Dejean, A., Petitclerc, F., Azémar, F., Pélozuelo, L., Talaga, S., Leponce, M., et al. (2018). Aquatic life in Neotropical rainforest canopies: Techniques using artificial phytotelmata to study the invertebrate communities inhabiting therein. Comptes Rendus – Biologies, 341(1), 20–27.
Abstract: In Neotropical rainforest canopies, phytotelmata (“plant-held waters”) shelter diverse aquatic macroinvertebrate communities, including vectors of animal diseases. Studying these communities is difficult because phytotelmata are widely dispersed, hard to find from the ground and often inaccessible. We propose here a method for placing in tree crowns “artificial phytotelmata” whose size and shape can be tailored to different research targets. The efficacy of this method was shown while comparing the patterns of community diversity of three forest formations. We noted a difference between a riparian forest and a rainforest, whereas trees alongside a dirt road cutting through that rainforest corresponded to a subset of the latter. Because rarefied species richness was significantly lower when the phytotelmata were left for three weeks rather than for six or nine weeks, we recommend leaving the phytotelmata for twelve weeks to permit predators and phoretic species to fully establish themselves.
Keywords: Artificial phytotelmata; Epiphytes; French Guiana; Invertebrate diversity; Neotropical rainforests
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Le Lann, C., Roux, O., Serain, N., Van Alphen, J. J. M., Vernon, P., & Van Baaren, J. (2011). Thermal tolerance of sympatric hymenopteran parasitoid species: does it match seasonal activity? Physiol. Entomol., 36(1), 21–28.
Abstract: Climatic changes result in an increased in mean temperature and in a higher incidence of extreme weather events such as heat and cold waves. For ectotherms, such as insect parasitoids, the ability to remain active under extreme climatic conditions is a significant key to fitness. The body size of individuals, and in particular their surface to volume ratio, may play a role in their resistance to thermal conditions. The thermal tolerances are investigated of two closely-related sympatric parasitoid species [Aphidius avenae Haliday and Aphidius rhopalosiphi De Stefani-Perez (Hymenoptera: Aphidiinae)] that have a similar ecology but differ in body size and phenologies. The critical thermal limits of individuals are assessed in both sexes of each parasitoid species and the influence of surface volume ratios on their thermal tolerances. Aphidius avenae is less resistant to low temperatures and more resistant to high temperatures than A. rhopalosiphi. The lower surface to volume ratio of A. avenae individuals may help them to remain active in summer when experiencing heat waves. However, body size is not the sole factor that plays a role in differences of thermal tolerance between species and body size may not be an adaptation to extreme temperatures but rather a by-product of developmental regulation. Closely-related sympatric species from the same ecological guild can have different thermal tolerances that may allow them to occur within the same habitat. The present study also highlights the importance of clearly defining how to measure critical thermal limits to determine the thermal tolerance of a species.
Keywords: Climate change; critical thermal limits; CTmax; CTmin; dry mass; guild; hind tibia length; seasonal activities; surface to volume ratio
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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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Maia, A. C. D., Gibernau, M., Carvalho, A. T., Gonçalves, E. G., & Schlindwein, C. (2013). The cowl does not make the monk: Scarab beetle pollination of the Neotropical aroid Taccarum ulei (Araceae: Spathicarpeae). Biological Journal of the Linnean Society, 108(1), 22–34.
Abstract: Taccarum ulei (Araceae, Spathicarpeae) is a seasonal geophytic aroid, native to north-eastern Brazil, that flowers during two months of the rainy season. Patterns of floral thermogenesis, pollination biology, and floral traits associated with pollination syndromes were studied and compared with those of other Araceae. Two species of cyclocephaline scarabs (Scarabaeidae, Cyclocephalini) were recognized as effective pollinators: Cyclocephala celata and Cyclocephala cearae. Larvae of an unidentified species of fruit fly (Melanolomaspp., Richardiidae, Diptera) were also frequently observed in inflorescences at various maturation stages, feeding on the connectives of male florets and fruits, and thus lowering the reproductive success of individual plants. Beetles were attracted by odoriferous inflorescences in the early evening of the first day of anthesis, during the female phase. The emission of attractive volatiles was coupled with intense thermogenic activity in the entire spadix, unlike other aroids in which only certain zones of the spadix heat up. Pollen release, which marks the beginning of the male phase on the subsequent evening, was not related to floral thermogenesis. Comparative multivariate analysis of the floral traits of T.ulei points to a beetle-pollinated aroid, although some of the observed traits of the species are not common to other taxa sharing this pollination strategy. Such incongruence might be explained by the evolutionary history of the tribe Spathicarpeae and potential pollinator shifts. © 2012 The Linnean Society of London.
Keywords: Flower predation; Nocturnal pollinators; Pollination syndromes; Scarabaeidae; Thermogenesis
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Malé, P. - J. G., Ferdy, J. - B., Leroy, C., Roux, O., Lauth, J., Avilez, A., et al. (2014). Retaliation in Response to Castration Promotes a Low Level of Virulence in an Ant-Plant Mutualism. Evol. Biol., 41(1), 22–28.
Abstract: The diversion of a host's energy by a symbiont for its own benefit is a major source of instability in horizontally-transmitted mutualisms. This instability can be counter-balanced by the host's retaliation against exploiters. Such responses are crucial to the maintenance of the relationship. We focus on this issue in an obligate ant-plant mutualism in which the ants are known to partially castrate their host plant. We studied plant responses to various levels of castration in terms of (1) global vegetative investment and (2) investment in myrmecophytic traits. Castration led to a higher plant growth rate, signalling a novel case of gigantism induced by parasitic castration. On the other hand, completely castrated plants produced smaller nesting and food resources (i.e. leaf pouches and extra floral nectaries). Since the number of worker larvae is correlated to the volume of the leaf pouches, such a decrease in the investment in myrmecophytic traits demonstrates for the first time the existence of inducible retaliation mechanisms against too virulent castrating ants. Over time, this mechanism promotes an intermediate level of castration and enhances the stability of the mutualistic relationship by providing the ants with more living space while allowing the plant to reproduce. © 2013 Springer Science+Business Media New York.
Keywords: Allomerus decemarticulatus; Cheater; Evolutionary conflict; Hirtella physophora; Mutualism breakdown; Overexploitation
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Vincent, G., Sabatier, D., Blanc, L., Chave, J., Weissenbacher, E., Pélissier, R., et al. (2012). Accuracy of small footprint airborne LiDAR in its predictions of tropical moist forest stand structure. Remote Sens. Environ., 125, 23–33.
Abstract: We predict stand basal area (BA) from small footprint LiDAR data in 129 one-ha tropical forest plots across four sites in French Guiana and encompassing a great diversity of forest structures resulting from natural (soil and geological substrate) and anthropogenic effects (unlogged and logged forests). We use predictors extracted from the Canopy Height Model to compare models of varying complexity: single or multiple regressions and nested models that predict BA by independent estimates of stem density and quadratic mean diameter. Direct multiple regression was the most accurate, giving a 9.6% Root Mean Squared Error of Prediction (RMSEP). The magnitude of the various errors introduced during the data collection stage is evaluated and their contribution to MSEP is analyzed. It was found that these errors accounted for less than 10% of model MSEP, suggesting that there is considerable scope for model improvement. Although site-specific models showed lower MSEP than global models, stratification by site may not be the optimal solution. The key to future improvement would appear to lie in a stratification that captures variations in relations between LiDAR and forest structure. © 2012 Elsevier Inc.
Keywords: Basal area; Lidar; Tropical moist forest
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Malé, P. - J. G., Leroy, C., Lusignan, L., Petitclerc, F., Quilichini, A., & Orivel, J. (2015). The reproductive biology of the myrmecophyte, Hirtella physophora, and the limitation of negative interactions between pollinators and ants. Arthropod-Plant Interactions, 9(1), 23–31.
Abstract: Myrmecophytism occurs in plants that offer ants a nesting space and, often, food rewards in exchange for protection from predators and competitors. Such biotic protection by ants can, however, interfere with the activity of pollinators leading to potential negative consequences for the plant’s reproduction. In this study, we focused on the association between the understory myrmecophyte, Hirtella physophora (Chrysobalanaceae), and its obligate ant partner, Allomerus decemarticulatus (Myrmicinae). We investigated the reproductive biology of H. physophora and the putative mechanisms that may limit ant–pollinator conflict. Our results show that H. physophora is an obligate outcrosser, self-incompatible, and potentially insect-pollinated species. The reproduction of H. physophora relies entirely on pollen transfer by pollinators that are likely quite specific. Potential interference between flower-visiting insects during pollination may also be lessened by a spatial and temporal segregation of ant and pollinator activities, thus enabling pollen transfer and fruit production. © 2014, Springer Science+Business Media Dordrecht.
Keywords: Ant-plant; Ant–pollinator interactions; Floral structure and display; Plant reproductive biology; Spatial and temporal segregation
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Dulormne, M., Musseau, O., Muller, F., Toribio, A., & Bâ, A. (2010). Effects of NaCl on growth, water status, N2 fixation, and ion distribution in Pterocarpus officinalis seedlings. Plant and Soil, 327(1), 23–34.
Abstract: Pterocarpus officinalis (Fabaceae) dominates in the swamp forests of the Lesser Antilles, submitted to strong variations of soil salinity (30-445 mM). This study aimed to assess the effect of salinity on growth, nodulation, N2 fixation, water status and ions content in P. officinalis and to clarify the mechanisms involved. Seedlings inoculated or not with two strains from areas of contrasting salinity levels (< to 50 or 445 mM) were watered with 0, 171 and 342 mM solutions of NaCl in greenhouse conditions. Non-inoculated seedlings were tolerant to a salinity of 171 mM, with no significant effect on seedling biomass. Evapotranspiration per unit of leaf area (E/TLa) remained unchanged at 171 mM. Maintenance of a constant E/TLa and especially the control of ion transport to the upper parts of the plant could explain seedling salt tolerance up to intermediate salinity conditions (171 mM). The two strains have a 99.8% genetic identity in spite of differences in their original habitats, this explaining the similar response of the symbiosis to salinity. The higher salt sensitivity of inoculated seedlings was linked to the sensitivity of both Bradyrhizobium strains (reduction of free-living cells) and to that of the nodulation process (fewer nodules and inhibition of N2-fixation) to intermediate salinity. © Springer Science + Business Media B.V. 2009.
Keywords: Bradyrhizobium; Leaf water potential; Nodulation; Salt; Swamp forest
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Fine, P. V. A., & Baraloto, C. (2016). Habitat Endemism in White-sand Forests: Insights into the Mechanisms of Lineage Diversification and Community Assembly of the Neotropical Flora. Biotropica, 48(1), 24–33.
Abstract: White-sand forests represent natural laboratories of evolution over their long history throughout Amazonia and the Guiana Shield and pose significant physiological challenges to the plants and animals they host. The study of diversification in plant lineages comprising species endemic to white-sand forest can therefore give insights into processes of evolution and community assembly in tropical forests. In this article, we synthesize recent studies of white-sand forests to integrate patterns of plant species distribution with processes of lineage diversification and community assembly in the white-sand flora. We contrast lineages that have radiated uniquely in these habitats (e.g., Pagamea, Rubiaceae), with cosmopolitan lineages comprising specialists to white-sand forests and other habitats that may have arisen via ecological speciation across habitat gradients (e.g., Protium, Burseraceae). In both cases, similar suites of functional traits have evolved, including investment in dense, long-lived tissues that are well-defended structurally and chemically. White-sand endemics, therefore, play an important role in biodiversity conservation because they represent unique combinations of functional and phylogenetic diversity. Furthermore, white-sand endemics may respond differently than other tropical forest plant species to contemporary global changes because they comprise resilient functional types that may better withstand increased drought, temperature, and invasions of exotic pests in these regions. © 2016 The Association for Tropical Biology and Conservation.
Keywords: Amazon; Endemic; Functional traits; Habitat specialization; Niche conservatism; Speciation
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Djenontin Tindo, S., Amusant, N., Dangou, J., Wotto, D. V., Avlessi, F., Dahouénon-Ahoussi, E., et al. (2012). Screening of Repellent, Termiticidal and Preventive activities on Wood, of Azadirachta indica and Carapa procera (Meliaceae) seeds oils. ISCA J. Biological Sci., 1(3), 25–29.
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