Characterizing individual, population and community effects of sublethal levels of aquatic toxicants: an experimental case study using Daphnia

SUMMARY. 1. The relationship between toxicant-induced changes in the feeding behaviour of the cladoceran, Daphnia catawba (Coker), and subsequent effects at population and community levels were experimentally addressed.
2. We adapted a method for measuring the thoracic appendage beat rate of individuals (termed the TAR and positively correlated with daphnid feeding rate) after exposure to toxicant at known levels, for use as a behavioural bioassay for low levels of aquatic toxicants. The TAR declined significantly with an increase in both sublethal and lethal levels of the surfactant, sodium dodecyl sulphate (SDS).
3. We also measured population level effects (i.e. rates of reproduction, survival, and R ₀), and found that reductions in these values occurred at the same concentrations as the effects on individual behaviour.
4. In most cases, the changes in feeding behaviour occurred more rapidly (≤30h) than changes in population parameters (days to weeks).
5. We conclude that toxicant-induced changes in individual feeding behaviour can provide a quicker estimate of effects on individuals and of potential community effects (i.e. effects on their prey populations) than measurements of population parameters. In addition, due to its sensitivity at low levels of toxicants, the behavioural bioassay may be particularly helpful in identifying effects of sublethal levels of aquatic pollutants.     

The movement and dispersal of Liriomyza trifolii (Diptera: Agromyzidae) in a chrysanthemum greenhouse

Investigation of the dispersal of Liriomyza trifolii in a 1–2 ha chrysanthemum greenhouse indicated that the average distance flown by female flies was greater than that flown by male flies. However, flies of both sexes were found at the furthest distance from the release point (102 m) which indicates that flies in the greenhouse could be considered to be a single inter-breeding population. When the data were fitted to a generalised distance-dispersal model, examination of the parameters revealed density decreased with distance more rapidly for males than females. Also, the model showed that males tended to be slightly more attracted to each other than were females. The applicability of these results to the development of pest management systems for L. trifolii is discussed.     

Records of upwelling, seasonality and growth in stable-isotope profiles of Pliocene mollusk shells from Florida

Oxygen and carbon isotopic profiles across the shells of well-preserved bivalves and gastropods from the Pliocene Pinecrest Beds near Sarasota, Florida, provide detailed records of the paleoen-vironmental and paleoclimatic conditions under which these high-density shell beds accumulated, as well as offer insight into shell-growth rates and longevity. Eight turritellid gastropods were analyzed from within and surrounding two Turritella-rich beds, an upper bed within unit 2(2.5-2.0 Ma) and a lower bed situated near the top of the main shell bed, unit 6/7(3.5-2.5 Ma). Three bivalves plus another turritellid specimen from a lower horizon (middle of unit 6/7), considered to represent offshore, normal-marine conditions, were also analyzed. The isotopic profiles of all shells reflect year-round shell growth in a seasonal, subtropical to warm-temperate paleoenvironment. Cyclical patterns in δ¹⁸O reflect annual variations in water temperature which on average ranged from 15 to 24d?C; minimum paleoseasonality contrasts varied from 7 to 9d?C. Summer paleo-temperatures compare favorably with those detemined from ostracodes, whereas winter temperatures appear slightly cooler. Except for one pectinid specimen, temperature differences between horizons and specimens are small. Annual δ¹⁸O cycles indicate: Turritella apicalis lived longer and grew slightly faster than Turritella gladeensis; and, shell growth rates and increment formation in Mercenaria campechiensis are comparable to modern Florida populations. Coincident episodes of heavy δ¹⁸O and light δ¹⁸C in both turritellids and bivalves suggest a pattern of seasonal upwelling. This cool, nutrient-rich, upwelled water may be partially responsible for the great abundance of Pinecrest fossils. □Stable isotopes, Pliocene, Pinecrest Beds, Florida, upwelling, paleotemperature, mollusk, Turritella.      

Changes in Distribution of Acid-Phosphatase Activity During Wound Regeneration in Coleus

Changes in the pattern of distribution of acid-phosphatase activitywere followed during the period of regeneration and wound-vesselformation in Coleus internodes. The activity of this enzymewas associated with three phases of wound regeneration, thefirst of which was detected only in the damaged surface cellsduring the first few days after wounding. The second phase wasassociated with the undamaged cells immediately surroundingthe wound and this travelled gradually inwards from the woundsurface to the deeper tissues as a wave of activity during regeneration.This activity preceded cell division in the zone around thewound and was not detectable once the new cell walls had formed.The third phase was associated with the differentiation of cellsof the new vascular tissues which formed around the wound connectingthe original severed vascular bundle.     

Asymptotes of diseases caused by non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars

A model describing disease progress of non-specialised fungal pathogens in intraspecific mixed stands of cereal cultivars (Jeger, Griffiths & Jones, 1981b) has been extended beyond the logarithmic phase of disease development. The extended. logistic model indicates that whatever the outcome in the early stages (disease less than or more than the mean of disease in the pure stands), disease will eventually level off at a value equal to the mean of disease asymptotes in the pure stands. The time scale involved in such levelling-off, however, means that substantial benefit may still be expected from deployment of such mixtures. Analytical solutions for the model are obtained for the special case where the ratio of disease asymptote to initial disease is the same for each pure stand.     

attempted prebiotic synthesis of pseudouridine

Pseudouridine is a modified base found in all tRNA and rRNA. Hence, it is reasonable to think that pseudouridine was important in the early evolution, if not the origin, of life. Since uracil reacts rapidly with formaldehyde and other aldehydes at the C-5 position, it is plausible that pseudouridine could be synthesized in a similar way by the reaction of the C-5 of uracil with the C-1 of ribose. The determining factor is whether the ribose could react with the uracil faster than ribose decomposes. However, both rates are determined by the amount of free aldehyde in the ribose. Various plausible prebiotic reactions were investigated and none showed pseudouridine above the detection limit (<0.01%). Only unreacted uracil and ribose decomposition products could be observed. Thus the rate of addition of ribose to uracil is much slower than the decomposition of ribose under any reasonable prebiotic conditions. Unless efficient non-biological catalysts for any of these reactions exist, pseudouridine would not have been synthesized to any significant extent without the use of biologically produced enzymes.