Long-term dynamics of small-bodied and large-bodied cladocerans during the eutrophication of a shallow reservoir,with special attention for Chydorus sphaericus

Eutrophication in Tjeukemeer involved a gradualincrease in chlorophyll concentrations from ca. 30 mg m^-3in 1968–69 to 125 mg m^-3 in 1976.From 1976 onwards, chlorophyll concentrations remainedat a high level fluctuating between100–225 mg m^-3. Hillbricht-Illkowska (1977)hypothesized that small-bodied species will becomeincreasingly abundant and dominant over large-bodiedspecies with increasing eutrophication. We tested thishypothesis using observations from life historyexperiments on Chydorus sphaericus, combinedwith data from 25 years of field observations on thepopulation dynamics of cladocerans in Tjeukemeer.In life history experiments with C. sphaericus,the fitness measure r in treatments with naturallake seston and laboratory cultured green algae wassignificantly higher on lake seston from Tjeukemeer,containing a high proportion of detritus. Thissuggests that detrital particles are good quality foodfor C. sphaericus. Field observations during theperiod 1968–1976 showed that all three categories ofcladocerans: C. sphaericus,'other' small-bodiedcladocerans (predominantly Bosmina spp.) andlarge-bodied cladocerans (predominantly Daphniagaleata), increased in biomass with increasingchlorophyll concentration. However, of these threecladoceran categories only sphaericus showeda distinct and significant increase whereas the othertwo only showed a marginally significant increase.During the period 1977–1992, both 'other' small-bodiedcladocerans and C. sphaericus significantlydecreased in biomass with increasing chlorophyllconcentration, whereas the biomass of the large-bodiedcladocerans significantly increased with increasingchlorophyll content. These observations are not inagreement with the hypothesis that small-bodiedzooplankton become increasingly abundant withincreasing eutrophication. We suggest that theobserved trends are partially caused by a food effect,and partially caused by predation pressure. Daphnia shows a better response to the increase indetritus and filaments of Cyanobacteria thansmall-bodied cladocerans, but is more vulnerable tofish predation. Densities of 0+ zooplanktivorous fishshow strong annual fluctuations in Tjeukemeer, andbecause of hydrological conditions, 0+ fish abundancein this lake is probably negatively related tochlorophyll content.     

Influence of bulky substituents on the regioselective group-transfer reactions of diorganozinc compounds with N, N′-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene

Diorganozinc compounds R₂Zn (R=alkyl or aryl) react with N,N′-bis(2,6-di-isopropylphenyl)-1,4-diaza-1,3-butadiene, (i-Pr₂Ph)N=CHCHp=N(i-Pr₂Ph) (i-Pr₂Ph-DAB) to give thermally unstable 1:1 coordination complexes R₂Zn(i-Pr2Ph-DAB), which subsequently undergo a slow regioselective alkyl or aryl group-transfer reaction from the zinc atom to an imine-nitrogen or a carbon atom of the NCCN system of the i-Pr₂Ph-DAB ligand. In the case of R=methyl, n-propyl, n-butyl, s-butyl, neopentyl and benzyl, C-alkylation occurs with a subsequent 1,2- hydrogen shift in the amino-imino skeleton affording RZn[(i-Pr₂Ph)N-CH₂-CR=N(i-Pr₂Ph)], whereas for R=t- butyl the C-alkylated product t-BuZn[(i-Pr₂Ph)N---CH(t-Bu)---CH=N(i-Pr₂Ph)] is stable. Surprisingly, diphenylzinc reacts with i-Pr₂Ph-DAB exclusively to give the N-arylated product PhZn[(i-Pr₂Ph)N=CHCH=N(Ph)(i-Pr₂Ph)].     

Systematic evaluation of the adrenocortical function in patients with paracoccidioidomycosis

Limited cortisol response to ACTH stimulation has been documented in 22 to 48% of patients with paracoccidioidomycosis (PM). Different approaches to interpret the test and inadequate selection of patients preclude an accurate appraisal of the actual incidence of adrenal insufficiency in PM. Rapid cosyntropin (ACTH) stimulation tests were performed in 38 consecutive patients (9 with the localized and 29 with the disseminated form of PM) and 40 normal controls. Subnormal cortisol responses to ACTH (60 minutes post-ACTH values below 455 nmol/l, 95% confidence limits) were found in only 4 patients (14%) with disseminated PM. If a retrospective sample of 6 patients studied previously (in whom tests were indicated due to clinical suspicion of Addison's disease) were included, or if the absolute cortisol increment above baseline was used for interpretation, we would find figures closer to those previously reported (23 and 24%, respectively). These data reflect that non-systematic evaluation or selection of a substandard criterion to interpret the test overestimates the frequency of adrenocortical insufficiency in PM.     

Mixed-function oxidase activity in seabirds and its relationship to oil pollution

1. The hepatic activity of epoxide hydrolase, aldrin epoxidase, aminopyrine N-demethylase, 7-ethoxyresorufin O-deethylase, benzo(a)pyrene 3-hydroxylase and UDP glucuronyl transferase was determined in adult herring gulls (Larus argentatus) at various stages of the breeding season. 2. MFO activity was measured for adult Leach's storm-petrels (Oceanodroma leucorhoa), guillemot (Uria aalge) and Atlantic puffins (Fratercula arctica). For most assays the values were highest for the puffin. 3. MFO activity in both nestling and adult Atlantic puffins was determined. The degree of induction caused by a single internal dose of Prudhoe Bay crude oil in adult puffins and that caused by multiple internal doses in nestling puffins was measured.     

The effect of selected human steroid hormones upon the growth of dermatophytes with different adaptation to man

The inhibitory effect exerted by steroid hormones on thein vitro growth characteristics of dermatophytes is poorly understood. As a hypothesis this inhibition could result from fungal adaptation to the human host. Therefore, in this study the susceptibility of representative anthropophilic, zoophilic and geophilic dermatophytes to hormonal inhibition was compared. As a result, in agar dilution assaysprogesterone,testosterone, andestradiol proved to reduce fungal growth, whereashydrocortisone had no such effect. In general, anthropophilic dermatophytes were shown to be more responsive to steroid hormones than geophilic species, suggesting a correlation of steroid susceptibility with adaptation to human skin. However, since fungal response to hormones consisted of growth inhibition and occurred only at steroid concentrations much higher than present in human skin, it cannot be assumed to contribute to this adaptation.