Effects of temperature and food level on growth and development of a planktonic water mite

We analysed the relative effects of food availability and temperature on rates of growth and development of a predatory planktonic water mite, Piona exigua. Growth in length of mites fed Daphnia, Ceriodaphnia and Chydorus was analysed by Gompertz or von Bertalanffy curves; these curves were compared by parallel curve analysis. Growth rates of nymphs and adult female mites increased with temperature; the duration of the imagochrysalis stage decreased. Females grown at 10 °C were smaller at final size than females grown at 15 °C, 18 °C or 22 °C. Females reared at food levels of 15 or 30 prey l⁻¹ grew more slowly and were smaller than those provided with 60 or 120 prey l⁻¹. Nymphs grew more slowly when Daphnia were the only prey, than when smaller prey were available. Food level did not affect nymph growth at 10 °C or 15 °C, but growth at 18 °C or 22 °C may have been slowed at the lowest food levels. Synergistic effects of temperature and food level on nymph growth were apparent only from analysis of growth curves and not from stage duration data.     

Radiative properties of hardwood leaves to ultraviolet irradiation

Spectral reflectance and transmittance of leaves to ultraviolet irradiation were determined under laboratory conditions for seven species of hardwood trees, namely red oak (Quercus rubra, L), black oak (Q. velutina, Lamarch), white oak (Q. alba, L.), sugar maple (Acer saccharum), Norway maple (A. plantanoides), hickory (Carya tomemtosa), sweetgum (Liquidambar styraciflua), and black oak litter. The experimental system consisted of a solar simulator, an integrating sphere, and a spectroradiometer. Experiments were repeated three to five times for both adaxial and abaxial surfaces of fresh leaves chosen at randomly. The spectral distributions and simple averages of the radiative properties in the wavelength ranges of ultraviolet-B (UV-B, 280–320 nm) and ultraviolet-A (UV-A, 320–400 nm) were determined. The spectral distributions of reflectance were similar between adaxial and abaxial surfaces, although the magnitude varied among tree species. Leaf reflectance was very low for the ultraviolet spectrum in general and varied among species and between adaxial and abaxial surfaces. It was generally higher over the UV-A waveband compared to UV-B, and higher on the abaxial than adaxial surface. The broadband reflectance in the UV-A range (over all species) was 5.0 and 3.9% for abaxial and adaxial surface, respectively, compared to 3.5 and 2.8% in UV-B. The transmittance through leaves was extremely small in the UV-B (<0.1%) and nearly zero in the UV-A spectral range. Consequently, the absorptance of ultraviolet radiation by leaves, as determined from the measured reflectance and transmittance, was quite high, being more than 90% for all the combinations of species and wavebands examined. The reported results are useful for studies requiring spectral radiative properties of the examined leaves with respect to ultraviolet irradiation.     

Distribution of the phytoplankton from the Guri Reservoir (Venezuela)

The distribution of phytoplankton species of a tropical blackwater reservoir is discussed on the basis of spatial differences in water composition and of species abundance and diversity. Spatial heterogeneity in water composition identified three different environments within the reservoir itself: (1) strongly colored waters, high turbidity and iron concentrations at the inflow; (2) calcium enriched, nearly uncolored waters at El Pao Bay; (3) lightly colored water, higher transparency and a higher ratio monovalent to divalent cations in the main body of the reservoir. Three corresponding phytoplankton associations were found. Principal Component Analysis helped to explore the relationship of particular species with the abiotic factors. Among them, water color, turbidity, and mineralization proved to be determinant in habitat diversification.     

Feeding biology of two brachionid rotifers: Brachionus quadridentatus and Brachionus plicatilis

Brachionus quadridentatus and Brachionus plicatilis were examined in laboratory cultures to investigate their (1) food requirements and (2) ability to select particles on the basis of size. Growth experiments showed that the Chlorophyceans Nannochloris sp. and Chlorella vulgaris possess good nutritional value for these rotifers. However, B. quadridentatus declined in cultures with Microcystis firma, detritus of Enteromorpha sp. or Pseudomonas sp. (bacteria) as a sole source of food, thus indicating that these foods were inadequate. Utilization of latex microspheres by these two species indicate that they respond to particle size in different ways: B. quadridentatus had a higher selectivity index for 3 and 5 µm beads, while B. plicatilis had a higher selectivity index for 2 µm beads.     

Variation in growth and age at maturity in bluegill sunfish: genetic or environmental effects?

Populations of bluegill sunfish Lepomis macrochirus , experiencing heavy juvenile predation, showed increased growth rates and increased age and size at maturity relative to populations experiencing decreased predation on juveniles but increased predation on adults. This study examined bluegills experimentally from both types of populations and a cross between them in a common environment to determine if variation in growth and age at maturity is genetically or environmentally induced. Two factorial experiments, varying strain of bluegills and resource availability, were used to evaluate differences in growth rate. One experiment, varying strain of bluegills, was used to assess differences in age at maturity. Growth was strongly influenced by resource level, but growth rate did not vary among populations. Nearly all bluegills in each population matured at 1 year of age in a common environment. Thus, variation observed in source populations must be mostly attributable to differences in the environment between populations. At least three factors could potentially cause differences in growth and age at maturity: (1) variation in resource availability; (2) variation in demographic structure; and (3) variation in size-specific mortality rates caused by differences in predator abundance between populations. Observed patterns of variation between populations are best explained by effects of differences in predator populations.     

Body water content over a range of ambient salinities in the sheepshead minnow

Body water content was determined on groups of Cyprinodon variegatus after sequential acclimation to ambient salinities in the range from fresh water to 100%. A multiple linear regression model applied to the data included body mass ( M ) of individuals and acclimation salinity ( S ) as independent variables, and body water content ( W ) as the dependent variable. The model that described the relationship was W (g) = 0·059 + 0·723 M (g)–0001 S (%). Converting values of body water content to percent of wet body mass produced a range of values from 74·5% in fresh water to 72·0% at 100%, only a 2·5% difference in body water content over this wide range of ambient salinities.     

Chloride-activated water permeability in the frog corneal epithelium

We have previously reported that the isolated frog corneal epithelium (a Cl^–-secreting epithelium) has a large diffusional water permeability (P_dw 1.8×10^–4 cm/s). We now report that the presence of Cl^– in the apical-side bathing solution increases the diffusional water flux, J_dw (in both directions) by 63% from 11.3 to 18.4 l min^–1 · cm^–2 with 60 mm [Cl] exerting the maximum effect. The presence of Cl^– in the basolateral-side bathing solution had no effect on the water flux. In Cl^–-free solutions amphotericin B increased J_dw by 29% but only by 3% in Cl^–-rich apical-side bathing solution, suggesting that in Cl^–-rich apical side bathing solution, the apical barrier is no longer rate limiting. Apical Br^– (75 mm) also increased J_dw by 68%. The effect of Cl^– on J_dw was observed within 1 min after its addition to the apicalside bathing solution. HgCl₂ (0.5 mm) reduced the Cl^–-increased P_dw by 31%. The osmotic permeability (P_f) was also measured under an osmotic gradient yielding values of 0.34 and 2.88 (x 10^–3 cm/s) in Cl^–-free and Cl^–-rich apical-side bathing solutions respectively. It seems that apical Cl^–, or Cl^– secretion into the apical bath could activate normally present but inactive water channels. In the absence of Cl^–, water permeability of the apical membrane seems to be limited to the permeability of the lipid bilayer.This work was supported by National Eye Institute grants EY-00160 and EY-01867.     

Extracellular ATP binding proteins as potential receptors in mucociliary epithelium: Characterization using [32P]3′-O-(4-benzoyl)benzoyl ATP,a photoaffinity label

3-O-(4-benzoyl)benzoyl ATP (BzATP) was used as a photoaffinity analog of ATP to label potential ATP receptors in ciliated cells. Like ATP, without photoactivation, BzATP stimulated the ciliary beat frequency in tissue culture up to threefold. Irradiation of intact cells in the presence of [-³²P]BzATP followed by SDS-PAGE and autoradiography revealed two labeled proteins with molecular masses of 46 and 96 kDa (p46 and p96). Photolabeling of both proteins was susceptible to digestion with trypsin, implying that the labeled proteins are at least partially exposed on the extracellular surface of the plasma membrane. The dependence of ³²P incorporation in both proteins on [-³²P]BzATP concentration was similar. Labeling of p46 but not p96 required Ca²⁺ or Mg²⁺. Various nucleotides stimulated the ciliary frequency, and inhibited the photolabeling of p46 and p96. The rank order of apparent affinity for p46 is: ATP ÃDP>GTPS>ADP S, UTP, 2MeSATP, AMP-PNP >AMP-PCP>AMP>adenosine; for p96 it is: ADPADP S ATP AMP-PCP, AMP-PNP>GTPS AMP>2MeSATP, UTP, adenosine. The rank of stimulation of ciliary beat frequency is: ADPS, UTP 2MeSATP, GTPS, AMP-PNP, ATPADP>AMPPCP>adenosine>AMP. These results suggest the involvement of p46 in the stimulatory effect of extracellular ATP on the ciliary beat, as a P₂ purinoceptor. On the other hand, p96 may represent a P₂ purinoceptor or an ectonucleotidase.This work was supported by grants (to Z.P. and to V.S-B.) from the Fund for Basic Research administered by the Israel Academy of Science and Humanities.