Time perception: brain time or event time?

Recent experiments show that synchronous events can appear to an observer to occur at different times. Neural processing time delays are offered as an explanation of these temporal illusions, but equating perceived time with processing time leads to some thorny philosophical problems.     

Folic acid - vitamin and panacea or genetic time bomb?

We live in a health-conscious age - many of us supplement our diet with essential micronutrients through the discretionary use of multivitamin pills or judicious selection of foods that have a health benefit beyond that conferred by the nutrient content alone - the so-called 'functional foods'. Indeed, the citizens of some nations have little choice, with a mandatory fortification policy in place for certain vitamins. But do we ever stop to consider the consequences of an increased exposure to micronutrients? We examine this issue in relation to the B-group vitamin folic acid, and ask whether supplementation with this vitamin could introduce a strong genetic selection pressure - one that has the side effect of increasing the prevalence of some of the most significant, human life-threatening diseases. Are we affecting our genetics - is this a case of human evolution in progress by altering our diet?     

Competitive displacement or biotic resistance? Disentangling relationships between community diversity and invasion success of tall herbs and shrubs

Questions: Are negative invasion–diversity relationships due to biotic resistance of the invaded plant community or to post‐invasion displacement of less competitive species? Do invasion–diversity relationships change with habitat type or resident traits? Location/species: Lowlands and uplands of western and southern Germany, Heracleum mantegazzianum; mountain range in central Germany, Lupinus polyphyllus; and coastal dunes of northwest Germany, Rosa rugosa. Methods: We tested the significance and estimated regression slopes of invasion–diversity relationships using generalized linear (mixed effects) models relating invader cover and habitat type to species richness in different plant groups, stratified based on size, life cycle and community association. Results: We found negative, positive and neutral relationships between invader cover and species richness. There were negative linear correlations of invader cover with small plant species throughout, but no negative linear correlation with tall species. Invasion–diversity relationships tended to be more negative in early‐successional habitats, such as dunes or abandoned grasslands, than in late‐successional habitats. Conclusions: Invasion diversity–relationships are complex; they vary among habitat types and among different groups of resident species. Negative invasion–diversity relationships are due to asymmetric competitive displacement of inferior species and not due to biotic resistance. Small species are displaced in early‐successional habitats, while there is little effect on persistence of tall species.     

Natural and human impact in Mediterranean landscapes: An intriguing puzzle or only a question of time?

Time is a key factor to understand the effects of disturbance on natural communities or ecosystems. In Mediterranean landscapes, where nature and humans have been strongly intermingling since mid-Holocene, the relationships between plant ecology and palaeoecology and their role for the interpretation of natural and anthropogenic changes still needs to be clearly understood. Ecology and palaeoecology are both investigating such problems, but each of them cannot disentangle the specific role played by nature and by humans in shaping the present plant communities and landscapes. A new age of cooperation among researchers in ecology and palaeoecology is needed, and the integration of these closely related but separated research fields is necessary to explain the resulting dynamic puzzle. Plant ecologists should avoid the oversimplification of the actual causes as the exclusive drivers of plant communities and landscapes and force the exploitation of the available data to generate and test new hypotheses for past, present and future environmental reconstructions and management. Even when planning for the future biodiversity conservation, we need to properly use the existing information about millennia of human effects on the natural biotas, to properly set landscape management and conservation priorities.     

What determines emergence and net recruitment in an early succession plant community? Disentangling biotic and abiotic effects

Question: How do different regeneration scenarios shape species composition at two stages of plant community establishment (emergence and net recruitment) in an early succession? Location: Northern Spain. Methods: In a recently ploughed field, we created eight regeneration scenarios with light, water and nitrogen availability (five replicates each). Seedlings of all species were monitored from emergence to death during one year. Abiotic and biotic variables were measured per quadrat, i.e. soil texture, nutrient contents, seed bank densities and composition, neighbour plant species densitiy and cover. We used partial ordination methods in order to separate the effect of each environmental variable on species composition during emergence and adult net recruitment. Results: Light treatment determined annual plant density at time of emergence and recruitment, while water addition controlled the recruitment of perennials. Resource levels explained the emerged species composition; this effect was not translated into the recruited species composition. N‐addition and N + water addition were strongly associated to species abundances at the time of emergence. Seedling composition in summer was correlated with seed abundance of Cerastium spp. Neighbour species density and cover (mainly Arrhenatherum bulbosum, Agropyron repens and Picris echioides) explained significant fractions of species composition in the emergence and recruitment of the different cohorts. Interactions between species seem to vary in intensity among cohorts and in the key plant species that determined species abundance along succession. Conclusions: Our scenarios exerted contrasting and multilevel effects on the development of our early succession community. Resource availability differently affected plant density and species composition at different life stages. It is relevant to consider different life stages in plant community studies. However, regeneration conditions and other abiotic factors are not enough to explain how community composition varies.     

Glucose and sucrose: hazardous fast-food for industrial yeast?

Yeast cells often encounter a mixture of different carbohydrates in industrial processes. However, glucose and sucrose are always consumed first. The presence of these sugars causes repression of gluconeogenesis, the glyoxylate cycle, respiration and the uptake of less-preferred carbohydrates. Glucose and sucrose also trigger unexpected, hormone-like effects, including the activation of cellular growth, the mobilization of storage compounds and the diminution of cellular stress resistance. In an industrial context, these effects lead to several yeast-related problems, such as slow or incomplete fermentation, 'off flavors' and poor maintenance of yeast vitality. Recent studies indicate that the use of mutants with altered responses to carbohydrates can significantly increase productivity. Alternatively, avoiding unnecessary exposure to glucose and sucrose could also improve the performance of industrial yeasts.     

Disentangling snakebite dynamics in Colombia: How does rainfall and temperature drive snakebite temporal patterns?

The role of climate driving zoonotic diseases’ population dynamics has typically been addressed via retrospective analyses of national aggregated incidence records. A central question in epidemiology has been whether seasonal and interannual cycles are driven by climate variation or generated by socioeconomic factors. Here, we use compartmental models to quantify the role of rainfall and temperature in the dynamics of snakebite, which is one of the primary neglected tropical diseases. We took advantage of space-time datasets of snakebite incidence, rainfall, and temperature for Colombia and combined it with stochastic compartmental models and iterated filtering methods to show the role of rainfall-driven seasonality modulating the encounter frequency with venomous snakes. Then we identified six zones with different rainfall patterns to demonstrate that the relationship between rainfall and snakebite incidence was heterogeneous in space. We show that rainfall only drives snakebite incidence in regions with marked dry seasons, where rainfall becomes the limiting resource, while temperature does not modulate snakebite incidence. In addition, the encounter frequency differs between regions, and it is higher in regions where Bothrops atrox can be found. Our results show how the heterogeneous spatial distribution of snakebite risk seasonality in the country may be related to important traits of venomous snakes’ natural history.     

Melatonin and corticosterone regulation: Feeding time or the light:Dark cycle?

Under ad libitum feeding, male rats exhibit a marked rhythm of plasma and pineal melatonin; levels are low during the day and high at night. Restricting food availability to a 2 hour period during the light or dark does not markedly influence the melatonin rhythm, both groups having a crest in circulating melatonin during the dark. In contrast, plasma corticosterone levels are influenced by both the light-dark cycle and feeding. Animals fed early in the light period exhibit a biomodal corticosterone secretory pattern, with high steroid levels immediately prior to feeding and again just before lights-out, animals fed early in the dark have a single crest, just before food presentation. These data provide evidence for the dissociation of melatonin and corticosterone secretory patterns, providing support for the hypothesis that multiple regulators control neuroendocrine rhythmicity.     

Representation of time intervals in a double bisection task: Relative or absolute?

We examined if the representation of time intervals in a temporal discrimination task is based not only on their absolute but also on their relative durations. Six pigeons learned two temporal discriminations. In the first, red and green choices were correct following 2-s and 8-s samples, respectively. In the second, vertical and horizontal bar choices were correct following 4-s and 16-s samples, respectively. In a previous study [Zentall, T.R., Weaver, J.E., Clement, T.S., 2004. Pigeons group time intervals according to their relative duration. Psychon. Bull. Rev. 11, 113-117.], tests with 4-s samples and red/green comparisons revealed a bias for red, whereas tests with 8-s samples with vertical/horizontal comparisons revealed a bias for horizontal. These results were interpreted in terms of relative encoding of sample durations. We attempted to replicate this finding but instead of testing with only 4-s or 8-s samples, we tested with several other sample durations to obtain a psychometric function. Results were inconsistent with the relative encoding hypothesis.     

Partitioning floristic variance in Norwegian upland grasslands into within-site and between-site components: are the patterns determined by environment or by land-use?

This study presents a quantitative partitioning of the variance infloristic data from grazed semi-natural vegetation of summer farms inRøldal, western Norway. The data consist of 189 taxa recorded in 1074-m² sample plots within 10 summer farms with differentland-use histories. Thirty-five environmental variables were recorded,includingaltitude, slope, radiation, geology, soil chemistry, and past and presentland-use. A series of (partial) canonical correspondence analyses (CCAs) wereused to partition the total variation into within-farm and between-farmcomponents, and to investigate the explanatory power of different groups ofenvironmental and land-use variables at the two scales. The results show that:(1) although local gradients are of overriding importance for floristiccomposition, landscape-scale processes also contribute significantly to theobserved patterns; (2) the measured land-use and environmental factors accountfor comparable amounts of compositional variance at the two scales; and (3)evenif the relative contributions of the two classes of explanatory variables arecomparable, details differ, showing that broad-scale environmental and land-usepatterns are not just scaled-up versions of the fine-scale patterns or viceversa. These results support a multi-process view of vegetation patterns.     

Tensile fatigue in bone: are cycles-, or time to failure, or both, important?

In life, bones are subjected to fatigue loading which has different frequency and amplitude components, as well as various kinds of loading modes like tension, compression, shear and combinations of them. Considerable variability is observed in fatigue results of bone, which may be caused by these experimental variables or by the bone itself. In past studies the effect of magnitude and mode of loading have been examined in standard fatigue strength (stress vs. cycles to failure) diagrams. The effect of frequency is not clear, but there is clear evidence (from Carter & co-workers) that, at least in human bone, tension "fatigue" failure was determined solely by time rather than by cycles. We sought to confirm these results in the same and a different species. We cycled human and bovine bone in tension at two frequencies: 0.5 and 5 Hz. There was no cycle number effect; the results from the tests at the two frequencies were different if plotted and analysed as a function of cycles to failure, but were not separable if plotted and analysed as a function of time to failure. In this respect bone differs from tendon, in which failure in tension is a function of both cycles and time.     

How can storage time and temperature affect enzymic activities in urines?

We measured a tubular brush-border enzyme (alanine aminopeptidase, AAP) and a lysosomal hydrolase (N-acetyl-beta-D-glucosaminidase, NAG) in morning urines from 15 healthy normal subjects to check if different storage times and temperatures could modify enzyme concentrations. Short-term (24 h) storage time at room temperature or 4 degrees C does not affect AAP and NAG activities. Both enzymes are well preserved at -70 degrees C. AAP dramatically falls after 1 month at -20 degrees C, lowering to about 8% of the initial value after only 4 days of storage. On the contrary, NAG is well preserved at these storage conditions. Centrifugation has revealed not critical for measurement of these two enzymes.     

Ice nucleation in solutions and freeze-avoiding insects-homogeneous or heterogeneous?

This article challenges the common view that solutions and cold-hardy freeze-avoiding insects always freeze by heterogeneous nucleation. Data are presented to show that the nucleation temperatures of a variety of solutions and freeze-avoiding insects are a function of the water volume as described by the data previously published by Bigg in 1953. The article also points out that the relationships between melting point depression and depression of nucleation temperature are different for samples undergoing homogeneous nucleation and those undergoing heterogeneous nucleation. Aqueous solutions and freeze-avoiding insects display a relationship like that of homogeneously nucleated samples. It is also argued that the identity of the "impurities" assumed to cause heterogeneous nucleation in aqueous solutions and insects is obscure and that the "impurities" have features which make their existence rather unlikely.