Summary The results of the Viking Biology experiments are best explained by non-biological phenomena: The interaction of the reagents with the materials comprising the regolith. Conditions of water activity, temperature, availability of carbon sources and others in most regions of the planet are too extreme for survival and growth of any known Earth microorganisms. Although the possibility persists that some very unusual form of life is somewhere on that planet the evidence is best interpreted as negative. Even though there is no evidence for current life on Mars, whether or not life ever originated there is not known. 相似文献
Summary Examples are presented to illustrate some of the effects aberrant values, in particular, measurement errors, may have on estimates of the genetic parameters related to selection studies. It is shown that aberrant values may cause observed response to selection pressure to differ considerably from predicted response. Possible dangers of indiscriminate screening are also discussed. 相似文献
Abstract. Lower salt-marsh species occur more in the grazed than in the mown sites of a salt marsh in Schiermonnikoog in the Netherlands. This was demonstrated by a sowing experiment which determined which characteristic of the stand structure, height of the canopy or percentage of bare soil, is responsible for this difference. The total number of seedlings which emerged was negatively related to the height of the canopy and positively to the percentage of bare soil. The survival of seedlings of Suaeda maritima and Plantago maritima could be explained by the height of the canopy and for the latter species also by the percentage of bare soil. The survival of Aster tripolium and Plantago maritima was higher in grazed than in mown sites. Since the amount of bare soil was higher than seemed necessary for germination and survival, it was concluded that the taller canopy was responsible for the absence of lower salt-marsh species in the mown sites. 相似文献
Juvenile Nucella lapillus of two different shell phenotypes, exposed shore and protected shore, were maintained in running seawater under each of three experimental conditions for 94 d: a) laboratory control, b) exposed to the effluent of crabs (Cancer pagurus) fed frozen fish (fish-crab), and c) exposed to the effluent of crabs fed live conspecific snails (snail-crab). Rates of barnacle consumption and rates of body weight change varied significantly between phenotypes and among experimental conditions. Individuals from the protected-shore consumed consistently fewer barnacles and grew consistently less than those from the exposed shore. Body weight increases in the fish-crab treatments were from 25 to 50% less than those in the controls and body weights in the snail-crab treatment either did not change or actually decreased. The perceived risk of predation thus appears to have a dramatic effect on the rates of feeding and growth of N. lapillus.At the end of the experiment, size-adjusted final shell weights for both phenotypes were consistently higher than controls (no crab) in both the fish-crab and snail-crab treatments. In addition, apertural tooth height, thickness of the lip, and retractability (i.e. the extent to which a snail could withdraw into its shell), with few exceptions all varied in an adaptive manner in response to the various risk treatments. Similar changes in the shell form of starved snails exposed to the same stimuli suggest very strongly that the morphological responses of both phenotypes were not just due to differences in rates of growth. These differences, at least in part, represented a direct cueing of the shell form of Nucella lapillus to differences in the perceived risk of predation. Somewhat surprisingly, the extent of phenotypic plasticity appeared to differ between the populations examined. Both field and laboratory evidence suggest that the exposed-shore population was much more labile morphologically than the protected-shore population.In many instances, particularly among starved snails, the development of antipredatory shell traits was greater in the fish-crab treatment than in the snail-crab treatment. Because the scent of crabs was present in both treatments, these results suggest a) that, at the frequency/concentration used in the experiments, the scent of damaged conspecifics may have been a supernormal stimulus and b) that the morphological response in these treatments might have been greater if the stimulus had been provided at a lower level. 相似文献
In order to study the effects of temperature enhancement on alpine calcareous grassland species, a warming experiment was carried out in the Berchtesgaden National Park (Southeast Germany, Northern Calcareous Alps) between 2002 and 2004. The study was conducted in stands of the Carex sempervirens and the Carex firma communities; the two most widespread grassland types in the alpine zone of the Northern Calcareous Alps. The temperature of the vegetation stand and the upper soil was passively enhanced using open top chambers (OTCs). The construction of the OTCs was appropriate since temperature was clearly increased while water conditions (humidity, soil water content) were not changed.
By comparing manipulated (temperature enhancement) with non-manipulated plots, the effects of warming on growth and reproduction of selected key species were studied. To test if vegetation response to temperature enhancement is at least partly due to increases in nutrient availability, soil solution concentrations of nitrate and ammonium were analysed.
We found that most of the studied plant species are sensitive to temperature enhancement. Growth and/or reproduction of 12 of the 14 studied species were significantly stimulated by warming. Only two species showed no response; none of the species experienced decreases in growth or reproduction. Dwarf shrubs and graminoids showed a stronger response than herbaceous perennials. A significant effect of warming on nutrient availability could not be detected. The observed response of vegetation is therefore mainly caused by direct and not by indirect temperature effects. 相似文献
Genotype and water deficit effects on leaf 2-DE protein profiles of two Populus deltoides × Populus nigra, cv. ‘Agathe_F’ and ‘Cima’, were analysed over a short-term period of 18 days in glasshouse using 4-month-old rooted cuttings and over a long-lasting period of 86 days in open field using 4-year-old rooted cuttings. Leaf proteomes were analyzed using two-dimensional gel electrophoresis, and proteins were identified after database searching from MS peptide spectra.A reliable genotype effect was observed in the leaf proteome over experiment locations, water regimes and sampling dates. Quantitative differences between genotypes were found. Most of them corresponded to proteins matching isoforms or post-translational modification variants. However, ‘Cima’ displayed the highest abundance of antioxidant enzymes.In response to water deficit, about 10% of the reproducible spots significantly varied regardless of the experiment location, among which about 25% also displayed genotype-dependent variations. As a whole, while ‘Cima’ differed from ‘Agathe_F’ by increased abundance of enzymes involved in photorespiration and in oxidative stress, ‘Agathe_F’ was mainly differentiated by increased abundance of enzymes involved in photosynthesis. 相似文献