Non-uniform mechanical activity of quadriceps muscle during fatigue by repeated maximal voluntary contraction in humans

To determine the non-uniform surface mechanical activity of human quadriceps muscle during fatiguing activity, surface mechanomyogram (MMG), or muscle sound, and surface electromyogram (EMG) were recorded from the rectus femoris (RF), vastus lateralis (VL), and vastus medialis (VM) muscles of seven subjects during unilateral isometric knee extension exercise. Time- and frequency-domain analyses of MMG and of EMG fatigued by 50 repeated maximal voluntary contractions (MVC) for 3 s, with 3-s relaxation in between, were compared among the muscles. The mean MVC force fell to 49.5 (SEM 2.0)% at the end of the repeated MVC. Integrated EMG decreased in a similar manner in each muscle head, but a marked non-uniformity was found for the decline in integrated MMG (iMMG). The fall in iMMG was most prominent for RF, followed by VM and VL. Moreover, the median frequency of MMG and the relative decrease in that of EMG in RF were significantly greater (P < 0.05) than those recorded for VL and VM. These results would suggest a divergence of mechanical activity within the quadriceps muscle during fatiguing activity by repeated MVC. Accepted: 19 January 1999     

Diel pattern of first downstream post-emergence displacement in grayling, Thymallus thymallus (L., 1758)

The activity rhythm of emerging grayling, Thymallus thymallus , fry was studied under semi-natural rearing conditions, using special traps buried in the gravel. Emergence was mainly diurnal with a maximum in the first hours of daylight. Fry rested at the emergence site during the daylight and moved downstream at night, particularly during the first 3 hours of darkness. These results are compared with the known activity patterns of other salmonids.     

Emergence of Eucalyptus marginata (jarrah) from seed in Mediterranean-climate forest in response to overstorey,site, seedbed and seed harvesting

Abstract The effects of overstorey, type of site, seedbed, seeding date and seed harvesting by vertebrates and invertebrates on the emergence of Eucalyptus marginata (jarrah) seedlings were studied experimentally in the northern jarrah forest of Western Australia. Seed harvesting by small vertebrates substantially reduced emergence, whereas invertebrates only slightly reduced emergence. Ninety per cent of seed was removed within 1 day when it was on the soil surface and in the open, whereas seed removal was insignificant when the seed was covered by soil. Vertebrates harvested seed more effectively when the understorey and litter were removed and the seed was more visible on the soil surface. Seed harvesting by small vertebrates had less impact on a site where there had been bauxite mining, possibly because the surrounding area was being revegetated with large numbers of seed and the area afforded poor cover for vertebrates. Emergence was less where the overstorey was removed compared to where it was retained, and on the rehabilitated bauxite mined site compared to the forest sites. There was no difference in emergence between the low and high quality forest sites and so the emergence phase could not fully explain the variation in abundance off. marginata seedlings on different quality sites. Post emergence events are likely to be important in explaining this difference between low and high quality sites.     

Comparing four methods of augmentative release of Eretmocerus nr. emiratus against Bemisia argentifolii

Four methods were tested for release of Eretmocerus nr. emiratus (Hymenoptera:Aphelinidae) against the silverleaf whitefly,Bemisia argentifolii Bellows & Perring(Hemiptera: Aleyrodidae), in cotton and melons. Ten thousand parasitoids were released in 0.1ha plots as follows: (1) as adults in each ofthe four quadrants of the plot, (2) as pupae ingel-caps affixed to the undersides of leaves inthe center of each of four quadrants, (3) at thecenter of the plot in shaded paper cups, and (4)to simulate release from a drop-box. Survivalafter 3 d, dispersal, mating success,sex-ratio, cost, and delivery speed werecompared among the four methods. Significantlymore parasitoids were recovered after 3 d whenparasitoids were released using the paper cupmethod, however, few parasitoids were capturedoutside the area directly adjacent to therelease point. More parasitoids wererecaptured near the release points with thegel-cap and adult release methods, but becausethere were four release points per plot, thedistribution was more uniform. Few parasitoidswere recovered when parasitoids were releasedusing a simulated drop-box method. Althoughthe sex-ratio of released parasitoids was±70% males, more than 30% of the recoveredparasitoids were female. In melons, where thedensity of whiteflies was more than 20 times asgreat as in cotton, the sex-ratio of recapturedparasitoids was greater than 70% females forall treatments. The most expensive releasemethod was the drop-box at $38.79 per ha,followed by $13.02 for adults, $7.62 forgel-caps, and $3.31 for the paper cups. Thegel-cap method was superior in providing a muchmore even distribution of individualsthroughout the field, especially in melons, butconsiderable time was necessary to prepare thegel-caps for release. Of the four releasemethods tested, releasing parasitoids in papercups resulted in higher numbers recaptured, alow cost, and rapid delivery speed. BecauseE. nr. emiratus does not dispersefar from the release point, however, a greaternumber of release points with fewer parasitoidsper point should provide a more evendistribution of parasitoids throughout therelease field.     

Chronic effects of short-term contamination with the pyrethroid insecticide fenvalerate on the caddisfly Limnephilus lunatus

Larvae of the caddisfly Limnephilus lunatus Curtis were exposed to the pyrethroid fenvalerate for one hour and transferred to artificial outdoor stream systems, where their survival rate and emergence were monitored over 84 days. Lethal effects of the pyrethroid almost always appeared shortly after the short-term contamination, but chronic influences were also observed. At a concentration of only 0.01 µg l^–1 a slight increase in mortality over the entire period of observation, as well as a delay in development and hence in emergence occurred. Such reactions under field conditions may impair the survival of this species, and sublethal effects of brief pyrethroid contamination, previously largely ignored, can have important consequences for aquatic macroinvertebrates.     

Emergence of Chironomidae from Findley Lake and two ponds in the Cascade Mountains,U.S.A.

From Findley Lake and two ponds in the Cascade Mountains (U.S.A.) Chironomidae started to emerge as soon as the ice thawed in 1972 and 1973. The 1051 Chironomidae that emerged per m² from Findley Lake included 307 individuals ofTanytarsus and 358 ofProcladius. Tanytarsus outnumberedChironomus at all depths from 0 to 19.3 m. The 1506 Chironomidae that emerged per m² from the 4.5 m deep pond included 997 individuals ofTanytarsus. The 1490 Chironomidae that emerged per m² from the 2 m deep pond included 1363 Tanytarsus. The emerging biomass was 216 and 186 mg dry weight per m² in Findley Lake and the 4.5 m deep pond, respectively, and only 78 mg in the 2 m deep pond. Most species had their maximum emergence where there was organic detritus from the surrounding forest.Orthocladius emerged from sand bottom at 2.7 to 5.2 m depth.Stictochironomus emerged from mud and sand at 8.4 m depth.Chironomus emerged from soft mud at 15 to 27.5 m depth.     

The Role of Immunotoxic Environmental Contaminants in Facilitating the Emergence of Infectious Diseases in Marine Mammals

A series of high profile outbreaks of newly described diseases in humans, domestic animals and wildlife has attracted widespread interest in the topic of Emerging Infectious Diseases (EIDs). Marine mammals are no exception: since 1987 several mass mortalities have been observed following infection with viruses previously undescribed in the populations or species in question. As with terrestrial examples, some of these outbreaks have followed either migrations associated with large-scale ecological changes or the introduction of virus from domestic animals. However, marine mammals warrant special concern in the context of emerging infectious diseases: they typically occupy high trophic levels and can therefore be highly contaminated with immunotoxic chemicals. Persistent Organic Pollutants (POPs), including polychlorinated -biphenyls (PCBs), dibenzo-p-dioxins (PCDDs), -dibenzofurans (PCDFs) and related compounds, are demonstrated immunotoxicants in laboratory animals, as well as marine mammals. Immunotoxic contaminants may represent a factor that facilitates disease emergence, and may lead to the creation of susceptible “reservoirs” for new pathogens in contaminated marine mammal populations. The factors underlying the emergence and exchange of pathogens among marine mammals, domestic animals, and humans demand multidisciplinary study and invite regulatory and conservation scrutiny. The complexity of this issue may be best addressed through an integrated human and ecological risk assessment framework.     

Photosynthetic and growth responses to fire of the subtropical-temperate grass, Spartina argentinensis Parodi

Fire is a common phenomenon in grasslands but there is little experimental evidence of the mechanism involved in the rapid recovery of the plant growth. We tested under controlled conditions the hypothesis that after fire Spartina argentinensis leaves that restart growing have high photosynthetic rates. Photosynthetic rates and emergence of leaves and culms were registered. Initial photosynthetic rates were higher among plants which restarted growth after fire or clipping than in control ones, without effect of different water availability. High photosynthetic rate values remained during two months after fire or clipping treatments though then affected by water availability, and thereafter started declining towards the end of season. From January onwards no differences among treatments were detected except that control plants under water stress conditions had lower photosynthetic rates than all others. Leaf and culm emergence were promoted by both fire and clipping treatments. Though affect-ed by water availability, burned and clipped plants had the highest percentages of living tissues at the end of the experiment. Considering photosynthetic and growth responses after fire it can be concluded that burning is a regular component of the subtropical-temperate S. argentinensis habitat, among the South American grasslands.