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Chang, S. - S., Quignard, F., & Clair, B. (2017). The effect of sectioning and ultrasonication on the mesoporosity of poplar tension wood. Wood Science and Technology, 51(3), 507–516.
Abstract: Increasing interest in understanding tension stress generation in tension wood with fibres having a gelatinous layer (G-layer) has focused attention on the specific role of this layer. To distinguish its contribution from those of other wall layers, the G-layer of wood sections was isolated by ultrasonication. The aim of this study was to assess the effect of sectioning and of the ultrasonic treatment on the mesoporosity of tension wood using nitrogen adsorption–desorption analysis. The results showed that the process of isolating the G-layer using ultrasonication strongly affects its mesoporosity. Most damage was found to occur during sectioning rather than as a result of the 15-min ultrasonic treatment.
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Stahl, C., Fontaine, S., Klumpp, K., Picon-Cochard, C., Grise, M. M., Dezecache, C., et al. (2017). Continuous soil carbon storage of old permanent pastures in Amazonia. Glob Change Biol, 23(8), 3382–3392.
Abstract: Amazonian forests continuously accumulate carbon (C) in biomass and in soil, representing a carbon sink of 0.42–0.65 GtC yr−1. In recent decades, more than 15% of Amazonian forests have been converted into pastures, resulting in net C emissions (~200 tC ha−1) due to biomass burning and litter mineralization in the first years after deforestation. However, little is known about the capacity of tropical pastures to restore a C sink. Our study shows in French Amazonia that the C storage observed in native forest can be partly restored in old (≥24 year) tropical pastures managed with a low stocking rate (±1 LSU ha−1) and without the use of fire since their establishment. A unique combination of a large chronosequence study and eddy covariance measurements showed that pastures stored between −1.27 ± 0.37 and −5.31 ± 2.08 tC ha−1 yr−1 while the nearby native forest stored −3.31 ± 0.44 tC ha−1 yr−1. This carbon is mainly sequestered in the humus of deep soil layers (20–100 cm), whereas no C storage was observed in the 0- to 20-cm layer. C storage in C4 tropical pasture is associated with the installation and development of C3 species, which increase either the input of N to the ecosystem or the C:N ratio of soil organic matter. Efforts to curb deforestation remain an obvious priority to preserve forest C stocks and biodiversity. However, our results show that if sustainable management is applied in tropical pastures coming from deforestation (avoiding fires and overgrazing, using a grazing rotation plan and a mixture of C3 and C4 species), they can ensure a continuous C storage, thereby adding to the current C sink of Amazonian forests.
Keywords: carbon storage; CN coupling; deep soil; mixed-grass pasture; native forest
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Dejean, A., Rodríguez-Pérez, H., Carpenter, J. M., Azémar, F., & Corbara, B. (2017). The predatory behavior of the Neotropical social wasp Polybia rejecta. Behavioural Processes, 140, 161–168.
Abstract: Abstract We experimentally studied the predatory behavior of Polybia rejecta (Vespidae, Polistinae, Epiponini) towards 2–88 mm-long insects attracted to a UV light trap. Foragers, which began to hunt at 6:30, selected 4–14 mm-long prey insects. Prey detection by sight by hovering wasps was confirmed using decoys. After the wasps landed and walked along a sinuous path, prey were detected by contact or from a distance (1–3 cm). This was followed by seizure, stinging (contrarily to most other known cases), prey manipulation and retrieval. Prey that flew off might be caught in flight. The prey load, representing 30.7% of a forager’s weight, was optimized by capturing up to six small prey or two medium-sized prey successively (both of which might be consumed in situ). The foragers cut off the wings of larger prey or cut them into two pieces and returned to gather the second piece. The handling time increased exponentially with the weight of the prey. Partial loading (i.e., retrieving a load much inferior to the maximum possible) was likely related to social facilitation, a form of nest-based recruitment that was demonstrated through the experimental elimination of local enhancement by removing foragers (both mechanisms favor the exploitation of favorable patches).
Keywords: Epiponine wasps; Polistinae; Predation; Prey selection; Recruitment; Vespidae
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Pierrejean, I., Mehinto, T., & Beauchene, J. (2017). Comparative Analysis of Three Different Methods Used to Determine the Elastic Modulus for a Choice of Tropical Guianese Wood Species. Pro Ligno, 13(1), 3–17.
Abstract: This study compares variability in the longitudinal Modulus of Elasticity (MOE) values, measured by three different methods, for eight tropical wood species covering a wide range of densities, a property that has been little described in the literature for some of the species studied. The modulus of elasticity in wood species is one of the main mechanical properties measured to characterize wood materials. However, this property is seldom described for the tropical wood species studied here, and the method used is often variable. The aim is to answer the following questions. In the methods used, what are the main variability factors which influence modulus measurement? Is the modulus different with regard to the solicitation direction (radial or tangential)? Which relationship exists between modulus and density for these species?
The samples were subjected to the four-point bending test, then to the free vibration test and to the forced-vibration test (which allows tests on small samples).The samples were subjected to stress in radial and tangential directions. The modulus values obtained by the different methods were well correlated for most of the species. The relationship between modulus and density was very good at inter-specific level because sampling covered a wide range of densities. But this relationship was not so good for each of the species sampled.
This kind of test was not appropriate for detecting differences in behavior between the two directions of solicitation for these species. The main features of the three methods were summarized, highlighting the advantages of each for the species studied.
Keywords: density; modulus of elasticity; static and dynamic tests; tropical woods
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Denis, T., Richard-Hansen, C., Brunaux, O., Etienne, M. - P., Guitet, S., & Herault, B. (2017). Biological traits, rather than environment, shape detection curves of large vertebrates in neotropical rainforests. Ecol Appl, 27(5), 1564–1577.
Abstract: Line transect surveys are widely used in Neotropical rainforests to estimate the population abundance of medium- and large-sized vertebrates. The use of indices such as encounter rate has been criticized because the probability of animal detection may fluctuate due to the heterogeneity of environmental conditions among sites. In addition, the morphological and behavioral characteristics (biological traits) of species affect their detectability. In this study, we compared the extent to which environmental conditions and species’ biological traits bias abundance estimates in terra firme rainforests in French Guiana. The selected environmental conditions included both physical conditions and forest structure covariates, while the selected biological traits included the morphological and behavioral characteristics of species. We used the distance sampling method to model the detection probability as an explicit function of environmental conditions and biological traits and implemented a model selection process to determine the relative importance of each group of covariates. Biological traits contributed to the variability of animal detectability more than environmental conditions, which had only a marginal effect. Detectability was best for large animals with uniform or disruptive markings that live in groups in the canopy top. Detectability was worst for small, solitary, terrestrial animals with mottled markings. In the terra firme rainforests that represent ~80% of the Amazonia and Guianas regions, our findings support the use of relative indices such as the encounter rate to compare population abundance between sites in species-specific studies. Even though terra firme rainforests may appear similar between regions of Amazonia and the Guianas, comparability must be ensured, especially in forests disturbed by human activity. The detection probability can be used as an indicator of species’ vulnerability to hunting and, thus, to the risk of local extinction. Only a few biological trait covariates are required to correctly estimate the detectability of the majority of medium- and large-sized vertebrates. Thus, a biological trait model could be useful in predicting the detection probabilities of rare, uncommon, or localized species for which few data are available to fit the detection function.
Keywords: abundance; camouflage; distance sampling; encounter rate; French Guiana; hunting vulnerability; line transect; Neotropical terra firme rainforests; relative abundance
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Gruhn, G., Dumez, S., Moreau, P. - A., Roy, M., Morreale, O., Schimann, H., et al. (2017). The genus Resinicium in French Guiana and the West Indies: a morphological and molecular survey, revealing Resinicium grandisporum sp. nov. Cryptogamie, Mycologie, 38(4), 1–15.
Abstract: A revision of Resinicium collections (Basidiomycota, Hymenochaetales) from French Guiana and French West Indies is provided, and a new species, Resinicium grandisporum sp. nov., supported by morphological as well as phylogenetic analyses based on ITS DNA sequences, is described and illustrated. An updated key of the genus Resinicium is also provided, which includes species previously described from outside of the studied area.
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Duplais, C., & Estevez, Y. (2017). Tandem Biocatalysis Unlocks the Challenging de Novo Production of Plant Natural Products. ChemBioChem, 18(22), 2192–2195.
Abstract: Intimate partnership: Knowledge of the biocatalytic cascades in different cellular compartments is limited, but deciphering these systems in nature can be used to inspire synthetic strategies. Two studies report new insights into the biosynthesis of alkaloids and sesterterpenoids in plants. This highlight presents these novel biotransformations to illustrate how tandem biocatalysis can impact the future of natural product production.
Keywords: alkaloids; biosynthesis; enzyme catalysis; protein engineering; terpenes
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Birer, C., Tysklind, N., Zinger, L., & Duplais, C. (2017). Comparative analysis of DNA extraction methods to study the body surface microbiota of insects: A case study with ant cuticular bacteria. Mol Ecol Resour, 17(6), e34–e45.
Abstract: High-throughput sequencing of the 16S rRNA gene has considerably helped revealing the essential role of bacteria living on insect cuticles in the ecophysiology and behaviour of their hosts. However, our understanding of host-cuticular microbiota feedbacks remains hampered by the difficulties of working with low bacterial DNA quantities as with individual insect cuticle samples, which are more prone to molecular biases and contaminations. Herein, we conducted a methodological benchmark on the cuticular bacterial loads retrieved from two Neotropical ant species of different body size and ecology: Atta cephalotes (~15 mm) and Pseudomyrmex penetrator (~5 mm). We evaluated the richness and composition of the cuticular microbiota, as well as the amount of biases and contamination produced by four DNA extraction protocols. We also addressed how bacterial community characteristics would be affected by the number of individuals or individual body size used for DNA extraction. Most extraction methods yielded similar results in terms of bacterial diversity and composition for A. cephalotes (~15 mm). In contrast, greater amounts of artefactual sequences and contaminations, as well as noticeable differences in bacterial community characteristics were observed between extraction methods for P. penetrator (~5 mm). We also found that large (~15 mm) and small (~5 mm) A. cephalotes individuals harbour different bacterial communities. Our benchmark suggests that cuticular microbiota of single individual insects can be reliably retrieved provided that blank controls, appropriate data cleaning, and individual body size and functional role within insect society are considered in the experiment.
Keywords: 16S rRNA; bacterial communities; cuticular microbiome; insect cuticle; metabarcoding
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Mayer, V. E., Lauth, J., & Orivel, J. (2017). Convergent structure and function of mycelial galleries in two unrelated Neotropical plant-ants. Insectes Sociaux, 64(3), 365–371.
Abstract: The construction process and use of galleries by Azteca brevis (Myrmicinae: Dolichoderinae) inhabiting Tetrathylacium macrophyllum (Salicaceae) were compared with Allomerus decemarticulatus (Myrmicinae: Solenopsidini) galleries on Hirtella physophora (Chrysobalanaceae). Though the two ant species are phylogenetically distant, the gallery structure seems to be surprisingly similar and structurally convergent: both are pierced with numerous holes and both ant species use Chaetothyrialean fungi to strengthen the gallery walls. Al. decemarticulatus is known to use the galleries for prey capture and whether this is also the case for Az. brevis was tested in field experiments. We placed Atta workers as potential prey/threat on the galleries and recorded the behaviour of both ant species. We found considerable behavioural differences between them: Al. decemarticulatus was quicker and more efficient at capture than was Az. brevis. While most Atta workers were captured after the first 5 min by Al. decemarticulatus, significantly fewer were captured by Az. brevis even after 20 min. Moreover, the captured Atta were sometimes simply discarded and not taken to the nest by Az. brevis. As a consequence, the major function of the galleries built by Az. brevis may, therefore, be defense against intruders in contrast to Al. decemarticulatus which uses them mainly for prey capture. This may be due to a higher need for protein in Al. decemarticulatus compared to coccid-raising Az. brevis.
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Epelboin, L., Bourhy, P., Le Turnier, P., Schaub, R., Mosnier, E., Berlioz-Arthaud, A., et al. (2017). La leptospirose en Guyane française et sur le bouclier des Guyanes. État des connaissances en 2016. Bulletin de la Société de pathologie exotique, 110(3), 165–179.
Abstract: La leptospirose est une zoonose cosmopolite causée par les bactéries du genre Leptospira. Si sa répartition est vaste sur le globe, le climat chaud et humide de la zone intertropicale est particulièrement propice à son expansion. Dans la plupart des départements et territoires français d’outremer, la leptospirose est considérée comme un problème de santé publique. En Guyane, département français situé au nord-est de la forêt amazonienne, elle est considérée comme rare. L’objectif de cette revue est de faire l’état des lieux des connaissances sur la leptospirose humaine et animale en Guyane française et dans les pays environnants. Une recherche exhaustive a été conduite, à travers la littérature médicale indexée et informelle en français, anglais, espagnol et portugais. Ainsi, respectivement dix et quatre publications ont pu être identifiées sur la leptospirose humaine et animale en Guyane, publiées entre 1940 et 1995, sous formes de cas cliniques ou de séries de cas. Les publications concernant cette maladie dans les autres pays du plateau des Guyanes, Venezuela oriental, Guyana, Suriname, et État brésilien de l’Amapá, étaient également rares voire inexistantes. En revanche, les données récentes du centre national de la leptospirose français ont montré une augmentation récente et brutale du nombre de cas dans le département, probablement en partie due à la mise en place d’outils diagnostiques tels que la sérologie IgM Elisa. Il est en fait probable que la leptospirose soit une maladie négligée dans la région, du fait de l’absence d’outils diagnostiques rapidement disponibles, de la méconnaissance des cliniciens de cette pathologie et de l’existence de nombreux autres pathogènes à présentation clinique similaire (paludisme, arboviroses, fièvre Q, toxoplasmose amazonienne). La mise en place d’études de plus grande ampleur sur la leptospirose animale et humaine est nécessaire et urgente pour connaître le véritable poids de cette maladie dans notre région.
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