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Svensk, M., Coste, S., Gérard, B., Gril, E., Julien, F., Maillard, P., et al. (2020). Drought effects on resource partition and conservation among leaf ontogenetic stages in epiphytic tank bromeliads. Physiol. Plant., 170(4), 488–507.
Abstract: Studying the response to drought stress of keystone epiphytes such as tank bromeliads is essential to better understand their resistance capacity to future climate change. The objective was to test whether there is any variation in the carbon, water and nutrient status among different leaf ontogenetic stages in a bromeliad rosette subjected to a gradient of drought stress. We used a semi-controlled experiment consisting in a gradient of water shortage in Aechmea aquilega and Lutheria splendens. For each bromeliad and drought treatment, three leaves were collected based on their position in the rosette and several functional traits related to water and nutrient status, and carbon metabolism were measured. We found that water status traits (relative water content, leaf succulence, osmotic and midday water potentials) and carbon metabolism traits (carbon assimilation, maximum quantum yield of photosystem II, chlorophyll and starch contents) decreased with increasing drought stress, while leaf soluble sugars and carbon, nitrogen and phosphorus contents remained unchanged. The different leaf ontogenetic stages showed only marginal variations when subjected to a gradient of drought. Resources were not reallocated between different leaf ontogenetic stages but we found a reallocation of soluble sugars from leaf starch reserves to the root system. Both species were capable of metabolic and physiological adjustments in response to drought. Overall, this study advances our understanding of the resistance of bromeliads faced with increasing drought stress and paves the way for in-depth reflection on their strategies to cope with water shortage. © 2020 Scandinavian Plant Physiology Society
Keywords: chlorophyll; nitrogen; water; Bromeliaceae; drought; metabolism; photosynthesis; plant leaf; Bromeliaceae; Chlorophyll; Droughts; Nitrogen; Photosynthesis; Plant Leaves; Water
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Rodrigues, A. M., Amusant, N., Beauchene, J., Eparvier, V., Lemenager, N., Baudasse, C., et al. (2011). The termiticidal activity of Sextonia rubra (Mez) van der Werff (Lauraceae) extract and its active constituent rubrynolide. Pest Manage. Sci., 67(11), 1420–1423.
Abstract: Termites are degradation agents that inflict severe damage on wood. Some long-lasting Amazonian trees can resist these insects by producing toxic secondary metabolites. These metabolites could potentially replace synthetic termiticidal products which are becoming more restricted to use. Results: Sextonia rubra is resistant to termite-induced degradation. It has been demonstrated that this species naturally produces an ethyl-acetate-soluble termiticidal metabolite, rubrynolide, to protect its wood. Assays in the presence of tropical and invasive termites established that both rubrynolide and crude ethyl acetate extract from S. rubra wood can be used as a treatment for the protection of sensitive woods against termites. Conclusion: Rubrynolide and S. rubra extract are promising candidates for the replacement of synthetic termiticides. © 2011 Society of Chemical Industry.
Keywords: Nasutitermes macrocephalus; Reticulitermes flavipes; Rubrynolide; Sextonia rubra extract; Wood preservation
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Fortunel, C., Violle, C., Rourmet, C., Buatois, B., Navas, M. L., & Garnier, E. (2009). Allocation strategies and seed traits are hardly affected by nitrogen supply in 18 species differing in successional status. Perspect. Plant Ecol. Evol. Syst., 11(4), 267–283.
Abstract: Species performance depends on ecological strategies, revealed by suites of traits, conferring different relative ecological advantages in different environments. Although current knowledge on plant strategies along successional gradients is derived from studies conducted in situ, actually quantifying these strategies requires disentangling the effects of environmental factors from intrinsic differences between species. Here we tested whether allocation strategies and seed traits differ among successional stages and nitrogen levels. To this aim, we assessed biomass and nitrogen allocations and seed traits variations for 18 species, differing in life history and belonging to three stages of a Mediterranean old-field succession. These species were grown as monocultures in an experimental garden under limiting and non-limiting nitrogen supply. Early successional species allocated allometrically more nitrogen and proportionally more biomass to reproduction, and set more seeds than later successional species. Seed mass increased with successional status and was negatively related to seed number. Early successional species thus produced more but less-provisioned seeds, suggesting better colonization abilities. These patterns were not the sole consequence of the replacement of annuals by perennials along the successional gradient, since comparable trends were also observed within each life history. Allocation patterns were generally not altered by nitrogen supply and the higher nitrogen content in vegetative organs of plants grown under high nitrogen supply was not retranslocated from leaves to seeds during seed development. We therefore conclude that differences in plant ecological strategies in species characteristics from contrasting successional stages appear to be intrinsic properties of the studied species, and independent from environmental conditions. (c) 2009 Rubel Foundation, ETH Zurich. Published by Elsevier GmbH. All rights reserved.
Keywords: Allometry; Reproductive output; Seed mass; Nitrogen concentration of organs; Succession; Nitrogen supply
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Herault, B. (2007). Reconciling niche and neutrality through the Emergent Group approach. Perspect. Plant Ecol. Evol. Syst., 9(2), 71–78.
Abstract: Both niche and neutral theories have been suggested as potential frameworks for modelling biodiversity. Niche models assume that biological traits represent evolutionary adaptations and define individuals in terms of functional trade-offs. Neutral models assume that all individuals at a single trophic level are functionally equivalent on a per capita basis with respect to their birth, death, dispersal and speciation. The opinion of many researchers is that neutral and niche processes operate simultaneously to generate diversity without knowing how the unification of both models can be achieved. Recently, several theoretical papers have reported evidence on the evolutionary emergence of niche structures shaping the emergence of groups of similar species. In this way, an Emergent Group is defined as a set of species that have a similar functional niche owing to a convergent ecological strategy. Central to the Emergent Group concept are the assumptions of functional equivalence within and of functional divergence between Emergent Groups. Within an Emergent Group, species richness is subject to a zero-sum rule set by the balance between the rate of individual loss and of immigration. Between Emergent Groups, tradeoffs such as seed size/seedling competitivity, investment in reproductive system/investment in vegetative systems or competitive ability/predator invulnerability are cornerstones of the evolutionary divergence. Delineating Emergent Groups amounts to reaching a compromise between maximizing niche differentiation (i.e. maximizing differences in functional tradeoffs) between Emergent Groups and maximizing neutrality within Emergent Groups. Up to now, the Emergent Group concept has been mostly proposed by theoretical scientists but it should be tested by empirical ecologists. The way in which niche and neutral models could be combined provides a profitable opportunity for theoretical and empirical scientists to collaborate fruitfully. (c) 2007 Rubel Foundation, ETH Zurich. Published by Elsevier GmbH. All rights reserved.
Keywords: Biodiversity; ecological equivalency; biological traits; neutral theory; niche differentiation; redundancy
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Rifflet, A., Gavalda, S., Téné, N., Orivel, J., Leprince, J., Guilhaudis, L., et al. (2012). Identification and characterization of a novel antimicrobial peptide from the venom of the ant Tetramorium bicarinatum. Peptides, 38(2), 363–370.
Abstract: A novel antimicrobial peptide, named Bicarinalin, has been isolated from the venom of the ant Tetramorium bicarinatum. Its amino acid sequence has been determined by de novo sequencing using mass spectrometry and by Edman degradation. Bicarinalin contained 20 amino acid residues and was C-terminally amidated as the majority of antimicrobial peptides isolated to date from insect venoms. Interestingly, this peptide had a linear structure and exhibited no meaningful similarity with any known peptides. Antibacterial activities against Staphylococcus aureus and S. xylosus strains were evaluated using a synthetic replicate. Bicarinalin had a potent and broad antibacterial activity of the same magnitude as Melittin and other hymenopteran antimicrobial peptides such as Pilosulin or Defensin. Moreover, this antimicrobial peptide has a weak hemolytic activity compared to Melittin on erythrocytes, suggesting potential for development into an anti-infective agent for use against emerging antibiotic-resistant pathogens. © 2012 Elsevier Inc.
Keywords: Amp; Ant venom; Antibacterial peptide; Bicarinalin; Esi-Ms/Ms; Staphylococcus; Tetramorium bicarinatum
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Shepard, W. D., Clavier, S., & Cerdan, A. (2020). A generic key to the known larval elmidae (Insecta: Coleoptera) of French Guiana. Pap. Avulsos Zool., 60(Special), e202060.
Abstract: An identification key is provided for 21 larval types of Elmidae (riffle beetles) known to occur in French Guiana. Not all elmid genera known to occur in French Guiana are known in the larval stage. Nor are all the known larval types assigned to known elmid genera. © 2020, Universidade de Sao Paulo. All rights reserved.
Keywords: Biodiversity; Identification; Immatures; Neotropical; Survey
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Paine, C. E. T., Baraloto, C., Chave, J., & Herault, B. (2011). Functional traits of individual trees reveal ecological constraints on community assembly in tropical rain forests. Oikos, 120(5), 720–727.
Abstract: Niche differentiation and ecological filtering are primary ecological processes that shape community assembly, but their relative importance remains poorly understood. Analyses of the distributions of functional traits can provide insight into the community structure generated by these processes. We predicted the trait distributions expected under the ecological processes of niche differentiation and environmental filtering, then tested these predictions with a dataset of 4672 trees located in nine 1-ha plots of tropical rain forest in French Guiana. Five traits related to leaf function (foliar N concentration, chlorophyll content, toughness, tissue density and specific leaf area), and three traits related to stem function (trunk sapwood density, branch sapwood density, and trunk bark thickness), as well as laminar surface area, were measured on every individual tree. There was far more evidence for environmental filtering than for niche differentiation in these forests. Furthermore, we contrasted results from species-mean and individual-level trait values. Analyses that took within-species trait variation into account were far more sensitive indicators of niche differentiation and ecological filtering. Species-mean analyses, by contrast, may underestimate the effects of ecological processes on community assembly. Environmental filtering appeared somewhat more intense on leaf traits than on stem traits, whereas niche differentiation affected neither strongly. By accounting for within-species trait variation, we were able to more properly consider the ecological interactions among individual trees and between individual trees and their environment. In so doing, our results suggest that the ecological processes of niche differentiation and environmental filtering may be more pervasive than previously believed.
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Marcon, E., Herault, B., Baraloto, C., & Lang, G. (2012). The decomposition of Shannon's entropy and a confidence interval for beta diversity. Oikos, 121(4), 516–522.
Abstract: Beta diversity is among the most employed theoretical concepts in ecology and biodiversity conservation. Up to date, a self-contained definition of it, with no reference to alpha and gamma diversity, has never been proposed. Using Kullback-Leibler divergence, we present the explicit formula of Shannon's β entropy, a bias correction for its estimator and a confidence interval. We also provide the mathematical framework to decompose Shannon diversity into several hierarchical nested levels. From botanical inventories of tropical forest plots in French Guiana, we estimate Shannon diversity at the plot, forest and regional level. We believe this is a complete and usefulness toolbox for ecologists interested in partitioning biodiversity. © 2011 The Authors. Oikos © 2012 Nordic Society Oikos.
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Schmitt, S., Hérault, B., Ducouret, É., Baranger, A., Tysklind, N., Heuertz, M., et al. (2020). Topography consistently drives intra- and inter-specific leaf trait variation within tree species complexes in a Neotropical forest. Oikos, 129(10), 1521–1530.
Abstract: Tropical forests shelter the highest species diversity worldwide, although genus diversity is lower than expected. In the species-rich genera, species complexes are composed of closely-related species that share large amounts of genetic variation. Despite the key role of species complexes in diversification, evolution and functioning of ecological communities, little is known on why species complexes arise and how they are maintained in Neotropical forests. Examining how individual phenotypes vary along environmental gradients, within and among closely-related species within species complexes, can reveal processes allowing species coexistence within species complexes. We examined leaf functional trait variation with topography in a hyperdiverse tropical forest of the Guiana Shield. We collected leaf functional traits from 766 trees belonging to five species in two species complexes in permanent plots encompassing a diversity of topographic positions. We tested the role of topography on leaf functional trait variation with a hierarchical Bayesian model, controlling for individual tree diameter effect. We show that, mirroring what has been previously observed among species and communities, individual leaf traits covary from acquisitive to conservative strategy within species. Moreover, decreasing wetness from bottomlands to plateaus was associated with a shift of leaf traits from an acquisitive to a conservative strategy both across and within closely-related species. Our results suggest that intraspecific trait variability widens species’ niches and converges at species’ margins where niches overlap, potentially implying local neutral processes. Intraspecific trait variability favors local adaptation and divergence of closely-related species within species complexes. It is potentially maintained through interspecific sharing of genetic variation through hybridization. © 2020 Nordic Society Oikos. Published by John Wiley & Sons Ltd
Keywords: intraspecific variability; leaf traits; Paracou; species complex; syngameon; tropical forests; Bayesian analysis; coexistence; divergence; genetic variation; hierarchical system; leaf area; local adaptation; niche overlap; species diversity; topography; tropical forest; Guyana Shield
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Vleminckx, J., Fortunel, C., Valverde-Barrantes, O., Paine, C. E. T., Engel, J., Petronelli, P., et al. (2021). Resolving whole-plant economics from leaf, stem and root traits of 1467 Amazonian tree species. Oikos, 130(7), 1193–1208.
Abstract: It remains unclear how evolutionary and ecological processes have shaped the wide variety of plant life strategies, especially in highly diverse ecosystems like tropical forests. Some evidence suggests that species have diversified across a gradient of ecological strategies, with different plant tissues converging to optimize resource use across environmental gradients. Alternative hypotheses propose that species have diversified following independent selection on different tissues, resulting in a decoupling of trait syndromes across organs. To shed light on the subject, we assembled an unprecedented dataset combining 19 leaf, stem and root traits for 1467 tropical tree species inventoried across 71 0.1-ha plots spanning broad environmental gradients in French Guiana. Nearly 50% of the overall functional heterogeneity was expressed along four orthogonal dimensions, after accounting for phylogenetic dependences among species. The first dimension related to fine root functioning, while the second and third dimensions depicted two decoupled leaf economics spectra, and the fourth dimension encompassed a wood economics spectrum. Traits involved in orthogonal functional strategies, five leaf traits in particular but also trunk bark thickness, were consistently associated with a same gradient of soil texture and nutrient availability. Root traits did not show any significant association with edaphic variation, possibly because of the prevailing influence of other factors (mycorrhizal symbiosis, phylogenetic constraints). Our study emphasises the existence of multiple functional dimensions that allow tropical tree species to optimize their performance in a given environment, bringing new insights into the debate around the presence of a whole plant economic spectrum in tropical forest tree communities. It also emphasizes the key role that soil heterogeneity plays in shaping tree species assembly. The extent to which different organs are decoupled and respond to environmental gradients may also help to improve our predictions of species distribution changes in responses to habitat modification and environmental changes.
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