Reflections on Plant and Soil Nematode Ecology: Past,Present and Future

The purpose of this review is to highlight key developments in nematode ecology from its beginnings to where it stands today as a discipline within nematology. Emerging areas of research appear to be driven by crop production constraints, environmental health concerns, and advances in technology. In contrast to past ecological studies which mainly focused on management of plant-parasitic nematodes, current studies reflect differential sensitivity of nematode faunae. These differences, identified in both aquatic and terrestrial environments include response to stressors, environmental conditions, and management practices. Methodological advances will continue to influence the role nematodes have in addressing the nature of interactions between organisms, and of organisms with their environments. In particular, the C. elegans genetic model, nematode faunal analysis and nematode metagenetic analysis can be used by ecologists generally and not restricted to nematologists.     

Function of defensive volatiles in pedunculate oak (Quercus robur) is tricked by the moth Tortrix viridana

The indirect defences of plants are comprised of herbivore‐induced plant volatiles (HIPVs) that among other things attract the natural enemies of insects. However, the actual extent of the benefits of HIPV emissions in complex co‐evolved plant‐herbivore systems is only poorly understood. The observation that a few Quercus robur L. trees constantly tolerated (T‐oaks) infestation by a major pest of oaks (Tortrix viridana L.), compared with heavily defoliated trees (susceptible: S‐oaks), lead us to a combined biochemical and behavioural study. We used these evidently different phenotypes to analyse whether the resistance of T‐oaks to the herbivore was dependent on the amount and scent of HIPVs and/or differences in non‐volatile polyphenolic leaf constituents (as quercetin‐, kaempferol‐ and flavonol glycosides). In addition to non‐volatile metabolic differences, typically defensive HIPV emissions differed between S‐oaks and T‐oaks. Female moths were attracted by the blend of HIPVs from S‐oaks, showing significantly higher amounts of (E)‐4,8‐dimethyl‐1,3,7‐nonatriene (DMNT) and (E)‐β‐ocimene and avoid T‐oaks with relative high fraction of the sesquiterpenes α‐farnesene and germacrene D. Hence, the strategy of T‐oaks exhibiting directly herbivore‐repellent HIPV emissions instead of high emissions of predator‐attracting HIPVs of the S‐oaks appears to be the better mechanism for avoiding defoliation.     

Brain Networks Supporting Execution of Mathematical Skills versus Acquisition of New Mathematical Competence

This fMRI study examines how students extend their mathematical competence. Students solved a set of algebra-like problems. These problems included Regular Problems that have a known solution technique and Exception Problems that but did not have a known technique. Two distinct networks of activity were uncovered. There was a Cognitive Network that was mainly active during the solution of problems and showed little difference between Regular Problems and Exception Problems. There was also a Metacognitive Network that was more engaged during a reflection period after the solution and was much more engaged for Exception Problems than Regular Problems. The Cognitive Network overlaps with prefrontal and parietal regions identified in the ACT-R theory of algebra problem solving and regions identified in the triple-code theory as involved in basic mathematical cognition. The Metacognitive Network included angular gyrus, middle temporal gyrus, and anterior prefrontal regions. This network is mainly engaged by the need to modify the solution procedure and not by the difficulty of the problem. Only the Metacognitive Network decreased with practice on the Exception Problems. Activity in the Cognitive Network during the solution of an Exception Problem predicted both success on that problem and future mastery. Activity in the angular gyrus and middle temporal gyrus during feedback on errors predicted future mastery.     

Exposure to infant scent lowers serum testosterone in father common marmosets (Callithrix jacchus)

Common marmoset (Callithrix jacchus) males are bi-parental non-human primates that show extensive paternal behaviour. Fathers are in direct sensory contact with their infants during the natal period. We found that fathers exposed to isolated scents of their infant displayed a significant drop in serum testosterone levels within 20min after exposure, whereas parentally naive males did not. These data suggest that infant's scent may have a causal role in regulating paternal testosterone in their fathers. This is the first study to demonstrate that olfactory cues have an acute effect on paternal care.     

Poor reporting of scientific leadership information in clinical trial registers

Background

In September 2004, the International Committee of Medical Journal Editors (ICMJE) issued a Statement requiring that all clinical trials be registered at inception in a public register in order to be considered for publication. The World Health Organization (WHO) and ICMJE have identified 20 items that should be provided before a trial is considered registered, including contact information. Identifying those scientifically responsible for trial conduct increases accountability. The objective is to examine the proportion of registered clinical trials providing valid scientific leadership information.

Methodology/Principal Findings

We reviewed clinical trial entries listing Canadian investigators in the two largest international and public trial registers, the International Standard Randomized Controlled Trial Number (ISRCTN) register, and ClinicalTrials.gov. The main outcome measures were the proportion of clinical trials reporting valid contact information for the trials'' Principal Investigator (PI)/Co-ordinating Investigator/Study Chair/Site PI, and trial e-mail contact address, stratified by funding source, recruiting status, and register. A total of 1388 entries (142 from ISRCTN and 1246 from ClinicalTrials.gov) comprised our sample. We found non-compliance with mandatory registration requirements regarding scientific leadership and trial contact information. Non-industry and partial industry funded trials were significantly more likely to identify the individual responsible for scientific leadership (OR = 259, 95% CI: 95–701) and to provide a contact e-mail address (OR = 9.6, 95% CI: 6.6–14) than were solely industry funded trials.

Conclusions/Significance

Despite the requirements set by WHO and ICMJE, data on scientific leadership and contact e-mail addresses are frequently omitted from clinical trials registered in the two leading public clinical trial registers. To promote accountability and transparency in clinical trials research, public clinical trials registers should ensure adequate monitoring of trial registration to ensure completion of mandatory contact information fields identifying scientific leadership     

The structure and orientation of the C-terminus of LRAP

Amelogenin is the predominant protein found during enamel development and is thought to be the biomineralization protein controlling the unique elongated hydroxyapatite crystals that constitute enamel. The secondary structure of biomineralization proteins is thought to be important in the interaction with hydroxyapatite. Unfortunately, very little data are available on the structure or the orientation of amelogenin, either in solution or bound to hydroxyapatite. The C-terminus contains the majority of the charged residues and is predicted to interact with hydroxyapatite; thus, we used solid-state NMR dipolar recoupling techniques to investigate the structure and orientation of the C-terminus of LRAP, a naturally occurring splice variant of full-length amelogenin. Using ¹³C{¹⁵N} Rotational Echo DOuble Resonance (REDOR), the structure of the C-terminus was found to be largely random coil, both on the surface of hydroxyapatite as well as lyophilized from solution. The orientation of the C-terminal region with respect to hydroxyapatite was investigated for two alanine residues (Ala⁴⁶ and Ala⁴⁹) using ¹³C{³¹P} REDOR and one lysine residue (Lys⁵²) using ¹⁵N{³¹P} REDOR. The residues examined were found to be 7.0, 5.7, and 5.8 Å from the surface of hydroxyapatite for Ala⁴⁶, Ala⁴⁹, and Lys⁵², respectively. This provides direct evidence that the charged C-terminus is interacting closely with hydroxyapatite, positioning the acidic amino acids to aid in controlling crystal growth. However, solid-state NMR dynamics measurements also revealed significant mobility in the C-terminal region of the protein, in both the side chains and the backbone, suggesting that this region alone is not responsible for binding.     

Sensitivity of Nematode Life-History Groups to Ions and Osmotic Tensions of Nitrogenous Solutions

Guild designation of nematodes of similar trophic function and life-history strategy provides a basis for using nematode faunal analyses in an integrative assessment of soil food web condition. Omnivorous and predaceous nematodes, categorized at the upper end of a colonizer-persister (c-p) continuum of nematode functional guilds are generally not abundant in cropped soil. These nematodes are more sensitive to heavy metal concentrations than those in other c-p groups, but whether sensitivity to agrochemicals contributes to the observed low abundance of high c-p groups in cropped soils is less well understood. An exposure assay in solution was used to compare the sensitivity of nematodes representing various guilds obtained from field soils and from laboratory culture to several nitrogen sources. Nematodes in c-p groups 4 and 5 were more sensitive to nitrogen solutions than nematodes representing lower c-p groups. There were both osmotic and specific ion effects—the latter most evident in exposure of nematodes to NaNO₂ and (NH₄)₂SO₄. The RC₅₀ (concentration resulting in nematode recovery of one half of that of distilled water) for (NH₄)₂SO₄ was < 0.052 M-N for c-p groups 4 and 5 compared to much greater values (0.34 to 0.81 M-N) for c-p groups 1 to 3. In non-ionic polyethylene glycol (PEG) solutions, osmotic tensions of 0.40 to 0.43 MPa reduced the recovery of exposed nematodes by half (RT₅₀; water potential of solution resulting in nematode recovery of one half of that of distilled water) for c-p groups 4 and 5 compared to > 1.93 MPa for c-p groups 1 to 3. RT₅₀ values for urea solutions, also non-ionic, were greater than for PEG. Caenorhabditis elegans N2 (c-p 1) and Meloidogyne javanica (c-p 3) reared on solid medium and in hydroponic culture, respectively, were slightly more sensitive to specific ion and osmotic effects than nematodes of similar c-p groups obtained from soil. The greater sensitivity of c-p 4 and 5 nematodes to nitrogen solutions suggests that fertilizers may contribute to the low abundance of these nematodes in annual cropping systems. This study supports the use of nematode faunal analyses as indicators of chemical stress in soil.     

Genetic structure of the mating-type locus of Chlamydomonas reinhardtii.

Portions of the cloned mating-type (MT) loci (mt(+) and mt(-)) of Chlamydomonas reinhardtii, defined as the approximately 1-Mb domains of linkage group VI that are under recombinational suppression, were subjected to Northern analysis to elucidate their coding capacity. The four central rearranged segments of the loci were found to contain both housekeeping genes (expressed during several life-cycle stages) and mating-related genes, while the sequences unique to mt(+) or mt(-) carried genes expressed only in the gametic or zygotic phases of the life cycle. One of these genes, Mtd1, is a candidate participant in gametic cell fusion; two others, Mta1 and Ezy2, are candidate participants in the uniparental inheritance of chloroplast DNA. The identified housekeeping genes include Pdk, encoding pyruvate dehydrogenase kinase, and GdcH, encoding glycine decarboxylase complex subunit H. Unusual genetic configurations include three genes whose sequences overlap, one gene that has inserted into the coding region of another, several genes that have been inactivated by rearrangements in the region, and genes that have undergone tandem duplication. This report extends our original conclusion that the MT locus has incurred high levels of mutational change.