Undulatory fish swimming: from muscles to flow

Undulatory swimming is employed by many fish for routine swimming and extended sprints. In this biomechanical review, we address two questions: (i) how the fish's axial muscles power swimming; and (ii) how the fish's body and fins generate thrust. Fish have adapted the morphology of their axial musculature for high power output and efficiency. All but the superficial muscle fibres are arranged along curved trajectories, and the myomeres form nested cones. Two conflicting performance goals shape the fibre trajectories of the axial muscles. Maximum power output requires that all fibres contract uniformly. In a bending fish, uniform contraction in a single myomere can be ensured by curved fibre trajectories. However, uniform strain is only desirable if all muscle fibres have the same contractile properties. The fish needs several muscle‐fibre types that generate maximum power at different contraction speeds to ensure effective muscle power generation across a range of swimming speeds. Consequently, these different muscle‐fibre types are better served by non‐uniform contractions. High power output at a range of swimming speeds requires that muscle fibres with the same contractile properties contract uniformly. The ensuing helical fibre trajectories require cone‐shaped myomeres to reduce wasteful internal deformation of the entire muscle when it contracts. It can be shown that the cone‐shaped myomeres of fish can be explained by two design criteria: uniform contraction (uniform strain hypothesis) and minimal internal deformation (mechanical stability hypothesis). So far, only the latter hypothesis has found strong support. The contracting muscle causes the fish body to undulate. These body undulations interact with the surrounding water to generate thrust. The resulting flow behind the swimming fish forms vortex rings, whose arrangement reflects the fish's swimming performance. Anguilliform swimmers shed individual vortex rings during steady swimming. Carangiform swimmers shed a connected chain of vortex rings. The currently available sections through the total flow fields are often not an honest representation of the total momentum in the water – the wake of carangiform swimmers shows a net backward momentum without the fish accelerating – suggesting that our current picture of the generated flow is incomplete. To accelerate, undulatory swimmers decrease the angle of the vortex rings with the mean path of motion, which is consistent with an increased rate of backward momentum transfer. Carangiform swimmers also enlarge their vortex rings to accelerate and to swim at a higher speed, while eel, which are anguilliform swimmers, shed stronger vortex rings.     

Veterinarians’ perspective on a voluntary Johne’s disease prevention program in Ontario and western Canada

A survey was conducted to assess the beliefs of veterinarians on Johne’s disease (JD) and their attitudes towards the Canadian, risk assessment based, JD prevention program. The veterinarians surveyed believed Mycobacterium avium subsp. paratuberculosis may have zoonotic potential, liked the risk assessment based program, and thought it could lead to the prevention of other on-farm diseases.     

Effect of fungicides on the complex of <Emphasis Type="Italic">Fusarium</Emphasis> species and saprophytic fungi colonizing wheat kernels

Fusarium head blight of wheat, often associated with mycotoxin contamination of food and feed is caused by various Fusarium species. The efficacy of fungicide sprays for the control of the disease and mycotoxins varies from being highly effective to even increasing mycotoxin levels. The potential role of antagonistic fungi in this variability was investigated assessing sensitivity of Fusarium species and saprophytic fungi colonizing wheat kernels to fungicides. Saprophytes were tested for their antagonistic activity to the prevalent Fusarium species Fusarium avenaceum, Fusarium culmorum, Fusarium graminearum, and Fusarium poae. Fungal isolates from mature winter wheat kernels were Alternaria alternata, Arthrinium sp., Aspergillus niger, Epicoccum sp., Microdochium spp., Rhizopus oryzae and Trichoderma sp. In dual culture A. niger, R. oryzae and Trichoderma hamatum were more effective in reducing mycelial growth of Fusarium species than Microdochium majus; A. alternata and Epicoccum sp. were ineffective because of slow growth rates. Saprophytic fungi were sensitive to triazoles; however, prothioconazole and tebuconazole had stronger effects on mycelial growth of Fusarium species. ED₅₀ values also indicated significant differences in the sensitivity of Fusarium species to triazoles (range 0.1–1.7 mg l⁻¹). Azoxystrobin and fluoxastrobin were largely ineffective in inhibiting in vitro growth of Fusarium spp.; sensitivity of the other fungi was generally lower, except for M. majus which was highly sensitive. Due to differences in fungicide sensitivity among Fusarium spp. and ear-colonizing fungi antagonistic to Fusarium spp. fungicides are likely to modify the balance within the mycoflora of wheat ears which may also affect the mycotoxin contamination of grain.     

Report on the 42nd joint meeting of the DPG-working group Nematology and the working group “free living nematodes”

Journal of Plant Diseases and Protection -     

Immunohistochemical investigation of Foxp3 expression in the intestine in healthy and diseased dogs

ABSTRACT: Intestinal immune regulation including development of oral tolerance is of great importance for the maintenance of intestinal homeostasis. Concerning this, regulatory T cells (Tregs) occupy a pivotal role in cell-mediated immunosuppression. Dysregulation of mucosal immunology leading to an abnormal interaction with commensal bacteria is suggested to play a key role in the pathogenesis of Inflammatory Bowel Disease (IBD) in men and dogs. The aim of this study was to characterise the expression of Foxp3 in the normal canine gut of 18 dogs (mean age: 6.03 years), in 16 dogs suffering from IBD (mean age: 5.05 years), and of 6 dogs with intestinal nematode infection (mean age: 0.87 years) using immunohistochemistry. In the duodenum, Tregs in healthy dogs declined from villi (median: 10.67/62 500 μm2) to crypts (median: 1.89/62 500 μm2). Tregs were further increased in the villi of middle-aged dogs (median: 18.92/62 500 μm2) in contrast to juvenile (median: 3.50/62 500 μm2) and old (median: 9.56/62 500 μm2) individuals. Compared to healthy controls, animals suffering from IBD revealed reduced numbers of Tregs in duodenal villi (median: 4.13/62 500 μm2). Dogs with intestinal nematode infection displayed increased numbers of Tregs (median: 21.06/62 500 μm2) compared to healthy animals.Age-related changes indicate a progressive establishment of oral tolerance and immunosenescence in the canine elderly. The results further suggest that a defect in Treg homeostasis may be involved in the pathogenesis of canine IBD. In contrast, increased numbers of Tregs in the duodenum may be due to nematode infection.     

In search for the ecological and toxicological relevance of sediment re-mobilisation and transport during flood events

In response to increasing concerns about the potential toxicological impacts of (extreme) flood events, scientists from several disciplines have joined to form the interdisciplinary research project named FLOODSEARCH. FLOODSEARCH is one of the recent Pathfinder Projects supported by the German Excellence Initiative via the Exploratory Research Space at RWTH Aachen (ERS). FLOODSEARCH aims to combine methodologies of hydraulic engineering and ecotoxicology in a new interdisciplinary approach to assess the risks associated with the re-mobilisation of particulate bound contaminants often observed after severe flood events. Impacts of extreme flood events and aspects of re-mobilisation of sediment-bound toxic compounds will be characterised and evaluated in controlled experiments fusing flood simulation technologies with biological effects assessment. The overall goal is to establish a novel and more realistic approach towards flood event testing that can be applied to a number of different questions and species. Specifically, model aquatic species such as rainbow trout (Onchorhynchus mykiss) will be exposed to particle-bound contaminants in flood-like conditions in a specifically designed annular flume that permits monitoring of both physical/chemical and biological parameter. Ultimately, this approach will assist to further our understanding of the potential biological risks associated with increasingly frequent extreme flood events, e.g., as a consequence of climate change, by bridging the gap between the physical (re-)mobilisation of contaminants and resulting toxicological impacts on aquatic organisms. Thus, it is the objective of the project to derive relationships between the hydrodynamic parameters such as velocities and turbulences, the parameters associated to sediment transport such as sediment concentration and grain sizes and the biological parameters.     

Primed N2O emission from native soil nitrogen: A 15N‐tracing laboratory experiment

Soils can naturally be a source of the potent greenhouse gas nitrous oxide (N₂O). By contrast, the largest anthropogenic source of N₂O is the application of nitrogen (N) fertilizer on agricultural soil, but it is unclear if fertilizer‐supported N₂O emission only originates from the fertilizer N directly or through additionally stimulated N₂O production from native soil N. Even though native soil N also includes mineral N already in soil before fertilizer application, organic N is the principal native N pool and thereby provides for mineral N cycling and N₂O emission. Here, we tested (1) the contribution of native soil N to N₂O emission after mineral N fertilizer application and (2) whether it is affected by different soil organic matter (SOM) contents by conducting a laboratory ¹⁵N‐tracing experiment with agricultural soil from a long‐term field trial with two treatments. Both field treatments are fertilized with mineral N, whereas only one of the two receives liquid manure causing higher SOM content. Soil sampling was conducted in March 2016 shortly before fertilizer application in the field. The application of ¹⁵N‐labeled fertilizer more than doubled the N₂O production from native N sources compared to the non‐fertilized control incubations. This primed N₂O production contributed by 5–8% to the fertilizer‐induced N₂O emission after one week of incubation and was similar for both field treatments regardless of liquid manure application. Therefore, further research is needed to link N₂O priming to its potential production pathways and sources. While the observed effect may be important in soils, the amount of applied N fertilizer remains the largest concern being responsible for the majority of N₂O emission.     

Sind Pollenspritzungen oder Pollendispenser Alternativen zur herkömmlichen Bestäubung der Apfelbäume durch Bienen?

The efficacy of different methods of applying cv. ‘Golden Delicious‘ pollen to ‘Cox Orange‘ apple trees inside insect-proof cages was investigated: (1) spraying pollen suspended in water directly into the trees while they were in bloom (treatment A); (2) pollen transfer by honeybees (treatment B) or by bumblebees (treatment C), both of which had to pass through a dispenser loaded with cv. ‘Golden Delicious‘ pollen; (3) transfer by honeybees of pollen from cv ‘Golden Delicious‘ trees bearing compatible pollen and maintained in pots within the same cages (treatment D). Naturally pollinated cv. ‘Cox Orange‘ apple trees outside the cages in the orchard served as controls. For methods A–C normal commercially available ‘Golden Delicious‘ pollen was used for hand pollination, and its efficacy was assessed with reference to the amount of fruit that set. The fruit-set at the time of harvesting differed significantly (Nemenyi test) with the different methods of pollination: 1.0% (±2.0) of the blossoms ripened to yield marketable apples after treatment A, 6.1% (±5.2) after treatment B, 4.9% (±4.6) after treatment C, and 20.4% (±11.5) after treatment D, while the corresponding figure for the control trees was 7.3% (±2.8) and that for hand pollination, 41,9%. The low fruit-set after an aqueous suspension of cv. ‘Golden Delicious‘ pollen was sprayed on the test trees shows that this procedure did not result in adequate pollination. The density of pollen grains was determined on filter papers during spraying and was an average of 3 (±2.6, range 0.0–8.6) pollen grains/cm². When the pollen dispensers were used, the fruit-set was lower than on the hand-pollinated control trees. Despite the success of manual pollination with exogenous cv. ‘Golden Delicious‘ pollen, pollen spraying to enhance pollination, as specified in current instructions, cannot be recommended for commercial apple growing in Germany.     

Extended summaries sci pesticides group symposium biological control: Use of living organisms in the management of invertebrate pests,pathogens and weeds.

The following are extended summaries based on material presented at a meeting of the SCI Pesticides Group, held on 19-20 October 1992 at the SCI, 14/15 Belgrave Square, London SWIX 8PS, UK. The summaries published here are entirely the responsibility of the authors and do not necessarily reflect the views of the Editorial Board of Pesticide Science.     

Enantioselective transformation of the herbicides diclofop-methyl and fenoxaprop-ethyl in soil

The separate enantiomers of diclofop-methyl and fenoxaprop-ethyl were incubated with two soils under aerobic conditions. Rapid hydrolysis to the corresponding acids diclofop and fenoxaprop was observed. At various time intervals after soil treatment the parent compound and its free acid were extracted and the extracts were investigated by high-performance liquid chromatography. The determination of the K:S-ratio using a chiral stationary phase revealed that no racemisation of the esters took place. However, inversion of the hydrolysis products was observed. In both soils the acids with the S-configuration showed a significantly higher inversion tendency than the acids with the R-configuration. In one soil the S-acids of both herbicides were inverted (50% inversion in 4–7 days) to yield, ultimately, a residue containing 70% R- and 30% S-enantiomer.