Dispersal and gene flow in free-living marine nematodes

Dispersal and gene flow determine connectivity among populations, and can be studied through population genetics and phylogeography. We here review the results of such a framework for free-living marine nematodes. Although field experiments have illustrated substantial dispersal in nematodes at ecological time scales, analysis of the genetic diversity illustrated the importance of priority effects, founder effects and genetic bottlenecks for population structuring between patches <1 km apart. In contrast, only little genetic structuring was observed within an estuary (<50 km), indicating that these small scale fluctuations in genetic differentiation are stabilized over deeper time scales through extensive gene flow. Interestingly, nematode species with contrasting life histories (extreme colonizers vs persisters) or with different habitat preferences (algae vs sediment) show similar, low genetic structuring. Finally, historical events have shaped the genetic pattern of marine nematodes and show that gene flow is restricted at large geographical scales. We also discuss the presence of substantial cryptic diversity in marine nematodes, and end with highlighting future important steps to further unravel nematode evolution and diversity

Chemical weed control in triticale (x Triticosecale Wittmack): review of five years of field experiments

During 5 subsequent growing seasons field experiments were carried out at the experimental farm of the University College Ghent (Belgium) to evaluate the selectivity and efficacy of herbicides applied for chemical weed control in triticale (x Triticosecale Wittmack). The experiments were set up on a sandy loam soil, according to a completely randomised block design with 4 replicates. Several herbicides and combinations of herbicides were applied pre- and post-emergence, at different rates. The influence of the different treatments on weed diversity, weed density, growth inhibition and chlorosis of the crop and grain yield were studied. Results obtained from these field trials indicated differences between the different treatments

Carbon Nanotubes as Schottky Barrier Transistors

We show that carbon nanotube transistors operate as unconventional "Schottky barrier transistors", in which transistor action occurs primarily by varying the contact resistance rather than the channel conductance. Transistor characteristics are calculated for both idealized and realistic geometries, and scaling behavior is demonstrated. Our results explain a variety of experimental observations, including the quite different effects of doping and adsorbed gases. The electrode geometry is shown to be crucial for good device performance.Comment: 4 pages, 5 figures, appears in Physical Review Letter

Salinity effects on competition between cryptic species of the nematode Rhabditis (Pellioditis) marina

Behind the morphological similarity of many species, a substantial hidden genetic diversity can be found. This cryptic diversity has been well documented in the marine nematode, Rhabditis (Pellioditis) marina, where several cryptic species occur sympatrically. Despite the growing knowledge about its cryptic diversity, little is known about potential differences in the ecology and functional roles of the different species. In this experiment four cryptic species of Rhabditis (Pellioditis) marina were reared together, starting from identical initial abundances at two different salinity concentrations to investigate differences in their environmental preferences and how they may affect the outcome of their competitive interactions. Every fifth day of the experiment one third of the adults was removed from the population for analyzing the genetic composition of the population; adult and juvenile population dynamics were also examined. The first results show a difference in population dynamics dependent on the salinity. At low salinity, a population crash occurred after 15 days in all the populations. Only half of the populations recovered from this bottleneck and reached higher abundances than before. Genetic analyses revealed that the composition of these populations consists solely of individuals of one cryptic species. This effect was totally absent in the populations reared at higher salinity. Two explanations are possible: (1) the different cryptic species have different survival rates at different salinities and (2) the competitive interactions between them differ at different salinities. We are currently identifying the sampled adults using a restriction fragment analysis to assess these explanations and to elucidate the effect of salinity on the coexistence of cryptic species of Rhabditis (Pellioditis) marina

Ph.D. holders on the Belgian labour market

In which sector do Ph.D. graduates end up working? What is the minimum and desired education level for their current job? Which skills do they need in their current job, and how does this compare to the skills acquired during the Ph.D. track? These questions are answered by looking at responses of a sample of 4190 doctorate holders in the Belgian Careers of Doctorate Holders Survey 2010 (CDH)

Differences in life-histories refute ecological equivalence of cryptic species and provide clues to the origin of bathyal Halomonhystera (Nematoda)

The discovery of morphologically very similar but genetically distinct species complicates a proper understanding of the link between biodiversity and ecosystem functioning. Cryptic species have been frequently observed to co-occur and are thus expected to be ecological equivalent. The marine nematode Halomonhystera disjuncta contains five cryptic species (GD1-5) that co-occur in the Westerschelde estuary. In this study, we investigated the effect of three abiotic factors (salinity, temperature and sulphide) on life-history traits of three cryptic H. disjuncta species (GD1-3). Our results show that temperature had the most profound influence on all life-cycle parameters compared to a smaller effect of salinity. Life-history traits of closely related cryptic species were differentially affected by temperature, salinity and presence of sulphides which shows that cryptic H. disjuncta species are not ecologically equivalent. Our results further revealed that GD1 had the highest tolerance to a combination of sulphides, high salinities and low temperatures. The close phylogenetic position of GD1 to Halomonhystera hermesi, the dominant species in sulphidic sediments of the Hakon Mosby mud volcano (Barent Sea, 1280 m depth), indicates that both species share a recent common ancestor. Differential life-history responses to environmental changes among cryptic species may have crucial consequences for our perception on ecosystem functioning and coexistence of cryptic species

Phosphate removal in agro-industry: pilot- and full-scale operational considerations of struvite crystallization

Pilot-scale struvite crystallisation tests using anaerobic effluent from potato processing industries were performed at three different plants. Two plants (P1 & P2) showed high phosphate removal efficiencies, 89 + 3% and 75 + 8%, resulting in final effluent levels of 12 + 3 mg PO4/3- -P/L and 11 + 3 mg PO4/3- -P/L, respectively. In contrast, poor phosphate removal (19 + 8%) was obtained at the third location (P3). A noticeable difference in the influent Ca2+/PO4/3- -P molar ratio was observed between the test sites, ranging from 0.27 + 0.08 (P1), 0.62 + 0.18 (P2) and 0.41 + 0.04 (P3). A negative effect on struvite formation occurred when a Ca2+/PO4/3- -P molar ratio of 1.25 + 0.11 was obtained after initial pH increase in the stripper at P3. A full-scale struvite plant treating 90–110 m3/h of anaerobic effluent from a diary industry also showed Ca2+ interference. Initially in this plant, influent phosphate levels ranging from 40 to 45 mg PO4/3- -P/L were decreased to below 10 mg PO4/3- -P/L, but no struvite was produced. A shift in Ca2+/PO4/3- -P molar ratio from 2.69 to 1.36 by an increased phosphate concentration resulted in average total phosphorus removal of 78 + 7%, corresponding with effluent levels of 14 + 4 mg Ptotal/L(9 + 3 mg PO4/3- -P/L). Under these conditions pure spherical struvite pellets of 2–6 mm were produced