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Aubry-Kientz, M., Rossi, V., Cornu, G., Wagner, F., & Herault, B. (2019). Temperature rising would slow down tropical forest dynamic in the Guiana Shield. Sci. Rep., 9, 10235.
Abstract: Increasing evidence shows that the functioning of the tropical forest biome is intimately related to the climate variability with some variables such as annual precipitation, temperature or seasonal water stress identified as key drivers of ecosystem dynamics. How tropical tree communities will respond to the future climate change is hard to predict primarily because several demographic processes act together to shape the forest ecosystem general behavior. To overcome this limitation, we used a joint individual-based model to simulate, over the next century, a tropical forest community experiencing the climate change expected in the Guiana Shield. The model is climate dependent: temperature, precipitation and water stress are used as predictors of the joint growth and mortality rates. We ran simulations for the next century using predictions of the IPCC 5AR, building three different climate scenarios (optimistic RCP2.6, intermediate, pessimistic RCP8.5) and a control (current climate). The basal area, above-ground fresh biomass, quadratic diameter, tree growth and mortality rates were then computed as summary statistics to characterize the resulting forest ecosystem. Whatever the scenario, all ecosystem process and structure variables exhibited decreasing values as compared to the control. A sensitivity analysis identified the temperature as the strongest climate driver of this behavior, highlighting a possible temperature-driven drop of 40% in average forest growth. This conclusion is alarming, as temperature rises have been consensually predicted by all climate scenarios of the IPCC 5AR. Our study highlights the potential slow-down danger that tropical forests will face in the Guiana Shield during the next century. © 2019, The Author(s).
Keywords: article; biomass; climate change; controlled study; diagnostic test accuracy study; driver; human; joint; mortality rate; precipitation; prediction; sensitivity analysis; simulation; statistics; tree growth; tropical rain forest; water stress
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Barassé, V., Touchard, A., Téné, N., Tindo, M., Kenne, M., Klopp, C., et al. (2019). The peptide venom composition of the fierce stinging ant tetraponera aethiops (formicidae: Pseudomyrmecinae). Toxins, 11(12), 732.
Abstract: In the mutualisms involving certain pseudomyrmicine ants and different myrmecophytes (i.e., plants sheltering colonies of specialized “plant-ant” species in hollow structures), the ant venom contributes to the host plant biotic defenses by inducing the rapid paralysis of defoliating insects and causing intense pain to browsing mammals. Using integrated transcriptomic and proteomic approaches, we identified the venom peptidome of the plant-ant Tetraponera aethiops (Pseudomyrmecinae). The transcriptomic analysis of its venom glands revealed that 40% of the expressed contigs encoded only seven peptide precursors related to the ant venom peptides from the A-superfamily. Among the 12 peptide masses detected by liquid chromatography-mass spectrometry (LC-MS), nine mature peptide sequences were characterized and confirmed through proteomic analysis. These venom peptides, called pseudomyrmecitoxins (PSDTX), share amino acid sequence identities with myrmeciitoxins known for their dual offensive and defensive functions on both insects and mammals. Furthermore, we demonstrated through reduction/alkylation of the crude venom that four PSDTXs were homo- and heterodimeric. Thus, we provide the first insights into the defensive venom composition of the ant genus Tetraponera indicative of a streamlined peptidome.
Keywords: Defensive venom; Dimeric peptides; Peptidome; Tetraponera aethiops
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Bodin, S. C., Scheel-Ybert, R., Beauchene, J., Molino, J. - F., & Bremond, L. (2019). CharKey: An electronic identification key for wood charcoals of French Guiana. Iawa J., 40(1), 75–91.
Abstract: Tropical tree floras are highly diverse and many genera and species share similar anatomical patterns, making the identification of tropical wood charcoal very difficult. Appropriate tools to characterize charcoal anatomy are thus needed to facilitate and improve identification in such species-rich areas. This paper presents the first computer-aided identification key designed for charcoals from French Guiana, based on the wood anatomy of 507 species belonging to 274 genera and 71 families, which covers respectively 28%, 67% and 86% of the tree species, genera and families currently listed in this part of Amazonia. Species of the same genus are recorded together except those described under a synonym genus in Détienne et al. (1982) that were kept separately. As a result, the key contains 289 'items' and mostly aims to identify charcoals at the genus level. It records 26 anatomical features leading to 112 feature states, almost all of which are illustrated by SEM photographs of charcoal. The descriptions were mostly taken from Détienne et al.'s guidebook on tropical woods of French Guiana (1982) and follow the IAWA list of microscopic features for hardwood identification (Wheeler et al. 1989). Some adjustments were made to a few features and those that are unrelated to charcoal identification were excluded. The whole tool, named CharKey, contains the key itself and the associated database including photographs. It can be downloaded on Figshare at https://figshare.com/s/d7d40060b53d2ad60389 (doi: 10.6084/m9.figshare.6396005). CharKey is accessible using the free software Xper 2 , specifically conceived for taxonomic description and computer aided-identification.
Keywords: anthracology; Charcoal anatomy; computeraided identification; Note: Supplementary material can be accessed in the online edition of this journal via brill.com/iawa.; tropical flora; Xper 2
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Bréchet, L., Courtois, E. A., Saint-Germain, T., Janssens, I. A., Asensio, D., Ramirez-Rojas, I., et al. (2019). Disentangling Drought and Nutrient Effects on Soil Carbon Dioxide and Methane Fluxes in a Tropical Forest. Front. Environ. Sci., 7(180).
Abstract: Tropical soils are a major contributor to the balance of greenhouse gas (GHG) fluxes in the atmosphere. Models of tropical GHG fluxes predict that both the frequency of drought events and changes in atmospheric deposition of nitrogen (N) will significantly affect dynamics of soil carbon dioxide (CO2) and methane (CH4) production and consumption. In this study, we examined the combined effect of a reduction in precipitation and an increase in nutrient availability on soil CO2 and CH4 fluxes in a primary French Guiana tropical forest. Drought conditions were simulated by intercepting precipitation falling through the forest canopy with tarpaulin roofs. Nutrient availability was manipulated through application of granular N and/or phosphorus (P) fertilizer to the soil. Soil water content (SWC) below the roofs decreased rapidly and stayed at continuously low values until roof removal, which as a consequence roughly doubled the duration of the dry season. After roof removal, SWC slowly increased but remained lower than in the control soils even after 2.5 months of wet-season precipitation. We showed that drought-imposed reduction in SWC decreased the CO2 emissions (i.e., CO2 efflux), but strongly increased the CH4 emissions. N, P, and N × P (i.e., NP) additions all significantly increased CO2 emission but had no effect on CH4 fluxes. In treatments where both fertilization and drought were applied, the positive effect of N, P, and NP fertilization on CO2 efflux was reduced. After roof removal, soil CO2 efflux was more resilient in the control plots than in the fertilized plots while there was only a modest effect of roof removal on soil CH4 fluxes. Our results suggest that a combined increase in drought and nutrient availability in soil can locally increase the emissions of both CO2 and CH4 from tropical soils, for a long term.
Keywords: carbon dioxide; drought; fertilization; methane; nitrogen; phosphorus; soil GHG fluxes; tropical forest
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Cantera, I., Cilleros, K., Valentini, A., Cerdan, A., Dejean, T., Iribar, A., et al. (2019). Optimizing environmental DNA sampling effort for fish inventories in tropical streams and rivers. Sci. Rep., 9, 3085.
Abstract: Environmental DNA (eDNA) metabarcoding is a promising tool to estimate aquatic biodiversity. It is based on the capture of DNA from a water sample. The sampled water volume, a crucial aspect for efficient species detection, has been empirically variable (ranging from few centiliters to tens of liters). This results in a high variability of sampling effort across studies, making comparisons difficult and raising uncertainties about the completeness of eDNA inventories. Our aim was to determine the sampling effort (filtered water volume) needed to get optimal inventories of fish assemblages in species-rich tropical streams and rivers using eDNA. Ten DNA replicates were collected in six Guianese sites (3 streams and 3 rivers), resulting in sampling efforts ranging from 17 to 340 liters of water. We show that sampling 34 liters of water detected more than 64% of the expected fish fauna and permitted to distinguish the fauna between sites and between ecosystem types (stream versus rivers). Above 68 liters, the number of detected species per site increased slightly, with a detection rate higher than 71%. Increasing sampling effort up to 340 liters provided little additional information, testifying that filtering 34 to 68 liters is sufficient to inventory most of the fauna in highly diverse tropical aquatic ecosystems. © 2019, The Author(s).
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Caron, H., Molino, J. - F., Sabatier, D., Léger, P., Chaumeil, P., Scotti-Saintagne, C., et al. (2019). Chloroplast DNA variation in a hyperdiverse tropical tree community. Ecology and Evolution, 9(8), 4897–4905.
Abstract: We investigate chloroplast DNA variation in a hyperdiverse community of tropical rainforest trees in French Guiana, focusing on patterns of intraspecific and interspecific variation. We test whether a species genetic diversity is higher when it has congeners in the community with which it can exchange genes and if shared haplotypes are more frequent in genetically diverse species, as expected in the presence of introgression. We sampled a total of 1,681 individual trees from 472 species corresponding to 198 genera and sequenced them at a noncoding chloroplast DNA fragment. Polymorphism was more frequent in species that have congeneric species in the study site than in those without congeners (30% vs. 12%). Moreover, more chloroplast haplotypes were shared with congeners in polymorphic species than in monomorphic ones (44% vs. 28%). Despite large heterogeneities caused by genus-specific behaviors in patterns of hybridization, these results suggest that the higher polymorphism in the presence of congeners is caused by local introgression rather than by incomplete lineage sorting. Our findings suggest that introgression has the potential to drive intraspecific genetic diversity in species-rich tropical forests.
Keywords: chloroplast DNA; DNA barcoding; genetic diversity; hybridization; incomplete lineage sorting; introgression; species diversity; tropical trees
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Céréghino, R., Corbara, B., Hénaut, Y., Bonhomme, C., Compin, A., & Dejean, A. (2019). Ant and spider species as surrogates for functional community composition of epiphyte-associated invertebrates in a tropical moist forest. Ecological Indicators, 96, 694–700.
Abstract: Epiphytes represent up to 50% of all plant species in rainforests, where they host a substantial amount of invertebrate biomass. Efficient surrogates for epiphyte invertebrate communities could reduce the cost of biomonitoring surveys while preventing destructive sampling of the plants. Here, we focus on the invertebrate communities associated to tank bromeliads. We ask whether the presence of particular ant and/or spider taxa (easily surveyed taxa) that use these plants as nesting and/or foraging habitats predicts functional trait combinations of aquatic invertebrate communities hosted by the plants. Functional community composition of invertebrates was predicted both by bromeliad habitat features and the presence of certain ant and spider species. The ant Azteca serica preferred wider bromeliad rosettes that trap large amount of detritus, indicating interstitial-like food webs dominated by deposit feeders that burrow in fine particulate organic matter. Leucauge sp. spiders preferred narrower bromeliad rosettes bearing smaller detrital loads, thereby indicating a dominance of pelagic filter-feeding and predatory invertebrates in the water-filled leaf axils. Both Neoponera villosa ants and Eriophora sp. spiders preferred rosettes at intermediate size bearing moderate amounts of detritus, indicating a benthic food web dominated by leaf shredders and gathering collectors. Owing to the animal diversity and biomass supported by rainforest epiphytes, our approach would deserve to be further tested on a range of epiphytes involved in tight interactions with invertebrates. In this context, surrogate species could serve both as indicators of functional diversity, and as early-warning indicators of network disassembly.
Keywords: Functional traits; Indicator species; Phytotelmata; Rainforests; Surrogacy; Tank bromeliads
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Chaves, C. L., Blanc-Jolivet, C., Sebbenn, A. M., Mader, M., Meyer-Sand, B. R. V., Paredes-Villanueva, K., et al. (2019). Nuclear and chloroplastic SNP markers for genetic studies of timber origin for Hymenaea trees. Conserv. Gen. Res., 11(3), 329–331.
Abstract: We developed nuclear and chloroplastic single nucleotide polymorphism (SNP) and INDEL (insertion/deletion) markers using restriction associated DNA sequencing (RADSeq) and low coverage MiSeq genome sequencing to set up a genetic tracking method of the geographical origin of Hymenaea sp. From two initial sets of 358 and 32 loci used to genotype at least 94 individuals, a final set of 75 nSNPs, 50 cpSNPs and 6 INDELs identifying significant population structure was developed. © 2018, Springer Nature B.V.
Keywords: DNA fingerprints; Geographical origin; MiSeq; RADSeq
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Ciminera, M., Auger-Rozenberg, M. - A., Caron, H., Herrera, M., Scotti-Saintagne, C., Scotti, I., et al. (2019). Genetic Variation and Differentiation of Hylesia metabus (Lepidoptera: Saturniidae): Moths of Public Health Importance in French Guiana and in Venezuela. J. Med. Entomol., 56(1), 137–148.
Abstract: Hylesia moths impact human health in South America, inducing epidemic outbreaks of lepidopterism, a puriginous dermatitis caused by the urticating properties of females' abdominal setae. The classification of the Hylesia genus is complex, owing to its high diversity in Amazonia, high intraspecific morphological variance, and lack of interspecific diagnostic traits which may hide cryptic species. Outbreaks of Hylesia metabus have been considered responsible for the intense outbreaks of lepidopterism in Venezuela and French Guiana since the C20, however, little is known about genetic variability throughout the species range, which is instrumental for establishing control strategies on H. metabus. Seven microsatellites and mitochondrial gene markers were analyzed from Hylesia moths collected from two major lepidopterism outbreak South American regions. The mitochondrial gene sequences contained significant genetic variation, revealing a single, widespread, polymorphic species with distinct clusters, possibly corresponding to populations evolving in isolation. The microsatellite markers validated the mitochondrial results, and suggest the presence of three populations: one in Venezuela, and two in French Guiana. All moths sampled during outbreak events in French Guiana were assigned to a single coastal population. The causes and implications of this finding require further research.
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Clair, B., Ghislain, B., Prunier, J., Lehnebach, R., Beauchene, J., & Alméras, T. (2019). Mechanical contribution of secondary phloem to postural control in trees: the bark side of the force. New Phytol, 221(1), 209–217.
Abstract: Summary To grow straight, plants need a motor system that controls posture by generating forces to offset gravity. This motor function in trees was long thought to be only controlled by internal forces induced in wood. Here we provide evidence that bark is involved in the generation of mechanical stresses in several tree species. Saplings of nine tropical species were grown tilted and staked in a shadehouse and the change in curvature of the stem was measured after releasing from the pole and after removing the bark. This first experiment evidenced the contribution of bark in the up-righting movement of tree stems. Combined mechanical measurements of released strains on adult trees and microstructural observations in both transverse and longitudinal/tangential plane enabled us to identify the mechanism responsible for the development of asymmetric mechanical stress in the bark of stems of these species. This mechanism does not result from cell wall maturation like in wood, or from the direct action of turgor pressure like in unlignified organs, but is the consequence of the interaction between wood radial pressure and a smartly organized trellis structure in the inner bark.
Keywords: bark; Malvaceae; maturation stress; secondary phloem; tree biomechanics
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