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1.
Sequential medical trials involving paired data 总被引:2,自引:0,他引:2
2.
Sara Ceballos Florentina Álvarez-Marqués 《Journal of experimental marine biology and ecology》2006,339(2):189-203
The reproductive activity and the physiological state of the calanoid copepods Calanus helgolandicus and Calanoides carinatus were investigated off the coast of NW Spain during autumn to evaluate the effect of short food resources on both populations. Phytoplankton biomass was low, and neither phytoplankton size distribution nor composition was suitable to support high reproductive rates. Accordingly, egg production rates (EPR) were much lower than maximum rates for both species, pointing to food limitation. The reproductive index (RI), which represents the proportion of females with mature gonads, was < 50% at each of the three zones into which the sampling area was divided (coast, shelf and ocean). Potential recruitment rates were very low except at some nearshore stations, where the highest concentrations of chlorophyll-a (Chl-a), diatoms, dinoflagellates and large cells were found. EPR of C. helgolandicus and C. carinatus were correlated with phytoplankton biomass and unaffected by temperature. Phytoplankton carbon ingestion explained ca. 50% of the variability in EPR for both species. At most of the stations, herbivory was insufficient to cover the carbon requirements for reproduction and respiration, so females probably fed on heterotrophic prey to meet their demands. However, given the low fecundity observed, this omnivorous diet did not seem to be optimum for reproduction, and a severe food limitation is thus suggested. Furthermore, the high C/N values measured point to a notable lipid storage, but given the low EPR found, lipid reserves were probably invested into female maintenance rather than into gonad maturation. C. helgolandicus and C. carinatus populations did not mirror phytoplankton biomass distribution, but they correlated well when considering only copepodites V (CV). The CV could be preparing for the overwintering, storing lipid reserves to ensure a successful diapause, and they could also be advected by the poleward current detected during the study. Females showed a diel feeding rhythm, with highest ingestion rates during night. From our results, it follows that C. helgolandicus and C. carinatus females did not perform diel vertical migrations. We suggest that this behaviour is likely due to the food-limiting conditions, which make it more advantageous to remain at the surface during daytime. 相似文献
3.
G. E. Walker 《Plant and Soil》1984,78(3):431-432
Summary
Aphelenchus avenae and various unidentified bacteria and actinomycetes were cultured from soil samples taken from a pine-forest and a wheat-field.
The nematode failed to reproduce in significant numbers on cultures of these micro-organisms and was apparently unable to
utilize them as food sources. 相似文献
4.
Invertebrate offspring are usually larger in colder environments. To test for possible effects of covariates (e.g. maternal phenotype and feeding conditions) on this pattern, we performed a laboratory experiment to look at the effect of temperature on newborn weight in the planktonic crustacean Daphnia magna. Three tempèratures (12°C, 16°C and 22°C) and two food levels (10,000 cells ml–1 and 150,000 cells ml–1) were used, and offspring were examined from the first five clutches of mothers that had been maintained under the constant experimental conditions for three generations. Preliminary analysis suggested that newborn weight was significantly affected by temperature although patterns in the data were not clear cut. In addition, the covariates mother weight and clutch size were positively and negatively correlated with newborn weight, respectively; and later clutches tended to contain heavier offspring. Therefore, in an effort to control for the effects of the covariates, repeated-measures analysis of covariance was performed using ratio values of newborn weight/mother weight (relative newborn weight) as the dependent variable, clutch size as the covariate and clutch number as the repeated measures term. Now, temperature as a main effect in an ANCOVA model did not significantly influence relative newborn weight. The repeatedmeasure term clutch number also became nonsignificant, indicating that when differences in mother weight due to age were accounted for there were no overall differences in relative newborn weight between clutches from a particular mother. Temperature effects on relative newborn weight were only significant as part of interaction terms with food concentration and with clutch number. Thus there were different weight responses to temperature within food levels, and between clutch numbers within food levels. Under the low-food conditions newborn were heaviest at 16°C, lightest at 12°C and intermediate at 22°C. Conversely, under the high-food condition newborn were lightest at 16°C, heaviest at 12°C and again intermediate at 22°C. However, newborn tended to be heavier under the low food condition, and food concentration was highly significant as a main effect. Mother growth rate showed no significant relationship with newborn weight. It is concluded that direct temperature effects on relative newborn weight are marginal and nonsignificant. Temperature effects through interactions with food concentration and clutch number are important determinants of newborn weight, but relatively speaking account for only a small proportion of observed variance in newborn weight (25%), compared with the direct effect of food concentration (67%). 相似文献
5.
The advantage of using terrestrial isopods in toxicity studies is that a battery of parameters can be tested at different levels of biological complexity. Feeding parameters for example link organism level response to potential ecological consequences but a problem with using feeding parameters in toxicity tests with terrestrial isopods is their high variability. The aim of our study was to set benchmark values for feeding parameters for isopod Porcellio
scaber (Isopoda, Crustacea) in laboratory-controlled experiments. In the work presented here, the daily feeding rate of the central 50% of the control population of Porcellio
scaber and a correlation between feeding rate and isopod weight were set. Values outside these ranges need additional evaluation to increase the relevance of test outcomes. We suggest using benchmark values for feeding parameters as well as the coefficient of variation (a) to identify animals with altered feeding parameters with respect to controls, and (b) to assess the data quality in each experiment. 相似文献
6.
Variables Influencing the Effect of a Meal on Brain Tryptophan 总被引:7,自引:5,他引:2
Previous work from our laboratory points to plasma free tryptophan being a useful predictor of brain tryptophan concentration in many circumstances. Other work, in particular various studies on the acute effects of food intake, has emphasized the roles of plasma total tryptophan and of plasma large neutral amino acids that compete with tryptophan for transport to the brain. We have now studied associations between the above variables under different dietary conditions. Rats were allowed to feed for restricted periods during a 12-h light-12-h dark cycle. In the first study, rats were given access to a carbohydrate diet for 2 h midway through the light cycle and following an 18-h fast. The resultant rise of brain tryptophan was explicable largely by the associated fall in large neutral amino acids. In a second study, rats were adapted to a regimen whereby they were allowed access to the standard laboratory diet for 4 h during the dark cycle for 3 weeks. A postprandial decrease in brain tryptophan was associated with a fall in free tryptophan and of its ratio to competing amino acids. The brain change could be attributed neither to changes in plasma total tryptophan (which increased) nor to changes of its ratio to the competers (which remained unchanged). Results as a whole are thus consistent with changes of plasma free tryptophan and large neutral amino acid concentrations affecting brain tryptophan concentration under different dietary circumstances. It is suggested that these influences serve to maintain brain tryptophan when dietary supplies are defective. 相似文献
7.
C. P. McPhee P. C. Trappett 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1987,73(6):926-931
Summary Two lines of mice were selected for high post-weaning weight gain (3 to 6 weeks) adjusted for 3 week weight. One line (F) was grown on freely available food and the other (S) on a feeding scale set at the same level for all mice. Food intake of the S line averaged 80% of the F line. The realised heritabilities after 6 generations of selection were 0.38±0.06 and 0.33±0.07 for the F and S lines, respectively. In generation 7, mice from the F and S lines and from an unselected control line (C) were compared on both free and set levels of feeding from 3 weeks to 9 weeks of age. Measurements taken were growth rate, appetite, food conversion efficiency (weight gain/food intake) and body composition (fat, protein, ash, water). The F and S lines grew more rapidly and efficiently than the C line on both levels of feeding, each line performing best on the level of feeding on which it was selected. The average genetic correlation between growth rates of the same line on the two feeding levels was 0.54±0.10. The F line grew 19% faster and was 9% more efficient than the S line on free feeding but the S line grew 15% faster and was 15% more efficient than the F line on set feeding. Relative to the C line, food intake per day on free feeding was 4% higher in the F line and 6% lower in the S line. There was no difference between the lines in food intake/g body weight. The rate of deposition of all body components increased in both selection lines. In the F, S and C lines respectively, efficiencies of gains in body components (102x gain/food) were 1.79, 1.31 and 1.06 for fat, 1.53, 1.63 and 1.22 for protein and 5.88, 6.45 and 4.98 for protein + water. Apparently energy lost as heat was reduced in both the F and S lines. The partitioning of energy retained was altered in favour of more fat in the F line and more protein in the S line. 相似文献
8.
Feeding responses of the oligophagous tobacco hornworm to allelochemicals prevalent in their host plants were determined in food choice-tests using filter paper discs laced with a test solution or water (control). Six solanaceous alkaloids, tomatine, tomatidine, solanine, solanocapsine, atropine and nicotine, were tested and only tomatine and solanocapsine were found to influence preference behavior. Solanocapsine (5 mM) deters feeding whereas tomatine (1 mM) stimulates feeding slightly. No synergistic effect of either tomatine or tomatidine with sucrose was found.The responses to tomatine are affected by previous feeding experience. Tomatine slightly stimulates feeding in larvae reared on tomato (Lycopersicon esculentum), but slightly deters feeding in larvae reared on Jerusalem cherry (Solanum pseudocapsicum). Such induced preference is absent for the other alkaloids tested, which indicates that these alkaloids do not by themselves induce preferences for the plants containing them.The non-alkaloid allelochemicals, chlorogenic acid, rutin, and 2-tridecanone also influenced food choice behavior. Chlorogenic acid is slightly stimulatory at its natural concentration (1mM), but strongly deterrent at higher concentrations. Rutin stimulates feeding in a concentration-dependent manner. Its activity must be due to the glycosylated structure, because both the aglycone (quercetin) and the sugar moiety (rutinose) are neutral. Removal of the glucose part of rutin, as in quercitrin, results in feeding deterrent activity. 2-Tridecanone is neutral at its concentration in cultivated tomato (1 mM), but strongly deterrent and toxic at higher concentrations. Preference behavior is not affected by solanesol, GABA, and a mixture of host plant compounds stimulatory for anothe solanaceous-specific feeder, the Colorado potato beetle (Leptinotarsa decemlineata).We conclude that the prevalent solanaceous alkaloids and other allelochemicals tested do not play important roles in food selection of the tobacco hornworm, although some may make small contributions.
Résumé Des experiences de choix de chenilles oligophages de M. sexta ont été réalisees avec des disques de papier filtre imbiles d'eau ou de solutions des substances allélochimiques dominantes dans les plantes consommées. Sur les six alcaloïdes de solanées examinés: tomatine, tomatidine, solanine, solanocapsine, atropine et nicotine, seuls la tomatine et la solanocapsine ont influé sur le choix; la solanocapsine (5 mM) empêche la prise de nourriture, tandis que la tomatine (1 mM) la stimule légèrement. Aucun effet synergique de la tomatine ou de la tomatidine n'a été observé en présence de sucrose.La réponse à la tomatine est modifiée par la prise de nourriture antérieure. Elle stimule légèrement l'alimentation de chenilles élevées sur tomates (Lycopersicon esculentum), mais dissuade légèrement les chenilles élevées sur Solanum pseudocapsicum. II n'y a pas d'action induite semblable avec les autres alcalïdes examinés, ce qui indique que ces alcaloïdes ne peuvent pas induire par eux-mêmes de préférences pour les plantes qui les contiennent.Des substances allélochimiques non-alcaloïdes: acide chlorogénique, rutine, et 2-tridécanone, influent aussi sur le comportement de choix alimentaire. L'acide chlorogénique est légèrement stimulant à sa concentration naturelle (1 mM), mais fortement dissuasif aux concentrations supérieures. La rutine stimule la prise de nourriture en fonction de sa concentration. Son activité doit être due à sa structure glucosylate, puisqu'aussi bien l'aglycone (quercitine) que la moiteé sucrée (rutinose) sont neutres. La suppression de la partie glucose de la rutine, comme dans le cas de la quercitine, a un effet dissuasif. A sa concentration dans la tomate cultivée (1 mM), le 2-tridécanone est neutre, mais il est fortement dissuasif et toxique à des concentrations supérieures.Le comportement de choix n'est pas modifié par le solanésol, le GABA, et par un mélange de composés végétaux stimulant un consommateur spécifique de solanées, comme le doryphore (Leptinotarsa decemlineata).Nous pouvons conclure que les principaux alcaloïdes et autres substances allélochimiques des solanées que nous avons examinés n'interviennent pas d'une façon importante, mais peuvent avoir une influence secondaire, dans les choix alimentaires de Manduca sexta.相似文献
9.
J. Crossa C. O. Gardner 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1989,77(1):33-38
Summary The maize (Zea mays L.) improvement program of the International Maize and Wheat Improvement Center (CIMMYT) develops broad-based maize populations and, until recently, improved all of them through full-sib family selection with international testing. The purpose of this study was to estimate the genetic and genetic × environment variance components for ten of those populations and to measure expected yield improvement from full-sib selection. Mean yield ranged from 3.35–6.81 t ha–1. For five populations the average yield in the last cycle was higher than in the initial cycles. Several populations showed no improvement or yielded less in the final cycle of selection, either because selection intensity was low or because strong selection pressure was applied simultaneously for several traits. Variation resulting from differences among family means within cycles and from interaction between families and locations within cycles were significant in all populations and cycles. Results indicate that variability among full-sib families was maintained throughout the cycles for all populations. The large
ge
2
/
g
2
ratio shown by most populations suggests that yield response per cycle could be maximized if the environments in which progenies are tested were subdivided and classified into similar subsets. The proportion of the predicted response realized in improved yield varied for each population.Journal Paper No. 8640, Nebraska Agric. Res. Div. Project No. 12-159. Research was supported in part by USAID/USDA/ CSRS Research Grant No. 86-CRSR-2-2789 相似文献
10.
JONATHAN B. LOSOS HARRY W. GREENE 《Biological journal of the Linnean Society. Linnean Society of London》1988,35(4):379-407
A survey of 35 species indicates that monitor lizards (Varanus) typically hunt over large areas, search in particular microhabitats, and feed frequently on a wide variety of prey, many of which are relatively small. There is ontogenetic, seasonal, and geographic variation in diet. With some exceptions, invertebrates are the predominant prey, but rare predation on vertebrates is often energetically significant. A few monitors specialize on prey types that occur as occasional items in the diet of species with more generalized diets; these include crabs, snails, orthopterans, lizards, and large mammals. For most species, prey specialization occurs via habitat selection and a variety of prey types and sizes are eaten, as expected for widely searching predators. Comparisons with other anguimorphans suggest that derived features of Varanus are associated with high body temperature and activity levels; specialized chemoreception; and rapid, skillful capture of hidden and/or potentially hard to catch prey. Occasional ingestion of moderately large prey is primitive for Varanoidca (Helodermatidae +Varanidae), accentuating a trend that is perhaps primitive for anguimorphan lizards. Reduction of very large prey prior to ingestion is a derived attribute within Varanus , seen infrequently in several larger species and commonly in V. komodoensis. This study illustrates the synthesis of comparative natural history in a phylogenetic context, a method that addresses the history of organismal change. 相似文献