Adjustment of vibratory signals to ambient temperature in a host-searching parasitoid

Abstract.  Certain ichneumonid parasitoids (Hymenoptera) use self-produced vibrations transmitted on plant substrate, so-called vibrational sounding, to locate their immobile concealed pupal hosts. An ambient temperature dependency with higher frequencies and intensities at higher temperatures is postulated because signals are of myogenic origin. Here, temperature influence on vibratory signals is analysed in the temperate parasitoid Pimpla turionellae under different thermal conditions using plant-stem models to elicit host-searching behaviour. Signals are measured with laser Doppler vibrometry and analysed for time parameters and frequency components applying fast-Fourier transformations. The results reveal an unexpected effect of ambient temperature on signals produced by the female wasps. Although average values of time parameters (pulse trains, pulse train periods, inter pulse duration) are unchanged by ambient temperature, the frequency parameters show an inverse thermal effect. Within the temperature range tested (8–26 °C), decreasing temperature leads to significantly higher frequency and intensity of the self-produced vibrations in the temperate species. This inverse thermal effect may be explained by a temperature-coupled signal production in the frequency domain to compensate negative low-temperature effects on the mechanoreceptors by increased muscle activity. The option of heterothermy to produce signals reliably during vibrational sounding under low temperature is also discussed.     

The Nicotiana attenuata GLA1 lipase controls the accumulation of Phytophthora parasitica‐induced oxylipins and defensive secondary metabolites

Nicotiana attenuata plants silenced in the expression of GLYCEROLIPASE A1 (ir‐gla1 plants) are compromised in the herbivore‐ and wound‐induced accumulation of jasmonic acid (JA). However, these plants accumulate wild‐type (WT) levels of JA and divinyl‐ethers during Phytophthora parasitica infection. By profiling oxylipin‐enriched fractions with targeted and untargeted liquid chromatography‐tandem time‐of‐flight mass spectrometry approaches, we demonstrate that the accumulation of 9‐hydroxy‐10E,12Z‐octadecadienoic acid (9‐OH‐18:2) and additional C₁₈ and C₁₉ oxylipins is reduced by ca. 20‐fold in P. parasitica‐infected ir‐gla1 leaves compared with WT. This reduced accumulation of oxylipins was accompanied by a reduced accumulation of unsaturated free fatty acids and specific lysolipid species. Untargeted metabolic profiling of total leaf extracts showed that 87 metabolites accumulated differentially in leaves of P. parasitica‐infected ir‐gla1 plants with glycerolipids, hydroxylated‐diterpene glycosides and phenylpropanoid derivatives accounting together for ca. 20% of these 87 metabolites. Thus, P. parasitica‐induced oxylipins may participate in the regulation of metabolic changes during infection. Together, the results demonstrate that GLA1 plays a distinct role in the production of oxylipins during biotic stress responses, supplying substrates for 9‐OH‐18:2 and additional C₁₈ and C₁₉ oxylipin formation during P. parasitica infection, whereas supplying substrates for the biogenesis of JA during herbivory and mechanical wounding.     

Cryobanking of viable biomaterials: implementation of new strategies for conservation purposes

Cryobanking, the freezing of biological specimens to maintain their integrity for a variety of anticipated and unanticipated uses, offers unique opportunities to advance the basic knowledge of biological systems and their evolution. Notably, cryobanking provides a crucial opportunity to support conservation efforts for endangered species. Historically, cryobanking has been developed mostly in response to human economic and medical needs — these needs must now be extended to biodiversity conservation. Reproduction technologies utilizing cryobanked gametes, embryos and somatic cells are already vital components of endangered species recovery efforts. Advances in modern biological research (e.g. stem cell research, genomics and proteomics) are already drawing heavily on cryobanked specimens, and future needs are anticipated to be immense. The challenges of developing and applying cryobanking for a broader diversity of species were addressed at an international conference held at Trier University (Germany) in June 2008. However, the magnitude of the potential benefits of cryobanking stood in stark contrast to the lack of substantial resources available for this area of strategic interest for biological science — and society at large. The meeting at Trier established a foundation for a strong global incentive to cryobank threatened species. The establishment of an Amphibian Ark cryobanking programme offers the first opportunity for global cooperation to achieve the cryobanking of the threatened species from an entire vertebrate class.     

Stem-boring insects of fragmented Calamagrostis habitats: herbivore–parasitoid community structure and the unpredictability of grass shoot abundance

Abstract.1. Communities of stem-boring insects attacking the grass Calamagrostis epigeios (L.) Roth were analysed from twenty-five pure stands of C. epigeios differing in area and isolation. Insect communities comprised nine phytophagous and eighteen entomophagous species. Most abundant herbivores (attacking > 1% of all shoots) were Tetramesa eximia (Giraud) (Hym. Eurytomidae), Eurytoma sp. (Hym. Eurytomidae), Lasioptera calamagrostidis (Rübs.) (Dipt. Cecidomyiidae), and Eriopeltis sp. (Hom. Pseudococcidae). About 28% of the twenty-seven species were monophagous, 61% oligophagous (restricted to Poaceae), and 11% polyphagous. Although herbivores generally attacked thick shoots, species-specific differences in the attacked mean diameter were found.2. The main purpose of this study was to analyse the relative effects of area, isolation and unpredictability of available food resources on the abundance of herbivores, parasitoids and resulting tritrophic effects. Variability of shoot abundance varied greatly between years, and even more between habitats within the same year. On average, shoot density per habitat increased or decreased 2.4-fold between succeeding years.3. Variability of grass shoot abundance was not related to habitat characteristics such as area, isolation, biomass, shoot density, changes in area or shoot density between years, or shoot features like internode number or diameter, but was negatively influenced by shading of trees. Similarly, habitat area or isolation did not correlate with other habitat features.4. Grass shoot abundance was the most important predictor of species abundance and attack rate of herbivores. In contrast to expectations, area and isolation of habitats did not explain differences in species richness, and only influenced abundance of three species. In addition, even the experimental removal of all grass shoots (and thereby, of all stem-boring insects) from five habitats in winter did not negatively influence colonization the following year. These results suggest a surprisingly high mobility of this rather specialized community of stem-boring insects that appeared to superimpose on area and isolation effects. Unpredictability of grass shoot abundance was presumably the main selection pressure for the obviously high dispersal abilities of the Calamagrostis insects.5. Per cent parasitism was mainly influenced by the percentage of attacked shoots. Parasitism of T. eximia by its major parasitoid also correlated with habitat connectivity, emphasizing the hypothesis that a continuum of habitats should be particularly favourable for the third trophic level.     

Melanocytes Respond to Mechanical Stretch by Activation of Mitogen‐Activated Protein Kinases (MAPK)

Cells of human epidermis are permanently targeted by mechanical stimuli. Besides mechanical forces from external sources the body itself generates mechanical forces via muscle contractions and growth processes. Recently, it was demonstrated that mechanical stretch is connected to enhanced proliferation in epidermal cells. The underlying biochemical events are still a matter of debate. Here we show that mechanical stretch leads to activation of both ERK1/2 and SAPK/JNK in human melanocytes and keratinocytes. In response to a 5 min single stretch ERK1/2 becomes moderately induced in melanocytes and peaked 30 min after the stimulus. In keratinocytes strong activation of ERK1/2 is present directly after the stimulus. SAPK/JNK shows the same activation pattern in both cell species – a slow but steady activation. The different kinetics of both MAPK suggest that different signalling cascades were activated. Future studies should evaluate the relevance of stretch‐dependent MAPK activation in triggering the cell proliferation.     

Polarity of Xylem Formation in Isolated Stem Segments of Pinus silvestris

The culture of isolated stem sogments was used as a technique to study polarity of xylem formation in Pinus silvestris L. Cambial activity was greatest at the apical or the basal end, whichever received the complete fresh medium, but decreased more abruptly with increasing distance when the basal end was so supplied. Whether gradients of activity increased basipetally or acropetally also depended upon the end to which the auxin and the sugar components were supplied. Ring-barking of segments, then cultur-ing them with apical supply of medium to the xylem, resulted in inhibition of xylem production below, and above, the ring. Cambial activity at the apical ends of such segments was expressible as a logarithmic function of the uninterrupted length of contiguous extraxylary tissues. The involvement of polarity phenomena in control of cambial activity in isolated stem segments is confirmed.