have a biogeography?

It has been stated that small organisms do not have barriers for distribution and will not show biogeographic discreteness. General models for size-mediated biogeographies establish a transition region between ubiquitous dispersal and restricted biogeography at about 1–10 mm. We tested patterns of distribution versus size with water mites, a group of freshwater organisms with sizes between 300 μm and 10 mm.We compiled a list of all known water mite species for Sierra del Guadarrama (a mountain range in the centre of the Iberian Peninsula) from different authors and our own studies in the area. Recorded habitats include lotic, lentic and interstitial environments. Species body size and world distribution were drawn from our work and published specialized taxonomic literature. The null hypothesis was that distribution is size-independent. The relationship between distribution and size was approached via analysis of variance and between size and habitat via logistic regression. Contrary to expectations, there is no special relationship between water mite size and area size distribution. On the other hand, water mite size is differentially distributed among habitats, although this ecological sorting is very weak. Larger water mites are more common in lentic habitats and smaller water mites in lotic habitats. Size-dependent distribution in which small organisms tend to be cosmopolitan breaks down when the particular biology comes into play. Water mites do not fit a previously proposed size-dependent biogeographical distribution, and are in accordance with similar data published on Tardigrada, Rotifera, Gastrotricha and the like.     

Do neurons have a voltage or a current threshold for action potential initiation?

The majority of neural network models consider the output of single neurons to be a continuous, positive, and saturating firing ratef(t), while a minority treat neuronal output as a series of delta pulses (t — t _i ). We here argue that the issue of the proper output representation relates to the biophysics of the cells in question and, in particular, to whether initiation of somatic action potentials occurs when a certain thresholdvoltage or a thresholdcurrent is exceeded. We approach this issue using numerical simulations of the electrical behavior of a layer 5 pyramidal cell from cat visual cortex. The dendritic tree is passive while the cell body includes eight voltage- and calcium-dependent membrane conductances.We compute both the steady-state (I ^static (V _m )) and the instantaneous (I _o (V_m)) I–V relationships and argue that the amplitude of the local maximum inI ^static (V _m ) corresponds to the current thresholdI _th for sustained inputs, while the location of the middle zero-crossing ofI _o corresponds to a fixed voltage thresholdV _th for rapid inputs. We confirm this using numerical simulations: for rapid synaptic inputs, spikes are initiated if the somatic potential exceedsV _th, while for slowly varying inputI _th must be exceeded. Due to the presence of the large dendritic tree, no charge thresholdQ _th exists for physiological input.Introducing the temporal average of the somatic membrane potential (V _m) while the cell is spiking repetitively, allows us to define a dynamic I-V relationship ^dynamic ((V _m)). We find an exponential relationship between (V _m) and the net current sunk by the somatic membrane during spiking (diode-like behavior). The slope ofI/dynamic((V _m)) allows us to define a dynamic input conductance and a time constant that characterizes how rapidly the cell changes its output firing frequency in response to a change in its input.     

Do N-glycoproteins have preference for specific sequons?

Protein N-glycosylation requires the presence of asparagine (N) in the consensus tri-peptide NXS/T (where X is any amino acid, S is serine and T is threonine). Several factors affect the glycosylation potential of NXS/T sequons and one such factor is the type of amino acid at position X. While proline was shown to negatively affect N-glycosylation, the nature of other amino acids at this position is not clear. Using Markov chain analysis of tri-peptide NXS/T from viral, archaeal and eukaryotic proteins as well as experimentally confirmed N-glycosylated sequons from eukaryotic proteins, we show here that the occurrence of most sequon types differ significantly from the expected probability. Sequon types with F, G, I, S, T and V amino acids are consistently preferred while those with P and charged amino acids are under-represented in all four groups. Further, proteins contained far fewer number of possible sequon types (maximum 20 types for NXS or NXT taken separately) for any given number of sequons, which may be explained based on random sampling. Consistent with the present finding, majority of the over-represented sequons found in two important viral envelope glycoproteins (hemagglutinin of influenza A H3N2 and glycoprotein120 of HIV-1) are indeed preferred sequon types, which may provide a selective advantage. Accordingly, although there seems to be some preference for sequons, this preference may not be unique to N-glycosylation.     

Do miRNAs have a deep evolutionary history?

The recent discovery of microRNAs (miRNAs) in unicellular eukaryotes, including miRNAs known previously only from animals or plants, implies that miRNAs have a deep evolutionary history among eukaryotes. This contrasts with the prevailing view that miRNAs evolved convergently in animals and plants. We re-evaluate the evidence and find that none of the 73 plant and animal miRNAs described from protists meet the required criteria for miRNA annotation and, by implication, animals and plants did not acquire any of their respective miRNA genes from the crown ancestor of eukaryotes. Furthermore, of the 159 novel miRNAs previously identified among the seven species of unicellular protists examined, only 28 from the algae Ectocarpus and Chlamydomonas, meet the criteria for miRNA annotation. Therefore, at present only five groups of eukaryotes are known to possess miRNAs, indicating that miRNAs have evolved independently within eukaryotes through exaptation of their shared inherited RNAi machinery.     

Do spherical tokamaks have a thermonuclear future?

This work has been initiated by the publication of a review by B.V.Kuteev et al., ??Intense Fusion Neutron Sources?? [Plasma Physics Reports 36, 281 (2010)]. It is stated that the key thesis of the above review that a spherical tokamak can be recommended for research neutron sources and for demonstration hybrid systems as an alternative to expensive ??classical?? tokamaks of the JET and ITER type is inconsistent. The analysis of the experimental material obtained during the last 10 years in the course of studies on the existing spherical tokamaks shows that the TIN-ST fusion neutron source spherical tokamak proposed by the authors of the review and intended, according to the authors?? opinion, to replace ??monsters?? in view of its table-top dimensions (2 m³) and laboratory-level energetics cannot be transformed into any noticeable stationary megawatt-power neutron source competing with the existing classical tokamaks (in particular, with JET with its quasi-steady DT fusion power at a level of 5 MW). Namely, the maximum plasma current in the proposed tokamak will be not 3 MA, as the authors suppose erroneously, but, according to the present-day practice of spherical tokamaks, within 0.6?C0.7 MA, which will lead to a reduction on the neutron flux by two to three orders of magnitude from the expected 5 MW. The possibility of the maintenance of the stationary process itself even in such a ??weakened?? spherical tokamak is very doubtful. The experience of the largest existing devices of this type (such as NSTX and MAST) has shown that they are incapable of operating even in a quasi-steady operating mode, because the discharge in them is spontaneously interrupted about 1 s after the beginning of the current pulse, although its expected duration is of up to 5 s. The nature of this phenomenon is the subject of further study of the physics of spherical tokamaks. This work deals with a critical analysis of the available experimental data concerning such tokamaks and a discussion of the potential possibility of their use in thermonuclear research.     

Do asparagine-linked carbohydrate chains in glycoproteins have a preference for β-bends?

X-ray structures of the conformation of carbohydrate moieties and connected regions of glycoproteins are summarized. Evidence is presented that there is some preference for carbohydrate attachment at -bends. Evolution may have favored glycosylation to occur at bends to ensure free mobility of the carbohydrate moieties.     

Do you have a probiotic in your future?

The possibility of using microbes to maintain health, and to prevent or treat disease is a topic as old as microbiology. However, one factor impeding the introduction of effective probiotics has been our very limited understanding of the composition of the human microbiome, as well as the biological requirements for these organisms. With advances in understanding the microbiome and its metagenome in humans and other mammals, we now can build a more robust scientific basis to develop probiotic strategies. Increasing knowledge of intramicrobial competition and cooperation, as well as host-microbe cross-signaling, will facilitate design of new probiotics and the modeling of their deployment, leading to eventual clinical trials.     

Commentary: Do we have a consistent terminology for species diversity? The fallacy of true diversity

There is no single best index that can be used to answer all questions about species diversity. Entropy-based diversity indices, including Hill’s indices, cannot account for geographical and phylogenetic structure. While a single diversity index arises if we impose several constraints—most notably that gamma diversity be completely decomposed into alpha and beta diversity—there are many ecological questions regarding species diversity for which it is counterproductive, requiring decomposability. Non-decomposable components of gamma diversity may quantify important intrinsic ecological properties, such as resilience or nestedness.     

Commentary: Do we have a consistent terminology for species diversity? Back to basics and toward a unifying framework

After decades of misusing the term diversity in community ecology, over the last 5 years some papers have offered important advances toward developing a more rigorous mathematical background, which allows us to achieve more clarity in the terminology for the vast range of biological phenomena that have been placed under the umbrella of this term. Some points have been clearly stated in previous papers of this Views and Comments section, and new terms have even been proposed for specific cases, but other issues, such as the need for the prefix true have not been discussed. Our aim is to clarify some of the terms and concepts, the proper use of which appears still to remain unclear, and to provide biologists with a simplified version of the general framework resulting from recent contributions, with an emphasis on identifying points of consensus in the field. We also comment on the possibility of extending the basics of this general framework to other facets of the broad term biodiversity, such as functional or phylogenetic diversity.     

Do blind cavefish have behavioral specializations for active flow-sensing?

Blind cavefish use a form of active sensing in which burst-coast swimming motions generate flow signals detected by the lateral line. To determine if blind cavefish have evolved behavioral specializations for active flow-sensing, including the ability to regulate flow signal production through lateral line feedback, the swimming kinematics of blind and sighted morphs of Astyanax were compared before and after 24?h of familiarization with a novel, dark environment and with and without lateral line functionality. Although both morphs showed little difference in the vast majority of kinematic parameters measured, blind morphs differed significantly from sighted morphs in having a much higher incidence of swim cycle sequences devoid of sharp turns. Both lateral line deprivation and familiarization with the arena led to significant declines in this number for blind, but not sighted morphs. These findings suggest that swimming kinematics are largely conserved, but that blind morphs have nevertheless evolved enhanced abilities to use lateral line feedback when linking swim cycles into continuous, straight trajectories for exploratory purposes. This behavioral specialization can best be understood in terms of the intermittent and short-range limitations of active flow-sensing and the challenges they pose for spatial orientation and navigation.     

Do fern gametophytes have the capacity for irradiance acclimation?

Ferns present two alternant generations: sporophyte and gametophyte. In the present work we address the question of whether fern gametophytes have the potential to acclimate to different irradiances as vascular plants do. We studied the gametophytes of three different fern species belonging to the Aspleniaceae family with different ecological requirements (Asplenium trichomanes, Asplenium scoloprendrium and Ceterach officinarum). Fern spores were germinated and the gametophytes cultivated under photon flux density (PFD) of 10, 50 or 100 μmol m⁻² s⁻¹. From the early stages of spore germination (the formation of the 5-celled germinal filament), photosynthetic apparatus acclimates showing the typical patterns of photochemical responses to high or low PFD. In agreement with the photochemical pattern of acclimation, higher contents of xanthophyll cycle pigments and α-tocopherol was observed in plants grown under high PFD. The α/β-carotene ratio, used as indicator of the acclimation of the photosynthetic apparatus, also sustained the initial hypothesis except for A. trichomanes. We conclude that fern gametophytes display a complete array of photosynthetic and photoprotective traits that allow an effective acclimation to PFD.     

Do delta F508 heterozygotes have a selective advantage?

In this paper the fitness of the delta F508 heterozygote is assessed and the age of the delta F508 mutation in the cystic fibrosis locus is estimated. Data from three microsatellite loci are applied. The analysis is performed conditional on the present-day frequency of the delta F508 mutation and based on assumptions about the demographic history of the European population and the mutation rate in the three microsatellite loci. It is shown that the data gives evidence of positive selection (up to 2-3% per delta F508 heterozygote), but also that data could be explained by negative selection of roughly the same order of magnitude. The age of the delta F508 mutation is subsequently estimated; it is found that the mutation is at least 580 generations old, but could be much older depending on the microsatellite mutation rate and the exact number of substitutions experienced in the history of the three microsatellite loci.     

Do fishes have nociceptors? Evidence for the evolution of a vertebrate sensory system.

Nociception is the detection of a noxious tissue-damaging stimulus and is sometimes accompanied by a reflex response such as withdrawal. Pain perception, as distinct from nociception, has been demonstrated in birds and mammals but has not been systematically studied in lower vertebrates. We assessed whether a fish possessed cutaneous nociceptors capable of detecting noxious stimuli and whether its behaviour was sufficiently adversely affected by the administration of a noxious stimulus. Electrophysiological recordings from trigeminal nerves identified polymodal nociceptors on the head of the trout with physiological properties similar to those described in higher vertebrates. These receptors responded to mechanical pressure, temperatures in the noxious range (more than 40 degrees C) and 1% acetic acid, a noxious substance. In higher vertebrates nociceptive nerves are either A-delta or C fibres with C fibres being the predominating fibre type. However, in the rainbow trout A-delta fibres were most common, and this offers insights into the evolution of nociceptive systems. Administration of noxious substances to the lips of the trout affected both the physiology and the behaviour of the animal and resulted in a significant increase in opercular beat rate and the time taken to resume feeding, as well as anomalous behaviours. This study provides significant evidence of nociception in teleost fishes and furthermore demonstrates that behaviour and physiology are affected over a prolonged period of time, suggesting discomfort.     

Do coral-reef fish faunas have a distinctive taxonomic structure?

Do the highly diverse fish faunas that associate with coral reefs have distinguishing taxonomic and ecological characteristics, as proposed by Choat and Bellwood (1991) and Bellwood (1996)? Does a 50?my old (Eocene) fossil fish fauna from Italy represent a coral-reef fish assemblage that provides unique information about the evolution of such assemblages, as claimed by Bellwood (1996)? I compared the structure of the reef fish faunas of adjacent tropical regions rich and poor in coral reefs, in both America and Polynesia, and found that they exhibit no substantive differences in relative species richness among families of typical “coral-reef” fishes. While coral-rich regions have larger reef fish faunas, a variety of factors probably contribute to such differences. Thus coral-reef fish faunas may lack a distinctive taxonomic structure. A similar comparative approach would be useful for assessing whether assemblages of fishes on coral reefs have distinctive ecological characteristics. Based on patterns of habitat use by modern tropical shorefishes, the Italian Eocene fauna includes few definite reef fishes, and may well consist primarily of non-reef fishes preserved in a non-reef habitat. Until we know more about the environment in which those fossils were preserved, that fauna can contribute little to understanding how coral reef fish assemblages have evolved.