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Servigne, P., Orivel, J., Azémar, F., Carpenter, J., Dejean, A., & Corbara, B. (2020). An uneasy alliance: a nesting association between aggressive ants and equally fierce social wasps. Insect Science, 27(1), 122–132.
Abstract: Although the Neotropical territorially dominant arboreal ant Azteca chartifex Forel is very aggressive towards any intruder, its populous colonies tolerate the close presence of the fierce polistine wasp Polybia rejecta (F.).
In French Guiana, 83.33% of the 48 P. rejecta nests recorded were found side by side with those of A. chartifex. This nesting association results in mutual protection from predators (i.e., the wasps protected from army ants; the ants protected from birds).
We conducted field studies, laboratory-based behavioral experiments and chemical analyses to elucidate the mechanisms allowing the persistence of this association. Due to differences in the cuticular profiles of the two species, we eliminated the possibility of chemical mimicry.
Also, analyses of the carton nests did not reveal traces of marking on the envelopes. Because ant forager flows were not perturbed by extracts from the wasps' Dufour's and venom glands, we rejected any hypothetical action of repulsive chemicals. Nevertheless, we noted that the wasps 'scraped' the surface of the upper part of their nest envelope using their mandibles, likely removing the ants' scent trails, and an experiment showed that ant foragers were perturbed by the removal of their scent trails. This leads us to use the term 'erasure hypothesis'. Thus, this nesting association persists thanks to a relative tolerance by the ants towards wasp presence and the behavior of the wasps that allows them to 'contain' their associated ants through the elimination of their scent trails, direct attacks, 'wing-buzzing' behavior and ejecting the ants.
Keywords: Azteca chartifex ants; interspecific association; mutualism; Polybia rejecta wasps; scent trail erasure
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Mahoui, S., Moulay, M. S., & Omrane, A. (2020). Finite element approach to linear parabolic pointwise control problems of incomplete data. International Journal of Systems Science, 51(14), 2597–2609.
Abstract: In this paper we give a priori error estimates for finite element approximations of linear parabolicproblems with pointwise control and incomplete data. We discretise the optimal control problemby using piecewise linear and continuous finite elements for the space discretisation of the state,and we use the backward Euler scheme for time discretisation. We prove a priori error estimates forthe state, the adjoint-state as well as for the low-regret pointwise optimal control.
Keywords: Optimal control problem ; low-regret control ; pointwise control ; finite element method ; a priori error estimates
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Longo, M., Saatchi, S., Keller, M., Bowman, K., Ferraz, A., Moorcroft, P. R., et al. (2020). Impacts of Degradation on Water, Energy, and Carbon Cycling of the Amazon Tropical Forests. J. Geophys. Res. Biogeosci., 125(8), e2020JG005677.
Abstract: Selective logging, fragmentation, and understory fires directly degrade forest structure and composition. However, studies addressing the effects of forest degradation on carbon, water, and energy cycles are scarce. Here, we integrate field observations and high-resolution remote sensing from airborne lidar to provide realistic initial conditions to the Ecosystem Demography Model (ED-2.2) and investigate how disturbances from forest degradation affect gross primary production (GPP), evapotranspiration (ET), and sensible heat flux (H). We used forest structural information retrieved from airborne lidar samples (13,500 ha) and calibrated with 817 inventory plots (0.25 ha) across precipitation and degradation gradients in the eastern Amazon as initial conditions to ED-2.2 model. Our results show that the magnitude and seasonality of fluxes were modulated by changes in forest structure caused by degradation. During the dry season and under typical conditions, severely degraded forests (biomass loss ≥66%) experienced water stress with declines in ET (up to 34%) and GPP (up to 35%) and increases of H (up to 43%) and daily mean ground temperatures (up to 6.5°C) relative to intact forests. In contrast, the relative impact of forest degradation on energy, water, and carbon cycles markedly diminishes under extreme, multiyear droughts, as a consequence of severe stress experienced by intact forests. Our results highlight that the water and energy cycles in the Amazon are driven by not only climate and deforestation but also the past disturbance and changes of forest structure from degradation, suggesting a much broader influence of human land use activities on the tropical ecosystems. ©2020. The Authors.
Keywords: Amazon; drought; ecosystem modeling; evapotranspiration; forest degradation; remote sensing; carbon cycle; deforestation; dry season; evapotranspiration; hydrological cycle; logging (timber); net primary production; remote sensing; sensible heat flux; tropical forest; understory; water stress; Amazon River
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Honorio Coronado, E. N., Blanc-Jolivet, C., Mader, M., García-Dávila, C. R., Gomero, D. A., del Castillo Torres, D., et al. (2020). SNP markers as a successful molecular tool for assessing species identity and geographic origin of trees in the economically important South American legume genus Dipteryx. J. Hered., 111(4), 346–356.
Abstract: Dipteryx timber has been heavily exploited in South America since 2000s due to the increasing international demand for hardwood. Developing tools for the genetic identification of Dipteryx species and their geographical origin can help to promote legal trading of timber. A collection of 800 individual trees, belonging to 6 different Dipteryx species, was genotyped based on 171 molecular markers. After the exclusion of markers out of Hardy-Weinberg equilibrium or with no polymorphism or low amplification, 83 nuclear, 29 chloroplast, 13 mitochondrial single nucleotide polymorphisms (SNPs), and 2 chloroplast and 5 mitochondrial INDELS remained. Six genetic groups were identified using Bayesian Structure analyses of the nuclear SNPs, which corresponded to the different Dipteryx species collected in the field. Seventeen highly informative markers were identified as suitable for species identification and obtained self-assignment success rates to species level of 78-96%. An additional set of 15 molecular markers was selected to determine the different genetic clusters found in Dipteryx odorata and Dipteryx ferrea, obtaining self-assignment success rates of 91-100%. The success to assign samples to the correct country of origin using all or only the informative markers improved when using the nearest neighbor approach (69-92%) compared to the Bayesian approach (33-80%). While nuclear and chloroplast SNPs were more suitable for differentiating the different Dipteryx species, mitochondrial SNPs were ideal for determining the genetic clusters of D. odorata and D. ferrea. These 32 selected SNPs will be invaluable genetic tools for the accurate identification of species and country of origin of Dipteryx timber. © The American Genetic Association 2020. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com
Keywords: Cumaru; Genetic assignment; Leguminosae; Timber verification; article; chloroplast; genetic association; genetic marker; geographic origin; indel mutation; nonhuman; single nucleotide polymorphism; species identification; structure analysis; tonka bean; Dipteryx; Fabaceae
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Talaga, S., Dejean, A., Azémar, F., Dumont, Y., & Leroy, C. (2020). Impacts of biotic and abiotic parameters on immature populations of Aedes aegypti. J. Pest Sci., 93(3), 941–952.
Abstract: In recent centuries, the mosquito Aedes aegypti has spread into most urban areas throughout the tropics. This species is considered the main vector of the chikungunya, dengue, yellow fever and Zika viruses and causes major public health issues. The aim of this study is to investigate the relative influence of biotic and abiotic parameters on immature populations of Ae. aegypti. During a one-year-long field experiment, we monitored 108 macroinvertebrate aquatic communities inhabiting four types of water containers across three different urbanized sites in a Neotropical city. A multimodel inference approach revealed that, in addition to abiotic parameters, biotic interactions with aquatic organisms had an important influence on the abundance of Ae. aegypti and that the urbanized site considered influences the outcomes of the interactions. Controphic species other than mosquitoes aided Ae. aegypti development, suggesting a mechanism of facilitation through a chain of processes. However, the abundance of Ae. aegypti was lowered by competition with native mosquito species in the slightly urbanized area and by predation in more urbanized areas. Competitive displacement and reduction, as well as predation by native aquatic organisms, can be considered a form of ecosystem service. The conservation and/or augmentation of natural enemies should improve the short- and long-term success of incompatible and/or sterile insect techniques, thus opening up perspectives for the future of mosquito management. © 2020, Springer-Verlag GmbH Germany, part of Springer Nature.
Keywords: Biocontrol agents; Competition; Ecosystem services; Mosquito control; Mosquito management; Predation; abiotic factor; biotic factor; competitive displacement; disease vector; maturation; mosquito; pest control; Aedes aegypti; Hexapoda; Zika virus
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Touchard, A., Aili, S. R., Téné, N., Barassé, V., Klopp, C., Dejean, A., et al. (2020). Venom Peptide Repertoire of the European Myrmicine Ant Manica rubida: Identification of Insecticidal Toxins. J. Proteome Res., 19(4), 1800–1811.
Abstract: Using an integrated transcriptomic and proteomic approach, we characterized the venom peptidome of the European red ant, Manica rubida. We identified 13 “myrmicitoxins” that share sequence similarities with previously identified ant venom peptides, one of them being identified as an EGF-like toxin likely resulting from a threonine residue modified by O-fucosylation. Furthermore, we conducted insecticidal assays of reversed-phase HPLC venom fractions on the blowfly Lucilia caesar, permitting us to identify six myrmicitoxins (i.e., U3-, U10-, U13-, U20-MYRTX-Mri1a, U10-MYRTX-Mri1b, and U10-MYRTX-Mri1c) with an insecticidal activity. Chemically synthesized U10-MYRTX-Mri1a, -Mri1b, -Mri1c, and U20-MYRTX-Mri1a irreversibly paralyzed blowflies at the highest doses tested (30-125 nmol·g-1). U13-MYRTX-Mri1a, the most potent neurotoxic peptide at 1 h, had reversible effects after 24 h (150 nmol·g-1). Finally, U3-MYRTX-Mri1a has no insecticidal activity, even at up to 55 nmol·g-1. Thus, M. rubida employs a paralytic venom rich in linear insecticidal peptides, which likely act by disrupting cell membranes.
Keywords: glycosylated toxin; peptidome; polycationic α-helix; predation; pyroglutamate; reversible neurotoxicity
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Vleminckx, J., Bauman, D., Demanet, M., Hardy, O. J., Doucet, J. - L., & Drouet, T. (2020). Past human disturbances and soil fertility both influence the distribution of light-demanding tree species in a Central African tropical forest. J. Veg. Sci., 31(3), 440–453.
Abstract: Questions: In vast areas of Central African forests, the upper canopy is presently dominated by light-demanding tree species. Here, we confront three hypotheses to explain this dominance: (a) these species have expanded their distribution because of widespread past slash-and-burn activities, as suggested by important charcoal amounts recorded in the soils of the region; (b) their abundance is rather explained by soil properties, as this guild establishes preferentially on favourable physico-chemical conditions for rapid growth; (c) soil properties have been substantially influenced by past human disturbances and those two effects cannot be disentangled. Location: Pallisco-CIFM logging concession, southeastern Cameroon (300,000 ha). Methods: We quantified soil charcoal abundance and measured ten soil variables at the basis of 60 target trees that belonged to a list of three long-living pioneer light-demanding (LLP) and four shade-bearer (SB) species. We identified all stems with a diameter at breast height (DBH) ≥ 20 cm within a distance of 15 m around each target tree. Species were characterised by their wood-specific gravity (WSG), which reflected their light requirement. Multiple regression models were used to quantify and test the relative effects of charcoal abundance and soil variables on the mean WSG of the 60 tree communities, as well as the abundance of three guilds: LLP, SB, and non-pioneer light demanders (NPLD). Results: The mean WSG was the only response variable significantly explained by soil variables and charcoal abundance combined. It was significantly negatively associated with soil calcium and Mg content and with charcoal abundance, with soil and charcoal influencing the mean WSG independently. Conclusion: Our study provides evidence that past human disturbances and soil fertility have independently promoted the establishment of light-demanding species in western Central African forests, thereby shedding light on tree community assembly rules in these ecosystems which remain considerably understudied compared to the tropical forests of other continents. © 2020 International Association for Vegetation Science
Keywords: light-demanding species; moist tropical forests; past human disturbances; shade-bearer species; soil charcoal abundance; soil properties; tree community assemblages; wood-specific gravity; anthropogenic effect; forest canopy; forest ecosystem; shifting cultivation; soil fertility; soil property; tree; tropical forest; Cameroon
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Perrot, T., Guillaume, S., Nadine, A., Jacques, B., Philippe, G., Stéphane, D., et al. (2020). A reverse chemical ecology approach to explore wood natural durability. Microb. Biotechnol., 13(5), 1673–1677.
Abstract: The natural durability of wood species, defined as their inherent resistance to wood-destroying agents, is a complex phenomenon depending on many biotic and abiotic factors. Besides the presence of recalcitrant polymers, the presence of compounds with antimicrobial properties is known to be important to explain wood durability. Based on the advancement in our understanding of fungal detoxification systems, a reverse chemical ecology approach was proposed to explore wood natural durability using fungal glutathione transferases. A set of six glutathione transferases from the white-rot Trametes versicolor were used as targets to test wood extracts from seventeen French Guiana neotropical species. Fluorescent thermal shift assays quantified interactions between fungal glutathione transferases and these extracts. From these data, a model combining this approach and wood density significantly predicts the wood natural durability of the species tested previously using long-term soil bed tests. Overall, our findings confirm that detoxification systems could be used to explore the chemical environment encountered by wood-decaying fungi and also wood natural durability. © 2020 The Authors. Microbial Biotechnology published by John Wiley & Sons Ltd and Society for Applied Microbiology.
Keywords: glutathione transferase; Article; biodegradation; data base; detoxification; ecology; enzyme activity; enzyme metabolism; forest; molecular dynamics; physical parameters; species identification; thermal analysis; Trametes versicolor; wood; wood durability
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Birer, C., Moreau, C. S., Tysklind, N., Zinger, L., & Duplais, C. (2020). Disentangling the assembly mechanisms of ant cuticular bacterial communities of two Amazonian ant species sharing a common arboreal nest. Mol. Ecol., 29(7), 1372–1385.
Abstract: Bacteria living on the cuticle of ants are generally studied for their protective role against pathogens, especially in the clade of fungus-growing ants. However, little is known regarding the diversity of cuticular bacteria in other ant host species, as well as the mechanisms leading to the composition of these communities. Here, we used 16S rRNA gene amplicon sequencing to study the influence of host species, species interactions and the pool of bacteria from the environment on the assembly of cuticular bacterial communities on two phylogenetically distant Amazonian ant species that frequently nest together inside the roots system of epiphytic plants, Camponotus femoratus and Crematogaster levior. Our results show that (a) the vast majority of the bacterial community on the cuticle is shared with the nest, suggesting that most bacteria on the cuticle are acquired through environmental acquisition, (b) 5.2% and 2.0% of operational taxonomic units (OTUs) are respectively specific to Ca. femoratus and Cr. levior, probably representing their respective core cuticular bacterial community, and (c) 3.6% of OTUs are shared between the two ant species. Additionally, mass spectrometry metabolomics analysis of metabolites on the cuticle of ants, which excludes the detection of cuticular hydrocarbons produced by the host, were conducted to evaluate correlations among bacterial OTUs and m/z ion mass. Although some positive and negative correlations are found, the cuticular chemical composition was weakly species-specific, suggesting that cuticular bacterial communities are prominently environmentally acquired. Overall, our results suggest the environment is the dominant source of bacteria found on the cuticle of ants. © 2020 John Wiley & Sons Ltd
Keywords: ant gardens; bacterial communities; cuticular microbiome; insect cuticle; metabarcoding
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Sommeria-Klein, G., Zinger, L., Coissac, E., Iribar, A., Schimann, H., Taberlet, P., et al. (2020). Latent Dirichlet Allocation reveals spatial and taxonomic structure in a DNA-based census of soil biodiversity from a tropical forest. Mol. Ecol. Resour., 20(2), 371–386.
Abstract: High-throughput sequencing of amplicons from environmental DNA samples permits rapid, standardized and comprehensive biodiversity assessments. However, retrieving and interpreting the structure of such data sets requires efficient methods for dimensionality reduction. Latent Dirichlet Allocation (LDA) can be used to decompose environmental DNA samples into overlapping assemblages of co-occurring taxa. It is a flexible model-based method adapted to uneven sample sizes and to large and sparse data sets. Here, we compare LDA performance on abundance and occurrence data, and we quantify the robustness of the LDA decomposition by measuring its stability with respect to the algorithm's initialization. We then apply LDA to a survey of 1,131 soil DNA samples that were collected in a 12-ha plot of primary tropical forest and amplified using standard primers for bacteria, protists, fungi and metazoans. The analysis reveals that bacteria, protists and fungi exhibit a strong spatial structure, which matches the topographical features of the plot, while metazoans do not, confirming that microbial diversity is primarily controlled by environmental variation at the studied scale. We conclude that LDA is a sensitive, robust and computationally efficient method to detect and interpret the structure of large DNA-based biodiversity data sets. We finally discuss the possible future applications of this approach for the study of biodiversity. © 2019 John Wiley & Sons Ltd
Keywords: community ecology; environmental DNA; metabarcoding; OTU presence–absence; soil microbiome; topic modelling; bacterium; biodiversity; biology; classification; eukaryote; fungus; genetics; high throughput sequencing; isolation and purification; microbiology; parasitology; procedures; soil; Bacteria; Biodiversity; Computational Biology; Eukaryota; Fungi; High-Throughput Nucleotide Sequencing; Soil; Soil Microbiology
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