Maron, P. A., Schimann, H., Ranjard, L., Brothier, E., Domenach, A. M., Lensi, R., et al. (2006). Evaluation of quantitative and qualitative recovery of bacterial communities from different soil types by density gradient centrifugation. Eur. J. Soil Biol., 42(2), 65–73.
Abstract: Extracting and purifying a representative fraction of bacteria from soil is necessary for the application of many techniques of microbial ecology. Here the influence of different soil types on the quantitative and qualitative recovery of bacteria by soil grinding and Nycodenz density gradient centrifugation was investigated. Three soils presenting contrasted physicochemical characteristics were used for this study. For each soil, the total (AODC: acridine orange direct count) and culturable (cfa: colony-forming units) bacterial densities were measured in three distinct fractions: (i) the primary soil, (ii) the soil pellet (soil remaining after centrifugation), and (iii) the extracted cells. The automated-ribosomal intergenic spacer analysis (A-RISA) was used to characterize the community structure directly from the DNA extracted from each fraction. The physicochemical characteristics of soils were found to influence both the efficiency of bacterial cell recovery and the representativeness of the extracted cells in term of community structures between the different fractions. Surprisingly, the most representative extracted cells were obtained from the soil exhibiting the lowest efficiency of cell recovery. Our results demonstrated that quantitative and qualitative cell recovery using Nycodenz density gradient centrifugation are not necessarily related and could be differentially biased according to soil type. (c) 2006 Elsevier SAS. All rights reserved.
Keywords: bacterial community; soil; density gradient; DNA fingerprint
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Bourreau, D., Aimene, Y., Beauchene, J., & Thibaut, B. (2013). Feasibility of glued laminated timber beams with tropical hardwoods. Eur. J. Wood Wood Prod., 71(5), 653–662.
Abstract: A feasibility study of glulam was carried out in French Guiana using local wood species. The aim was to determine gluing parameters affording satisfactory behaviour to manufactured glulam in a tropical climate. Three abundant wood species, with special properties, were selected for the study and resorcinol-phenol-formaldehyde resin was used for bonding. Three industrial parameters were considered: adhesive spread rate, closed assembly time and gluing pressure. Delamination and shearing tests were carried out in accordance with European Standards. The tests revealed the influence of wood properties and manufacturing parameters on joint resistance. In fact, the results showed that specific gravity and the shrinkage coefficient greatly influenced the gluing step. Indeed, wood with a medium specific gravity needed more adhesive and more pressure than wood with a high specific gravity. In addition, planing and lamella thickness were found to affect glue joint resistance. © 2013 Springer-Verlag Berlin Heidelberg.
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Vedel, V., Apostolou, Z., Arthur, W., Akam, M., & Brena, C. (2010). An early temperature-sensitive period for the plasticity of segment number in the centipede Strigamia maritima. Evol Dev, 12(4), 347–352.
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Foucaud, J., Orivel, J., Loiseau, A., Delabie, J. H. C., Jourdan, H., Konghouleux, D., et al. (2010). Worldwide invasion by the little fire ant: routes of introduction and eco-evolutionary pathways. Evol. Appl., 3(4), 363–374.
Abstract: Biological invasions are generally thought to occur after human aided migration to a new range. However, human activities prior to migration may also play a role. We studied here the evolutionary genetics of introduced populations of the invasive ant Wasmannia auropunctata at a worldwide scale. Using microsatellite markers, we reconstructed the main routes of introduction of the species. We found three main routes of introduction, each of them strongly associated to human history and trading routes. We also demonstrate the overwhelming occurrence of male and female clonality in introduced populations of W. auropunctata, and suggest that this particular reproduction system is under selection in human-modified habitats. Together with previous researches focused on native populations, our results suggest that invasive clonal populations may have evolved within human modified habitats in the native range, and spread further from there. The evolutionarily most parsimonious scenario for the emergence of invasive populations of the little fire ant might thus be a two-step process. The W. auropunctata case illustrates the central role of humans in biological change, not only due to changes in migration patterns, but also in selective pressures over species.
Keywords: biological invasion; introduction routes; parthenogenesis; reproduction system; Wasmannia auropunctata
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Foucaud, J., Rey, O., Robert, S., Crespin, L., Orivel, J., Facon, B., et al. (2013). Thermotolerance adaptation to human-modified habitats occurs in the native range of the invasive ant Wasmannia auropunctata before long-distance dispersal. Evol. Appl., 6(4), 721–734.
Abstract: Key evolutionary events associated with invasion success are traditionally thought to occur in the introduced, rather than the native range of species. In the invasive ant Wasmannia auropunctata, however, a shift in reproductive system has been demonstrated within the native range, from the sexual non-dominant populations of natural habitats to the clonal dominant populations of human-modified habitats. Because abiotic conditions of human- modified habitats are hotter and dryer, we performed lab experiments on workers from a set of native and introduced populations, to investigate whether these ecological and genetic transitions were accompanied by a change in thermotolerance and whether such changes occurred before establishment in the introduced range. Thermotolerance levels were higher in native populations from human-modified habitats than in native populations from natural habitats, but were similar in native and introduced populations from human-modified habitats. Differences in thermotolerance could not be accounted for by differences in body size. A scenario based on local adaptation in the native range before introduction in remote areas represents the most parsimonious hypothesis to account for the observed phenotypic pattern. These findings highlight the importance of human land use in explaining major contemporary evolutionary changes. © 2013 The Authors.
Keywords: Adaptation; Heat shock; Invasive species; Natural selection and contemporary evolution; Thermotolerance
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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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Vedel, V., Brena, C., & Arthur, W. (2009). Demonstration of a heritable component of the variation in segment number in the centipede Strigamia maritima. Evol. Dev., 11(4), 434–440.
Abstract: Here we address the question of how arthropod segment number may evolve by reporting the results of further work on the model system Strigamia maritima. Recently, we showed that there was a plastic component of the variation in segment number within this species; now we demonstrate that there is also a heritable component. This is important because it enables a connection to be made between the known latitudinal trend among species of geophilomorph centipedes ( more segments at lower latitudes) and the parallel trend within them. This latter trend is best documented in S. maritima but is also known in several other species. However, while a general connection between the inter- and intraspecific trends can now be made, deciding upon a specific hypothesis of the nature of the selection involved is still problematic. We provide two alternative hypotheses, one based on the temperature-related plasticity in segment number being adaptive, the other based on it being nonadaptive.
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Malé, P. - J. G., Leroy, C., Dejean, A., Quilichini, A., & Orivel, J. (2012). An ant symbiont directly and indirectly limits its host plant's reproductive success. Evol. Ecol., 26(1), 55–63.
Abstract: In theory, mutualisms are intrinsically unstable, and the search for the maximum profit at the minimum cost should lead every mutualist to become a parasite. From an empirical point of view, mutualisms are ubiquitous and of major importance to ecosystems, suggesting the existence of mechanisms that enhance the maintenance of such relationships. We focused on the obligatory myrmecophytic association between the Neotropical plant Hirtella physophora (Chrysobalanaceae) and the ant Allomerus decemarticulatus (Myrmicinae). The plant shelters the ants in leaf pouches in exchange for protection from phytophagous insects. We experimentally demonstrated that the ants partially castrate their host plant by destroying almost two-thirds of its floral buds. The ants also impede pollination through their presence and interactions with pollinators. These results reveal that ant activity negatively affects the plant's reproduction both directly and indirectly. This dual negative effect does not result in the complete castration of the plant. We also highlight major limitations to plant reproduction due to the spontaneous abscission of flowers and to the limited quantity and/or poor quality of the pollen. These limitations must not be overlooked since they can alter the outcome of the association of H. physophora with its ant partner. We therefore conclude that the evolutionary fate of the relationship depends on both ant castration intensity and obstacles to plant fertilization not related to the presence of ants. © 2011 Springer Science+Business Media B.V.
Keywords: Cheater; Evolutionary conflict; Mutualism breakdown; Myrmecophyte; Pollination
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Talaga, S., Leroy, C., Céréghino, R., & Dejean, A. (2016). Convergent evolution of intraguild predation in phytotelm-inhabiting mosquitoes. Evol. Ecol., 30(6), 1133–1147.
Abstract: Intraguild predation (IGP) is a type of biological interaction involving the killing and consuming of competing species that exploit similar and often limited resources. This phenomenon is widespread among a great variety of taxonomic groups and has already been reported for mosquito (Diptera: Culicidae) larvae. Moreover, the larvae of certain mosquito species of the tribe Sabethini have evolved modified mouthparts ending in rigid apical structures signaling their capacity to be effective intraguild predators. We assumed that IGP confers a selective advantage under severe competitive conditions by both providing an immediate energetic gain and reducing potential competition. Because potential competition is likely to increase with decreasing habitat size, we hypothesized that the proportion of species with modified mouthparts would increase in smaller aquatic habitats. We tested this hypothesis by examining the mosquito species naturally associated with phytotelmata of decreasing sizes in French Guiana. We show that the degree of specialization in mosquito-phytotelm associations is high, suggesting a long coevolutive process. Indeed, short-term interaction experiments confirmed that species with modified mouthparts are able to prey upon similarly-sized intraguild prey and are, thus, effective intraguild predators. In addition, these species are larger and associated with smaller phytotelmata than those with typical mouthparts. Moreover, below a certain threshold of phytotelm size, only species with modified mouthparts were present. These results show that IGP confers a selective advantage under severe competitive conditions and results from the coadaptation of mosquito species to their specific phytotelm habitat. The presence of functionally analogous structures in different mosquito genera also implies that IGP has emerged from convergent evolution in small phytotelmata.
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Dejean, A., Petitclerc, F., & Azémar, F. (2020). Seasonality influences ant-mediated nutrient acquisition (myrmecotrophy) by a Neotropical myrmecophyte. Evol. Ecol., 34(4), 645–657.
Abstract: Tachia guianensis (Gentianaceae), a Neotropical understory myrmecophyte, shelters ant colonies in its hollow trunks and branches (domatia). In turn, it is protected from defoliators and obtains nutrients from ant-produced wastes (myrmecotrophy). Aiming to verify if seasonality influences nitrogen assimilation via ant wastes using the stable isotope nitrogen-15, we first studied Tachia’s phenology and its seasonal leaf production, and then the life cycle of its two more frequent guest ant species. We found that leaf production was much higher during the rainy than the dry season. Mature guest ant colonies produced sexuals regardless of the season and the net weight of the waste piles inside the domatia did not vary between seasons, so that the availability of nutrients to their host plant is steady year-long. By providing the two most frequent mutualistic guest ant species with food enriched with nitrogen-15, we showed that Tachia individuals assimilate more nitrogen from ant wastes during the rainy season, when the plant is physiologically active, compared to the dry season. Thus, one can deduce that the increase in nitrogen assimilation during the rainy season is determined by the increase in Tachia’s physiological activity during that season. Information gathered through a bibliographic compilation confirms that none of the 15 ant species known to be associated with myrmecophytes for which the life cycle was studied is characterized by seasonal reproduction (which would result in fluctuating waste production). The same is true for 49.7% of 167 tropical ant species (seasonal production for the remaining species). We concluded that, in contrast to the non-seasonal ant colony reproductive cycle, Tachia’s phenology determines the myrmecotrophic assimilation rate. © 2020, Springer Nature Switzerland AG.
Keywords: Ant-plant relationships; Mutualism; Myrmecophyte; Myrmecotrophy; Phenology; Stable isotopes; ant; herb; host plant; life cycle; myrmecochory; myrmecophyte; Neotropical Region; phenology; seasonality; stable isotope; understory; Gentianaceae; Tachia; Tachia guianensis
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