Dry-season retreat and dietary shift of the dart-poison frog Dendrobates tinctorius (Anura: Dendrobatidae)

A precipitação sazonal afeta a dinâmica das florestas tropicais e o comportamento das espécies que fazem parte desse ecossistema. A relação positiva entre os padrões de atividade dos anfíbios e a precipitação já foi demonstrada repetidas vezes. Os membros da família Dendrobatidae, um clado de saposvenenodeflecha neotropicais, são bemconhecidos por seu uso de hábitat e comportamento durante a estação chuvosa, mas seu comportamento durante a estação seca tem recebido pouca atenção. Estudamos o uso de hábitat e a dieta do dendrobatídeo Dendrobates tinctorius na Guiana Francesa durante as estações chuvosa e seca. Ao contrário de muitos outros dendrobatídeos, D. tinctorius não mantém territórios ao longo de toda a estação chuvosa. Ambos os sexos colonizam clareiras recentemente abertas e permanecem apenas poucas semanas nessas manchas, onde os animais consomem uma grande variedade de presas, principalmente formigas, besouros, vespas, larvas de insetos e ácaros. Durante a estação seca, os animais movem-se para locais de abrigo na floresta madura, como brácteas de palmeiras e ocos de árvores. Nesse período, são menos ativos e consomem um menor número de itens alimentares; consomem menos vespas e larvas de insetos e mais cupins. Formigas constituem a presa mais comum durante as duas estações. Discutimos os efeitos das mudanças sazonais no uso de hábitat sobre o comportamento territorial dos dendrobatídeos.Seasonal rainfall affects tropical forest dynamics and behavior of species that are part of these ecosystems. The positive correlation between amphibian activity patterns and rainfall has been demonstrated repeatedly. Members of Dendrobatidae, a clade of Neotropical dartpoison frogs, are well known for their habitat use and behavior during the rainy season, but their behavior during the dry season has received little attention. We studied habitat use and diet of the dendrobatid frog Dendrobates tinctorius in French Guiana during the rainy and dry seasons. Unlike many other dendrobatid frogs, D. tinctorius does not maintain territories for the entire rainy season. Both sexes colonize recently formed canopygaps and stay in these forest patches for only a few weeks. The frogs in these patches consume a great diversity of prey, consisting of ants, beetles, wasps, insect larvae, and mites. During the dry season, frogs move to retreat sites in mature forest, such as palm bracts and tree holes. The frogs are less active and consume fewer prey items in the dry season, and they consume fewer wasps and insect larvae, but more termites. Ants are the most common prey items during both the wet and dry seasons. We discuss the effects of shifts in seasonal habitat use on the territorial behavior of dendrobatid frogs

Charging mechanisms in persistent phosphors

The development of novel persistent phosphors is currently hampered by a limited understanding of the charging mechanism. Using x-ray absorption and thermoluminescence spectroscopy we evaluate the validity of recently proposed models for the charging mechanism

Settling on leaves or flowers: herbivore feeding site determines the outcome of indirect interactions between herbivores and pollinators

Herbivore attack can alter plant interactions with pollinators, ranging from reduced to enhanced pollinator visitation. The direction and strength of effects of herbivory on pollinator visitation could be contingent on the type of plant tissue or organ attacked by herbivores, but this has seldom been tested experimentally. We investigated the effect of variation in feeding site of herbivorous insects on the visitation by insect pollinators on flowering Brassica nigra plants. We placed herbivores on either leaves or flowers, and recorded the responses of two pollinator species when visiting flowers. Our results show that variation in herbivore feeding site has profound impact on the outcome of herbivore–pollinator interactions. Herbivores feeding on flowers had consistent positive effects on pollinator visitation, whereas herbivores feeding on leaves did not. Herbivores themselves preferred to feed on flowers, and mostly performed best on flowers. We conclude that herbivore feeding site choice can profoundly affect herbivore–pollinator interactions and feeding site thereby makes for an important herbivore trait that can determine the linkage between antagonistic and mutualistic networks.</p

In-plane local defect resonances for efficient vibrothermography of impacted carbon fiber reinforced plastics (CFRP)

It is well known that the efficiency of the vibrothermographic non-destructive testing (NDT) technique can be enhanced by taking advantage of local defect resonance (LDR) frequencies. Recently, the classical out-of-plane local defect resonance was extended towards in-plane LDR for enhanced efficiency of vibrometric NDT. This paper further couples the concept of this in-plane LDR to vibrothermography, on the basis of the promising potential of in-plane LDRs to enhance the rubbing (tangential) interaction and viscoelastic damping of defects. Carbon fiber-reinforced composites (CFRPs) with barely visible impact damage (BVID) are inspected and the significant contribution of in-plane LDRs in vibrational heating is demonstrated. Moreover, it is shown that the defect thermal contrast induced by in-plane LDRs is so high that it allows for easy detection of BVID by live monitoring of infrared thermal images during a single broadband sweep excitation. Thermal and vibrational spectra of the inspected surface are studied and the dominant contribution of in-plane LDR in vibration-induced heating is demonstrated

Vibrothermographic spectroscopy with thermal latency compensation for effective identification of local defect resonance frequencies of a CFRP with BVID

Vibrothermography using sinusoidal vibration excitation at the resonance frequencies of a defected area (so-called local defect resonance, or LDR) is a promising technique to boost the defect's deformation and its interfacial interactions and as such enhance resultant vibration-induced heating. Contrary to the classical high-power vibrothermography, low power excitation at an LDR frequency results in a reproducible thermal response and adequate quantification of the corresponding damage features. However, the technique is mainly limited by the fact that it requires a priori knowledge of the LDR frequencies (e.g. obtained from prior vibrational measurements). To overcome this limitation, a stand-alone vibrothermographic spectroscopy procedure is introduced in this paper. The proposed technique applies two consecutive broadband sweep vibrational excitations with ascending and descending frequency modulation rates to the sample. The surface of the excited sample is monitored with an IR camera. Both time derivative analysis and superposition of the recorded thermal responses are performed in order to compensate for the thermal latency of the defect-induced heating. This compensation approach enables proper identification of the actual LDR frequencies based on the apparent LDR frequencies of the thermal response. The method is applied on a carbon fiber reinforced polymer (CFRP) with barely visible impact damage (BVID), and multiple LDR frequencies are readily identified. The identified LDR frequencies are also individually evaluated by both lock-in vibrothermography and 3D scanning laser Doppler vibrometry, confirming the competence of the proposed technique for extracting LDR frequencies in a proper and fast way

Full wave field signal processing techniques for NDT of composites : a case study

Non-destructive testing of composites using full wave field analysis of guided waves is illustrated for a CFRP aircraft panel with production defects. The full wave field is measured using 3D scanning laser Doppler vibrometry for broadband chirp excitation through one piezoelectric actuator. First, the A0 mode is extracted through mode filtering in the frequency-wavenumber domain. Next, the measured chirp response is converted to a narrowband burst response. At last, the local wavenumber map is constructed and evaluated. A debonding defect between stiffener and base plate is detected and confirmed by the ultrasonic C-scan time-of-flight map

Automated extraction of local defect resonance for efficient non-destructive testing of composites

Local defect resonance (LDR) makes use of high frequency vibrations to get a localized resonant activation of the defect. One of the major difficulties with respect to the use of LDR for non-destructive testing is the actual identification of the LDR frequency. In this study, different post-processing methods are applied to broadband vibration data, obtained for a carbon fiber reinforced plastic with a flat bottom hole, in view of automated extraction of LDR features. Results are shown and discussed in the frequency domain. In order to reduce the computational effort for large datasets, principle component analysis (PCA) and frequency band data (FBD) calculation are investigated. The effect on the calculation time and the data size is investigated. Moreover, a signal-to-noise ratio is introduced to investigate the performance of both techniques with respect to the automated LDR detection algorithm. Finally, the effect of a reduced sampling is investigated with respect to the performance of the automated LDR extraction procedure

Genotypic variation in genome-wide transcription profiles induced by insect feeding: Brassica oleracea – Pieris rapae interactions

<p>Abstract</p> <p>Background</p> <p>Transcriptional profiling after herbivore attack reveals, at the molecular level, how plants respond to this type of biotic stress. Comparing herbivore-induced transcriptional responses of plants with different phenotypes provides insight into plant defense mechanisms. Here, we compare the global gene expression patterns induced by <it>Pieris rapae </it>caterpillar attack in two white cabbage (<it>Brassica oleracea </it>var. <it>capitata</it>) cultivars. The two cultivars are shown to differ in their level of direct defense against caterpillar feeding. Because <it>Brassica </it>full genome microarrays are not yet available, 70-mer oligonucleotide microarrays based on the <it>Arabidopsis thaliana </it>genome were used for this non-model plant.</p> <p>Results</p> <p>The transcriptional responses of the two cultivars differed in timing as characterized by changes in their expression pattern after 24, 48 and 72 hours of caterpillar feeding. In addition, they also differed qualitatively. Surprisingly, of all genes induced at any time point, only one third was induced in both cultivars. Analyses of transcriptional responses after jasmonate treatment revealed that the difference in timing did not hold for the response to this phytohormone. Additionally, comparisons between <it>Pieris rapae</it>- and jasmonate-induced transcriptional responses showed that <it>Pieris rapae </it>induced more jasmonate-independent than jasmonate-dependent genes.</p> <p>Conclusion</p> <p>The present study clearly shows that global transcriptional responses in two cultivars of the same plant species in response to insect feeding can differ dramatically. Several of these differences involve genes that are known to have an impact on <it>Pieris rapae </it>performance and probably underlie different mechanisms of direct defense, present in the cultivars.</p