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Nixon, S., Agwa, A., Robinson, S., Walker, A., Touchard, A., Schroeder, C., et al. (2020). Discovery and characterisation of novel peptides from Amazonian stinging ant venoms with antiparasitic activity. Toxicon, 177(1), S60.
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Christensen-Dalsgaard, K. K., Fournier, M., Ennos, A. R., & Barfod, A. S. (2007). Changes in vessel anatomy in response to mechanical loading in six species of tropical trees. New Phytol., 176(3), 610–622.
Abstract: It is well known that trees adapt their supportive tissues to changes in loading conditions, yet little is known about how the vascular anatomy is modified in this process. We investigated this by comparing more and less mechanically loaded sections in six species of tropical trees with two different rooting morphologies. We measured the strain, vessel size, frequency and area fraction and from this calculated the specific conductivity, then measured the conductivity, modulus of elasticity and yield stress. The smallest vessels and the lowest vessel frequency were found in the parts of the trees subjected to the greatest stresses or strains. The specific conductivity varied up to two orders of magnitude between mechanically loaded and mechanically unimportant parts of the root system. A trade-off between conductivity and stiffness or strength was revealed, which suggests that anatomical alterations occur in response to mechanical strain. By contrast, between-tree comparisons showed that average anatomical features for the whole tree seemed more closely related to their ecological strategy.
Keywords: hydraulic architecture; hydraulic-mechanical trade-off; mechanical adaptation; rooting morphology; tropical trees; vascular anatomy
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Yatabe, Y., Kane, N. C., Scotti-Saintagne, C., & Rieseberg, L. H. (2007). Rampant gene exchange across a strong reproductive barrier between the annual sunflowers, Helianthus annuus and H-petiolaris. Genetics, 175(4), 1883–1893.
Abstract: Plant species may remain morphologically distinct despite gene exchange with congeners, yet little is known about the genomewide pattern of introgression among species. Here we analyze the effects of persistent gene flow on genomic differentiation between the sympatric sunflower species Helianthus annuus and H. petiolaris. While the species are strongly isolated in testcrosses, genetic distances at 108 microsatellite loci and 14 sequenced genes are highly variable and much lower (on average) than for more closely related but historically allopatric congeners. Our analyses failed to detect a positive association between levels of genetic differentiation and chromosomal rearrangements (as reported in a prior publication) or proximity to QTL for morphological differences or hybrid sterility. However, a significant increase in differentiation was observed for markers within 5 cM of chromosomal breakpoints. Together, these results suggest that islands of differentiation between these two species are small, except in areas of low recombination. Furthermore, only microsatellites associated with ESTs were identified as outlier loci in tests for selection, which might indicate that the ESTs themselves are the targets of selection rather than linked genes (or that coding regions are not randomly distributed). In general, these results indicate that even strong and genetically complex reproductive barriers cannot prevent widespread introgression.
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Petit, M., Céréghino, R., Carrias, J. - F., Corbara, B., Dezerald, O., Petitclerc, F., et al. (2014). Are ontogenetic shifts in foliar structure and resource acquisition spatially conditioned in tank-bromeliads? Bot J Linn Soc, 175(2), 299–312.
Abstract: The phenotypic plasticity of plants has been explored as a function of either ontogeny (apparent plasticity) or environment (adaptive plasticity), although few studies have analyzed these factors together. In the present study, we take advantage of the dispersal of Aechmea mertensii bromeliads by Camponotus femoratus or Pachycondyla goeldii ants in shaded and sunny environments, respectively, to quantify ontogenetic changes in morphological, foliar, and functional traits, and to analyze ontogenetic and ant species effects on 14 traits. Most of the morphological (plant height, number of leaves), foliar (leaf thickness, leaf mass area, total water content, trichome density), and functional (leaf δ13C) traits differed as a function of ontogeny. Conversely, only leaf δ15N showed an adaptive phenotypic plasticity. On the other hand, plant width, tank width, longest leaf length, stomatal density, and leaf C concentration showed an adaptation to local environment with ontogeny. The exception was leaf N concentration, which showed no trend at all. Aechmea mertensii did not show an abrupt morphological modification such as in heteroblastic bromeliads, although it was characterized by strong, size-related functional modifications for CO2 acquisition. The adaptive phenotypic variation found between the two ant species indicates the spatially conditioned plasticity of A. mertensii in the context of insect-assisted dispersal. However, ant-mediated effects on phenotypic plasticity in A. mertensii are not obvious because ant species and light environment are confounding variables. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175, 299–312.
Keywords: Aechmea mertensii; Camponotus femoratus; French Guiana; leaf traits; mutualistic ants; natural stable isotopes; ontogeny; Pachycondyla goeldii; phenotypic plasticity; plant morphology
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Phillips, P. D., de Azevedo, C. P., Degen, B., Thompson, I. S., Silva, J. N. M., & van Gardingen, P. R. (2004). An individual-based spatially explicit simulation model for strategic forest management planning in the eastern Amazon. Ecol. Model., 173(4), 335–354.
Abstract: A model to simulate the ecological processes of tree growth, mortality and recruitment, and the processes of forest management, in the terra firme forests of the eastern Amazon is described. It is implemented within the SYMFOR (http://www.symfor.org) framework. It is based on measurements of all trees that have a diameter greater than 5 cm from experimental plots in the Jari Cellulose and Tapajos National Forest areas over a 16-year period. Ten species groups are used to describe the natural processes affecting tree behaviour. Growth rates are calculated for each species group using the tree diameter and a competition index. Mortality and recruitment are simulated as stochastic processes. Recruitment probability is based on the predicted growth rate of a hypothetical tree. Options exist to vary the human interaction with the forest reflecting forest management decisions, as for other SYMFOR models. Model evaluation compares the performance of the model with data describing forest recovery for 16 years following logging. The model was applied to simulate current forest management practice in the Brazilian Amazon, with 40 m(3) ha(-1) of timber extracted with a cutting cycle of 30 years. Results show that yields are sustained for three harvests following the first logging of primary forest, but that the composition of timber moves towards lightwooded species rather than hardwooded. The predicted size of extracted trees decreases and the number of trees extracted increases with successive harvests, leading to a prediction of increased costs and lower profits for the logging company despite constant yields. The standing volume of all trees just before harvest is reduced by 15% over 150 years, with pioneer species becoming increasingly prevalent in the stand. The model, in the SYMFOR framework, can be used to help understand the differences between alternative forest management strategies in the Brazilian Amazon. Such knowledge is required to improve forest management, regulation and certification, and help to conserve the worlds largest remaining tropical forest. (C) 2003 Elsevier B.V. All rights reserved.
Keywords: model; individual; tropical forest; tree; spatial; Brazil; Amazon; competition; species grouping; management; certification; regulation
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Stahl, C., Herault, B., Rossi, V., Burban, B., Bréchet, C., & Bonal, D. (2013). Depth of soil water uptake by tropical rainforest trees during dry periods: Does tree dimension matter? Oecologia, 173(4), 1191–1201.
Abstract: Though the root biomass of tropical rainforest trees is concentrated in the upper soil layers, soil water uptake by deep roots has been shown to contribute to tree transpiration. A precise evaluation of the relationship between tree dimensions and depth of water uptake would be useful in tree-based modelling approaches designed to anticipate the response of tropical rainforest ecosystems to future changes in environmental conditions. We used an innovative dual-isotope labelling approach (deuterium in surface soil and oxygen at 120-cm depth) coupled with a modelling approach to investigate the role of tree dimensions in soil water uptake in a tropical rainforest exposed to seasonal drought. We studied 65 trees of varying diameter and height and with a wide range of predawn leaf water potential (Ψpd) values. We confirmed that about half of the studied trees relied on soil water below 100-cm depth during dry periods. Ψpd was negatively correlated with depth of water extraction and can be taken as a rough proxy of this depth. Some trees showed considerable plasticity in their depth of water uptake, exhibiting an efficient adaptive strategy for water and nutrient resource acquisition. We did not find a strong relationship between tree dimensions and depth of water uptake. While tall trees preferentially extract water from layers below 100-cm depth, shorter trees show broad variations in mean depth of water uptake. This precludes the use of tree dimensions to parameterize functional models. © 2013 Springer-Verlag Berlin Heidelberg.
Keywords: Deuterium; Oxygen; Root; Soil water; Tropical rainforest
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Maia, A. C. D., Schlindwein, C., Navarro, D. M. A. F., & Gibernau, M. (2010). Pollination of Philodendron Acutatum (Araceae) in the Atlantic Forest of Northeastern Brazil: A Single Scarab Beetle Species Guarantees High Fruit Set. Int. J. Plant Sci., 171(7), 740–748.
Abstract: Philodendron acutatum (Araceae) is a hemiepiphyte common to the Atlantic Forest of northeastern Brazil. In two localities, we studied the species' breeding system and associations with flower-visiting insects, along with an analysis of its floral scent composition. The fruit set of self-incompatible P. acutatum was high, more than 90%, and inflorescences were exclusively pollinated by one species of scarab beetle, Cyclocephala celata (Scarabaeidae, Dynastinae). Pollinators are drawn toward the inflorescences at dusk by strong floral fragrances given off during the female phase of anthesis, along with endogenous heating of the spadix, whose temperatures were recorded at more than 11 degrees C above ambient air. Two other species of flower-visiting Cyclocephala were also consistently recovered in blacklight trappings during the flowering period of P. acutatum. The fact that only C. celata was found in association with P. acutatum suggests a local reproductive dependence of the plant to this scarab beetle species. Dihydro-beta-ionone and 2-hydroxy-5-methyl-3-hexanone, a rare volatile molecule so far unreported as a floral compound, together accounted for more than 97% of the unique scent composition of P. acutatum and might be involved in specific attraction of C. celata.
Keywords: Cyclocephala; floral volatiles; pollination specificity; reproductive success; thermogenesis
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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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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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Barantal, S., Roy, J., Fromin, N., Schimann, H., & Hattenschwiler, S. (2011). Long-term presence of tree species but not chemical diversity affect litter mixture effects on decomposition in a neotropical rainforest. Oecologia, 167(1), 241–252.
Abstract: Plant litter diversity effects on decomposition rates are frequently reported, but with a strong bias towards temperate ecosystems. Altered decomposition and nutrient recycling with changing litter diversity may be particularly important in tree species-rich tropical rainforests on nutrient-poor soils. Using 28 different mixtures of leaf litter from 16 Amazonian rainforest tree species, we tested the hypothesis that litter mixture effects on decomposition increase with increasing functional litter diversity. Litter mixtures and all single litter species were exposed in the field for 9 months using custom-made microcosms with soil fauna access. In order to test the hypothesis that the long-term presence of tree species contributing to the litter mixtures increases mixture effects on decomposition, microcosms were installed in a plantation at sites including the respective tree species composition and in a nearby natural forest where these tree species are absent. We found that mixture decomposition deviated from predictions based on single species, with predominantly synergistic effects. Functional litter diversity, defined as either richness, evenness, or divergence based on a wide range of chemical traits, did not explain the observed litter mixture effects. However, synergistic effects in litter mixtures increased with the long-term presence of tree species contributing to these mixtures as the home field advantage hypothesis assumes. Our data suggest that complementarity effects on mixed litter decomposition may emerge through long-term interactions between aboveground and belowground biota.
Keywords: Amazonian rainforest; Chemical diversity; Decomposition; Functional diversity indices; Litter traits
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