Native and alien plant species richness in relation to spatial heterogeneity on a regional scale in Germany

Aim The aim of our study was to reveal relationships between richness patterns of native vs. alien plant species and spatial heterogeneity across varying landscape patterns at a regional scale. Location The study was carried out in the administrative district of Dessau (Germany), covering around 4000 km². Methods Data on plant distribution of the German vascular flora available in grid cells covering 5′ longitude and 3′ latitude (c. 32 km²) were divided into three status groups: native plants, archaeophytes (pre 1500 AD aliens) and neophytes (post 1500 AD aliens). Land use and abiotic data layers were intersected with 125 grid cells comprising the selected area. Using novel landscape ecological methods, we calculated 38 indices of landscape composition and configuration for each grid cell. Principal components analysis (PCA) with a set of 29 selected, low correlated landscape indices was followed by multiple linear regression analysis. Results PCA reduced 29 indices to eight principal components (PCs) that explained 80% cumulative variance. Multiple linear regression analysis was highly significant and explained 41% to 60% variance in plant species distribution (adjusted R²) with three significant PCs (tested for spatial autocorrelation) expressing moderate to high disturbance levels and high spatial heterogeneity. Comparing the significance of the PCs for the species groups, native plant species richness is most strongly associated with riverine ecosystems, followed by urban ecosystems, and then small‐scale rural ecosystems. Archaeophyte and neophyte richness are most strongly associated with urban ecosystems, followed by small‐scale rural ecosystems and riverine ecosystems for archaeophytes, and riverine ecosystems and small‐scale rural ecosystems for neophytes. Main conclusions Our overall results suggest that species richness of native and alien plants increases with moderate levels of natural and/or anthropogenic disturbances, coupled with high levels of habitat and structural heterogeneity in urban, riverine, and small‐scale rural ecosystems. Despite differences in the order of relevance of PCs for the three plant groups, we conclude that at the regional scale species richness patterns of native plants as well as alien plants are promoted by similar factors.     

A spatial genetics approach to inform vector control of tsetse flies (Glossina fuscipes fuscipes) in Northern Uganda

Tsetse flies (genus Glossina) are the only vector for the parasitic trypanosomes responsible for sleeping sickness and nagana across sub‐Saharan Africa. In Uganda, the tsetse fly Glossina fuscipes fuscipes is responsible for transmission of the parasite in 90% of sleeping sickness cases, and co‐occurrence of both forms of human‐infective trypanosomes makes vector control a priority. We use population genetic data from 38 samples from northern Uganda in a novel methodological pipeline that integrates genetic data, remotely sensed environmental data, and hundreds of field‐survey observations. This methodological pipeline identifies isolated habitat by first identifying environmental parameters correlated with genetic differentiation, second, predicting spatial connectivity using field‐survey observations and the most predictive environmental parameter(s), and third, overlaying the connectivity surface onto a habitat suitability map. Results from this pipeline indicated that net photosynthesis was the strongest predictor of genetic differentiation in G. f. fuscipes in northern Uganda. The resulting connectivity surface identified a large area of well‐connected habitat in northwestern Uganda, and twenty‐four isolated patches on the northeastern margin of the G. f. fuscipes distribution. We tested this novel methodological pipeline by completing an ad hoc sample and genetic screen of G. f. fuscipes samples from a model‐predicted isolated patch, and evaluated whether the ad hoc sample was in fact as genetically isolated as predicted. Results indicated that genetic isolation of the ad hoc sample was as genetically isolated as predicted, with differentiation well above estimates made in samples from within well‐connected habitat separated by similar geographic distances. This work has important practical implications for the control of tsetse and other disease vectors, because it provides a way to identify isolated populations where it will be safer and easier to implement vector control and that should be prioritized as study sites during the development and improvement of vector control methods.     

Microbial responses to solvent and alcohol stress

Increasing fuel prices and doubts over the long-term availability of oil are currently major global concerns. Such concerns have led to national policies and objectives to develop microbially produced alcohols as fuel additives or substitutes. However, in South Africa this solution poses the further dilemma of sourcing a suitable fermentative carbohydrate that will not impact negatively on the availability of staple foods. The solution lies in the use of lignocellulosic materials, currently a waste product of the food and agriculture industries, which could be used in conjunction with a catabolically suitable production strain. In the pursuit of lignocellulosic biofuel production, conventional fermentation strains have been shown to have limited catabolic versatility. However, catabolically versatile engineered strains and novel isolates engineered with ethanologenic pathways have subsequently been shown to exhibit limitations in solvent tolerance, hindering their full potential as economically viable production strains. A considerable volume of research has been reported on the general cellular mechanisms and physiological responses to solvent shock as well as adaptive changes responsible for solvent tolerant phenotypes in mutant progeny. Here we review a number of the more common cell responses to solvents with particular focus on alcohol tolerance.     

Genome sequence of the emerging pathogen Aeromonas caviae

Aeromonas caviae is a Gram-negative, motile and rod-shaped facultative anaerobe that is increasingly being recognized as a cause of diarrhea in children. Here we present the first genome sequence of an A. caviae strain that was isolated as the sole pathogen from a child with profuse diarrhea.     

RAPID DIVERSIFICATION OF SPERM PRECEDENCE TRAITS AND PROCESSES AMONG THREE SIBLING DROSOPHILA SPECIES

Postcopulatory sexual selection is credited with driving rapid evolutionary diversification of reproductive traits and the formation of reproductive isolating barriers between species. This judgment, however, has largely been inferred rather than demonstrated due to general lack of knowledge about processes and traits underlying variation in competitive fertilization success. Here, we resolved processes determining sperm fate in twice‐mated females, using transgenic Drosophila simulans and Drosophila mauritiana populations with fluorescently labeled sperm heads. Comparisons among these two species and Drosophila melanogaster revealed a shared motif in the mechanisms of sperm precedence, with postcopulatory sexual selection potentially occurring during any of the three discrete stages: (1) insemination; (2) sperm storage; and (3) sperm use for fertilization, and involving four distinct phenomena: (1) sperm transfer; (2) sperm displacement; (3) sperm ejection; and (4) sperm selection for fertilizations. Yet, underlying the qualitative similarities were significant quantitative differences in nearly every relevant character and process. We evaluate these species differences in light of concurrent investigations of within‐population variation in competitive fertilization success and postmating/prezygotic reproductive isolation in hybrid matings between species to forge an understanding of the relationship between microevolutionary processes and macroevolutionary patterns as pertains to postcopulatory sexual selection in this group.     

Critical role for the tapasin-docking site of TAP2 in the functional integrity of the MHC class I-peptide-loading complex

The transporter associated with Ag processing (TAP) translocates antigenic peptides into the endoplasmic reticulum for binding onto MHC class I (MHC I) molecules. Tapasin organizes a peptide-loading complex (PLC) by recruiting MHC I and accessory chaperones to the N-terminal regions (N domains) of the TAP subunits TAP1 and TAP2. To investigate the function of the tapasin-docking sites of TAP in MHC I processing, we expressed N-terminally truncated variants of TAP1 and TAP2 in combination with wild-type chains, as fusion proteins or as single subunits. Strikingly, TAP variants lacking the N domain in TAP2, but not in TAP1, build PLCs that fail to generate stable MHC I-peptide complexes. This correlates with a substantially reduced recruitment of accessory chaperones into the PLC demonstrating their important role in the quality control of MHC I loading. However, stable surface expression of MHC I can be rescued in post-endoplasmic reticulum compartments by a proprotein convertase-dependent mechanism.     

Trichloroethylene Degradation by Toluene-Oxidizing Bacteria Grown on Non-aromatic Substrates

The potential of trichloroethylene (TCE) to induce and non-aromatic growth substrates to support TCE degradation in five strains (Pseudomonas mendocina KR1, Ralstonia pickettii PKO1, Pseudomonas putida F1, Burkholderia cepacia G4, B. cepacia PR1) of toluene-oxidizing bacteria was examined. LB broth and acetate did not support TCE degradation in any of the wild-type strains. In contrast, fructose supported the highest specific levels of TCE oxidation observed in each of the strains tested, except B. cepacia G4. We discuss the potential mechanisms and implications of this observation. In particular, cells of P. mendocina KR1 degraded significant amounts of TCE during cell growth on non-aromatic substrates. Apparently, TCE degradation was not completely constrained by any given factor in this microorganism, as was observed with P. putida F1 (TCE was an extremely poor substrate) or B. cepacia G4 (lack of oxygenase induction by TCE). Our results indicate that multiple physiological traits are required to enable useful TCE degradation by toluene-oxidizing bacteria in the absence of aromatic cosubstrates. These traits include oxygenase induction, effective TCE turnover, and some level of resistance to TCE mediated toxicity.     

Family-level covariation between parasite resistance and mating system in a hermaphroditic freshwater snail

Genetic compatibility, nonspecific defenses, and environmental effects determine parasite resistance. Host mating system (selfing vs. outcrossing) should be important for parasite resistance because it determines the segregation of alleles at the resistance loci and because inbreeding depression may hamper immune defenses. Individuals of a mixed mating hermaphroditic freshwater snail, Lymnaea ovata, are commonly infected by a digenetic trematode parasite, Echinoparyphium recurvatum. We examined covariation between quantitative resistance to novel parasites and mating system by exposing snail families from four populations that differed by their inbreeding coefficients. We found that resistance was unrelated to inbreeding coefficient of the population, suggesting that the more inbred populations did not carry higher susceptibility load than the less inbred populations. Most of the variation in resistance was expressed among the families within the populations. In the population with the lowest inbreeding coefficient, resistance increased with outcrossing rate of the family, as predicted if selfing had led to inbreeding depression. In the other three populations with higher inbreeding coefficients, resistance was unrelated to outcrossing rate. The results suggest that in populations with higher inbreeding some of the genetic load has been purged, uncoupling the predicted relationship between outcrossing rate and resistance. Snail families also displayed crossing reaction norms for resistance when tested in two environments that presented low and high immune challenge, suggesting that genotype-by-environment interactions are important for parasite resistance.     

The high number of neurons contributes to the robustness of the locust flight-CPG against parameter variation

 Real pattern-generating networks often consist of more neurons than necessary for the production of a certain rhythm. We investigated the question of whether these neurons contribute to the robustness of a pattern-generating system of using the central pattern generator (CPG) for flight of the locust, generating the deafferented activity pattern of wing elevator and wing depressor motoneurons, as an example of a rhythm-generating system. The neuronal network was reconstructed, based on the known connectivity of the interneurons in the flight CPG, using a biologically orientated network simulator (BioSim 3.0). This simulator allows a physiologically realistic simulation of particular neurons as well as the synaptic connections between them. The flight CPG consists of at least five cyclic loops. The simulation shows that each of them is in principle able to produce a rhythm comparable to the rhythm produced by the whole network, i.e. the ‘deafferented’ flight pattern of elevator and depressor motoneurons. Varying the parameter ‘synaptic strength’ in each of these loops and in the complete system shows that this parameter can be changed within certain ranges without loosing the ability to produce oscillations. These ranges are much smaller in each of the subloops than in the whole network. This result demonstrates that the robustness of the system is increased by supranumerary neurons and connections. Changing the active properties of the simulated neurons so that they are able to produce plateau potentials has no effect on the robustness of the simulated network. Received: 13 April 1994/Accepted in revised form: 15 September 1994