Resource availability and the trichome defenses of tomato plants

We conducted two experiments to determine how resource availability influenced allocation by tomato (Lycopersicon esculentum) to trichomes, and how different patterns of trichome allocation by plants grown in different resource environments might then influence the behavior of tobacco hornworm (Manduca sexta) caterpillars. In the first experiment we used high and low levels of light and water, and then, using scanning electron microscopy, determined trichome densities on the leaves and stems. We sampled leaves and stems at several places throughout the plant to determine whether there were within-plant differences in allocation to trichomes. The results of the first experiment showed that resource availability influenced allocation to trichome growth. Patterns in high and low-light supported both the growth-differentiation balance hypothesis (GDBH) and the carbon-nutrient balance hypothesis (CNBH). However, the GDBH was not supported by differences among water treatments. Contrary, to predictions of the GDBH, plants with intermediate growth did not have the highest trichome densities, and plants with similar growth differed in trichome density. Possible biological and artifactual explanations are discussed. The first experiment also showed that there was within-plant variation in allocation to trichomes, and that plant resource availability may influence within-plant variation in allocation to trichomes. In the second experiment, we grew plants in high and low-light, and then monitored the behavior of tobacco hornworms on the stems of these plants in the laboratory. This experiment demonstrated that the light environment that tomato plants were grown in influenced the resting behavior of caterpillars. Furthermore, it demonstrated that both glandular and non-glandular trichomes impeded caterpillars from searching for food. Overall, this study indicated that plant resource availability can influence allocation to trichome defenses, and that these differences may affect insect herbivores.     

Estimating photosynthetic rate and annual carbon gain in conifers from specific leaf weight and leaf biomass

Summary Canopy photosynthesis is difficult to measure directly or to predict with complex models demanding knowledge of seasonal variation in environmental and physiological properties of the canopy. Trees in particular offer a challenge with their large, aerodynamically rough and seasonally-changing canopy properties. In this paper we assess the possibility of using specific leaf weight to predict seasonal and annual net photosynthetic rate in deciduous (Larix sp.) and evergreen (Picea abies) conifers.Annual photosynthetic rate and specific leaf weight of different positions of the crown in both species were highly correlated (r ²=0.930). Annual carbon uptake by different segments in a mature P. abies crown was closely related to leaf biomass. The relationship was improved by adjusting the leaf biomass of each segment in regard to its specific leaf weight relative to the maximum found in the canopy. The adjustment accounted for associated differences in photosynthetic activity. This combined structural index (leaf biomassxrelative specific leaf weight) could, when calibrated, predict the total annual carbon uptake by different parts of the crown. If direct measurements of photosynthesis are not available, the combined structural index may still serve as a comparative estimator of annual carbon uptake.     

Identification of genetic loci affecting the establishment and development of Echinococcus multilocularis larvae in mice

Alveolar echinococcosis (AE) is a severe hepatic disorder caused by larval infection by the fox tapeworm Echinococcus multilocularis. The course of parasitic development and host reactions are known to vary significantly among host species, and even among different inbred strains of mice. As reported previously, after oral administration of parasite eggs, DBA/2 (D2) mice showed a higher rate of cyst establishment and more advanced protoscolex development in the liver than C57BL/6 (B6) mice. These findings strongly suggest that the outcome of AE is affected by host genetic factor(s). In the present study, the genetic basis of such strain-specific differences in susceptibility/resistance to AE in murine models was studied by whole-genome scanning for quantitative trait loci (QTLs) using a backcross of (B6 × D2)F₁ and D2 mice with varying susceptibility to E. multilocularis infection. For cyst establishment, genome linkage analysis identified one suggestive and one significant QTL on chromosomes (Chrs.) 9 and 6, respectively, whereas for protoscolex development, two suggestive and one highly significant QTLs were detected on Chrs. 6, 17 and 1, respectively. Our QTL analyses using murine AE models revealed that multiple genetic factors regulated host susceptibility/resistance to E. multilocularis infection. Moreover, our findings show that establishment of the parasite cysts in the liver is affected by QTLs that are distinct from those associated with the subsequent protoscolex development of the parasite, indicating that different host factors are involved in the host–parasite interplay at each developmental stage of the larval parasite. Further identification of responsible genes located on the identified QTLs could lead to the development of effective disease prevention and control strategies, including an intensive screening and clinical follow-up of genetically high-risk groups for AE infection.     

Individual-based modeling of the spread of pine wilt disease: vector beetle dispersal and the Allee effect

Pine wilt disease is caused by the pinewood nematode Bursaphelenchus xylophilus, which is vectored by the Japanese pine sawyer beetle Monochamus alternatus. Due to their mutualistic relationship, according to which the nematode weakens and makes trees available for beetle reproduction and the beetle in turn carries and transmits the nematode to healthy pine trees, this disease has resulted in severe damage to pine trees in Japan in recent decades. Previous studies have worked on modeling of population dynamics of the vector beetle and the pine tree to explore spatial expansion of the disease using an integro-difference equation with a dispersal kernel that describes beetle mobility over space. In this paper, I revisit these previous models but retaining individuality: by considering mechanistic interactions at the individual level it is shown that the Allee effect, an increasing per-capita growth rate as population abundance increases, can arise in the beetle dynamics because of the necessity for beetles to contact pine trees at least twice to reproduce successfully. The incubation period after which a tree contacted by a first beetle becomes ready for beetle oviposition by later beetles is crucial for the emergence of this Allee effect. It is also shown, however, that the strength of this Allee effect depends strongly on biological mechanistic properties, especially on beetle mobility. Realistic individual-based modeling highlights the importance of how spatial scales are dealt with in mathematical models. The link between mechanistic individual-based modeling and conventional analytical approaches is also discussed.     

Predation pressure on an imperfect Batesian micicry complex in the presence of alternative prey

Summary Differential predation pressure and the probability of predation on a Batesian mimicry complex and on alternative prey were estimatedin a field experiment. The mimicry complex was composed of a noxious model (Eleodes obscura (Say)) and a palatable mimic (Stenomorpha marginata (LeConte)). House crickets (Acheta domesticus) (Linn.) were used as alternative prey. The experiment was conducted for 23 nights in August and September to approximate the peak seasonal activity time period during which both models and mimics normally are exposed to predation while foraging and depositing eggs. Each night thirty prey in ratios of 16 models: 7 mimics: 7 crickets were exposed for 2.5 h to a suite of predators consisting of pallid bats (Antrozous pallidus), striped skunks (Mephitis mephitis) and ringtails (Bassariscus astutus) that had free access to the prey. The model-mimic ratio was similar to that found in nature. Predators obtained prey on 11 of the 23 nights and preferred the alternative prey (crickets) in proportions higher than was expected from a predation rate that was equal on all species of prey. Mimics were taken by predators at a rate proportional to their abundance, while models were taken at a rate considerably lower than their relative abundance. This suggests that at least some of the predators could distinguish between models and mimics and were willing to eat the mimics at higher frequencies than they were willing to eat the models. However, although the mimicry is not perfect with respect to the entire predator suite, the mimics still gain an advantage by resembling the models, compared to the predation levels on the alternate prey.     

Vegetation dynamics in the fens of Chautagne (Savoie,France) after the cessation of mowing

The mechanisms controlling secondary succession on eutrophic peat are analyzed on an area of 500 ha marsh near the Lac du Bourget in the Rhône floodplain between Geneva and Lyon. After describing the succession, the authors compare the succession with that described for fens in England.During succession, three categories of phenomena occur:-Predictable phenomena based on the occurrence of well-established relationships between species with a high cover density. When mowing ceases, populations with increasingly higher biomasses reach dominance one by one.-Phenomena which were to be expected although the manner in which they occurred were more difficult to predict, such as the conditions in which woody plants take over.-Phenomena hidden in the framework of a synchronic analysis. The lowering of the water table, for example, can modify the entire community of species occurring in the sequence as well as the competition between species. The pecularities of each type of ecological situation made it difficult to develop general models.     

Assessment of QT liabilities in drug development

Since the publication, in 1997, of the CPMP (Committee for Proprietary Medicinal Products) Points to Consider document on "The assessment of potential for QT prolongation by non-cardiovascular medicinal products," both regulatory bodies and the pharmaceutical industry have paid increasing attention to the conduct of careful preclinical studies on the subject. Regulatory attention has focused on the drafting of Safety Pharmacology guidelines through the ICH (International Conference on Harmonization) process, which resulted in approval by the ICH and acceptance by the three main regions (USA, Europe, and Japan) of the ICH S7A guideline. The guideline does not deal only with cardiovascular studies and does not provide guidance on QT investigations. This part has been deferred to a second guideline (ICH S7B). Nevertheless, pharmaceutical companies have implemented screening strategies aimed at selecting compounds that do not present QT liabilities. These strategies can differ according to the pharmaceutical class, while experimental models differ according to the stage of development of the compound. Several in vitro models are employed in discovery (radioligand binding, high-throughput patch clamp, efflux, and fluorescence assays). These models, coupled with in silico methods, allow companies to screen a high number of compounds. Other in vitro models, applied later in the R&D process (action potential duration, APD, in Purkinje fibers or papillary muscle and the isolated heart) are useful in better describing the activity of compounds on cardiac ion channels. The most robust and accepted in vivo test is represented by telemetry studies in conscious non-rodents.     

Data bank of three-dimensional structures of disaccharides,a tool to build 3-D structures of oligosaccharides

This work presents the first part of a database of conformations for all the disaccharide fragments that are found inN-glycans. The conformational study of the five disaccharides found in the oligo-mannose type are presented here. For each disaccharide, several possible conformations are described. A method is presented to obtain realistic models of oligosaccharides using molecular mechanic methods. Analysis of some possible conformations of the oligo-mannose type glycan Man₆-GlcNAc₂ is given as an illustration of the possibilities.On post-doctoral leave from CERMAV-CNRS, Grenoble, France     

Regulation of vole populations by the nematode <Emphasis Type="Italic">Trichuris arvicolae</Emphasis>: insights from modelling

The goal of this study is to determine whether a parasitic nematode may regulate, or destabilise by inducing demographic cycles, its host populations. We explore three host–parasite systems through population dynamic models. The hosts considered are the fossorial water vole, Arvicola terrestris, the common vole Microtus arvalis and the bank vole Myodes (Clethrionomys) glareolus and the parasitic nematode is Trichuris arvicolae. Three differential equation-based mathematical models are developed including host immunity and the existence of trade-off between immunity and host survival. Using parameters estimated from field data and laboratory observations, all these models show that T. arvicolae can induce host population regulation but not demographic cycles. The regulation effect of the nematode is un-ambiguous for the water vole (reduction of 50.2% of the host population size), but less obvious for the common vole (5.9%) and even less for the bank vole (1.4%). Important biological parameters to be taken into account in such models are discussed. Experimental confirmation of the regulatory potential of the nematode and of the costs of mounting an immune response against this nematode are now required. Communicated by W. Lutz     

4种弹涂鱼鳃的形态度量学比较及其生态学意义

通过对背眼虎鱼亚科中薄氏大弹涂鱼(Boleophthalmus boddarti)、青弹涂鱼(Scartelaos histophorus)、新几内亚弹涂鱼(Periophthalmus novaeguineaensis)和点弹涂鱼(P.spilotus)3属4种弹涂鱼鳃参数的测定,比较了各种之间鳃的形态度量学差异。结果表明,4种弹涂鱼的鳃参数(Y)与其体重(W)均符合方程logY=log a+b logW,且各鳃参数与体重的相关性显著(R2=0.50～0.98,P0.05)。等体重的弹涂鱼相比较,青弹涂鱼的总鳃丝数、总鳃丝长(mm)、鳃丝一侧鳃小片数(/mm)、总鳃面积(mm2)和相对鳃面积(mm2/g)均最大,薄氏大弹涂鱼相应鳃参数次之,新几内亚弹涂鱼和点弹涂鱼相应鳃参数较小。弹涂鱼鳃结构的这种梯度退化,表明青弹涂鱼和薄氏大弹涂鱼水生性较强,而新几内亚弹涂鱼和点弹涂鱼陆生性较强。4种弹涂鱼的总鳃丝长和总鳃面积明显小于其他等体重水生鱼类,这与弹涂鱼的两栖生活特征相符。     

Model and whole-plant studies on the anchorage capabilities of bulbs

Though the resistance to uprooting of cylindrical roots and root systems has been extensively investigated, almost no research has been performed on the factors that influence the uprooting resistance of bulbs. However, engineers have modelled bulb-like foundations and have investigated their resistance to upward movements. This study combined engineering theory with practical biology, using model bulbs of different shapes and sizes, embedding them at different depths in different soil media, and pulling them out while recording the uprooting force. Uprooting resistances of the models was compared to those of real onion and garlic bulbs with and without their root systems. Cone shaped models resisted uprooting best at all embedment depths and in both soil types, always followed by bulb shaped and cylindrical models. These results are explicable in terms of engineering theory. Cones resisted uprooting best because their maximum diameter is embedded deepest. A bulb shape is an ideal compromise as it has no sharp edges, and also allows easy downward movement. In sand uprooting resistance increased faster with depth than with bulb diameter, whereas in agricultural soils, the uprooting force was proportional both to the depth and the diameter of the model. The tests on the plants showed that real bulbs anchor plants by similar mechanisms and amounts to the models. The bulbs accounted for between 15% and 50% of the uprooting resistance of the plant, so they can make an important contribution to anchorage, particularly towards the end of the season.     

Performing abstraction: two ways of modelling<Emphasis Type="Italic"> Arabidopsis thaliana</Emphasis>

What is the best way to analyse abstraction in scientific modelling? I propose to focus on abstracting as an epistemic activity, which is achieved in different ways and for different purposes depending on the actual circumstances of modelling and the features of the models in question. This is in contrast to a more conventional use of the term ‘abstract’ as an attribute of models, which I characterise as black-boxing the ways in which abstraction is performed and to which epistemological advantage. I exemplify my claims through a detailed reconstruction of the practices involved in creating two types of models of the flowering plant Arabidopsis thaliana, currently the best-known model organism in plant biology. This leads me to distinguish between two types of abstraction processes: the ‘material abstracting’ required in the production of Arabidopsis specimens and the ‘intellectual abstracting’ characterising the elaboration of visual models of Arabidopsis genomics. Reflecting on the differences between these types of abstracting helps to pin down the epistemic skills and research commitments used by researchers to produce each model, thus clarifying how models are handled by researchers and with which epistemological implications.     

Food Preference of Wireworms Analyzed with Multinomial Logit Models

Many species of wireworms (larvae of click beetles, Elateridae) are poly- phagous root herbivores. In grasslands under restoration succession with various grass species, we aim to determine the role of wireworms in aboveground vegetation succession. Therefore, it is crucial to know whether wireworms prefer some food plants to others. We have investigated the root preference to different grass species for Agriotes obscurus and Athous haemorrhoidalis and whether these preferences can be explained by covariates. In Experiment 1, individual wireworms could choose between four different plants, one of each species (Anthoxanthum odoratum, Festuca rubra, Holcus lanatus, and Lolium perenne). In Experiment 2, groups of wireworms were released into the soil in the center of 16 plants (4 from each species). We used multinomial logit models (MLMs) to analze the data. In the appendix the use of multinomial response models is clarified with a fictitious example, using the SAS statistic software package. No preference was found in Experiment 1. In Experiment 2 we found differences in attractiveness of plant species depending on wireworm species: A. obscurus preferred grass species from nutrient-rich grasslands (L. perenne and H. lanatus). Both wireworm species disliked F. rubra. The distance from the release point influenced the probability of being found at a certain place at the end of the experiment: wireworms tended to stay in the proximity of the release point. A. haemorrhoidalis was more often found farther from the point of release than A. obscurus. Dispersal was farther from the release point in experiments with young plants (6 weeks) compared to older ones (9 weeks). Results are discussed in a broad ecological context.     

Domain II Hairpin Structure in ITS1 Sequences as an Aid in Differentiating Recently Evolved Animal and Plant Pathogenic Fungi

The hypothesis that ITS structural features can be used to define fungal groups, where sequence analysis is unsatisfactory, was examined in plant and animal pathogenic fungi. Structural models of ITS1 regions were predicted for presumed closely related species in Colletotrichum and Trichophyton anamorphs of Arthroderma species. Structural alignment of models and comparison with ITS sequence analysis identified a variable region in a conserved hairpin formed from a common inverted repeat. Thirteen different hairpin structure models were obtained for Colletotrichum species and five different models were obtained for Trichophyton species. The different structure types could be matched to individual species and species complexes as defined by ITS sequence analysis.     

Dynamics of heat destruction of spores: A new view

Summary Discrepancies between actual, viable spore populations and those predicted by a classical model during heat sterilization of food and pharmaceutical products have long concerned food engineers and scientists as they pursue new sterilization techniques, including ultra-high temperature processes. Among potential causes of those discrepancies, activation of dormant spores is significant, and models addressing that factor were developed recently. This paper reviews historic and current views on the biology and models of microbial spore populations during heat sterilization. Activation and inactivation of viable spores are emphasized, with each viewed as a first-order reaction. Rate constants of those reactions may differ significantly, inactivation rates of dormant and activated spores may differ, and variations of all rate constants with temperature appear to be well described by Arrhenius equations. Model-based analyses show how categories of survivor response curves observed during isothermal heat treatments can arise from simultaneous activation and inactivation of spores in an overall population. Effects of different distributions of initial subpopulations, different distributions of rate constants, and heat shock for homogenizing an indicator population are shown. The complexity of new, multiple process models has not increased greatly, but the potential for accurate, dynamic prediction of product safety after prescribed sterilization has. The relevant biology is understood and accounted for more thoroughly, and it is anticipated that the new models will aid design and evaluation of new and improved sterilization processes for food and pharmaceuticals.Mention of brand or firm names does not constitute an endorsement by the US Department of Agriculture over others of a similar nature not mentioned.     

Predicting the onset of filamentous bulking in biological wastewater treatment systems by exploiting image analysis information

The performance of the activated sludge process is limited by the ability of the sedimentation tank (1) to separate the activated sludge from the treated effluent and (2) to concentrate it. Apart from bad operating strategies or poorly designed clarifiers, settling failures can mainly be attributed to filamentous bulking. Image analysis is a promising technique that can be used for early detection of filamentous bulking. The aim of this paper is therefore twofold. Foremost, correlations are sought between image analysis information (i.e., the total filament length per image, the mean form factor, the mean equivalent floc diameter, the mean floc roundness and the mean floc reduced radius of gyration) and classical measurements (i.e., the Sludge Volume Index (SVI)). Secondly, this information is both explored and exploited in order to identify dynamic ARX and state space-type models. Their performance is compared based on two criteria.     

The Reindeer Oestrids Hypoderma tarandi and Cephenemyia trompe (Diptera: Oestridae): Batesian Mimics of Bumblebees (Hymenoptera: Apidae: Bombus spp.)?

The color pattern (two areas on each of 20 transverse bands along the dorsal surface of the body) in two reindeer oestrids, Hypoderma tarandi and Cephenemyia trompe (Diptera: Oestridae), was analyzed and compared with that of different bumblebee species found in an oestrid study area in northern Norway. A clustering analysis and multidimensional scaling analysis of the resulting matrix of pairwise similarity coefficients indicated that Bombus lapponicus, B. alpinus, and B. monticola (Hymenoptera: Bombinae) comprise a Mullerian guild whose members serve as Batesian models for H. tarandi, and that B. pratorum, B. jonellus, and B. lucorum comprise a Mullerian guild whose members may serve as Batesian models for C. trompe. The oestrid mimics also resemble their models in size.     

Genetics of aliphatic glucosinolates. IV. Side-chain modification in Brassica oleracea

The biochemical and genetical relationship between aliphatic glucosinolates which have methylthioalkyl, methylsulphinylalkyl and alkenyl side chains has not been resolved by biochemical studies. In this study, two hypothetical models are tested by the genetic analysis of a backcross population between Brassica drepanensis and B. atlantica. The results support one of the models in which 3-methylthiopropyl glucosinolate is sequentially converted to 3-methylsulphinylpropyl, and then to 2-propenyl glucosinolate, by the action of dominant alleles at two loci. RFLP mapping positioned both loci on the same linkage group homologous to the B. napus N19 linkage group. The implication of the results for the genetic manipulation of glucosinolates in Brassica to improve flavour and nutritional properties, and in order to investigate plant-insect interactions, is discussed.