On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoidae)

A total of 90, weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 148, 222, 333, 500, 750 or 1125µg Cd⁺⁺ l^–1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22° C and 30 S. All populations exposed to concentrations down to 500µg Cd⁺⁺ l^–1 and 3 populations (out of 15) exposed to 333µg l^–1 became extinct within the experimental period of 30 weeks. Survival time significantly depended on concentration. A recovery phase from an initially high mortality preceded eventual population extinction after adding 500µg Cd⁺⁺ l^–1. In the initial phase, higher nauplii mortality prevailed. During these experiments on acute intoxication, no relationship could be established between survival and exploitation rate. However, experiments on the effects of stepwise increases in Cd concentration (results not yet published) produced evidence of such a relationship. In spite of increased mortality, no significant numbers of dead copepods were detected in weekly samples because of their rapid decomposition and cannibalism, which depends on the amount of food available. Sampling regimes of 5 times per week yielded significant numbers of dead individuals.     

On the dynamics of exploited populations ofTisbe holothuriae (Copepoda,Harpacticoida)

A total of 75 weekly exploited populations of the harpacticoid copepodTisbe holothuriae Humes were exposed to 0.06, 0.3, 1.5, 7.5 or 37.5 μg Cd⁺⁺l^?1, combined with exploitation rates of 10, 30, 50, 70 or 90% under conditions of surplus food supply at 22° C and 30‰ S. An unusually high mortality was observed for some weeks which could not be ascribed to the added amounts of Cd⁺⁺. A change in properties of supplied water is considered responsible for the unintentional perturbation which offered a further opportunity to study the effect of compensating reactions in stress situations. The results obtained clearly indicate an effect of exploitation rate on responses to detrimental influences. A superior performance has been found in populations exploited at higher rates. The findings are discussed with respect to earlier investigations on the population dynamics ofT. holothuriae.     

Cadmium induces hypertrophy accompanied by increased myc mRNA accumulation in NRK-49F cells

Previous studies showed that Cd⁺⁺ inhibits EGF-induced DNA synthesis that not EGF-induced myc mRNA accumulation or amino acid incorporation into protein in serum-starved NRK-49F cells. In this study, flow cytometry was used to analyze the DNA and protein content of individual cells stimulated with Cd⁺⁺ and/or epidermal growth factor (EGF). myc oncogene expression in these cells was also measured. It was found that, in both parental NRK-49F cells and in a clonal subpopulation, N1, Cd⁺⁺ induces an hypertrophic response. In parental NRK-49F cells, however, lower doses of Cd⁺⁺ (0.5 M) induced more pronounced hypertrophic responses than did higher doses (4 M); whereas in N1 cells, the Cd⁺⁺-induced hypertrophic response shows a pattern of increasing response with doses of Cd⁺⁺ from 0.5 to 4 M. myc mRNA accumulation measured 2 hours after stimulation correlated with the hypertrophic responses in both NRK-49F cells and in N1 cells. The results show that Cd⁺⁺-induced hypertrophy in NRK-49F cells is associated with increased myc oncogene mRNA accumulation, indicating that cell proliferation and cell hypertrophy may in part share common activation pathways.Abbreviations EGF Epidermal growth factor - FCM Flow cytometric analysis - FITC fluorescein isothiocyanate - PI propidium iodide     

Cadmium produces a delayed mitogenic response and modulates the EGF response in quiescent NRK cells

Recent studies have shown that cadmium, at subtoxic levels, may induce a response characteristic of that elicited by a type of growth factor that supports the anchorage independent growth of cells that are not fully transformed. That is, Cd⁺⁺ was found to replace transforming growth factor beta in supporting soft agar growth of NRK-49F cells. To tes the extent to which Cd⁺⁺ further mimics transforming growth factor beta in its effects and to establish response patterns that suggest possible molecular mechnisms of action, we have determined the effects of Cd⁺⁺ and/or epidermal growth factor (EGF) on DNA synthesis in quiescent NRK-49F cells. We found that subtoxic doses of Cd⁺⁺ modulate EGF-induced DNA synthesis in a dose-dependent fashion. Although Cd⁺⁺ effects on early (16–24 hr) EGF-induced DNA synthesis are primarily inhibitory, later effects involve stimulation as well. Subtoxic doses of Cd⁺⁺ did not stimulate DNA synthesis in quiescent cells within 24 hr of addition. At later times (40 or 64 hr), however, an increase in DNA synthesis of up to threefold was induced by 0.25 M Cd⁺⁺. This pattern of mitogenic response, involving inhibition of early growth-factor induced DNA synthesis and stimulation of late DNA synthesis, is consistent with that reported to be effected in some instances by transforming growth factor beta. Because a defined pattern of gene expression also is associated with the mitogenic responses to transforming growth factor beta, future studies at the molecular level can definitively test the degree to which Cd⁺⁺ and transforming growth factor beta effects are common.Abbreviations CFE colony forming efficiency - EGF epidermal growth factor - MT metallothionein - PGDF paltelet derived growth factor - TGF transforming growth factor     

Selection and characterization of cadmium-resistant suspension cultures of the wild tomato Lycopersicon peruvianum

Suspension cultures of Lycopersicon peruvianum were selected for resistance to cadmium by stepwise exposure to increasing concentrations of cadmium sulfate. Resistant cells grow in 1500 micromolar Cd⁺⁺. This resistance was retained for thirty generations without selection. Both resistant and parental sensitive cultures take up Cd⁺⁺ at similar rates and to the same final levels. Exposure of sensitive or resistant cultures to Cd⁺⁺, Cu⁺⁺, or Zn⁺⁺ leads to the intracellular accumulation of a low molecular weight, cysteine-rich, cadmium-binding protein. This metallothionein is induced over fifteen fold by 100 M cadmium and builds up to about five fold higher levels in the resistant cultures.Abbreviations Cd⁺⁺ divalent cadmium ion - Cu⁺⁺ divalent copper ion - Zn⁺⁺ divalent zinc ion - BA benzyl adenine - 2,4-D 2,4-dichlorophenoxyacetic acid - IAA indole-acetic acid     

Technical considerations for assessing alterations in skeletal muscle sarcoplasmic reticulum Ca++-sequestration functionin vitro

A multiple measurement system for assessing sarcoplasmic reticulum (SR) Ca⁺⁺-ATPase activity and Ca⁺⁺-uptake was used to examine the effects of SR fractionation and quick freezing on rat white (WG) and red (RG) gastrocnemius muscle.In vitro measurements were performed on whole muscle homogenates (HOM) and crude microsomal fractions (CM) enriched in SR vesicles before and after quick freezing in liquid nitrogen. Isolation of the CM fraction resulted in protein yields of 0.96±0.1 and 0.99±0.1 mg/g in WG and RG, respectively. The percent Ca⁺⁺-ATPase recovery for CM compared to HOM was 14.5% (WG) and 10.1% (RG). SR Ca⁺⁺-activated Ca⁺⁺-ATPase activity was not affected by quick freezing of HOM or CM, but basal ATPase was reduced (P<0.05) in frozen HOM (5.12±0.18–3.98±0.20 mole/g tissue/min in WG and from 5.39±0.20–4.48±0.24 mole/g tissue/min in RG). Ca⁺⁺-uptake was measured at a range of physiological free [Ca⁺⁺] using the Ca⁺⁺ fluorescent dye Indo-1. Maximum Ca⁺⁺-uptake rates when corrected for initial [Ca⁺⁺]_f were not altered in HOM or CM by quick freezing but uptake between 300 and 400nM free Ca⁺⁺ was reduced (P<0.05) in quick frozen HOM (1.30±0.1–0.66±0.1 mole/g tissue/min in WG and 1.04±0.2–0.60±0.1 mole/g tissue/min in RG). Linear correlations between Ca⁺⁺-uptake and Ca⁺⁺-ATPase activity measured in the presence of the Ca⁺⁺ ionophore A23187 were r=+0.25, (P<0.05) and r=+0.74 (P<0.05) in HOM and CM preparations, respectively, and were not altered by freezing. The linear relationships between HOM and CM maximum Ca⁺⁺-uptake (r=+0.44, P<0.05) and between HOM and CM Ca⁺⁺-ATPase activity (r=+0.34, P<0.05) were also not altered by tissue freezing. These data suggest that alterations in maximal SR Ca⁺⁺-uptake function and maximal Ca⁺⁺-ATPase activity may be measured in both HOM and CM fractions following freezing and short term storage. (Mol Cell Biochem139, 41–52, 1994)     

Snail populations,beech litter production,and the role of snails in litter decomposition

Summary The population densities of snails living in beech litter were studied form March 1968 to April 1969. Litter production over one year was measured and the role of snails in litter disappearance assessed.Snails were extracted from litter using a modified Vágvölgyi (1952) flotation method, extraction efficiencies being 84%. The mean annual population density of the twenty-one species of snail recorded on the main sampling site was estimated at 489/m². Carychium tridentatum was the most numerous species, with a mean density of 200/m². Acanthinula aculeata, Punctum pygmaeum and Vitrea contracta also had fairly high mean densities. The mean annual biomass was 699 mg dry wt./m² or 278 mg ash-free dry wt./m². Hygromia striolata and Oxychilus cellarius/alliarius were the most important species in terms of biomass on the main site. Within the limits of accuracy imposed by the sampling regime the population densities of four out of five of the species (C. tridentatum, A. aculeata, V. contracta, Retinella pura) studied remained unchanged throughout the year, whereas P. pygmaeum had a significantly higher autumn population. C. tridentatum populations were highly aggregated at all times of the year, most markedly so in June. Other species were aggregated at certain times of the year only. Samples taken from other sites showed total population densities of snails ranging from 185–1082 snails/m².A total tree litter production of 652 g/m²/annum was recorded of which 584g/m²/annum was of beech material. 72% fell in the October–December period. 58% of the beech litter-fall was leaves, 5.2% bud-scales, 27% fruits and 10% twigs and bark. Summation of appropriate field layer peak standing crops amounted to 23.3 g/m². This was considered as potential litter and was equivalent to 3.4% of the total litter input. The litter standing on the woodland floor in Septermber 1968 was 2,700 g/m², hence, assuming a steady state, litter turnover time was estimated as 4.5 years.It was calculated that the total snail population ingested 0.35–0.43% of the annual litter input, of which 49% was assimilated. The role of the individual species is examined in relation to concepts of key species in ecosystem functioning. The possible role of slugs in decomposition processes is also discussed.     

Introduction and recovery of Clavibacter michiganensis subsp. michiganensis from agricultural soil

Twelve phytopathogenic Clavibacter michiganensis subsp. michiganensis strains were introduced into non-sterile agricultural loam soil at an inoculum density of about log. 6.0 cfu g^–1 dry weight soil. The soil samples were incubated at 22°C under a 12h light, 12h dark cycle and the population densities followed over a 30-day period by plating subsamples of serial dilutions of soil on Brain Heart Infusion agar amended with 0.5% (w/v) yeast extract and 30 g mL^–1 nalidixic acid. In 5 soil samples C. michiganensis cfu were not detected after 30 days incubation. Initially, C. michiganensis cfu accounted for about 90% of the cfu recovered but decreased to less than 10% after 30 days. These results suggested that some C. michiganensis strains survive in this particular soil, while other strains exhibit poor survival and/or may be difficult to detect when present in low numbers.     

Studies on the Pentose Isomerases of Lactic Acid Bacteria

d-Xylose isomerase requires manganese ions for its action, but l-arabinose isomerase has a less specific on metal requirement. l-Arabinose isomerase is activated by addition of Mn⁺⁺ or Co⁺⁺, less effectively by addition of Zn⁺⁺, Ca⁺⁺, Mg⁺⁺, Sr⁺⁺ or Cd⁺⁺. Moreover, manganese and potassium ions for d-xylose isomerase, and manganese and cobaltous ions for l-arabinose isomerase were also shown to have protective effect on respective enzymes against thermal inactivation.     

Density-dependent regulation of natural and laboratory rotifer populations

Density-dependent regulation of abundance is fundamentally important in the dynamics of most animal populations. Density effects, however, have rarely been quantified in natural populations, so population models typically have a large uncertainty in their predictions. We used models generated from time series analysis to explore the form and strength of density-dependence in several natural rotifer populations. Population growth rate (r) decreased linearly or non-linearly with increased population density, depending on the rotifer species. Density effects in natural populations reduced r to 0 at densities of 1–10 l^–1 for 8 of the 9 rotifer species investigated. The sensitivities of these species to density effects appeared normally distributed, with a mean r=0 density of 2.3 l^–1 and a standard deviation of 1.9. Brachionus rotundiformis was the outlier with 10–100× higher density tolerance. Density effects in laboratory rotifer populations reduced r to 0 at population densities of 10–100 ml^–1, which is 10⁴ higher than densities in natural populations. Density effects in laboratory populations are due to food limitation, autotoxicity or to their combined effects. Experiments with B. rotundiformis demonstrated the absence of autotoxicity at densities as high as 865 ml^–1, a much higher density than observed in natural populations. It is, therefore, likely that food limitation rather than autotoxicity plays a major role in regulating natural rotifer populations.     

Effects of Cd++ on short-circuit current across epithelial membranes

Summary Cadmium ion (Cd⁺⁺) significantly increased potential difference (PD) and short-circuit current (SCC) across isolated frog skin when added to the outside Ringer's solution at 10^–4, 10^–3 and 5×10^–3 m concentration. Resistance was reduced by 10^–4 m Cd⁺⁺ but not significantly changed by the higher concentrations. When SCC was first stimulated by vasopressin, 10^–4 and 10^–3 m Cd⁺⁺ produced additive stimulation which was reversible by washing with Cd⁺⁺-free Ringer's. If SCC was first stimulated by Cd⁺⁺, further stimulation by vasopressin was additive with 10^–4 m Cd⁺⁺ but completely inhibited by 10^–3 m Cd⁺⁺. Elevating the calcium ion (Ca⁺⁺) concentration of the outer Ringer's from 10^–3 m to 5×10^–3 m or 10^–2 m prior to Cd⁺⁺ treatment did not reduce the magnitude of SCC stimulation by Cd⁺⁺. Removal of Ca⁺⁺ from the outside Ringer's with 2×10^–3 m EDTA increased SCC as predicted. Subsequent addition of 5×10^–3 m Cd⁺⁺ drastically reduced SCC below control levels while equimolar concentrations of Cd⁺⁺ and EDTA reduced SCC only to control levels. These results suggest that Cd⁺⁺ interacts with the components of the apical plasma membranes of epithelial cells which are associated with the stimulation of SCC by vasopressin and Ca⁺⁺ removal and may be a useful probe for elucidating these components.     

Accumulation of Cd2+ and Pb2+ in the suspension cultures of Agave amaniensis and Costus speciosus and the determination of the culture's growth and phytosteroid content

Cell suspension cultures of Agave amaniensis and Costus speciosus were grown in media containing Cd^{2 +} up to 25 and 20 mg l^–1, respectively, and Pb²⁺ up to 40 mg l^–1. The cultures hyper-accumulated Cd²⁺ up to 900 and 530 g g^–1 and Pb²⁺ up to 1390 and 1170 g g^–1 dry wt. in their respective biomasses. Increasing Pb²⁺ up to 30 mg l^–1 increased the biomass production and total sitosterol content of Costus speciosus by up to 1.7- and 1.3-fold, respectively.     

Specific Cd2+ uptake of encapsulated Aureobasidium pullulans biosorbents

Calcium alginate capsules containing Aureobasidium pullulans cells were prepared by an in-situ one-step method. The Cd²⁺uptakes of free biosorbent and capsule biosorbent were described well by the Freundlich isotherms. The Cd²⁺ uptake of capsule biosorbent was lower than that of free biosorbent with Cd^{2 +}at 100 mg l^–1. The total cadmium uptake of capsule biosorbent increased with the increase in encapsulated cell density and plateaued at a value of 23 g Cd²⁺/capsule with 150 g dry biosorbent l^–1 core volume of a capsule. The specific cadmium uptake of encapsulated biosorbent was 85% to that of free biosorbent at 35 g biosorbent dry weight l^–1 core volume of a capsule, decreased to 35% at 176 g biosorbent dry weight l^–1.     

Abundance, Annual Survival, and Recruitment of Unexploited and Exploited Lake Charr, Salvelinus Namaycush, Populations at the Experimental Lakes Area, Northwestern Ontario

We studied abundance, annual survival, and recruitment of nine lake charr, Salvelinus namaycush, populations at the Experimental Lakes Area, Ontario, for periods of 9–24 years. We used the Jolly–Seber mark-recapture method to evaluate abundance and annual survival in all populations, and total catches of individual year classes to evaluate recruitment. Seven populations were unexploited and unaffected by whole-lake experiments. One population was exploited prior to mark-recapture study and another was affected by experimental acidification. Abundance ranged from 8 to 24 fish ha^–1 in the unaffected populations. Annual survival ranged from 78% to 93%yr^–1 in all populations except the exploited population. This population may have been additionally affected by northern pike, Esox lucius, predation. Yearly recruitment was relatively constant in all populations and related to lake charr abundance. Lake charr abundance did not recover in populations affected by exploitation or acidification. Unexploited lake charr populations were characterized by relatively constant abundance, high annual survival, and relatively constant annual recruitment.     

Effects of Cd++ on short-circuit current across epithelial membranes

Summary Cadmium ion (Cd⁺⁺) was found not to inhibit active sodium transport across the isolated frog skin when added in 10^–3 m concentration to the basal-lateral surface. The same Cd⁺⁺ concentration similarly had no effect on Na⁺ transport across the isolated epithelial cell layer from the frog skin, although this dose of Cd⁺⁺ did inhibit Na⁺ transport across the frog urinary bladder and large intestine. When 10^–3 m Cd⁺⁺ was added to the apical surface of the isolated frog skin or to the isolated epithelial cells from the frog skin, sodium transport was reversibly stimulated, in contrast to the irreversible inhibition noted above. If equimolar cysteine was added with Cd⁺⁺ to the apical surface of the skin, however, active Na⁺ transport was irreversibly inhibited. In conjunction with the inhibition produced by equimolar Cd⁺⁺ and cysteine, isotopic Cd⁺⁺ permeation into the tissue was three times higher when added with cysteine than in the absence of cysteine. Thus, the effects of Cd⁺⁺ on epithelial Na⁺ transport is variable according to the epithelium studied and the presence of potential carrier molecules.     

Determination of the density of cells from sedimentation studies at 1G

To obtain a possible correlation between cell density and cell size, the size of individual cells was measured under the microscope and their sedimentation velocity was measured; the density is obtained with Stoke's Law. Specifically, HeLa cells were sedimented in Joklik's medium at 30°C in a vertical glass tube with 2 mm×2 mm horizontal opening and cells observed with a horizontally aligned microscope. The overall mean density difference of HeLa cells at 30°C was 0.0316+–0.0044 g/cm³, resulting in a density of 1.0357 g/cm³ (with a density of 1.0040 g/cm³ for Joklik's medium at 30°C). Six size fractions had densities which were essentially the same within the errors of the mean densities of the fractions (from 0.0081 to 0.0202 g/cm³). The considerably varying deviations of individual densities from the mean suggested superimposed phenomena (see also Table I for microspheres of precise size). Careful observation in balancing countercurrent flow revealed microconvection over 5 to 15 m regions, most likely based on small thermal differences in the horizontal plane.     

Cd++ inhibits EGF-induced DNA synthesis but not EGF induced myc mRNA accumulation in serum starved NRK-49F cells

Cd⁺⁺ inhibits EGF-induced ³H-thymidine incorporation in serum deprived NRK-49F cells in a dose dependent pattern. The underlying mechanisms for this inhibition are largely unknown. EGF-induced myc mRNA accumulation in NRK-49F cells and the effects of Cd⁺⁺ on this response were examined under conditions that result in partial or complete inhibition of EGF-induced DNA synthesis. It was found that doses of Cd⁺⁺ that inhibit EGF-induced DNA synthesis do not inhibit EGF-induced protein synthesis and myc mRNA accumulation. Cd⁺⁺ doses of 0.5 µM and 1 µM were found actually to increase EGF-induced myc mRNA accumulation and amino acid incorporation. These results show that the effect of Cd⁺⁺ on EGF-induced DNA synthesis is not due to inhibition of entrance into G₁, but rather that Cd⁺⁺ acts on events subsequent to myc accumulation; that is, events associated with either G₁ progression, entry into S or DNA synthesis.Abbreviations EGF Epidermal Growth Factor - ³HTdr Tritium thymidine - MeAIB Methylaminoisobutyrate     

Density dependence,boundedness, and attraction: detecting stability in stochastic systems

Summary By analogy with deterministic stability, the stability of stochastic ecological systems can be viewed as a tendency for population densities to avoid dynamic boundaries (i.e. boundedness) or to approach a dynamic attractor (i.e. attraction). At the population level, these two views generate predictions consistent with density dependence. I therefore devised two new statistical tests of attraction, the random-walk attraction test and the randomized attraction test; I then used them successfully, along with randomization techniques that detect boundedness and two autocorrelation methods, to test for density dependence in published sequences of population densities. The attraction tests identify the apparent attractor, the band of densities toward which density tends to shift between generations. Locating the apparent attractor can generate a prediction of the next direction of density change; for data from a dragonfly assemblage, about 80% of these predictions were correct. From the single-population tests, I also developed two multispecies tests of attraction (the multispecies random-walk and randomized attraction tests) and two multispecies tests of boundedness (the multispecies permutation and randomization tests). These detected attraction and boundedness in the dragonfly assemblage and attraction in a collection of laboratory fruitfly populations. An evaluation of the statistical power of the new density attraction tests indicates a strong dependence on the sequence length n and on the number of populations m: power increases with n and particularly with m. Nevertheless, detecting attraction becomes likely even in populations with strong linear density-dependence only with n>30 or for shorter sequences in multispecies assemblages.     

The effect of different algal densities of Scenedesmus acuminatus on the population growth of Moina micrura Kurz (Crustacea: Anomopoda,Moinidae)

Six densities (0.5 × 10⁶, 1.0 × 10⁶, 1.5 × 10⁶, 2.0 × 10⁶, 3.0 × 10⁶, and 4.0 × 10⁶ cells ml^–1) of the micro-alga Scenedesmus acuminatus, were fed to the cladoceran, Moina micrura, in 40-litre glass aquaria. Moina population increased with increasing cell densities of Scenedesmus only up to treatment 3 (i.e. 1.5 × 10⁶ cells ml^–1) where a peak population of 11303 individuals per litre was obtained. Moinapopulation growth was inhibited at higher algal densities. The percentage of egg-bearing females and the number of eggs per egg-bearing females, followed a similar pattern. Comparatively, the peak production density of approximately 11000 Moina per litre, is interesting from a mass production point of view and indicates that S. acuminatus is a satisfactory micro-alga food for M. micrura.     

Effects of soil-added Cl on growth ofAndropogon scoparius and possible implications for heavy metal research

Soil additions of Cl^–, as NaCl, over the 0 to 400 ppm Cl^– range did not affect germination forAndropogon scoparius. Height and top dry weight were significantly reduced by 300 ppm soil added Cl^–. Although not conclusive, these results did indicate that growth and germination effects reported for Cd⁺⁺, added as CdCl₂, are probably due to Cd⁺⁺ rather than to a Cl^– or salt effect. Reported Pb⁺⁺ effects, where Pb⁺⁺ is added as PbCl₂, however may be at least partially due to a Cl^– or salt effect.Contribution from Purdue University Agricultural Experiment Station, West Lafayette, Indiana 47907. AES Journal No. 6934. This work was supported by federal funds from the National Science Foundation—RANN Program.