Sedimentary records of accelerated nutrient loading in Florida lakes

Transfer functions relating trophic state (Carlson's TSI_{chlorophyll-a}) to present day accumulation rate of (1) nutrients, (2) cations, and (3) organic sediment, are computed using Binford's ²¹⁰Pb-dilution method. As computed from surficial sediments of 27 lakes, former trophic states are reconstructed for recent (²¹⁰Pb-dated) sedimentary histories of 14 lakes. Of the three kinds of models potentially available, model (3) (TSI vs. organic accumulation) is the weakest statistically, and may be unduly influenced by exceptional deposition and/or preservation of allochthonous organic matter. At present, however, it is the only model applicable to all 14 of the histories tested. Results are encouraging in that model accurately predicts observed TSI's in several mesotrophic and eutrophic lakes. Clearly significant increases (accelerations) are inferred only for a of the most eutrophic lakes of the set, while the model consistently overpredicts TSI's of the 7 most oligotrophic lakes. As Whitmore's diatom-assemblage index is a better predictor of TSI than is model (3) in the one eutrophic lake in which it has been tested, we expect more persuasive results when models (1) and (2) can be tested within a more complete set of analytical data. We were surprised to find 3 severely disturbed lakes among the 12 that show little or no acceleration in rate of eutrophication in recent decades, but we defer attempts at explanation until former nutrient loading can be tested by model (1).     

Adaptation to High-Intensity, Low-Wavelength Light among Surface Blooms of the Cyanobacterium Microcystis aeruginosa

Natural populations of the nuisance bloom cyanobacterium Microcystis aeruginosa obtained from the eutrophic Neuse River, N.C., revealed optimal chlorophyll a-normalized photosynthetic rates and resistance to photoinhibition at surface photosynthetically active radiation (PAR) intensities. At saturating PAR levels these populations exhibited higher photosynthetic rates in quartz than in Pyrex vessels. Eucaryotic algal populations obtained from the same river failed to counteract photoinhibition. At saturating PAR levels, such populations generally yielded lower photosynthetic rates in quartz containers than they did in Pyrex containers. Cultivation of natural Microcystis populations under laboratory conditions led to physiologically distinct populations which had photoinhibitory characteristics similar to those of other cultured cyanobacterial and eucaryotic algae. Our findings indicate that (i) photosynthetic production among natural surface populations is best characterized and quantified in quartz rather than Pyrex incubation vessels; (ii) extrapolation of natural photoinhibitory trends from laboratory populations is highly subjective to culture and PAR histories and may yield contradictory results; and (iii) buoyant surface-dwelling populations, rather than exhibiting senescence, are poised at optimizing PAR utilization, thereby maintaining numerical dominance in eutrophic waters when physico-chemical conditions favor bloom formation.     

Energy partitioning in three species of nematode from polysaprobic environments

Summary The partitioning of energy in three species of nematode, Paroigolaimella bernensis, Diplogasteritus nudicapitatus and Rhabditis curvicaudata, from a polysaprobic environment is considered. Temperature was shown to have a profound impact on the rate at which these organisms obtained food resources and on the partitioning of energy into growth, reproduction and maintenance. Declining temperature resulted in a reduction in energy consumption and in production and maintenance costs. Absorption efficiencies were relatively low, rarely exceeding 20% and lying on average between 5–15%. Net production efficiencies varied throughout the life-cycle, but attained maximum levels of 70–80%. Females achieved higher net production efficiency than males. The physiology and ecological implications are discussed.     

Central place foraging by beavers (Castor canadensis): a test of foraging predictions and the impact of selective feeding on the growth form of cottonwoods (Populus fremontii)

Summary Several predictions of central place foraging theory were tested. As predicted, beavers foraged more selectively at increasing distance from the central place. With increasing distance from the river's edge, beavers cut fewer branches and deleted small branches from their diet. Large branches were favored at all distances, which differs from patterns observed in previous studies of beaver foraging. This difference, however, is expected and supports Schoener's (1979) predictions which are based on differences between provisioning costs and item size.The selective harvesting of branches predicted by foraging theory affects plant growth form and may influence plant reproductive patterns. High rates of branch removal caused cottonwoods to develop a shrubby architecture. The importance of selective branch choice by beavers on patterns of cottonwood reproduction (i.e., delayed sexual maturity and induced cloning) is discussed.     

Inoculation and production of container-grown red alder seedlings

Summary The inoculation ofAlnus rubra (red alder) withFrankia sp. can lead to a highly efficient symbiosis. Several factors contribute to the successful establishment of nitrogenfixing nodules: (1) quantity and quality ofFrankia inoculant; (2) time and method of inoculation; (3) nutritional status of the host plant.Frankia isolates were screened for their ability to nodulate and promote plant growth of container-grown red alder. Inoculations were performed on seedlings and seeds. Apparent differences in symbiotic performance could be seen when seeds or seedlings were inoculated. Plants inoculated at planting performed significantly better than those inoculated four weeks later in terms of shoot height, nodule number and shoot dry weight. If inoculation was delayed further, reduction in shoot height, nodule number and shoot dry weight resulted. The effect of fertilizer was also investigated with regard to providing optimal plant growth after inoculation. Plants receiving 1/5 Hoagland's solution minus nitrogen showed maximal plant growth with abundant nodulation. Plants receiving 1/5 Hoagland's solution with nitrogen showed excellent plant growth with significantly reduced nodulation.     

Calcium Enhances In Vitro Free Radical-Induced Damage to Brain Synaptosomes, Mitochondria, and Cultured Spinal Cord Neurons

Preincubation of rat brain synaptosomes with xanthine and xanthine oxidase (X/XO) in Ca2+-free Krebs buffer resulted in a 27% inhibition of synaptosomal gamma-aminobutyric acid (GABA) uptake. Addition of 1.5 mM CaCl2 increased the inhibition with X/XO to 46%, and inhibition was essentially complete when the calcium ionophore A23187 also was included. In other studies, preincubation of purified rat brain mitochondria with the combination of X/XO and 4 microM CaCl2 produced a significant (38%) decrease in state 3 respiration with glutamate/malate as substrate that was not seen with either X/XO or Ca2+ alone. Similar results were obtained using cultured mouse spinal cord neurons in which incubation with X/XO/ADP/FeCl2 and A23187 produced membrane damage as assessed by a 32% reduction of neuronal Na+, K+-ATPase activity. Neither X/XO/ADP/FeCl2 nor A23187 alone caused detectable inhibition. These results demonstrate the synergistic damaging effect of free radicals and Ca2+ on membrane function. In addition, they suggest that free radical-induced peroxidation of membrane lipid, occurring focally during complete or nearly complete ischemia in vivo, could result in intense cellular perturbation when coupled with increased intracellular Ca2+.     

The decolorization of the polymeric dye Poly-Blue (polyvinalamine sulfonate-anthroquinone) by lignin degrading fungi

Summary In this work we have investigated the decolorization of the polymeric dye Poly-B411 by several fungi. Only fungi with known lignin degrading ability were able to decolorize the dye. Pleurotus ostreatus sp. florida decolorized the dye both in solid and liquid media. Decolorizing ability developed in the absence of the dye but only when the fungus had been previously cultivated on lignin containing substrates.The work was supported by a grant from the Charles Wolfson Trust     

On the low viscosity blood of two cold water,marine sculpins

Summary The viscosities of blood from shorthorn sculpin (Myoxocephalus scorpius), longhorn sculpin (Myoxocephalus octodecemspinosus) and winter flounder (Pseudopleuronectes americanus) were compared using a cone-plate viscometer. Both species of sculpin were almost identical with respect to blood and plasma viscosity at the temperatures (0 and 15°C) and shear rates (2.3–90/s) examined. In contrast, the viscosities of winter flounder blood and plasma were considerably greater than those observed in the sculpins. This difference in blood viscosity between the shorthorn sculpin and the winter flounder persisted over the hematocrit range of 0 to 40% red blood cells. The viscosity of the plasma and the interactions between plasma proteins and red blood cells appeared to be the major reasons for the relatively high viscosity of the flounder blood. Although a proportion of the flounder blood viscosity was attributable to fibrinogen, other plasma proteins also appeared to play a significant role. The relatively low blood viscosity of the sculpin species may confer a circulatory advantage during periods of low water temperatures.     

Determination of DNA content in the nurse and follicle cells from wild type and mutant Drosophila melanogaster by DNA-Feulgen cytophotometry

DNA replication patterns in the nurse and follicle cells of wild type and a female sterile mutant, fs(1)1304, of Drosophila melanogaster have been studied by DNA-Feulgen cytophotometry, using a cell dispersal technique that allowed the measurement of DNA amounts in individual nuclei from egg chambers of known developmental stages. DNA-Feulgen values associated with various ovarian nuclei from egg chambers at different stages of development were used to assess a base line DNA content for ovarian tissues and to estimate the extent of DNA replication in the nurse cells and follicle cells of growing and mature egg chambers. Our data show that both the nurse and follicle cells undergo multiple cycles of endonuclear DNA replication and that there may be selective amplification as well as underreplication by portions of the genome in these highly polyploid, ovarian cells. Alternative models are proposed to account for the DNA replication patterns observed. Comparisons of DNA-Feulgen levels in wild type ovarian nuclei with those found for the fs(1)1304 mutant and its heterozygote in the balanced stock fs/FM3, show that equivalent DNA levels are present in follicle cell nuclei from all three types of females. Nurse cell nuclei in the homozygous fs stock, however, fail to achieve the same high DNA levels observed in both fs/FM3 and wild type nurse cell nuclei. Although the nuclei of follicle cells in ovaries from fs/fs females appear morphologically like those surrounding egg chambers in wild type ovaries, nurse cell nuclei from mutant females show a more compacted organization of their chromatin than found for nurse cell nuclei from wild type ovaries at similar developmental stages. Our findings suggest that a major effect of the fs(1)1304 mutation may be on the coiling behavior of chromatin and the conformation of DNA-protein moieties in both nurse cell and follicle cell nuclei. These changes in chromatin structure apparently are manifest by perturbations in DNA replication patterns and normal gene function in these biosynthetically active cells.     

Midbody sealing after cytokinesis in embryos of the sea urchin Arabacia punctulata

Summary Cytokinesis consists of a contractile phase followed by sealing of the connecting midbody to form two separated cells. To determine how soon the midbody sealed after cleavage furrow contraction, the fluorescent dye Lucifer Yellow CH(457.3 M.W.) was microinjected into cells at various intervals after cleavage had begun. Mitotic PtK₂ cells were recorded with video-microscopy so that daughter cells in the epithelial sheet could be identified for several hours after cell division. One daughter cell of each pair followed was microinjected to determine whether the dye diffused into the other daughter cell. For intervals up to four hours after the beginning of cytokinesis, diffusion took place between daughter cells. After this time the dye did not spread between daughter cells. In sea urchin blastomeres of the first, second and third divisions, Lucifer Yellow passed between daughter blastomeres only during the first 15 min after cytokinesis. If one cell of a two-cell, four-cell or eight-cell embryo was microinjected more than 15 min after the last cleavage, the dye remained in the injected cell and was distributed to all progeny of that cell, resulting in blastulae that were either one-half, one-quarter or one-eighth fluorescent, respectively. Thus, although cleavage furrow contraction takes approximately the same amount of time in sea urchin blastomeres and PtK₂ cells, the time of midbody sealing differs dramatically in the two cell types. Our results also indicate the importance of knowing the mitotic history of cells when injecting dyes into interphase cells for the purpose of detecting gap junctions.