Sampling efficacy for the red imported fire ant Solenopsis invicta (Hymenoptera: Formicidae)

Cost-effective detection of invasive ant colonies before establishment in new ranges is imperative for the protection of national borders and reducing their global impact. We examined the sampling efficiency of food-baits and pitfall traps (baited and nonbaited) in detecting isolated red imported fire ant (Solenopsis invicta Buren) nests in multiple environments in Gainesville, FL. Fire ants demonstrated a significantly higher preference for a mixed protein food type (hotdog or ground meat combined with sweet peanut butter) than for the sugar or water baits offered. Foraging distance success was a function of colony size, detection trap used, and surveillance duration. Colony gyne number did not influence detection success. Workers from small nests (0- to 15-cm mound diameter) traveled no >3 m to a food source, whereas large colonies (>30-cm mound diameter) traveled up to 17 m. Baited pitfall traps performed best at detecting incipient ant colonies followed by nonbaited pitfall traps then food baits, whereas food baits performed well when trying to detect large colonies. These results were used to create an interactive model in Microsoft Excel, whereby surveillance managers can alter trap type, density, and duration parameters to estimate the probability of detecting specified or unknown S. invicta colony sizes. This model will support decision makers who need to balance the sampling cost and risk of failure to detect fire ant colonies.     

Effects of Visual Feedback-Induced Variability on Motor Learning of Handrim Wheelchair Propulsion

BackgroundIt has been suggested that a higher intra-individual variability benefits the motor learning of wheelchair propulsion. The present study evaluated whether feedback-induced variability on wheelchair propulsion technique variables would also enhance the motor learning process. Learning was operationalized as an improvement in mechanical efficiency and propulsion technique, which are thought to be closely related during the learning process.Methods17 Participants received visual feedback-based practice (feedback group) and 15 participants received regular practice (natural learning group). Both groups received equal practice dose of 80 min, over 3 weeks, at 0.24 W/kg at a treadmill speed of 1.11 m/s. To compare both groups the pre- and post-test were performed without feedback. The feedback group received real-time visual feedback on seven propulsion variables with instruction to manipulate the presented variable to achieve the highest possible variability (1^st 4-min block) and optimize it in the prescribed direction (2^nd 4-min block). To increase motor exploration the participants were unaware of the exact variable they received feedback on. Energy consumption and the propulsion technique variables with their respective coefficient of variation were calculated to evaluate the amount of intra-individual variability.ResultsThe feedback group, which practiced with higher intra-individual variability, improved the propulsion technique between pre- and post-test to the same extent as the natural learning group. Mechanical efficiency improved between pre- and post-test in the natural learning group but remained unchanged in the feedback group.ConclusionThese results suggest that feedback-induced variability inhibited the improvement in mechanical efficiency. Moreover, since both groups improved propulsion technique but only the natural learning group improved mechanical efficiency, it can be concluded that the improvement in mechanical efficiency and propulsion technique do not always appear simultaneously during the motor learning process. Their relationship is most likely modified by other factors such as the amount of the intra-individual variability.     

Stable isotope variation of a highly heterogeneous shallow freshwater system

Food web structure is well known to vary widely among ecosystems. Recent research indicates that there can be a high degree of spatial heterogeneity within ecosystems as well. Xochimilco is a small heterogeneous freshwater system that has been transformed into a network of canals, small lakes, and wetlands. Located within Mexico City, this ecosystem has been intensively managed and highly impacted for more than 50 years. This system receives urban and agricultural runoff, with resulting impacts on water quality. The aquatic community is dominated by exotics such as carp (Cyprinus carpio) and tilapia (Oreocrhomis niloticus), though the system still supports endemic species such as the aquatic salamander, axolotl (Ambystoma mexicanum), and crayfish (Cambarellus montezumae), which are both endangered. In this study, we used carbon and nitrogen stable isotopes for the whole food web and gut content analysis from the exotic fishes to describe food web structure in different canals within Xochimilco. There were significant isotopic differences among canals. These differences may result from isotopic baseline differences as well as differences in actual food web structure: both are related to local spatial variation in water quality driven by nutrient inputs and exotic fishes. Within-ecosystem variability is likely to be seen in other perturbed shallow systems as well, and should be explicitly considered in future food web studies.     

Structural insights into substrate binding by the molecular chaperone DnaK

How substrate affinity is modulated by nucleotide binding remains a fundamental, unanswered question in the study of 70 kDa heat shock protein (Hsp70) molecular chaperones. We find here that the Escherichia coli Hsp70, DnaK, lacking the entire alpha-helical domain, DnaK(1-507), retains the ability to support lambda phage replication in vivo and to pass information from the nucleotide binding domain to the substrate binding domain, and vice versa, in vitro. We determined the NMR solution structure of the corresponding substrate binding domain, DnaK(393-507), without substrate, and assessed the impact of substrate binding. Without bound substrate, loop L3,4 and strand beta3 are in significantly different conformations than observed in previous structures of the bound DnaK substrate binding domain, leading to occlusion of the substrate binding site. Upon substrate binding, the beta-domain shifts towards the structure seen in earlier X-ray and NMR structures. Taken together, our results suggest that conformational changes in the beta-domain itself contribute to the mechanism by which nucleotide binding modulates substrate binding affinity.     

N2-Succinylornithine in ornithine catabolism of Pseudomonas aeruginosa

Most Pseudomonas aeruginosa PAO mutants which were unable to utilize l-arginine as the sole carbon and nitrogen source (aru mutants) under aerobic conditions were also affected in l-ornithine utilization. These aru mutants were impaired in one or several enzymes involved in the conversion of N²-succinylornithine to glutamate and succinate, indicating that the latter steps of the arginine succinyltransferase pathway can be used for ornithine catabolism. Addition of aminooxyacetate, an inhibitor of the N²-succinylornithine 5-aminotransferase, to resting cells of P. aeruginosa in ornithine medium led to the accumulation of N²-succinylornithine. In crude extracts of P. aeruginosa an ornithine succinyltransferase (l-ornithine:succinyl-CoA N²-succinyltransferase) activity could be detected. An aru mutant having reduced arginine succinyltransferase activity also had correspondingly low levels of ornithine succinyltransferase. Thus, in P. aeruginosa, these two activities might be due to the same enzyme, which initiates aerobic arginine and ornithine catabolism.Abbreviations OAT ornithine 5-aminotransferase - SOAT N²-succinylornithine 5-aminotransferase - Oru ornithine utilization - Aru arginine utilization