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

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

Hyperparasitoids exploit herbivore-induced plant volatiles during host location to assess host quality and non-host identity

Although consumers often rely on chemical information to optimize their foraging strategies, it is poorly understood how top carnivores above the third trophic level find resources in heterogeneous environments. Hyperparasitoids are a common group of organisms in the fourth trophic level that lay their eggs in or on the body of other parasitoid hosts. Such top carnivores use herbivore-induced plant volatiles (HIPVs) to find caterpillars containing parasitoid host larvae. Hyperparasitoids forage in complex environments where hosts of different quality may be present alongside non-host parasitoid species, each of which can develop in multiple herbivore species. Because both the identity of the herbivore species and its parasitization status can affect the composition of HIPV emission, hyperparasitoids encounter considerable variation in HIPVs during host location. Here, we combined laboratory and field experiments to investigate the role of HIPVs in host selection of hyperparasitoids that search for hosts in a multi-parasitoid multi-herbivore context. In a wild Brassica oleracea-based food web, the hyperparasitoid Lysibia nana preferred HIPVs emitted in response to caterpillars parasitized by the gregarious host Cotesia glomerata over the non-host Hyposoter ebeninus. However, no plant-mediated discrimination occurred between the solitary host C. rubecula and the non-host H. ebeninus. Under both laboratory and field conditions, hyperparasitoid responses were not affected by the herbivore species (Pieris brassicae or P. rapae) in which the three primary parasitoid species developed. Our study shows that HIPVs are an important source of information within multitrophic interaction networks allowing hyperparasitoids to find their preferred hosts in heterogeneous environments.</p

A new species of Colostethus (Anura, Dendrobatidae) from French Guiana with a redescription of Colostethus beebei (Noble, 1923) from its type locality

A new species of Colostethus, long mistaken for Colostethus beebei, is described from French Guiana. The new species can be distinguished from congeners by absence of median lingual process, first finger longer than second, third finger not distinctly swollen in males, differences in tadpole morphology, coloration and pattern (e.g. absence of dorsolateral stripe), bioacoustics, and reproductive behavior. A complete redescription of Colostethus beebei plus description of its tadpole and call is provided on the basis of recently collected topotypic specimens. The range of C. beebei is restricted to the Kaieteur plateau, Pakaraima Mountains, Guyana

Intraspecific variation in herbivore-induced plant volatiles influences the spatial range of plant–parasitoid interactions

Chemical information influences the behaviour of many animals, thus affecting species interactions. Many animals forage for resources that are heterogeneously distributed in space and time, and have evolved foraging behaviour that utilizes information related to these resources. Herbivore-induced plant volatiles (HIPVs), emitted by plants upon herbivore attack, provide information on herbivory to various animal species, including parasitoids. Little is known about the spatial scale at which plants attract parasitoids via HIPVs under field conditions and how intraspecific variation in HIPV emission affects this spatial scale. Here, we investigated the spatial scale of parasitoid attraction to two cabbage accessions that differ in relative preference of the parasitoid Cotesia glomerata when plants were damaged by Pieris brassicae caterpillars. Parasitoids were released in a field experiment with plants at distances of up to 60 m from the release site using intervals between plants of 10 or 20 m to assess parasitism rates over time and distance. Additionally, we observed host-location behaviour of parasitoids in detail in a semi-field tent experiment with plant spacing up to 8 m. Plant accession strongly affected successful host location in field set-ups with 10 or 20 m intervals between plants. In the semi-field set-up, plant finding success by parasitoids decreased with increasing plant spacing, differed between plant accessions, and was higher for host-infested plants than for uninfested plants. We demonstrate that parasitoids can be attracted to herbivore-infested plants over large distances (10 m or 20 m) in the field, and that stronger plant attractiveness via HIPVs increases this distance (up to at least 20 m). Our study indicates that variation in plant traits can affect attraction distance, movement patterns of parasitoids, and ultimately spatial patterns of plant–insect interactions. It is therefore important to consider plant-trait variation in HIPVs when studying animal foraging behaviour and multi-trophic interactions in a spatial context.</p

Adapted dandelions increase seed dispersal potential when they are attacked by root herbivores

Plants allow their offspring to escape unfavourable local conditions through seed dispersal. Whether plants use this strategy to escape herbivores is not well understood. Here, we explore how different Taraxacum officinale populations modify seed dispersal in response to root herbivore attack by Melolontha melolontha in the field. Root herbivore attack increases seed dispersal potential through a reduction in seed weight in populations that have evolved under high root herbivore pressure, but not in populations that have evolved under low pressure. This increase in dispersal potential is associated with reduced germination, suggesting that adapted plants trade dispersal for establishment. Analysis of vegetative growth parameters suggests that increased dispersal is not the result of stress flowering. These results suggest that root herbivory selects for genotypes that increase their dispersal ability in response to herbivore attack

Intraspecific variation in herbivore community composition and transcriptional profiles in field-grown Brassica oleracea cultivars

Intraspecific differences in plant defence traits are often correlated with variation in transcriptional profiles and can affect the composition of herbivore communities on field-grown plants. However, most studies on transcriptional profiling of plant–herbivore interactions have been carried out under controlled conditions in the laboratory or greenhouse and only a few examine intraspecific transcriptional variation. Here, intraspecific variation in herbivore community composition and transcriptional profiles between two Brassica oleracea cultivars grown in the field is addressed. Early in the season, no differences in community composition were found for naturally occurring herbivores, whereas cultivars differed greatly in abundance, species richness, and herbivore community later in the season. Genome-wide transcriptomic analysis using an Arabidopsis thaliana oligonucleotide microarray showed clear differences for the expression levels of 26 genes between the two cultivars later in the season. Several defence-related genes showed higher levels of expression in the cultivar that harboured the lowest numbers of herbivores. Our study shows that herbivore community composition develops differentially throughout the season on the two B. oleracea cultivars grown in the field. The correlation between the differences in herbivore communities and differential expression of particular defence-related genes is discussed