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Fauset, S., Johnson, M. O., Gloor, M., Baker, T. R., Monteagudo M., A., Brienen, R. J. W., et al. (2015). Hyperdominance in Amazonian forest carbon cycling. Nature Communications, 6(6857).
Abstract: While Amazonian forests are extraordinarily diverse, the abundance of trees is skewed strongly towards relatively few â € hyperdominantâ €™ species. In addition to their diversity, Amazonian trees are a key component of the global carbon cycle, assimilating and storing more carbon than any other ecosystem on Earth. Here we ask, using a unique data set of 530 forest plots, if the functions of storing and producing woody carbon are concentrated in a small number of tree species, whether the most abundant species also dominate carbon cycling, and whether dominant species are characterized by specific functional traits. We find that dominance of forest function is even more concentrated in a few species than is dominance of tree abundance, with only â ‰1% of Amazon tree species responsible for 50% of carbon storage and productivity. Although those species that contribute most to biomass and productivity are often abundant, species maximum size is also influential, while the identity and ranking of dominant species varies by function and by region. © 2015 Macmillan Publishers Limited. All rights reserved.
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Leba, L. - J., Musset, L., Pelleau, S., Estevez, Y., Birer, C., Briolant, S., et al. (2015). Use of Plasmodium falciparum culture-adapted field isolates for in vitro exflagellation-blocking assay. Malaria Journal, 14, 234.
Abstract: Background: A major requirement for malaria elimination is the development of transmission-blocking interventions. In vitro transmission-blocking bioassays currently mostly rely on the use of very few Plasmodium falciparum reference laboratory strains isolated decades ago. To fill a piece of the gap between laboratory experimental models and natural systems, the purpose of this work was to determine if culture-adapted field isolates of P. falciparum are suitable for in vitro transmission-blocking bioassays targeting functional maturity of male gametocytes: exflagellation. Methods: Plasmodium falciparum isolates were adapted to in vitro culture before being used for in vitro gametocyte production. Maturation was assessed by microscopic observation of gametocyte morphology over time of culture and the functional viability of male gametocytes was assessed by microscopic counting of exflagellating gametocytes. Suitability for in vitro exflagellation-blocking bioassays was determined using dihydroartemisinin and methylene blue. Results: In vitro gametocyte production was achieved using two isolates from French Guiana and two isolates from Cambodia. Functional maturity of male gametocytes was assessed by exflagellation observations and all four isolates could be used in exflagellation-blocking bioassays with adequate response to methylene blue and dihydroartemisinin. Conclusion: This work shows that in vitro culture-adapted P. falciparum field isolates of different genetic background, from South America and Southeast Asia, can successfully be used for bioassays targeting the male gametocyte to gamete transition, exflagellation. © 2015 Leba et al.
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Molina, L., Broquet, G., Imbach, P., Chevallier, F., Poulter, B., Bonal, D., et al. (2015). On the ability of a global atmospheric inversion to constrain variations of CO2 fluxes over Amazonia. Atmospheric Chemistry and Physics, 15(14), 8423–8438.
Abstract: The exchanges of carbon, water and energy between the atmosphere and the Amazon basin have global implications for the current and future climate. Here, the global atmospheric inversion system of the Monitoring of Atmospheric Composition and Climate (MACC) service is used to study the seasonal and interannual variations of biogenic CO<inf>2</inf> fluxes in Amazonia during the period 2002-2010. The system assimilated surface measurements of atmospheric CO<inf>2</inf> mole fractions made at more than 100 sites over the globe into an atmospheric transport model. The present study adds measurements from four surface stations located in tropical South America, a region poorly covered by CO<inf>2</inf> observations. The estimates of net ecosystem exchange (NEE) optimized by the inversion are compared to an independent estimate of NEE upscaled from eddy-covariance flux measurements in Amazonia. They are also qualitatively evaluated against reports on the seasonal and interannual variations of the land sink in South America from the scientific literature. We attempt at assessing the impact on NEE of the strong droughts in 2005 and 2010 (due to severe and longer-than-usual dry seasons) and the extreme rainfall conditions registered in 2009. The spatial variations of the seasonal and interannual variability of optimized NEE are also investigated. While the inversion supports the assumption of strong spatial heterogeneity of these variations, the results reveal critical limitations of the coarse-resolution transport model, the surface observation network in South America during the recent years and the present knowledge of modelling uncertainties in South America that prevent our inversion from capturing the seasonal patterns of fluxes across Amazonia. However, some patterns from the inversion seem consistent with the anomaly of moisture conditions in 2009. © Author(s) 2015.
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Aimene, Y. E., & Nairn, J. A. (2015). Simulation of transverse wood compression using a large-deformation, hyperelastic–plastic material model. Wood Science and Technology, 49(1), 21–39.
Abstract: Transverse compression of wood is a process that induces large deformations. The process is dominated by elastic and plastic cell wall buckling. This work reports a numerical study of the transverse compression and densification of wood using a large-deformation, elastic–plastic constitutive law. The model is isotropic, formulated within the framework of hyperelasticity, and implemented in explicit material point method (MPM) software. The model was first validated for modeling of cellular materials by compression of an isotropic cellular model specimen. Next, it was used to model compression of wood by first validating use of isotropic, transverse plane properties for tangential compression of hardwood, and then by investigating both tangential and radial compression of softwood. Importantly, the discretization of wood specimens used MPM methods to reproduce accurately the complex morphology of wood anatomy for different species. The simulations have reproduced observations of stress–strain response during wood compression including details of inhomogeneous deformation caused by variations in wood anatomy. © 2014, Springer-Verlag Berlin Heidelberg.
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Moore, A. L., McCarthy, M. A., Parris, K. M., & Moore, J. L. (2014). The optimal number of surveys when detectability varies. PLoS ONE, 9(12), e115345.
Abstract: The survey of plant and animal populations is central to undertaking field ecology. However, detection is imperfect, so the absence of a species cannot be determined with certainty. Methods developed to account for imperfect detectability during surveys do not yet account for stochastic variation in detectability over time or space. When each survey entails a fixed cost that is not spent searching (e.g., time required to travel to the site), stochastic detection rates result in a trade-off between the number of surveys and the length of each survey when surveying a single site. We present a model that addresses this trade-off and use it to determine the number of surveys that: 1) maximizes the expected probability of detection over the entire survey period; and 2) is most likely to achieve a minimally-acceptable probability of detection. We illustrate the applicability of our approach using three practical examples (minimum survey effort protocols, number of frog surveys per season, and number of quadrats per site to detect a plant species) and test our model's predictions using data from experimental plant surveys. We find that when maximizing the expected probability of detection, the optimal survey design is most sensitive to the coefficient of variation in the rate of detection and the ratio of the search budget to the travel cost. When maximizing the likelihood of achieving a particular probability of detection, the optimal survey design is most sensitive to the required probability of detection, the expected number of detections if the budget were spent only on searching, and the expected number of detections that are missed due to travel costs. We find that accounting for stochasticity in detection rates is likely to be particularly important for designing surveys when detection rates are low. Our model provides a framework to do this. © 2014 Moore et al.
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Rutishauser, E., Herault, B., Baraloto, C., Blanc, L., Descroix, L., Sotta, E. D., et al. (2015). Rapid tree carbon stock recovery in managed Amazonian forests. Current Biology, 25(18), R787–R788.
Abstract: Summary While around 20% of the Amazonian forest has been cleared for pastures and agriculture, one fourth of the remaining forest is dedicated to wood production [1]. Most of these production forests have been or will be selectively harvested for commercial timber, but recent studies show that even soon after logging, harvested stands retain much of their tree-biomass carbon and biodiversity [2,3]. Comparing species richness of various animal taxa among logged and unlogged forests across the tropics, Burivalova et al.[4] found that despite some variability among taxa, biodiversity loss was generally explained by logging intensity (the number of trees extracted). Here, we use a network of 79 permanent sample plots (376 ha total) located at 10 sites across the Amazon Basin [5] to assess the main drivers of time-to-recovery of post-logging tree carbon (Table S1). Recovery time is of direct relevance to policies governing management practices (i.e., allowable volumes cut and cutting cycle lengths), and indirectly to forest-based climate change mitigation interventions. © 2015 Elsevier Ltd.
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Nirma, C., Eparvier, V., & Stien, D. (2015). Reactivation of antibiosis in the entomogenous fungus Chrysoporthe sp. SNB-CN74. Journal of Antibiotics, 68(9), 586–590.
Abstract: Chrysoporthe sp. SNB-CN74 was isolated from a Nasutitermes corniger nest, and its ethyl acetate extract was found to exhibit very strong antibacterial activity. Two antibacterial metabolites were isolated, (-)-R-skyrin (2) and (+)-rugulosin A (3). Eventually, the fungus lost its antibiotic potential when subcultured, and the use of yeast extract induced the re-expression of these two antibiotics. Yeast extract possibly activated a cryptic pathway by mimicking the presence of an ecological competitor. © 2015 Japan Antibiotics Research Association All rights reserved.
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Aubry-Kientz, M., Rossi, V., Wagner, F., & Herault, B. (2015). Identifying climatic drivers of tropical forest dynamics. Biogeosciences, 12(19), 5583–5596.
Abstract: In the context of climate change, identifying and then predicting the impacts of climatic drivers on tropical forest dynamics is becoming a matter of urgency. To look at these climate impacts, we used a coupled model of tropical tree growth and mortality, calibrated with forest dynamic data from the 20-year study site of Paracou, French Guiana, in order to introduce and test a set of climatic variables. Three major climatic drivers were identified through the variable selection procedure: drought, water saturation and temperature. Drought decreased annual growth and mortality rates, high precipitation increased mortality rates and high temperature decreased growth. Interactions between key functional traits, stature and climatic variables were investigated, showing best resistance to drought for trees with high wood density and for trees with small current diameters. Our results highlighted strong long-term impacts of climate variables on tropical forest dynamics, suggesting potential deep impacts of climate changes during the next century. © Author(s) 2015.
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Guitet, S., Herault, B., Molto, Q., Brunaux, O., & Couteron, P. (2015). Spatial structure of above-ground biomass limits accuracy of carbon mapping in rainforest but large scale forest inventories can help to overcome. PLoS ONE, 10(9), e0138456.
Abstract: Precise mapping of above-ground biomass (AGB) is a major challenge for the success of REDD+ processes in tropical rainforest. The usual mapping methods are based on two hypotheses: a large and long-ranged spatial autocorrelation and a strong environment influence at the regional scale. However, there are no studies of the spatial structure of AGB at the landscapes scale to support these assumptions.We studied spatial variation in AGB at various scales using two large forest inventories conducted in French Guiana. The dataset comprised 2507 plots (0.4 to 0.5 ha) of undisturbed rainforest distributed over the whole region. After checking the uncertainties of estimates obtained from these data, we used half of the dataset to develop explicit predictive models including spatial and environmental effects and tested the accuracy of the resulting maps according to their resolution using the rest of the data. Forest inventories provided accurate AGB estimates at the plot scale, for a mean of 325 Mg.ha-1. They revealed high local variability combined with a weak autocorrelation up to distances of no more than10 km. Environmental variables accounted for a minor part of spatial variation. Accuracy of the best model including spatial effects was 90 Mg.ha-1 at plot scale but coarse graining up to 2-km resolution allowed mapping AGB with accuracy lower than 50 Mg.ha-1. Whatever the resolution, no agreement was found with available pan-tropical reference maps at all resolutions.We concluded that the combined weak autocorrelation and weak environmental effect limit AGB maps accuracy in rainforest, and that a trade-off has to be found between spatial resolution and effective accuracy until adequate “wall-to-wall” remote sensing signals provide reliable AGB predictions. Waiting for this, using large forest inventories with low sampling rate (<0.5%) may be an efficient way to increase the global coverage of AGB maps with acceptable accuracy at kilometric resolution. Copyright: © 2015 Guitet et al.
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Touchard, A., Dejean, A., & Orivel, J. (2015). Intraspecific variations in the venom peptidome of the ant Odontomachus haematodus (Formicidae: Ponerinae) from French Guiana. Journal of Hymenoptera Research, 47, 87–101.
Abstract: Ant venoms are complex cocktails of toxins employed to subdue prey and to protect the colony from predators and microbial pathogens. Although the extent of ant venom peptide diversity remains largely unexplored, previous studies have revealed the presence of numerous bioactive peptides in most stinging ant venoms. We investigated the venom peptidome of the ponerine ant Odontomachus haematodus using LC-MS analysis and then verified whether the division of labor in the colonies and their geographical location are correlated with differences in venom composition. Our results reveal that O. haematodus venom is comprised of 105 small linear peptides. The venom composition does not vary between the different castes (i.e., nurses, foragers and queens), but an intraspecific variation in peptide content was observed, particularly when the colonies are separated by large distances. Geographical variation appears to increase the venom peptide repertoire of this ant species, demonstrating its intraspecific venom plasticity.
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