Coexistence of Tetranychus urticae (Acarina: Tetranychidae) with different capacities for diapause: comparative life-history traits

Summary Individuals of the two-spotted spider mite, Tetranychus urticae Koch (Acarina: Tetranychidae), with and without a capacity for diapause, coexist in central Japan. Diapause appears to be adaptive because females in diapause suffered less mortality than non-diapausing individuals when frozen at –24°C for more than 4 h. However non-diapausing females showed good survival up to 4 h of freezing. Active non-diapausing mites survived on rose leaves in Kyoto (35°N) throughout the winters of 1988–1989 and 1989–1990. Cultures of mites with low (LD) and high (HD) diapause capacities at 18°C and 9L-15D photoperiod were successfully selected from the rose population and from a population on chrysanthemum in Nara (34.4°N). Their life-history traits at 15, 20, 25 and 30°C were characterized. HD and LD mites from both populations were of similar ages at first reproduction at 15–30° C. However, at temperatures 20° C, HD individuals produced more eggs than LD individuals, resulting in higher fecundity and intrinsic rate of natural increase. These traits allow HD individuals, which stop breeding between October and April, to increase faster in summer than LD individuals. This provides a mechanism, together with climatic fluctuations, in maintaining the coexistence of diapausing and non-diapausing T. urticae in Kyoto where winter conditions are rarely lethal to the non-diapausing individuals.     

Dichogamy,gender variation and bet-hedging inPseudowintera colorata

Summary Temporal patterns of variability in the longevity of the male and female phases of individual flowers and in the gender expression of plants of a dichogamous New Zealand tree,Pseudowintera colorata (Winteraceae), were documented in field studies. Two measures for the duration of phases in a dichogamous flower are distinguished; the nominal phases based on morphological features of the flower, and the effective phases reflecting the duration of their functions. Flower and phase longevity and phenotypic gender varied considerably throughout the season and among individuals. Temporal variability in phenotypic gender was loosely synchronized among the 12 plants sampled. Three effects of an environmental factor (temperature) were noted. First, increased temperatures shortened the duration of the female phase but had no effect on the duration of the male phase. Second, pollination frequency was positively correlated with temperature. These results indirectly suggest that increased pollination may shorten the duration of the female phase. Third, average population maleness, measured as the proportion of open flowers in the population on a given day which were in the male phase, was positively correlated with temperature. It is postulated that temperature indirectly influences temporal patterns of gender expression in the population through its differential effects on the longevity of the male and female phases in individual flowers. A theoretical model of bet-hedging shows that, if the direction of an environmental effect on the proportions of the sexual phases is irreversible, selection favours asynchronous dichogamy and reduces the temporal variability as much as possible. If the direction of the response is reversible, heterodichogamy is favoured.     

Growth, dry matter partitioning, and diurnal activities of RuBP carboxylase in citrus seedlings maintained at two levels of CO2

The long-term response of citrus rootstock seedlings to CO₂ enrichment was examined in Carrizo estrange ( Poncirua trifoliata (L.) Raf. x Citrus sinensis (L.) Osbeck] and Swingle citrumelo ( P. trifoliate x C. parodist Macf.]. Plaotlets 14 weeks old were transferred to outdoor controlled-environment chambers and maintained for 5 months from Feb. 14 to July 21. During this period, new growth (cm) of citrange and citrumelo shoots at 660 μl1⁻¹ was 94 and 69% greater, respectively, than at 330 μ1 1⁻¹. Total dry weight of both rootstock shoots had increased by over 100%. Growth of few species is affected this markedly by elevated CO₂ levels.
More carbon was partitioned to above-ground organs in CO₂-enriched citrus seedlings. Stem dry matter per unit length was also 32 and 44% greater in citrange and citrumelo, respectively. Total leaf area was increased by 124% in citrange and 85% in citrumelo due to greater leaf number and size. Variations in overall relative growth rate appeared to be related to the rapid, sequential, flush-type growth in citrus, in which an entire shoot segment with its associated leaves remains an active sink until fully expanded. RuBP carboxylase (EC 4.1.1.39) activity in leaves of recently-expanded flushes was higher in citrumelo plants grown at 660 vs 330 μ1 1⁻¹ CO₂ and changed diurnally for citrange (but not citrumelo) leaves at both CO₂ levels. The results are consistent with the hypothesis that positive long-term effects of CO² enrichment may be greater in species or during growth periods where sink capacity for carbon utilization is high.     

Phosphorus deficiency induced by nitrogen input in Douglas fir in the Netherlands

Summary A re-examination of earlier NPK fertilization experiments in Douglas fir stands on sandy soils shows the effects of high nitrogen input by air pollution during the last 10–15 years on plant nutrition at these sites. In 1960, experimental plots showed a positive growth reaction to nitrogen, phosphorus, and potassium fertilization. All suffered from severe phosphorus deficiency in 1984, low phosphorus in the needles was invariably accompanied by a high nitrogen content, with all N/P ratios between 20 and 30. The same conclusion emerges from an independent investigation of nutrient status of a selection of Douglas fir stands. Hence, if stand productivity and a balanced nutrient status of the trees is to be maintained, the increase in atmospheric input of nitrogen calls for supplementary fertilization. Given the current N/P ratios in the needles, a positive growth response to phosphorus fertilization is to be expected.     

Maximal exercise capacity in adolescent European and Amerindian high-altitude natives

Forty-seven highland natives were given maximal exercise tests on a treadmill ergometer at 3,600 m. The subjects were grouped into four subsamples on the basis of ethnicity (European vs. Aymara) and age (young vs. old adolescent). Two-way ANOVA indicated that VO2max adjusted for body size did not differ significantly between ethnic groups but was significantly larger in older than younger boys within each ethnic group (p less than .05). This finding does not support the hypothesis that Amerindian highland natives have adapted genetically to hypoxia but is consistent with the hypothesis that the relatively high VO2max's of highlanders are acquired by developmental adaptation. Several measures of ventilation and oxygen transport capacity differed significantly between ethnic groups, suggesting that growing European and Aymara boys may respond somewhat differently to the stress of high-altitude hypoxia. However, despite these differences, VO2max, an integrated measure of the overall functional capacity of the oxygen transport system, did not differ significantly between ethnic groups, suggesting that both groups are equally capable of meeting the body's oxygen requirements during maximal exercise at high altitude.     

Phytoplankton community structure and distribution in the nearshore zone of Lake Ontario

Spatial and temporal distributions of phytoplankton were studied during 1979 in the nearshore zone of Lake Ontario. Genera such as Dinobryon, Oscillatoria, and Gymnodinium tended to be found at discrete depths whereas other genera such as Cryptomonas and Rhodomonas tended to be more uniformly distributed throughout the water column. The discrete depth distribution of some of these genera compared with the weak thermal stabilization of the area suggests depth selection and habitat preference within the algal community.Physical processes probably played a major role in regulating the timing and duration of vertical diatom pulses, and resuspension from the sediment played a major role as to the timing of the autumn growth. Vertical mixing in the nearshore zone was sufficient for some diatom genera such as Tabellaria to maintain populations throughout the summer. These mixing processes, however, affect the stability of community structures and associations that develop within the water column. The role of physical processes and their potential effects on algal production in the Great Lakes is discussed.     

Ethanol-sensitive mutants of Saccharomyces cerevisiae

Saccharomyces cerevisiae mutants unable to grow at ethanol concentrations at which the wild type strain S288C does grow, have been isolated. Some of them show additional phenotypic alterations in colony size, temperature sensitivity and viability in ethanol, which cosegregate with the growth sensitivity in ethanol. 21 selected monogenic ethanol-sensitive mutants define 20 complementation groups, denominated ETA1 to ETA20, which indicates that there is a high number of genes involved in the ethanol tolerance/sensitivity mechanism.Out of 21 selected monogenic mutants, 20 are not altered in the glycolytic pathway since, when maintained in glucosesupplemented medium, they can produce as much ethanol as the wild type and at about the same velocity. Nor do any of the mutants seem to be altered in the lipid biosynthetic pathway since, whether grown in the absence or in the presence of ethanol, their concentration of fatty acids and ergosterol is similar to that of the wild type under the same conditions. Therefore growth sensitivity to ethanol does not seem necessarily to be related to carbohydrate or lipid metabolism.Non-common abbreviations YP yeast extract peptone medium - YPD yeast extract peptone dextrose agar or medium - YPG yeast extract peptone glycerol agar - YPDE yeast extract peptone dextrose ethanol agar or medium - SD yeast nitrogen base dextrose agar - SPO yeast extract potassium acetate glucose agar - PD parental ditype - NPD non-parental ditype - TT tetratype     

Zn buffering capacity and Zn accumulation in Swiss chard for some sludge-amended soils

Zinc sorption by soils can greatly affect its availability to plants. This study was conducted to determine the relationship between the Zn sorption capacity and plant Zn accumulation in five sludge-amended soils using Swiss chard (Beta vulgaris L.) as an indicator plant. Zinc sorption as a function of Zn concentration and pH was determined for the soils which received no sludge amendment; also DTPA (diethylenetriaminepentaacetic acid) extractable Zn was determined in all soils. Whereas the responses of DTPA-Zn and plant Zn to pH and the quantities of Zn sorbed were similar, the logarithm of DTPA-Zn accounted for only 82% of the variability in the logarithm of Zn accumulation by the plants. The variability was better explained when pH was included with DTPA-Zn in stepwise multiple regressions. The Zn buffering capacity, defined as the ratio of the change in quantity of Zn sorbed ( Zn_s) to the change in Zn solution concentration (Zn₁) (or Zn_s/Zn₁), and the estimated quantity of Zn sorbed were used as a basis to measure Zn intensity. Zinc intensity, which reflects Zn solution concentration, was the predominant factor controlling Zn accumulation by Swiss chard, judging from the good fit of the values of both parameters to the Michaelis-Menten equation. The maximum Zn accumulation was approximately 9 mmol kg^–1.Scientific paper no. 8901-29, Department of Agronomy and Soils, College of Agriculture and Home Economics Research Center. Washington State University, Pullman, WA 99164, USA.Scientific paper no. 8901-29, Department of Agronomy and Soils, College of Agriculture and Home Economics Research Center. Washington State University, Pullman, WA 99164, USA.     

Water-storage capacity ofThuja,Tsuga andAcer stems measured by dehydration isotherms

Water-storage capacity was measured inThuja occidentalis L.,Tsuga canadensis (L.) Carr., andAcer saccharum Marsh. during the dehydration of stem segments 1.5–2.5 cm in diameter. Stem water potential was measured with a temperature-corrected stem hygrometer and cavitations were detected acoustically. Water loss was measured by weight change. Dehydration isotherms consistently displayed three phases. The first phase, from water potential (Ψ) 0 to about −0.2 MPa, had a high capacitance (C>0.4kg water lost· (1 of tissue)⁻¹· MPa⁻¹) and we have attributed this high C to capillary water as defined by Zimmermann (1983, Xylem structure and the ascent of sap, Springer-Verlag). The second phase from Ψ=−0.5 to about −2.0 had the lowest C values (<0.02 kg·l⁻¹·MPa⁻¹) and was accompanied by a few cavitation events. This phase may have been a transition zone between capillary storage and water released by cavitation events as well as water drawn from living cells of the bark. The third phase also had a high C (about 0.07–0.22kg·l⁻¹·MPa⁻¹) and was associated with many cavitation events while Ψ declined below about −2.5 MPa; we presume the high capacitance was the consequence of water released by cavitation events. We discuss the ecological adaptive advantage of these three phases of water-storage in trees. In moist environments, water withdrawn from capillary storage may be an important fraction of transpiration, but may be of little adaptive advantage. For most of the growth season trees draw mainly on elastic storage, but stem elastic storage is less than leaf elastic storage and therefore unlikely to be important. In very dry environments, water relased by cavitation events might be important to the short-term survival of trees.     

Meteorological factors and the time of onset of chest pain in acute myocardial infarction

Analysis of the time of onset of chest pain in 2254 patients with a myocardial infarction admitted to a coronary care unit in Leicester during a 10-year period shows an association with temperature and humidity. During both the most cold and humid times of the year, the relationship is a strong one. A generalized linear model with a log link was used to fit the data and the backward elimination selection procedure suggested a humid, cold day might help to trigger the occurrence of myocardial infarction. In addition, cold weather was found to have a stronger effect on the male population while those men aged between 50 and 70 years were more sensitive to the effect of high humidity.