Genetic parameters of size through sexual maturity have been relatively unexplored for Pacific salmon. In this study, individually tagged coho salmon were raised in freshwater, and the heritabilities of size and growth rate were estimated at several intervals between 13 and 24 months of age (spawning). Heritability estimates for size were moderate to high from 13 to 19 months of age, ranging from 0.36 to 0.50, and lower from 21 months to spawning at 24 months, ranging from 0.17 to 0.32. Heritabilities of specific growth rates estimated over 3-month intervals were moderate from 16 to 21 months of age, ranging from 0.21 to 0.34. Genetic and phenotypic correlations between sizes measured at different ages were moderate to high, ranging from about 0.7 to 1.0. Correlations between growth rate and size indicated that the larger fish were the fastest growing between 16 and 19 months of age and were slower growing between 19 and 21 months of age. 相似文献
Several aspects of community organization wereanalyzed comparatively in a small side-arm of theParaná River (Correntoso) and a shallowfloodplain lake (El Tigre) (31° 41 S and60° 42 W), in relation to the hydrology of thesystem. Taxonomic and morphological composition inthe river differed from that in the lake: the riverhad lower species richness (151 vs 218),different contributions of some Classes to totalspecies number (higher Cyano-, Zygo- andDiatomophyceae vs higher Chlorophyceae), anddiffent proportions of nannoplanktonic algae (67.5%vs 80.7%) and netplanktonic filamentousspecies (18.2% vs 4.2%). Phytoplanktonbiomass, higher in the lake than in the river due tothe retention time, was mostly dominated bynannoplankton and netplankton. Loticphytoplankton was dominated by typical fluvialspecies of Diatomophyceae (R-strategists). Riverconditions seem to maintain a subclimacticcommunity, which was little impacted by the flushingof populations from floodplain lakes. Water levelwas the main factor controlling phytoplanktonbiomass, species diversity (H), evenness (E) andcommunity change rate () in the river. Inthe lake, phytoplankton had an autogenicsuccessional sequence during the isolation phase (C-to S-strategists) and other responses todisturbance, mainly during the flood(R-strategists). Frequent changes in phytoplanktoncomposition, biomass, H, E and , revealed aenvironmental instability in the lake, which may beexplained by interactions of external factors(hydrology and climatology) and those of internalorigin, such as nutrients and grazing. 相似文献
Freeze-thawing of Escherichia coli cells caused a release of cell membrane components such as protein, phospholipids and lipopolysaccharides. A greater amount of release and a lesser extent of cell survival were seen in slow freeze-thawing than in rapid freeze-thawing. Several dehydrogenases in the cells were also freed. The mode of release was also dependent on the rate of freeze-thawing.The materials released by slow freeze-thawing were found to be mostly composed of outer membrane components, whereas the materials released by rapid freeze-thawing contained cytoplasmic as well as outer membrane components. The chemical composition of these fragments differed significantly from that of the original membranes. The relative content of cytoplasmic membrane-bound enzymes in these fragments also differed from that of the cytoplasmic membrane.The fragmentation was assumed to have resulted mainly from the crystallization of external water. In slow freeze-thawing, it was considered that the phase separation of the membrane phospholipid bilayer increased the possibility of outer membrane fragmentation. Rapid freeze-thawing caused cytoplasmic membrane damage to the cells as well as to the outer membrane. In rapid freeze-thawing, the effect of phase separation appeared to be small because of rapid passage through the transition temperatures.The presence of 10% glycerol completely inhibited the release of cellular materials and enzymes. Cell survival was maintained at a high level in the glycerol-treated samples whether freeze-thawed slowly or rapidly. 相似文献
1. 1.|The purpose of this study was to determine the threshold specific absorption rate (SAR) during exposure to 2450 MHz continuous wave (CW) microwaves that affected thermoregulatory behaviour in mice.
2. 2.|A Plexiglas shuttle box was placed inside a waveguide imposed with a temperature gradient. The temperature gradient allowed the mice to select a particular section of the shuttle box which was, presumably, related to their state of thermal comfort. Exposing the mice to 2450 MHz inside the waveguide at SARs of 0–5.3 W kg−1 for 1 h caused no significant change in their preferred ambient temperature.
3. 3.|Increasing SAR from 5.3 to 18.1 W kg−1 caused the animals to shift their position to the cooler end of the shuttle box.
4. 4.|Following termination of microwave exposure animals that had selected a cool ambient temperature returned to the warm side of the shuttle box.
5. 5.|It is concluded that for mice exposed to radiation at 2450 MHz the thermoregulatory behaviour is significantly affected at SARs of 5.3 to 9.9 W kg−1.
Summary Eleven grass species varying in potential relative growth rate (RGR) were investigated for differences in chemical composition by pyrolysis mass spectrometry. The spectral data revealed correlations between RGR and the relative composition of several biopolymers. Species with a low potential RGR contained relatively more cell wall material such as lignin, hemicellulose, cellulose, polysaccharide-bound ferulic acid and hydroxyproline-rich protein, whereas species with a high potential RGR showed relatively more cytoplasmic elements such as protein (other than those incorporated in cell walls) and sterols. 相似文献
A method is described for determining the way in which growth rate varies with plant nutrient concentration using a simple
nutrient interruption technique incorporating only 2 treatments. The method involves measuring the changes in growth and nutrient
composition of otherwise well-nourished plants after the supply of one particular nutrient has been withheld. Critical concentrations
are estimated from the relationship between the growth rate (expressed as a fraction of that for control plants of the same
size which remained well-nourished throughout) and the concentration of the growth-limiting nutrient in the plants as deficiency
developed. Trials of the method using young lettuce plants showed that shoot growth rate was directly proportional to total
N (nitrate plus organic N) concentration, and linearly or near-linearly related to K and P concentration over a wide range;
the corresponding relationship for nitrate was strongly curvi-linear. Critical concentrations (corresponding to a 10% reduction
in growth rate) determined from these results were similar to critical values calculated from models derived from field data,
but were generally higher than published estimates of critical concentration (based on reductions in shoot weight) for plants
of a similar size. Reasons for these discrepancies are discussed. Nitrate, phosphate or potassium concentrations in sap from
individual leaf petioles were highly sensitive to changes in shoot growth rate as deficiency developed, with the slope of
the relationships varying with leaf position, due to differences both in their initial concentration and in the rates at which
they were utilized in individual leaves. Each nutrient was always depleted more quickly in younger leaves than in older ones,
providing earlier evidence of deficiency for diagnostic purposes. Although the plants were capable of accumulating nitrate,
phosphate and potassium well in excess of that needed for optimum dry matter production during periods of adequate supply,
the rate of mobilization of these reserves was insufficient to prevent reductions in growth rate as the plants became deficient.
This brings into question the validity of the conventional concept that luxury consumption provides a store of nutrients which
are freely available for use in times of shortage. The implications of these results for the use of plant analysis for assessing
plant nutrient status are discussed. 相似文献
Theoretical and analytical problems of the dynamics of distribution and abundance in animal communities were examined. In many communities, species with low abundance and of limited spatial occurrence (i.e., rare species) typically form a conspicuous peak when a frequency distribution of the number of species is constructed with respect to the proportion of sites occupied within an area of distribution. Models of distribution dynamics, including a new model proposed here, were compared with a range of animal community data using a new procedure to assess single- and bi-modal patterns in frequency distributions of spatial occurrence. Data reveal that single-modality with an excess of rare species occurs more frequently than bimodality. Even when bimodality is detected, the mode representing wide-spread species is in the majority of cases smaller than that for rare species. Thus, a new model in which the rate of local extinctions is assumed to be negatively related to patch occupancy (or population abundance) is in better agreement with observed data than earlier models. Some problems of analysis, in particular model assumptions and testing, are discussed. 相似文献