Experience teaches plants to learn faster and forget slower in environments where it matters

The nervous system of animals serves the acquisition, memorization and recollection of information. Like animals, plants also acquire a huge amount of information from their environment, yet their capacity to memorize and organize learned behavioral responses has not been demonstrated. In Mimosa pudica—the sensitive plant—the defensive leaf-folding behaviour in response to repeated physical disturbance exhibits clear habituation, suggesting some elementary form of learning. Applying the theory and the analytical methods usually employed in animal learning research, we show that leaf-folding habituation is more pronounced and persistent for plants growing in energetically costly environments. Astonishingly, Mimosa can display the learned response even when left undisturbed in a more favourable environment for a month. This relatively long-lasting learned behavioural change as a result of previous experience matches the persistence of habituation effects observed in many animals.     

Measurement of Scaled Residual Dipolar Couplings in Proteins Using Variable-angle Sample Spinning

NMR spectra of ubiquitin in the presence of bicelles at a concentration of 25% w/v have been recorded under sample spinning conditions for different angles of rotation. For an axis of rotation equal to the magic angle, the (1)H/(15)N HSQC recorded without any (1)H decoupling in the indirect dimension corresponds to the classical spectrum obtained on a protein in an isotropic solution and allows the measurement of scalar J-couplings (1) J (NH). For an angle of rotation smaller than the magic angle, the bicelles orient with their normal perpendicular to the spinning axis, whereas for an angle of rotation greater than the magic angle the bicelles orient with their normal along the spinning axis. This bicelle alignment creates anisotropic conditions that give rise to the observation of residual dipolar couplings in ubiquitin. The magnitude of these dipolar couplings depends directly on the angle that the rotor makes with the main magnetic field. By changing this angle in a controlled manner, residual dipolar couplings can be either scaled up or down thus offering the possibility to study simultaneously a wide range of dipolar couplings in the same sample.     

Coral recovery may not herald the return of fishes on damaged coral reefs

The dynamic nature of coral reefs offers a rare opportunity to examine the response of ecosystems to disruption due to climate change. In 1998, the Great Barrier Reef experienced widespread coral bleaching and mortality. As a result, cryptobenthic fish assemblages underwent a dramatic phase-shift. Thirteen years, and up to 96 fish generations later, the cryptobenthic fish assemblage has not returned to its pre-bleach configuration. This is despite coral abundances returning to, or exceeding, pre-bleach values. The post-bleach fish assemblage exhibits no evidence of recovery. If these short-lived fish species are a model for their longer-lived counterparts, they suggest that (1) the full effects of the 1998 bleaching event on long-lived fish populations have yet to be seen, (2) it may take decades, or more, before recovery or regeneration of these long-lived species will begin, and (3) fish assemblages may not recover to their previous composition despite the return of corals.     

A comparison of national approaches to setting ecological status boundaries in phytobenthos assessment for the European Water Framework Directive: results of an intercalibration exercise

The European Union (EU)’s Water Framework Directive (WFD) requires that all Member States participate in intercalibration exercises in order to ensure that ecological status concepts and assessment levels are consistent across the EU. This paper describes one such exercise, performed by the countries in the Central/Baltic Geographical Intercalibration Group stretching from Ireland in the west to Estonia in the east and from the southern parts of Scandinavia to the northern regions of Spain and Italy (but excluding alpine regions, which were intercalibrated separately). In this exercise, methods used to measure ecological status of rivers using benthic diatoms were compared. Ecological status is estimated as the ratio between the observed value of a biological element and the value expected in the absence of significant human impact. Approaches to defining the ‘reference sites’, from which these ‘expected’ values were derived, varied from country to country. Minimum criteria were established as part of the exercise but there was still considerable variation between national reference values, reflecting typological differences that could not be resolved during the exercise. A simple multimetric index was developed to compare boundary values using two widely used diatom metrics. Boundary values for high/good status and good/moderate status set by each participant were converted to their equivalent values of this intercalibration metric using linear regression. Variation of ±0.05 EQR units around the median value was considered to be acceptable and the exercise provided a means for those Member States who fell significantly above or below this line to review their approaches and, if necessary, adjust their boundaries. Handling editor: J. Padisak     

Climatic forcing and larval dispersal capabilities shape the replenishment of fishes and their habitat‐forming biota on a tropical coral reef

Fluctuations in marine populations often relate to the supply of recruits by oceanic currents. Variation in these currents is typically driven by large‐scale changes in climate, in particular ENSO (El Nino Southern Oscillation). The dependence on large‐scale climatic changes may, however, be modified by early life history traits of marine taxa. Based on eight years of annual surveys, along 150 km of coastline, we examined how ENSO influenced abundance of juvenile fish, coral spat, and canopy‐forming macroalgae. We then investigated what traits make populations of some fish families more reliant on the ENSO relationship than others. Abundance of juvenile fish and coral recruits was generally positively correlated with the Southern Oscillation Index (SOI), higher densities recorded during La Niña years, when the ENSO‐influenced Leeuwin Current is stronger and sea surface temperature higher. The relationship is typically positive and stronger among fish families with shorter pelagic larval durations and stronger swimming abilities. The relationship is also stronger at sites on the coral back reef, although the strongest of all relationships were among the lethrinids (r = .9), siganids (r = .9), and mullids (r = .8), which recruit to macroalgal meadows in the lagoon. ENSO effects on habitat seem to moderate SOI–juvenile abundance relationship. Macroalgal canopies are higher during La Niña years, providing more favorable habitat for juvenile fish and strengthening the SOI effect on juvenile abundance. Conversely, loss of coral following a La Niña‐related heat wave may have compromised postsettlement survival of coral dependent species, weakening the influence of SOI on their abundance. This assessment of ENSO effects on tropical fish and habitat‐forming biota and how it is mediated by functional ecology improves our ability to predict and manage changes in the replenishment of marine populations.     

Functional studies of membrane-bound and purified human Hedgehog receptor Patched expressed in yeast

The Sonic Hedgehog (Shh) signalling pathway plays an important role both in embryonic development and in adult stem cell function. Inappropriate regulation of this pathway is often due to dysfunction between two membrane receptors Patched (Ptc) and Smoothened (Smo), which lead to birth defects, cancer or neurodegenerative diseases. However, little is known about Ptc, the receptor of the Shh protein, and the way Ptc regulates Smo, the receptor responsible for the transduction of the signal. To develop structure-function studies of these receptors, we expressed human Ptc (hPtc) in the yeast Saccharomyces cerevisiae. We demonstrated that hPtc expressed in a yeast membrane fraction is able to interact with its purified ligand Shh, indicating that hPtc is produced in yeast in its native conformational state. Using Surface Plasmon Resonance technology, we showed that fluorinated surfactants preserve the ability of hPtc to interact with its ligand after purification. This is the first report on the heterologous expression and the purification of a native and stable conformation of the human receptor Ptc. This work will allow the scale-up of hPtc production enabling its biochemical characterization, allowing the development of new therapeutic approaches against diseases induced by Shh signalling dysfunction.     

XRCC4 protein interactions with XRCC4-like factor (XLF) create an extended grooved scaffold for DNA ligation and double strand break repair

The XRCC4-like factor (XLF)-XRCC4 complex is essential for nonhomologous end joining, the major repair pathway for DNA double strand breaks in human cells. Yet, how XLF binds XRCC4 and impacts nonhomologous end joining functions has been enigmatic. Here, we report the XLF-XRCC4 complex crystal structure in combination with biophysical and mutational analyses to define the XLF-XRCC4 interactions. Crystal and solution structures plus mutations characterize alternating XRCC4 and XLF head domain interfaces forming parallel super-helical filaments. XLF Leu-115 ("Leu-lock") inserts into a hydrophobic pocket formed by XRCC4 Met-59, Met-61, Lys-65, Lys-99, Phe-106, and Leu-108 in synergy with pseudo-symmetric β-zipper hydrogen bonds to drive specificity. XLF C terminus and DNA enhance parallel filament formation. Super-helical XLF-XRCC4 filaments form a positively charged channel to bind DNA and align ends for efficient ligation. Collective results reveal how human XLF and XRCC4 interact to bind DNA, suggest consequences of patient mutations, and support a unified molecular mechanism for XLF-XRCC4 stimulation of DNA ligation.     

Mississippian (early Carboniferous) radiolarian biostratigraphy of northern Thailand (Chiang Dao area)

Well-preserved Carboniferous radiolarian faunas were obtained from ribbon-bedded siliceous sediments (radiolarites) north of Chiang Dao city, Chiang Mai province, northern Thailand. These sediments are rich in identifiable radiolarian faunas, including more than 44 species and sub-species belonging to 15 genera. Among them, Albaillellaria and Latentifistularia are dominant, but few Entactinaria are present. Five Early Carboniferous radiolarian assemblage zones are recognised and compared to those of Germany, France and North America. They are, in ascending order: the Albaillella paradoxa gr. assemblage; the Albaillella indensis gr. assemblage: the Albaillella cartalla-Albaillella furcata furcata assemblage which includes the Palaeolithocyclia rota subassemblage; and the A. furcata rockensis-Latentifistula impella gr. assemblage. The age assignment of each assemblage is well-controlled by co-occurring conodonts, which are abundant during this time interval in the area. The Thai radiolarian assemblage zones are rather similar to those of Germany and North America, indicating that the albaillellarian form has a global distribution and can be readily used as a world key indicative fauna. These results also provide an additional data set indicating that distal oceanic deposits are present in northern Thailand from the Devonian to the Late Triassic, which provides evidence for a long-lived oceanic realm between the Indochina and Shan-Thai continental terranes (nearly 200 My).     

Emotional Modulation of Attention: Fear Increases but Disgust Reduces the Attentional Blink

Background

It is well known that facial expressions represent important social cues. In humans expressing facial emotion, fear may be configured to maximize sensory exposure (e.g., increases visual input) whereas disgust can reduce sensory exposure (e.g., decreases visual input). To investigate whether such effects also extend to the attentional system, we used the “attentional blink” (AB) paradigm. Many studies have documented that the second target (T2) of a pair is typically missed when presented within a time window of about 200–500 ms from the first to-be-detected target (T1; i.e., the AB effect). It has recently been proposed that the AB effect depends on the efficiency of a gating system which facilitates the entrance of relevant input into working memory, while inhibiting irrelevant input. Following the inhibitory response on post T1 distractors, prolonged inhibition of the subsequent T2 is observed. In the present study, we hypothesized that processing facial expressions of emotion would influence this attentional gating. Fearful faces would increase but disgust faces would decrease inhibition of the second target.

Methodology/Principal Findings

We showed that processing fearful versus disgust faces has different effects on these attentional processes. We found that processing fear faces impaired the detection of T2 to a greater extent than did the processing disgust faces. This finding implies emotion-specific modulation of attention.

Conclusions/Significance

Based on the recent literature on attention, our finding suggests that processing fear-related stimuli exerts greater inhibitory responses on distractors relative to processing disgust-related stimuli. This finding is of particular interest for researchers examining the influence of emotional processing on attention and memory in both clinical and normal populations. For example, future research could extend upon the current study to examine whether inhibitory processes invoked by fear-related stimuli may be the mechanism underlying the enhanced learning of fear-related stimuli.