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Agrawal, A. A., Boroczky, K., Haribal, M., Hastings, A. P., White, R., A., Jiang, R. - W., et al. (2021). Cardenolides, toxicity, and the costs of sequestration in the coevolutionary interaction between monarchs and milkweeds. PNAS, 118(16), e2024463118.
Abstract: For highly specialized insect herbivores, plant chemical defenses are often co-opted as cues for oviposition and sequestration. In such interactions, can plants evolve novel defenses, pushing herbivores to trade off benefits of specialization with costs of coping with toxins? We tested how variation in milkweed toxins (cardenolides) impacted monarch butterfly ( Danaus plexippus ) growth, sequestration, and oviposition when consuming tropical milkweed ( Asclepias curassavica ), one of two critical host plants worldwide. The most abundant leaf toxin, highly apolar and thiazolidine ring–containing voruscharin, accounted for 40% of leaf cardenolides, negatively predicted caterpillar growth, and was not sequestered. Using whole plants and purified voruscharin, we show that monarch caterpillars convert voruscharin to calotropin and calactin in vivo, imposing a burden on growth. As shown by in vitro experiments, this conversion is facilitated by temperature and alkaline pH. We next employed toxin-target site experiments with isolated cardenolides and the monarch’s neural Na + /K + -ATPase, revealing that voruscharin is highly inhibitory compared with several standards and sequestered cardenolides. The monarch’s typical >50-fold enhanced resistance to cardenolides compared with sensitive animals was absent for voruscharin, suggesting highly specific plant defense. Finally, oviposition was greatest on intermediate cardenolide plants, supporting the notion of a trade-off between benefits and costs of sequestration for this highly specialized herbivore. There is apparently ample opportunity for continued coevolution between monarchs and milkweeds, although the diffuse nature of the interaction, due to migration and interaction with multiple milkweeds, may limit the ability of monarchs to counteradapt.
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Chanson, A., Moreau, C. S., & Duplais, C. (2021). Assessing Biosynthetic Gene Cluster Diversity of Specialized Metabolites in the Conserved Gut Symbionts of Herbivorous Turtle Ants. Frontiers in Microbiology, 12, 678100.
Abstract: Cephalotes are herbivorous ants (>115 species) feeding on low-nitrogen food sources, and they rely on gut symbionts to supplement their diet by recycling nitrogen food waste into amino acids. These conserved gut symbionts, which encompass five bacterial orders, have been studied previously for their primary nitrogen metabolism; however, little is known about their ability to biosynthesize specialized metabolites which can play a role in bacterial interactions between communities living in close proximity in the gut. To evaluate the biosynthetic potential of their gut symbionts, we mine 14 cultured isolate genomes and gut metagenomes across 17 Cephalotes species to explore the biodiversity of biosynthetic gene clusters (BGCs) producing specialized metabolites. The diversity of BGCs across Cephalotes phylogeny was analyzed using sequence similarity networking and BGC phylogenetic reconstruction. Our results reveal that the conserved gut symbionts involved in the nutritional symbiosis possess 80% of all the 233 BGCs retrieved in this work. Furthermore, the phylogenetic analysis of BGCs reveals different patterns of distribution, suggesting different mechanisms of conservation. A siderophore BGC shows high similarity in a single symbiont across different ant host species, whereas a BGC encoding the production of non-ribosomal peptides (NRPs) found different symbionts within a single host species. Additionally, BGCs were abundant in four of the five bacterial orders of conserved symbionts co-occurring in the hindgut. However, one major symbiont localized alone in the midgut lack BGCs. Because the spatial isolation prevents direct interaction with other symbionts, this result supports the idea that BGCs are maintained in bacteria living in close proximity but are dispensable for an alone-living symbiont. These findings together pave the way for studying the mechanisms of BGC conservation and evolution in gut bacterial genomes associated with Cephalotes. This work also provides a genetic background for further study, aiming to characterize bacterial specialized metabolites and to understand their functional role in multipartite mutualisms between conserved gut symbionts and Cephalotes turtle ants.
Keywords: insect-microbe mutualism, ants, metagemonic, biosynthetic gene cluster, gut bacteria, Cephalotes
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Heu, K., Romoli, O., Schonbeck, J. C., Ajenoe, R., Epelboin, Y., Kircher, V., et al. (2021). The Effect of Secondary Metabolites Produced by Serratia marcescens on Aedes aegypti and Its Microbiota. Frontiers in Microbiology, 12, 645701.
Abstract: Serratia marcescens is a bacterial species widely found in the environment, which very efficiently colonizes mosquitoes. In this study, we isolated a red-pigmented S. marcescens strain from our mosquito colony (called S. marcescens VA). This red pigmentation is caused by the production of prodigiosin, a molecule with antibacterial properties. To investigate the role of prodigiosin on mosquito- S. marcescens interactions, we produced two white mutants of S. marcescens VA by random mutagenesis. Whole genome sequencing and chemical analyses suggest that one mutant has a nonsense mutation in the gene encoding prodigiosin synthase, while the other one is deficient in the production of several types of secondary metabolites including prodigiosin and serratamolide. We used our mutants to investigate how S. marcescens secondary metabolites affect the mosquito and its microbiota. Our in vitro tests indicated that S. marcescens VA inhibits the growth of several mosquito microbiota isolates using a combination of prodigiosin and other secondary metabolites, corroborating published data. This strain requires secondary metabolites other than prodigiosin for its proteolytic and hemolytic activities. In the mosquito, we observed that S. marcescens VA is highly virulent to larvae in a prodigiosin-dependent manner, while its virulence on adults is lower and largely depends on other metabolites
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Picard, N., Mortier, F., Ploton, P., Liang, J., Derroire, G., Bastin, J. - F., et al. (2021). Using Model Analysis to Unveil Hidden Patterns in Tropical Forest structures. Frontiers in Ecology and Evolution, 9, 599200.
Abstract: When ordinating plots of tropical rain forests using stand-level structural attributes such as biomass, basal area and the number of trees in different size classes, two patterns often emerge: a gradient from poorly to highly stocked plots and high positive correlations between biomass, basal area and the number of large trees. These patterns are inherited from the demographics (growth, mortality and recruitment) and size allometry of trees and tend to obscure other patterns, such as site differences among plots, that would be more informative for inferring ecological processes. Using data from 133 rain forest plots at nine sites for which site differences are known, we aimed to filter out these patterns in forest structural attributes to unveil a hidden pattern. Using a null model framework, we generated the anticipated pattern inherited from individual allometric patterns. We then evaluated deviations between the data (observations) and predictions of the null model. Ordination of the deviations revealed site differences that were not evident in the ordination of observations. These sites differences could be related to different histories of large-scale forest disturbance. By filtering out patterns inherited from individuals, our model analysis provides more information on ecological processes
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Llusia, J., Asensio, D., Sardans, J., Filella, I., Peguero, G., Grau, O., et al. (2021). Contrasting nitrogen and phosphorus fertilization effects on soil terpene exchanges in a tropical forest. Science of the Total Environment, 802, 149769.
Abstract: Production, emission, and absorption of biogenic volatile organic compounds (BVOCs) in ecosystem soils and associated impacts of nutrient availability are unclear; thus, predictions of effects of global change on source-sink dynamic under increased atmospheric N deposition and nutrition imbalances are limited. Here, we report the dynamics of soil BVOCs under field conditions from two undisturbed tropical rainforests from French Guiana. We analyzed effects of experimental soil applications of nitrogen (N), phosphorus (P), and N + P on soil BVOC exchanges (in particular of total terpenes, monoterpenes, and sesquiterpenes), to determine source and sink dynamics between seasons (dry and wet) and elevations (upper and lower elevations corresponding to top of the hills (30 m high) and bottom of the valley). We identified 45 soil terpenoids compounds emitted to the atmosphere, comprising 26 monoterpenes and 19 sesquiterpenes; of these, it was possible to identify 13 and 7 compounds, respectively. Under ambient conditions, soils acted as sinks of these BVOCs, with greatest soil uptake recorded for sesquiterpenes at upper elevations during the wet season (-282 μg m-2 h-1). Fertilization shifted soils from a sink to source, with greatest levels of terpene emissions recorded at upper elevations during the wet season, following the addition of N (monoterpenes: 406 μg m-2 h-1) and P (sesquiterpenes: 210 μg m-2 h-1). Total soil terpene emission rates were negatively correlated with total atmospheric terpene concentrations. These results indicate likely shifts in tropical soils from sink to source of atmospheric terpenes under projected increases in N deposition under global change, with potential impacts on regional-scale atmospheric chemistry balance and ecosystem function.
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Hiltner, U., Huth, A., Hérault, B., Holtmann, A., Brauning, A., & Fischer, R. (2021). Climate change alters the ability of neotropical forests to provide timber and sequester carbon. Forest Ecology and Management, 492, 119166.
Abstract: Logging is widespread in tropical regions, with approximately 50% of all humid tropical forests (1.73 × 109 ha) regarded as production forests. To maintain the ecosystem functions of carbon sequestration and timber supply in tropical production forests over a long term, forest management must be sustainable under changing climate conditions. Individual-based forest models are useful tools to enhance our understanding about the long-term effects of harvest and climate change on forest dynamics because they link empirical field data with simulations of ecological processes. The objective of this study is to analyze the combined effects of selective logging and climate change on biomass stocks and timber harvest in a tropical forest in French Guiana. By applying a forest model, we simulated natural forest dynamics under the baseline scenario of current climate conditions and compared the results with scenarios of selective logging under climate change. The analyses revealed how substantially forest dynamics are altered
under different scenarios of climate change. (1) Repeated logging within recovery times decreased biomass and timber harvest, irrespective of the intensity of climate change. (2) With moderate climate change as envisaged by the 5th IPCC Assessment Report (representative concentration pathway 2.6), the average biomass remained the same as in the baseline scenario (−1%), but with intensive climate change (RCP 8.5), the average biomass decreased by 12%. (3) The combination of selective logging and climate change increased the likelihood of changes in forest dynamics, driven mainly by rising temperatures. Under RCP 8.5, the average timber harvest was almost halved, regardless of the logging cycle applied. An application-oriented use of forest models will help to identify opportunities to reduce the effects of unwanted ecosystem changes in a changing environment. To ensure that ecosystem functions in production forests are maintained under climate change conditions, appropriate management strategies will help to maintain biomass and harvest in production forests.
Keywords: Exploitation forestière ; Changement climatique ; séquestration du carbone ; Production du bois ; Atténuation des effets du changement climatique ; gestion forestière durable ; forêt tropicale ; Région néotropicale ; Biomasse ; biomasse aérienne des arbres ; gestion de la santé des forêts ; modèle de croissance forestière ; biodiversité forestière
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Nixon, S. A., Robinson, S. D., Agwa, A., J., Walker, A. A., Choudhay, S., Touchard, A., et al. (2021). Multipurpose peptides: The venoms of Amazonian stinging ants contain anthelmintic ponericins with diverse predatory and defensive activities. Biochemical Pharmacology, 192, 114693.
Abstract: In the face of increasing drug resistance, the development of new anthelmintics is critical for controlling nematodes that parasitise livestock. Although hymenopteran venom toxins have attracted attention for applications in agriculture and medicine, few studies have explored their potential as anthelmintics. Here we assessed hymenopteran venoms as a possible source of new anthelmintic compounds by screening a panel of ten hymenopteran venoms against Haemonchus contortus, a major pathogenic nematode of ruminants. Using bioassay-guided fractionation coupled with liquid chromatography-tandem mass spectrometry, we identified four novel anthelmintic peptides (ponericins) from the venom of the neotropical ant Neoponera commutata and the previously described ponericin M−PONTX−Na1b from Neoponera apicalis venom. These peptides inhibit H. contortus development with IC50 values of 2.8–5.6 μM. Circular dichroism spectropolarimetry indicated that the ponericins are unstructured in aqueous solution but adopt α-helical conformations in lipid mimetic environments. We show that the ponericins induce non-specific membrane perturbation, which confers broad-spectrum antimicrobial, insecticidal, cytotoxic, hemolytic, and algogenic activities, with activity across all assays typically correlated. We also show for the first time that ponericins induce spontaneous pain behaviour when injected in mice. We propose that the broad-spectrum activity of the ponericins enables them to play both a predatory and defensive role in neoponeran ants, consistent with their high abundance in venom. This study reveals a broader functionality for ponericins than previously assumed, and highlights both the opportunities and challenges in pursuing ant venom peptides as potential therapeutics.
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de Thoisy, B., Duron, O., Epelboin, L., Musset, L., Quénel, P., Roche, B., et al. (2021). Ecology, evolution, and epidemiology of zoonotic and vector-borne infectious diseases in French Guiana: Transdisciplinarity does matter to tackle new emerging threats. Infection, Génétics and Evolution, 93, 104916.
Abstract: French Guiana is a European ultraperipheric region located on the northern Atlantic coast of South America. It constitutes an important forested region for biological conservation in the Neotropics. Although very sparsely populated, with its inhabitants mainly concentrated on the Atlantic coastal strip and along the two main rivers, it is marked by the presence and development of old and new epidemic disease outbreaks, both research and health priorities. In this review paper, we synthetize 15 years of multidisciplinary and integrative research at the interface between wildlife, ecosystem modification, human activities and sociodemographic development, and human health. This study reveals a complex epidemiological landscape marked by important transitional changes, facilitated by increased interconnections between wildlife, land-use change and human occupation and activity, human and trade transportation, demography with substantial immigration, and identified vector and parasite pharmacological resistance. Among other French Guianese characteristics, we demonstrate herein the existence of more complex multi-host disease life cycles than previously described for several disease systems in Central and South America, which clearly indicates that today the greater promiscuity between wildlife and humans due to demographic and economic pressures may offer novel settings for microbes and their hosts to circulate and spread. French Guiana is a microcosm that crystallizes all the current global environmental, demographic and socioeconomic change conditions, which may favor the development of ancient and future infectious diseases.
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Maggia, M. - E., Decaëns, T., Lapied, E., Dupont, L., Roy, V., Schimann, H., et al. (2021). At each site its diversity: DNA barcoding reveals remarkable earthworm diversity in neotropical rainforests of French Guiana. Applied Soil Ecology, 164, 103932.
Abstract: Despite their recognized essential role in soil, earthworms in tropical environments are still understudied. The aim of this study was to re-evaluate the diversity at the regional scale, as well as to investigate the environmental and spatial drivers of earthworm communities. We sampled earthworm communities across a range of habitats at six localities in French Guiana using three different sampling methods. We generated 1675 DNA barcodes and combined them with data from a previous study. Together, all sequences clustered into 119 MOTUs which were used as proxy to assess species richness. Only two MOTUs were common between the six localities and 20.2% were singletons, showing very high regional species richness and a high number of rare species. A canonical redundancy analysis was used to identify key drivers of the earthworm community composition. The RDA results and beta-diversity calculations both show strong species turnover and a strong spatial effect, resulting from dispersal limitations that are responsible for the current community composition. Sampling in different microhabitats allowed the discovery of 23 MOTUs that are exclusively found in decaying trunks and epiphytes, highlighting hidden diversity of earthworms outside of soil.
Keywords: DNA barcoding Tropical rainforest Community ecology Diversity level Sampling methods
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Diatta, B. D., Niass, O., Diouf, M., Guéye, M., Houel, E., & Boetsch, G. (2021). Diversité et composition phytochimique des bâtonnets frotte-dents (cure-dents) proposés chez les Peul de la commune de Tessékéré (Ferlo Nord, Sénégal). Journal of Applied Biosciences, 158, 16267–16281.
Abstract: Objectifs : Le but de cette étude était de déterminer la composition phytochimique et la teneur en grandes classes chimiques des tiges les plus utilisées comme bâtonnets frotte-dents chez les peul de Widou Thiengoli au Nord Ferlo (Sénégal). Méthodes et résultats : Des entretiens ouverts semi structurés ont permis de recueillir les plantes les plus utilisées. L’indice de fidélité renseigne sur la convergence des usages quant à l’emploi des plantes comme bâtonnets frotte-dent comparé aux autres pratiques cosmétiques. L’étude de la composition phytochimique des tiges a ciblé 8 classes chimiques. Les tanins et les saponines sont très fréquents ; les terpénoïdes et les leuco-anthocyanines presque inexistants. Un dosage des flavonoïdes, alcaloïdes et polyphénols, réalisé chez des extraits aqueux, a porté sur 12 plantes. Les meilleures teneurs en polyphénols et alcaloïdes sont recueillies chez Anogeissus leiocarpa, et la meilleure en flavonoïdes chez Commiphora africana. Conclusion et applicabilité des résultats : Ces résultats permettent de sélectionner à travers la composition phytochimique des plantes, les espèces présentant de potentielles activités antimicrobiennes, car renfermant des composés phytochimique doués de fonctions germicides, au- delà de la fonction mécanique connue des bâtonnets dans l’élimination de la plaque dentaire.
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