Patch size effects are more important than genetic diversity for plant–herbivore interactions in Brassica crops

1. Considerable evidence suggests that the diversity within plant communities may strongly affect the strength of species interactions, but the majority of studies only considered interspecific diversity. 2. This paper examines the effect of intraspecific genetic diversity within Brassica fields on two Brassica specialists, cabbage root fly, and diamondback moth, and on a parasitoid attacking diamondback moths. Genetic diversity was manipulated both in a replacement and an additive design. 3. Both herbivore densities and parasitism rates were higher in smaller plots, with limited responses to increased within‐plot diversity. All species showed variable densities across genotypes, and preference hierarchies were species specific. 4. Responses to plot size in root flies scaled with the diameter‐to‐area ratio, suggesting that patch detectability affected local density, whereas responses by diamondback moths and parasitoids deviated from this ratio. These species differences could be traced to differences in the residence time within patches, where diamondback moths typically spend longer and more variable time periods in patches than root flies. 5. The lack of response to genetic diversity by both herbivores suggests that egg‐laying rates are affected by decisions on the plant and not by attraction from a distance, neither to the plant itself nor the patch. Patterns of differential attack may then be due to different acceptability for studied genotypes. 6. Future theories on insect responses to spatial heterogeneity should focus on species traits and how traits interact with information landscapes in the field.     

Disturbance mediates the effects of nutrients on developing assemblages of epibiota

Local dynamics such as resource enhancement (e.g. nutrient supply) and stochastic events of destruction (disturbances that provide new space) are hypothesized to counteractively affect species diversity and composition. We tested the independent and interactive effects of nutrients and disturbance on the development of assemblages of epibiota attached to vertical surfaces in an oligotrophic system. Nutrient concentrations were manipulated at three levels (ambient, medium and high) while disturbance was manipulated by removing biomass at seven frequencies (0×, 2×, 3×, 4×, 5×, 7×, 12×). Nutrient and disturbance regimes had opposing effects on diversity such that species richness increased with resource enhancement (nutrients) and declined with disturbance. These results support the model that increased heterogeneity of distribution of limiting resources allows the coexistence of species with low and high resource requirements.     

Differential Effect of w3 PUFA Supplementations on Na,K-ATPase and Mg-ATPase Activities: Possible Role of the Membrane w6/w3 Ratio

Several functional properties of Na,K-ATPase are strongly dependent on membrane fatty acid composition, but the underlying mechanism is still not well defined. We have studied the effects of two types of supplementations enriched in the w3 polyunsaturated fatty acids on the Na,K-ATPase and Mg-ATPase activities in sciatic nerve (SN) and red blood cells (RBC). Eight groups of rats, controls and diabetics, received a standard diet, supplemented or not with 30 or 60 mg/kg/day of docosahexaenoic acid (DHA) or with soybean for eight weeks. Diabetes induced significant decrease of Na,K-ATPase activity in SN (-23%) and RBC (-25%), without affecting Mg-ATPase activity. In RBC, soybean and DHA supplementations caused significant increases in Na,K-ATPase activity (in various range, +13% to +145%) in all groups, and in Mg-ATPase activity in control soybean (+65%), control and diabetic DHA high dose (+39%, +53%) and diabetic DHA low dose (+131%) groups. In SN, the soybean caused a significant decrease in Na,K-ATPase activity (-26%) and still more in the diabetic group (-53%). The DHA diet induced a slight decrease in activity in control groups, whilst during diabetes, at high dose, we noted an aggravation of this decrease (-36%). Mg-ATPase activity was not modified by supplementations except for the low dose of DHA where the activity was slightly decreased in the control group (-16%). The supplementations induced multiple tissue-specific modifications in the membrane fatty acid composition of RBC and of SN homogenates. Several specific correlations have been found between variations in fatty acids amounts and Na,K-ATPase activity in these tissues but only in RBC for Mg-ATPase activity. Indeed, we observed that the variations in Na,K-ATPase activity are positively and significantly correlated with changes in the omega6/omega3 ratio in SN as well as in RBC. These data clearly show, for the first time, that the diet could modulate the Na,K-ATPase activity via the omega6/omega3 ratio in the membranes. A similar correlation was observed with Mg-ATPase activity in RBC, suggesting also a dietary regulation of the enzyme; but for the SN, this activity might be regulated by a different omega6/omega3 ratio or by another pathway.     

Xenopus U3 snoRNA GAC-Box A' and Box A sequences play distinct functional roles in rRNA processing

Mutations in the 5' portion of Xenopus U3 snoRNA were tested for function in oocytes. The results revealed a new cleavage site (A0) in the 3' region of vertebrate external transcribed spacer sequences. In addition, U3 mutagenesis uncoupled cleavage at sites 1 and 2, flanking the 5' and 3' ends of 18S rRNA, and generated novel intermediates: 19S and 18.5S pre-rRNAs. Furthermore, specific nucleotides in Xenopus U3 snoRNA that are required for cleavages in pre-rRNA were identified: box A is essential for site A0 cleavage, the GAC-box A' region is necessary for site 1 cleavage, and the 3' end of box A' and flanking nucleotides are required for site 2 cleavage. Differences between metazoan and yeast U3 snoRNA-mediated rRNA processing are enumerated. The data support a model where metazoan U3 snoRNA acts as a bridge to draw together the 5' and 3' ends of the 18S rRNA coding region within pre-rRNA to coordinate their cleavage.     

The palatability of flavoured novel floating pellets made with brewer's spent grain to captive carp

Abstract

The palatability to common carp, Cyprinus carpio L. of three newly developed differently flavoured floating pellets made from a high proportion (40%) of brewer's spent grain (BSG) was tested using a multiple-offer feeding experiment. The addition of ‘bold’ flavours, such as vanilla or strawberry essence, may help mask the unpleasant taste of some piscicides; however, their inclusion must not compromise uptake by carp. There were no significant differences between the consumption rates of the three varieties, and all flavours were readily consumed. Therefore, it is suggested that highly flavoured pellets made with BSG have a strong potential to mask the flavour of an unpalatable toxin, and further research is now needed to test this hypothesis.     

The addition of CO2 to traditional taste solutions alters taste quality

Previous studies of the effect of carbonation on taste perception have suggested that it may be negligible, manifesting primarily in increases in the perceived intensity of weak salt and sour stimuli. Assuming CO2 solutions in the mouth stimulate only trigeminal nerve endings, this result is not altogether surprising; however, there are neurophysiological data indicating that CO2 stimulates gustatory as well as trigeminal fibers. In that case, carbonation might alter the quality profile of a stimulus without producing substantial changes in overall taste intensity--much as occurs when qualitatively different taste stimuli are mixed. To address this possibility, subjects were asked to rate the total taste intensity of moderate concentrations of stimuli representing each of the basic tastes and their binary combinations, with an without added carbonation. They then subdivided total taste intensity into the proportions of sweetness, saltiness, sourness, bitterness and 'other taste qualities' they perceived. The addition of carbonation produced only small increases in ratings of total taste intensity. However, rather dramatic alterations in the quality profiles of stimuli were observed, particularly for sweet and salty tastes. The nature of the interaction is consistent with a direct effect of carbonation/CO2 on the gustatory system, although the possibility that at least some of the observed effects reflect trigeminal-gustatory interactions cannot be ruled out.      

Glycoside and Polysaccharide Hydrolase Activity of the Rumen Anaerobic Fungus Caecomyces communis (Sphaeromonas communis SENSU ORPIN) at Early and Final Stages of the Developmental Cycle

The rumen anaerobic fungus Caecomyces communis was grown in a fermentor in Lowe medium. We studied four polysaccharide hydrolases and three glycoside hydrolases at early and final stages. We found a difference in cell association for these enzymes depending on the developmental stage. The endocellulase and β-D-fucosidase were early synthesized, and their activities decreased at the end of the developmental cycle. On the contrary, the β-D-glucosidase, β-D-xylosidase and xylanase activities increased during the cycle. The avicelase and the CM-cellulase activities linked with thalli increased, whereas the extracellular activities of these enzymes decreased.