Grangier, J., Orivel, J., Negrini, M., & Dejean, A. (2008). Low intraspecific aggressiveness in two obligate plant-ant species. Insect. Soc., 55(3), 238–240.
Abstract: Little is known about the aggressiveness of plant-ants typically living in isolated trees nor about how that aggressiveness varies based on this isolation. Here, we examine intra- and interspecific aggressiveness between workers of two Allomerus species associated with two different myrmecophytes. In both cases, the level of intraspecific aggressiveness is very low whatever the distance separating the tested nests, while interspecific conflicts are always violent. Similar patterns of aggressiveness have been reported in various ant species, but the strictly arboreal life of Allomerus ants associated with the isolation of their adult colonies highlight different ecological conditions that might explain the lack of aggressiveness between conspecifics.
Keywords: aggressiveness; Allomerus; myrmecophytes; plant-ants; recognition ability
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Clair, B., Almeras, T., Yamamoto, H., Okuyama, T., & Sugiyama, J. (2006). Mechanical behavior of cellulose microfibrils in tension wood, in relation with maturation stress generation. Biophys. J., 91(3), 1128–1135.
Abstract: A change in cellulose lattice spacing can be detected during the release of wood maturation stress by synchrotron x-ray diffraction experiment. The lattice strain was found to be the same order of magnitude as the macroscopic strain. The fiber repeat distance, 1.033 nm evaluated for tension wood after the release of maturation stress was equal to the conventional wood values, whereas the value before stress release was larger, corresponding to a fiber repeat of 1.035 nm, nearly equal to that of cotton and ramie. Interestingly, the fiber repeat varied from 1.033 nm for wood to 1.040 nm for algal cellulose, with an increasing order of lateral size of cellulose microfibrils so far reported. These lines of experiments demonstrate that, before the stress release, the cellulose was in a state of tension, which is, to our knowledge, the first experimental evidence supporting the assumption that tension is induced in cellulose microfibrils.
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de Grandcourt, A., Epron, D., Montpied, P., Louisanna, E., Bereau, M., Garbaye, J., et al. (2004). Contrasting responses to mycorrhizal inoculation and phosphorus availability in seedlings of two tropical rainforest tree species. New Phytol., 161(3), 865–875.
Abstract: This work aimed at understanding the role of mycorrhizal status in phosphorus efficiency of tree seedlings in the tropical rainforest of French Guyana. Mycorrhizal colonization, growth, phosphorus content, net photosynthesis and root respiration were determined on three occasions during a 9-month growth period for seedlings of two co-occurring species (Dicorynia guianensis and Eperua falcata) grown at three soil phosphorus concentrations, with or without inoculation with arbuscular mycorrhizas. Seedlings of both species were unable to absorb phosphorus in the absence of mycorrhizal association. Mycorrhizal seedlings exhibited coils that are specific of Paris-type mycorrhizae. Both species benefited from the mycorrhizal symbiosis in terms of phosphorus acquisition but the growth of E. falcata seedlings was unresponsive to this mycorrhizal improvement of phosphorus status, probably because of the combination of high seed mass and P reserves, with low growth rate. The two species belong to two different functional groups regarding phosphorus acquisition, D. guianensis being an obligate mycotrophic species.
Keywords: phosphorus; growth; efficiency; Paris-type arbuscular mycorrhizas; tropical rainforest; seedlings; Dicorynia guianensis; Eperua falcata
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Almeras, T., Gril, J., & Yamamoto, H. (2005). Modelling anisotropic maturation strains in wood in relation to fibre boundary conditions, microstructure and maturation kinetics. Holzforschung, 59(3), 347–353.
Abstract: A generalisation of existing mechanical models is proposed to account for the relation between wood macroscopic properties and fibre microstructure and chemical composition. It is applied to understanding of the origin of anisotropic maturation strains measured at the outermost surface of the xylem. Various assumptions are considered for boundary conditions of the fibre during the progressive maturation process and are applied to experimental data from the literature. Assumptions that the fibre is fully restrained in displacement, or fully unrestrained or unrestrained in the transverse direction only are all incompatible with observations. Indeed, within the tree, the fibre is restrained in the longitudinal and tangential directions, but unrestrained in the radial direction towards the bark. Mixed boundary conditions must be introduced to correctly simulate both longitudinal and tangential maturation strains. In the context of an analytical axisymmetric model, this is estimated by considering a parameter of partial release of tangential stress during maturation. Consistence with data and with finite element computation in the case of a square fibre confirmed that, because of the unrestrained radial condition, a large part of the tangential maturation stress is released in situ.
Keywords: anisotropy; boundary conditions; cell-wall maturation; growth strain; multilayer model; residual stress; wood fibre
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Scotti-Saintagne, C., Mariette, S., Porth, I., Goicoechea, P. G., Barreneche, T., Bodenes, K., et al. (2004). Genome scanning for interspecific differentiation between two closely related oak species [Quercus robur L. and Q petraea (Matt.) Liebl.]. Genetics, 168(3), 1615–1626.
Abstract: Interspecific differentiation values (G(ST)) between two closely related oak species (Quercus petraea and Q. robur) were compiled across different studies with the aim to explore the distribution of differentiation at the genome level. The study was based on a total set of 389 markers (isozymes, AFLPs, SCARs, microsatellites, and SNPs) for which allelic frequencies were estimated in pairs of populations sampled throughout the sympatric distribution of the two species. The overall distribution of GST values followed an L-shaped curve with most markers exhibiting low species differentiation (G(ST) < 0.01) and only a few loci reaching >10% levels. Twelve percent of the loci exhibited significant G(ST) deviations to neutral expectations, suggesting that selection contributed to species divergence. Coding regions expressed higher differentiation than noncoding regions. Among the 389 markers, 158 could be mapped on the 12 linkage groups of the existing Q. robur genetic map. Outlier loci with large G, values were distributed over 9 linkage groups. One cluster of three outlier loci was found within 0.51 cM; but significant autocorrelation of GST was observed at distances <2 cM. The size and distribution of genomic regions involved in species divergence are discussed in reference to hitchhiking effects and disruptive selection.
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Yazdani, R., Scotti, I., Jansson, G., Plomion, C., & Mathur, G. (2003). Inheritance and diversity of simple sequence repeat (SSR) microsatellite markers in various families of Picea abies. Hereditas, 138(3), 219–227.
Abstract: A large number of sequence-specific SSRs were screened by using electrophoresis on metaphore agarose gels with the bands visualized by ethidium bromide staining. Many SSRs appeared as codominant and many as dominant markers, with presence or absence of bands. A simple Mendelian inheritance pattern for most codominant and dominant SSR loci was found. For many codominant SSR markers, null alleles were detected. The proportion of dominant microsatellites detected in this study (close to 50 %) was much higher than that commonly reported in many other studies. A high proportion of dominant markers together with a high frequency of codominant markers with null alleles may represent two important limitations for the use of microsatellites in different studies. On the other hand, many polymorphic codominant SSR microsatellite markers were found to be highly repeatable, and can be used for population studies, seed certification, quality control of controlled crosses, paternity analysis, pollen contamination, and mapping of QTL in related families. In this paper, we report on the inheritance pattern and diversity of codominant and dominant SSR microsatellites in seven families of Picea abies sharing a common mother.
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Clair, B., Arinero, R., Leveque, G., Ramonda, M., & Thibaut, B. (2003). Imaging the mechanical properties of wood cell wall layers by atomic force modulation microscopy. IAWA J., 24(3), 223–230.
Abstract: Atomic Force Microscopy in force modulation mode was used to study the elastic properties of the different fibre wall layers of the tension wood of holm oak and normal wood of boco. The method is based on the measurement of the resonance frequency of the microscope lever in contact with the sample. This frequency is related to the reduced Young modulus E* = E/(1-nu(2)) of the material, supposed to be isotropic. 'Elastic' images of the cell are obtained simultaneously with the topographic images, which allows the observation of the mechanical properties of the cells at a nanometric scale. Layers G, S-1, S-2 and ML can clearly be distinguished. By comparison with known materials an estimation of the absolute modulus is given in the range 5-20 GPa, but should be considered with caution, because the inherent anisotropy of the materials has not been taken into account.
Keywords: wood; cell wall; mechanical properties; elastic modulus; tension wood
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Lobova, T. A., Mori, S. A., Blanchard, F., Peckham, H., & Charles-Dominique, P. (2003). Cecropia as a food resource for bats in French Guiana and the significance of fruit structure in seed dispersal and longevity. Am. J. Bot., 90(3), 388–403.
Abstract: Cecropia (Cecropiaceae) is a Neotropical genus of pioneer plants. A review of bat/plant dispersal interactions revealed that 15 species of Cecropia are consumed by 32 species of bats. In French Guiana, bats were captured in primary and secondary forests, yielding 936 fecal samples with diaspores, among which 162 contained fruits of C. obtusa, C. palmata, and C. sciadophylla. A comparative morphological and anatomical study of fruits and seeds taken directly from herbarium specimens, bat feces, and an experimental soil seed bank was made. Contrary to previous reports, the dispersal unit of Cecropia is the fruit not the seed. Bats consume the infructescence, digest pulp derived from the enlarged, fleshy perianth, and defecate the fruits. The mucilaginous pericarp of Cecropia is described. The external mucilage production of Cecropia may facilitate endozoochory. The exocarp and part of the mesocarp may be lost after passage through the digestive tract of bats, but fruits buried for a year in the soil seed bank remain structurally unchanged. Fruit characters were found to be useful for identifying species of bat-dispersed Cecropia. Bat dispersal is not necessary for seed germination but it increases seed survival and subsequent germination. Fruit structure plays a significant role in seed longevity.
Keywords: bat dispersal; Cecropia; French Guiana; fruit anatomy; fruit morphology; mucilage; Neotropical bats; soil seed bank
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Charles-Dominique, P., Chave, J., Dubois, M. A., De Granville, J. J., Riera, B., & Vezzoli, C. (2003). Colonization front of the understorey palm Astrocaryum sciophilum in a pristine rain forest of French Guiana. Glob. Ecol. Biogeogr., 12(3), 237–248.
Abstract: Aims Astrocaryum sciophilum (Miq.) Pulle (Arecaceae) is an understorey palm, endemic to north-eastern South America with a patchy distribution. We tested the hypothesis that the spatial distribution of this palm species is not in equilibrium but is slowly colonizing the forest understorey. Location Inventories and seed dispersal studies were conducted in the undisturbed tropical forest close to the Nouragues research station, French Guiana. Additional data were collected in the entire territory of French Guiana. Methods We studied the demography of A. sciophilum on a 20-ha plot located at the edge of its distribution. The age of the palms was estimated by postulating an exponentially decreasing abundance by age class. Direct seed dispersal experiments were also conducted, to estimate dispersal parameters. The seeds of A. sciophilum were dispersed only by rodents. This information was used to parameterize a forest growth simulator, to study the spatial spread of this species. Results Within the sampling plot, the density of A. sciophilum dropped sharply from about 500 individuals per hectare to zero. The maturation age was estimated to be 170+/-70 years, and over 55 years with 95% confidence. Seed-dispersal experiments yielded an average seed dispersal distance of 11 m and a maximum estimated dispersal distance of 125 m across a generational span of 55 years to maturity. Therefore, the maximal estimated colonization speed is 2.3 m/y. Conclusions Empirical results and numerical simulations suggest that the boundary of the A. sciophilum population is a colonization front, and that the range of this species is slowly expanding. The implications of this result in respect of palaeoenvironmental changes in this region are discussed.
Keywords: Astrocaryum sciophilum; French Guiana; neotropical palaeoecology; palm ecology; population edge; refuges; scatter-hoarding; seed dispersal; spatial pattern
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Millet, J., Pascal, J. P., & Kiet, L. C. (2010). Effects of Disturbance Over 60 Years on a Lowland Forest in Southern Vietnam. J. Trop. For. Sci., 22(3), 237–246.
Abstract: MILLET J, PASCAL JP & MET LC. 2010. Effects of disturbance over 60 years on a lowland forest in southern Vietnam. Tropical lowland forests are some of the most threatened in the world and this is particularly the case in Vietnam. This study aimed to identify changes in species composition and forest structure in the Tan Phu lowland forest resulting from disturbance over a 60 year period. Analysis of forest composition and structure rely on data from 25 plots of 0.5-ha size established in a lowland secondary forest. The five forest stands described differed greatly from the three forest stand types described in 1943. Some long-lived shade-tolerant species had been replaced by pioneer species, such as Cratoxylon formosum and Shorea roxburghii. In addition to altering composition, forest disturbances had resulted in large changes in forest structure. While in the past, forest stands had a large number of exploitable trees, current forest stands have few trees in the diameter class > 50 cm and sometimes no trees in the diameter class > 80 cm. This paper provides notable results on forest tree ecology, forest dynamics and on the state of secondary forests in Vietnam. This is particularly important as future goods and services will increasingly have to come from such forests.
Keywords: Lowland tropical forest; disturbance impact; floristic composition; forest structure; Tan Phu forest
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