The role of pre- and post- alighting detection mechanisms in the responses to patch size by specialist herbivores

Experimental data on the relationship between plant patch size and population density of herbivores within fields often deviates from predictions of the theory of island biogeography and the resource concentration hypothesis. Here we argue that basic features of foraging behaviour can explain different responses of specialist herbivores to habitat heterogeneity. In a combination of field and simulation studies, we applied basic knowledge on the foraging strategies of three specialist herbivores: the cabbage aphid (Brevicoryne brassicae), the cabbage butterfly (Pieris rapae L.) and the diamondback moth (Plutella xylostella L.), to explain differences in their responses to small scale fragmentation of their habitat. In our field study, populations of the three species responded to different sizes of host plant patches (9 plants and 100 plants) in different ways. Densities of winged cabbage aphids were independent of patch size. Egg‐densities of the cabbage butterfly were higher in small than in large patches. Densities of diamondback moth adults were higher in large patches than in small patches. When patches in a background of barley were compared with those in grass, densities of the cabbage aphid and the diamondback moth were reduced, but not cabbage butterfly densities. To explore the role of foraging behaviour of herbivores on their response to patch size, a spatially explicit individual‐based simulation framework was used. The sensory abilities of the insects to detect and respond to contact, olfactory or visual cues were varied. Species with a post‐alighting host recognition behaviour (cabbage aphid) could only use contact cues from host plants encountered after landing. In contrast, species capable with a pre‐alighting recognition behaviour, based on visual (cabbage butterfly) or olfactory (diamondback moth) cues, were able to recognise a preferred host plant whilst in flight. These three searching modalities were studied by varying the in flight detection abilities, the displacement speed and the arrestment response to host plants by individuals. Simulated patch size – density relationships were similar to those observed in the field. The importance of pre‐ and post‐ alighting detection in the responses of herbivores to spatial heterogeneity of the habitat is discussed.     

Proteasome inhibition: an early or late event in nitric oxide-induced neuronal death?

Nitric oxide (NO), ubiquitously expressed in the central nervous system, has been perceived to be a potential neuromodulator. Employing cultured murine primary cortical neurons, NO resulted in an inhibition of the ubiquitin-proteasome system (UPS) with a dose- and time-dependent decrease in cell viability. This is consistent with a previous study that reported a dysfunction of UPS with consequential apoptotic death in macrophage cell with NO treatment. However, it cannot be unclear if the drop in UPS efficiency is directly imposed on by NO. Therefore by using microarray analysis, our study revealed an early down-regulation or non-significant differential expression of genes encoding UPS proteins in NOC-18 (NO donor)-treated neurons as compared to an observed elevation of corresponding gene expression genes in lactacystin (classical proteasome inhibitor)-treated neurons (conducted earlier). Furthermore, time-course analysis of proteasome activity in NOC-18-treated neurons demonstrated a late onset of reduction. This is intriguing as it is well established that in an exclusive proteasome dysfunction-induced cell death, a compensatory feedback mechanism will be activated with an initial and concerted up-regulation of genes encoding proteins involved in UPS as seen when neurons were treated with lactacystin. Thus, it is highly suggestive that NO-triggered neuronal death takes on a different signaling cascade from that of a classical proteasome inhibitor, and that the late reduction of proteasome activity is a downstream event following the activation of apoptotic cellular signaling cascade. In intracellular condition, the proteasome is not NO preferred primary target responsible for the trigger of the cell death machinery. In conclusion, we presented novel findings that shed light into NO-induced cell death signaling cascade, which would be important in understanding the pathogenesis of neurodegenerative disorders such as Parkinson's disease.     

The relative importance of disturbance and environmental stress at local and regional scales in French coastal sand dunes

Questions: 1. Is there a primary role of disturbance at local scale and of environmental stress at regional scale? 2. Does disturbance increase or decrease environmental stress at local scale? Location: The Atlantic coastal dune system of the Aquitaine Region (France). Methods: Species biomass and 16 environmental variables were sampled in 128 quadrats along a local beach‐inland gradient and a regional North‐South gradient. Environmental data were analysed with ANOVAs and vegetation‐environment relationships with Canonical Correspondence Analysis. Results: At the local scale community composition was primarily driven by disturbance due to sand burial, whereas water and nutrient stress better explained regional differences. However, random biogeographical events are very likely to also affect community composition at the largest scale. The main interaction between environmental stress and disturbance was the mitigation of nutrient stress induced by disturbance at a local scale. This was due to a positive direct effect of sand burial and a positive indirect effect of wind (decrease in VPD by ocean spray). Although wind had also a significant effect on soil conductivity and pH, there was no evidence that these factors had any role in community composition. Conclusions: Our results support the hypothesis that disturbance had a primary role at local scale and environmental stress at regional scale but further research is needed to separate the effect of stress from that of dispersal at regional scale. We also demonstrated that environmental stress in primary succession may not always decline with decreasing disturbance.     

Gene expression data analysis using a novel approach to biclustering combining discrete and continuous data

Many different methods exist for pattern detection in gene expression data. In contrast to classical methods, biclustering has the ability to cluster a group of genes together with a group of conditions (replicates, set of patients or drug compounds). However, since the problem is NP-complex, most algorithms use heuristic search functions and therefore might converge towards local maxima. By using the results of biclustering on discrete data as a starting point for a local search function on continuous data, our algorithm avoids the problem of heuristic initialization. Similar to OPSM, our algorithm aims to detect biclusters whose rows and columns can be ordered such that row values are growing across the bicluster's columns and vice-versa. Results have been generated on the yeast genome (Saccharomyces cerevisiae), a human cancer dataset and random data. Results on the yeast genome showed that 89% of the one hundred biggest non-overlapping biclusters were enriched with Gene Ontology annotations. A comparison with OPSM and ISA demonstrated a better efficiency when using gene and condition orders. We present results on random and real datasets that show the ability of our algorithm to capture statistically significant and biologically relevant biclusters.     

Inducing segmental aneuploid mosaicism in the mouse through targeted asymmetric sister chromatid event of recombination

Loss or gain of whole chromosomes, or parts of chromosomes, is found in various pathological conditions, such as cancer and aneuploidy, and results from the missegregation of chromosomes during cellular division or abnormal mitotic recombination. We introduce a novel strategy for determining the consequences of segmental aneuploid mosaicism, called targeted asymmetric sister chromatin event of recombination (TASCER). We took advantage of the Cre/loxP system, used extensively in embryonic stem cells for generating deletions and duplications of regions of interest, to induce recombination during the G2 phase. Using two loxP sites in a Cis configuration, we generated in vivo cells harboring microdeletions and microduplications for regions of interest covering up to 2.2 Mb. Using this approach in the mouse provides insight into the consequences of segmental aneuploidy for homologous regions of the human chromosome 21 on cell survival. Furthermore, TASCER shows that Cre-induced recombination is more efficient after DNA replication in vivo and provides an opportunity to evaluate, through genetic mosaics, the outcome of copy number variation and segmental aneuploidy in the mouse.     

Pseudo-partial likelihood for proportional hazards models with biased-sampling data

We obtain a pseudo-partial likelihood for proportional hazards models with biased-sampling data by embedding the biased-sampling data into left-truncated data. The log pseudo-partial likelihood of the biased-sampling data is the expectation of the log partial likelihood of the left-truncated data conditioned on the observed data. In addition, asymptotic properties of the estimator that maximize the pseudo-partial likelihood are derived. Applications to length-biased data, biased samples with right censoring and proportional hazards models with missing covariates are discussed.     

pH Dependent photophysics and role of medium on photoinduced electron transfer between ruthenium polypyridyl complex and anthraquinone

The spectroscopic and photophysical properties of a synthetically versatile ruthenium complex [Ru(bpy)₂(LH₂)]²⁺ where LH₂ is 2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline and bpy is 2,2-bipyridyl and its analogue, [Ru(bpy)₂(LOMe)]²⁺ where the carboxyphenyl functionality is methylated are reported. Both complexes exhibit long-lived luminescence which for [Ru(bpy)₂(LH₂)]²⁺ is remarkably enhanced in aqueous compared to organic media. The pH dependence of the electronic absorption and emission spectra in water and acetonitrile are described and the influence of the protonation state of the 2-(4-carboxyphenyl)imidazo[4,5-f][1,10]phenanthroline ligand on the electronic structure of [Ru(bpy)₂(LH₂)]²⁺ is discussed. Oxidative quenching of the excited state of the complex by anthraquinone-2-carboxylic acid is investigated for both complexes. In polar media, this is a dynamic process suggesting that the quenching rate is controlled by bimolecular collision with a quenching rate constant, k_q, of approximately 6.7 × 10⁹ M⁻¹ s⁻¹ for [Ru(bpy)₂(LH₂)]²⁺. In contrast in aprotic solvent, dichloromethane, quenching occurs through a purely static mechanism indicating association between the luminophore and quencher, most likely through hydrogen bonding, between the carboxylic acid moieties of the ruthenium complex and the anthraquinone carboxylic derivative. The association constant for formation of the dyad was determined to be 565 L mol⁻¹ in dichloromethane and the rate of electron transfer was estimated to be 4.7 × 10⁷ s⁻¹. By contrast, for the analogous complex in which the carboxylate is methyl protected mixed static and dynamic quenching behaviour in aprotic solvent.     

Survival and metabolism of <Emphasis Type="Italic">Rana arvali</Emphasis>s during freezing

Freeze tolerance and changes in metabolism during freezing were investigated in the moor frog (Rana arvalis) under laboratory conditions. The data show for the first time a well-developed freeze tolerance in juveniles of a European frog capable of surviving a freezing exposure of about 72 h with a final body temperature of −3°C. A biochemical analysis showed an increase in liver and muscle glucose in response to freezing (respectively, 14-fold and 4-fold between 4 and −1°C). Lactate accumulation was only observed in the liver (4.1 ± 0.8 against 16.6 ± 2.4 μmol g⁻¹ fresh weight (FW) between 4 and −1°C). The quantification of the respiratory metabolism of frozen frogs showed that the aerobic metabolism persists under freezing conditions (1.4 ± 0.7 μl O₂ g⁻¹ FW h⁻¹ at −4°C) and decreases with body temperature. After thawing, the oxygen consumption rose rapidly during the first hour (6-fold to 16-fold) and continued to increase for 24 h, but at a lower rate. In early winter, juvenile R. arvalis held in an outdoor enclosure were observed to emerge from ponds and hibernate in the upper soil and litter layers. Temperature recordings in the substratum of the enclosure suggested that the hibernacula of these juvenile frogs provided sheltering from sub-zero air temperatures and reduced the time spent in a frozen state corresponding well with the observed freeze tolerance of the juveniles. This study strongly suggests that freeze tolerance of R. arvalis is an adaptive trait necessary for winter survival.     

Morphological, chemical and genetic differentiation of two subspecies of Cistus creticus L. (C. creticus subsp. eriocephalus and C. creticus subsp. corsicus)

Cistus creticus L., an aromatic species from the Mediterranean area, contains various diterpenes bearing the labdane skeleton. The production of essential oil from this species has potential economic value, but so far, it has not been optimized. In order to contribute to a better knowledge of this species and to its differentiation, the morphological characters, volatile chemical composition and genetic data of two subspecies (C. creticus subsp. eriocephalus and C. creticus subsp. corsicus) were investigated. The leaf trichomes were studied using scanning electron microscopy. The chemical composition of Corsican essential oil (C. creticus subsp. corsicus) has been reported using GC, GC/MS and ¹³C NMR; the main constituents were oxygenated labdane diterpenes (33.9%) such as 13-epi-manoyl oxide (18.5%). Using plant material (54 samples) collected from 18 geographically distinct areas of the islands of Corsica and Sardinia, the basis of variation in the headspace solid-phase microextraction volatile fraction and an inter-simple sequence repeat genetic analysis were also examined. It was shown that the two subspecies of C. creticus differed in morphology, essential oil production, volatile fraction composition and genetic data.