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1.
In this paper, by combining the harmonic mean approach with the Welch and the James procedure (see WELCH 1951, JAMES, 1951), we develop some robust procedures for testing parallelism in several straight lines under heteroscedasticity and nonnormality. Through Monte Carlo simulations it is shown that these new tests are quite robust with respect to departure from normality. For small sample sizes, however, the TAN-TABATABAI (1984) Fβ and F*β tests appear to be more powerful than the new tests, although when sample sizes are not small, there are hardly any differences between the Tan-Tabatabai Fβ and F*β tests and the new tests.  相似文献   

2.
Wenkai Li  Qinghua Guo 《Ecography》2013,36(7):788-799
It is very common that only presence data are available in ecological niche modeling. However, most existing methods for evaluating the accuracy of presence–absence (binary) predictions of species require presence–absence data. The aim of this study is to present a new method for accuracy assessment that does not rely on absence data. Two new statistics Fpb and Fcpb were derived based on presence–background data. With generated six virtual species, we used DOMAIN, generalized linear modeling (GLM), and maximum entropy (MAXENT) to produce different species presence–absence predictions. To investigate the effectiveness of the new statistics in accuracy assessment, we used Fpb, Fcpb, the traditional F‐measure (F), kappa coefficient, true skill statistic (TSS), area under the receiver operating characteristic curve (AUC), and the contrast validation index (CVI) to evaluate the accuracy of predictions, and the behaviors of these accuracy measures were compared. The effectiveness of Fpb for threshold selection and estimation of species prevalence was also investigated. Experimental results show that Fcpb is an estimate of F. The Pearson's correlation coefficient (COR) between Fcpb and F is 0.9882, with a root‐mean‐square error (RMSE) of 0.0171. In general, Fpb, Fcpb, F, kappa coefficient, TSS, and CVI can sort models by the accuracy of binary prediction, but AUC is not appropriate to evaluate the accuracy of binary prediction. For DOMAIN, GLM, and MAXENT, finding the threshold by maximizing Fpb and by maximizing F result in similar accuracies. In addition, the estimation of species prevalence based on binary output with maximizing Fpb as the thresholding method is significantly more accurate than simply averaging the original continuous output. The best estimate of prevalence is provided by the binary output of MAXENT, with an RMSE of 0.0116. Finally, we conclude that the new method is promising in accuracy assessment, threshold selection, and estimation of species prevalence, all of which are important but challenging problems with presence‐only data. Because it does not require absence data, the new method will have important applications in ecological niche modeling.  相似文献   

3.
We examined the intra-individual variation in resting frequency of the constant-frequency component of the second harmonic of the pulse (F rest) over 4 years in a laboratory colony of the Taiwanese leaf-nosed bat (Hipposideros terasensis). Patterns of change in F rest were observed when individuals were added to or removed from the colony so that we investigated whether F rest was affected by neighboring colony members. F rest of each bat continually showed a long-term gradual change throughout the year, and all bats in the colony increased or decreased their F rest in the same direction as a group non-seasonally. The greatest short-term changes were observed when new bats with a relatively low F rest joined the colony and F rest of new bats converged with those of the original colony members around 8 –16 days after their introduction. Conversely, a single individual showed sudden short-term decrease in F rest after its isolation from other colony members. These findings strongly indicate that F rest is flexible according to the presence of neighboring conspecific bats. We suggest that the audio-vocal feedback for conspecific pulses appears to be involved in the short- or long-term intra-individual variation in F rest other than factors previously thought such as age or season.  相似文献   

4.
F1-ATPase is a water-soluble portion of FoF1-ATP synthase and rotary molecular motor that exhibits reversibility in chemical reactions. The rotational motion of the shaft subunit γ has been carefully scrutinized in previous studies, but a tilting motion of the shaft has never been explicitly postulated. Here we found a change in the radius of rotation of the probe attached to the shaft subunit γ between two different intermediate states in ATP hydrolysis: one waiting for ATP binding, and the other waiting for ATP hydrolysis and/or subsequent product release. Analysis of this radial difference indicates a ∼4° outward tilting of the γ-subunit induced by ATP binding. The tilt angle is a new parameter, to our knowledge, representing the motion of the γ-subunit and provides a new constraint condition of the ATP-waiting conformation of F1-ATPase, which has not been determined as an atomic structure from x-ray crystallography.  相似文献   

5.
Leaf rust, caused by Puccinia triticina, is one of the most widespread diseases in common wheat (Triticum aestivum L.) globally. With the objective of identifying and mapping new genes for resistance to leaf rust, F1, F2 plants and F3 lines from a cross between resistant cultivar Bimai 16 and susceptible cultivar Thatcher were inoculated with Chinese Puccinia triticina pathotypes FHTT and PHTS in the greenhouse. In the first seedling test, Bimai 16, Thatcher, 20 F1 plants, 359 F2 plants and 298 F3 lines were inoculated with pathotype FHTT. A set of 1,255 simple sequence repeat (SSR) primer pairs were used to test the parents, and resistant and susceptible bulks. Seven polymorphic markers on chromosome 7BL were used for genotyping the F2 and F3 populations. The results indicated that Bimai 16 carried a single dominant resistance gene, temporarily designated LrBi16, closely linked to SSR markers Xcfa2257 and Xgwm344, with genetic distances of 2.8 and 2.9 cM, respectively. In the second seedling test, two dominant resistance genes were identified in Bimai 16 based on seedling reactions of 254 F2 plants inoculated with pathotype PHTS. One of the genes was LrBi16, and the other was likely to be LrZH84, which is located in chromosome 1BL. The seedling reaction pattern of plants with LrBi16 was different from that of the Thatcher lines, with Lr14a and Lr14b located on chromosome 7BL. It was concluded that LrBi16 is likely to be a new leaf rust resistance gene.  相似文献   

6.
Stripe rust, caused by Puccinia striiformis f. sp. tritici (PST), is one of the most damaging diseases in common wheat (Triticum aestivum L.). With the objective of identifying and tagging new genes for resistance to stripe rust, F1, F2 and F3 populations from the cross Zhou 8425B/Chinese Spring were inoculated with Chinese PST isolate CYR32 in the greenhouse. A total of 790 SSR primers were used to test the parents and resistant and susceptible bulks. The resulting seven polymorphic markers on chromosome 7BL were used for genotyping F2 and F3 populations. Results indicated that Zhou 8425B carries a single dominant resistance gene, temporarily designated YrZH84, closely linked to SSR markers Xcfa2040-7B and Xbarc32-7B with genetic distances of 1.4 and 4.8 cM, respectively. In a seedling test with 25 PST isolates, the reaction patterns of YrZH84 were different from those of lines carrying Yr2 and Yr6. It was concluded that YrZH84 is probably a new stripe rust resistance gene.  相似文献   

7.
Summary Diurnal measurements of low temperature (77K) fluorescence at 690 nm (PS II) from north, south, east, and west facing cladode surfaces of Opuntia basilaris in Death Valley, California were made on six occasions during 1985. The absolute levels of F o(instantaneous fluorescence) and F m(maximum fluorescence), as well as the ratio F v/F m(variable fluorescence, F m-F o, over maximum fluorescence), were greater in the north face relative to the other faces. Diurnal decreases in F o, F mand F v/F mwere found concomitant with increases in incident photon flux area density (PFD). F v/F mwas fairly low throughout the year, indicative of photoinhibition, but became somewhat elevated after a spring rain. In early fall the quantum yield of the south face was considerably depressed relative to that of the north face, and corresponding differences were observed in F v/F m. A decrease in PFD during growth of glasshouse plants led to an increase in chlorophyll concentration, F oand F m, but not F v/F m. Although there was some variability in the quantum yield of well watered glasshouse cladodes, a correlation was found between quantum yield and the light and CO2 saturated rate of photosynthesis. When O. basilaris was water stressed under glasshouse conditions, reductions in quantum yield, F m, and F v/F mwere observed. Reductions in F v/F malways indicated a reduced quantum yield, although the converse was not necessarily so in well watered glasshouse plants. The results of this study indicate that O. basilaris is likely to experience photoinhibition throughout much of its life in Death Valley.Abbreviations CAM crassulacean acid metabolism - MPa megapascal - PFD photon flux area density - PS II photosystem II - vater potential - F o instantaneous fluorescence - F m maximum fluoescence - F o variable fluorescence  相似文献   

8.
The F 0 and F M level fluorescence from a wild-type barley, a Chl b-less mutant barley, and a maize leaf was determined from 430 to 685 nm at 10 nm intervals using pulse amplitude-modulated (PAM) fluorimetry. Variable wavelengths of the pulsed excitation light were achieved by passing the broadband emission of a Xe flash lamp through a birefringent tunable optical filter. For the three leaf types, spectra of F V/F M (=(F M − F 0)/F M) have been derived: within each of the three spectra of F V/F M, statistically meaningful variations were detected. Also, at distinct wavelength regions, the F V/F M differed significantly between leaf types. From spectra of F V/F M, excitation spectra of PS I and PS II fluorescence were calculated using a model that considers PS I fluorescence to be constant but variable PS II fluorescence. The photosystem spectra suggest that LHC II absorption results in high values of F V/F M between 470 and 490 nm in the two wild-type leaves but the absence of LHC II in the Chl b-less mutant barley leaf decreases the F V/F M at these wavelengths. All three leaves exhibited low values of F V/F M around 520 nm which was tentatively ascribed to light absorption by PS I-associated carotenoids. In the 550–650 nm region, the F V/F M in the maize leaf was lower than in the barley wild-type leaf which is explained with higher light absorption by PS I in maize, which is a NADP-ME C4 species, than in barley, a C3 species. Finally, low values of F V/F M at 685 in maize leaf and in the Chl b-less mutant barley leaf are in agreement with preferential PS I absorption at this wavelength. The potential use of spectra of the F V/F M ratio to derive information on spectral absorption properties of PS I and PS II is discussed.  相似文献   

9.
The F1-ATP synthase complex constitutes the catalytic component of F1F0-ATP synthase, the primary ATP synthetic enzyme in the cell. Previous studies indicate that the glacier ice worm, Mesenchytraeus solifugus, maintains unusually high ATP levels that continue to rise as temperatures decline, suggesting that molecular changes within ice worm F1-ATP synthase subunits may contribute to this energetic anomaly. In this report, we compared ice worm F1-ATP synthase subunits (α, β, γ) with homologues across metazoan phyla (arthropod, chordate, nematode) and among a group of clitellate annelids (Enchytraeus albidus, Enchytraeus buchholzi, Lumbriculus variegatus, Theromyzon tessulatum). Amino acid alignments indicated that ice worm F1-ATP α and F1-ATP β subunits share strong sequence homology with their mesophilic counterparts, respectively, but that ATP γ has diverged more rapidly. Moreover, F1-ATP α and F1-ATP β displayed amino acid compositional changes consistent with trends observed in other cold adapted proteins, while F1-ATP γ diverged in unexpected directions (e.g., gains in size, charged residues). Several ice worm-specific amino acid substitutions map to positions near the F1-ATP β catalytic site while others occur near subunit contact sites.  相似文献   

10.
To evaluate the photoinhibition of colonial and unicellular cells of Microcystis aeruginosa under natural conditions, the maximum and effective quantum yields of photosystem II were measured from variable chlorophyll a fluorescence in samples from Lake Taihu during a summer bloom from June 19 to 21, 2006. Diurnal changes in the photoinhibition of Microcystis cells incubated immediately below the surface in clear bottles for 30 min and in situ samples under natural conditions were measured. At solar noon during the three days, the mean values of maximum quantum yield (F v/F m) and effective quantum yield (ΔF/F m′) for unicellular cells (F v/F m = 0.15, ΔF/F m′ = 0.10) were lower than those for colonial cells (F v/F m = 0.25, ΔF/F m′ = 0.15). For in situ samples, the values of F v/F m and ΔF/F m′ for colonial cells at solar noon on the three days (F v/F m 0.30, 0.25, 0.29; ΔF/F m′ 0.24, 0.21, 0.22) were also higher than those of unicellular cells (F v/F m 0.26, 0.18, 0.25; ΔF/F m′ 0.15, 0.11, 0.14). The results indicate that colony formation has a protective effect on Microcystis cells by reducing the occurrence of photoinhibition under high light intensities.  相似文献   

11.
The cooperativity in hemoglobin can be described by the Hill parameter n, the free energy of interaction ΔF1 and the allosteric free energy ΔFA. By this latter is meant here the free energy change associated with the transition from the deoxy to the oxy conformation in hemoglobin. In this paper some general relations between n, ΔF1 and ΔFA are given. A method is presented by which ΔFA can be calculated from oxygenation data.  相似文献   

12.
Leaf rust, caused by Puccinia triticina, is one of the most widespread diseases in common wheat (Triticum aestivum L.) worldwide. With the objective of identifying and mapping new genes for resistance to leaf rust, F1, F2 plants and F3 lines from a cross between resistant line Zhou 8425B and susceptible line Chinese Spring were inoculated with Chinese P. triticina races THTT and MBHP in the greenhouse. A total of 793 pairs of SSR primers were used to test the parents and resistant and susceptible bulks. Seven polymorphic chromosome 1B markers were used for genotyping the F2 and F3 populations. Zhou 8425B carried a single dominant resistance gene, temporarily designated LrZH84, linked to SSR markers gwm582 and barc8 with genetic distances of 3.9 and 5.2 cM, respectively. The Xbarc8 allele co-segregated with Lr26 in the F3 population. The Xgwm582 allele associated with LrZH84 was identified as a leaf rust resistance gene and shown to be present in the Predgornaia 2 parent of Zhou 8425B. The seedling reaction pattern of LrZH84 was different from those of lines with Lr26, Lr33, Lr44 and Lr46, all of which are located in chromosome 1B. It was concluded that LrZH84 is likely to be a new leaf rust resistance gene.  相似文献   

13.
Bacterial blight of rice, caused by Xanthomonas oryzae pv. oryzae (Xoo), is the most devastating disease of rice (Oryza sativa L). Rice lines that carry resistance (R) gene Xa10 confer race-specific resistance to Xoo strains harboring avirulence (Avr) gene avrXa10. Here we report on genetic study, disease evaluation and fine genetic mapping of the Xa10 gene. The inheritance of Xa10-mediated resistance to PXO99A(pHM1avrXa10) did not follow typical Mendelian inheritance for single dominant gene in F2 population derived from IR24 × IRBB10. A locus might be present in IRBB10 that caused distorted segregation in F2 population. To eliminate this locus, an F3 population (F3-65) was identified, which showed normal Mendelian segregation ratio of 3:1 for resistance and susceptibility. A new near-isogenic line (F3-65-1743) of Xa10 in IR24 genetic background was developed and designated as IRBB10A. IRBB10A retained similar resistance specificity as that of IRBB10 and provided complete resistance to PXO99A(pHM1avrXa10) from seedling to adult stages. Linkage analysis using existing RFLP markers and F2 mapping population mapped the Xa10 locus to the proximal side of E1981S with genetic distance at 0.93 cM. With five new RFLP markers developed from the genomic sequence of Nipponbare, Xa10 was finely mapped at genetic distance of 0.28 cM between proximal marker M491 and distal marker M419 and co-segregated with markers S723 and M604. The physical distance between M491 and M419 on Nipponbare genome is 74 kb. Seven genes have been annotated from this 74-kb region and six of them are possible Xa10 candidates. The results of this study will be useful in Xa10 cloning and marker-assisted breeding.  相似文献   

14.
Divergent natural selection is often thought to be the principal factor driving phenotypic differentiation between populations. We studied two ecotypes of the aquatic isopod Asellus aquaticus which have diverged in parallel in several Swedish lakes. In these lakes, isopods from reed belts along the shores colonized new stonewort stands in the centre of the lakes and rapid phenotypic changes in size and pigmentation followed after colonization. We investigated if selection was likely to be responsible for these observed phenotypic changes using indirect inferences of selection (FSTQST analysis). Average QST for seven quantitative traits were higher than the average FST between ecotypes for putatively neutral markers (AFLPs). This suggests that divergent natural selection has played an important role during this rapid diversification. In contrast, the average QST between the different reed ecotype populations was not significantly different from the mean FST. Genetic drift could therefore not be excluded as an explanation for the minor differences between allopatric populations inhabiting the same source habitat. We complemented this traditional FSTQST approach by comparing the FST distributions across all loci (n = 67–71) with the QST for each of the seven traits. This analysis revealed that pigmentation traits had diverged to a greater extent and at higher evolutionary rates than size‐related morphological traits. In conclusion, this extended and detailed type of FSTQST analysis provides a powerful method to infer adaptive phenotypic divergence between populations. However, indirect inferences about the operation of divergent selection should be analyzed on a per‐trait basis and complemented with detailed ecological information.  相似文献   

15.
The emission spectra collected under conditions of open (F0) and closed (FM) photosystem II (PSII) reaction centres are close‐to‐independent from the excitation wavelength in Chlamydomonas reinhardtii and Chlorella sorokiniana, whereas a pronounced dependence is observed in Synechocystis sp. PCC6803 and Synechococcus PCC7942, instead. The differences in band‐shape between the F0 and FM emission are limited in green algae, giving rise only to a minor trough in the FV/FM spectrum in the 705–720 nm range, irrespectively of the excitation. More substantial variations are observed in cyanobacteria, resulting in marked dependencies of the measured FV/FM ratios on both the excitation and the detection wavelengths. In cyanobacteria, the maximal FV/FM values (0.5–0.7), observed monitoring at approximately 684 nm and exciting Chl a preferentially, are comparable to those of green algae; however, FV/FM decreases sharply below approximately 660 nm. Furthermore, in the red emission tail, the trough in the FV/FM spectrum is more pronounced in cyanobacteria with respect to green algae, corresponding to FV/FM values of 0.25–0.4 in this spectral region. Upon direct phycobilisomes excitation (i.e. >520 nm), the FV/FM value detected at 684 nm decreases to 0.3–0.5 and is close‐to‐negligible (approximately 0.1) below 660 nm. At the same time, the FV spectra are, in all species investigated, almost independent on the excitation wavelength. It is concluded that the excitation/emission dependencies of the FV/FM ratio arise from overlapped contributions from the three independent emissions of PSI, PSII and a fraction of energetically uncoupled external antenna, excited in different proportions depending on the respective optical cross‐section and fluorescence yield.  相似文献   

16.
Photoinhibition of photosynthesis in willow leaves under field conditions   总被引:7,自引:0,他引:7  
Erling Ögren 《Planta》1988,175(2):229-236
Chlorophyll fluorescence of leaves of a willow (Salix sp.) stand grown in the field in northern Sweden was measured on several occasions during the growing season of 1987. For leaves that received mostly full daylight, the F V/F P ratio declined roughtly 15% in the afternoon on cloudless days in July (F P is the fluorescence at the peak of the induction curve obtained at the prevailing air temperature after 45 min of dark adaptation, and F V is variable fluoresence, F V=F P-F O, where F O is minimal fluorescence). There was no decrease in the F V/F P ratio on cloudy days, while the effect was intermediate on changeable days. In view of this light dependence, together with the fact that the decline in the F V/F P ratio was paralleled with an equal decline in the corresponding fluorescence ratio F V/F M at 77K, and a similar decline in the maximum quantum yield of O2 evolution, it is suggested that the decline in the F V/F P ratio represents a damage in photosyntem II attributable to photoinhibition. Recovery of the F V/F P ratio in dim light following a decline on a cloudless day took 7–16 h to go to completion; the F V/F P ratio was fully restored the following morning. When all active leaves of a peripheral shoot were compared, the F V/F P ratio in the afternoon of a day of bright light varied greatly from leaf to leaf, though the majority of leaves showed a decline. This variation was matched by a pronounced variation in intercepted photon flux density. When leaves developed in the shade were exposed to full sunlight by trimming of the stand an increased sensitivity to photoinhibition was observed as compared to peripheral leaves. The present study indicates that peripheral willow shoots experienced in the order of 10–20% photoinhibition during an appreciable part of their life. This occurred even though the environmental conditions were within the optimal range of photosynthesis and growth.Abbreviations and symbols F O minimum fluorescence - F P fluorescence at the peak of the induction curve obtained at normal ambient temperatures - F V variable fluorescence - F M maximum fluorescence obtained at 77K - PPFD photosynthetic photon flux density  相似文献   

17.
Since the introduction of allozyme methods inthe mid 1960s it has been a standard practiceto report Wright's measure of populationsubdivision, F ST, for surveys ofgenetic variation. Its widespread use hasprovided us with a sense of what values can beexpected in particular situations and how theycan be interpreted. With some theoreticaljustification, F ST has also beenused to estimate rates of gene flow. Howeverthere are conditions under which F STis inappropriate for gene flow estimation andcan lead to incorrect or even absurdconclusions. These pitfalls have promptedcritics to suggest that F ST hasfailed to deliver what its proponents havepromised and should be abandoned. A furtherchallenge has been the development of newmethods that offer even greater promise. Thusit is reasonable to ask if perhaps it is timeto retire F ST and turn to new andmore powerful methods for the inference of geneflow from genetic markers. Here I will arguethat although gene flow should be estimated bymore powerful approaches whenever practical,F ST remains a useful measure of theaverage effects of gene flow and will continueto be used for comparative purposes.  相似文献   

18.
1. Global warming is occurring at an unprecedented rate. Information about how variable temperature affects insect life-history traits is still scarce. 2. The current study first evaluated the effects of two variable-temperature treatments [high-temperature-variation (HT) treatments and mild-temperature-variation (MT) treatments] on the life-history traits of a maternal generation (F0) of Rhopalosiphum padi, a serious global pest, using a constant normal-temperature (NT) treatment as a control. Following this, the life-history traits of the offspring generation (F1) under the NT, MT and HT scenarios were analysed. 3. The total developmental duration of the aphid F0 generation was significantly shortened by MT treatments, while it was significantly increased by HT treatments. Adult longevity and the fecundity of F0 were significantly decreased by HT treatments compared with those in the MT and NT treatments, whereas no significant difference was found between the latter two treatments. The HT treatments applied to the F0 generation significantly prolonged the total developmental duration of the F1 generation. The offspring adult longevity was not affected by the mothers' temperature experience. The offspring fecundity was significantly increased when the F0 generation experienced MT treatments. The intrinsic rate of increase (rm) was significantly decreased when the F0 generation experienced an HT scenario. However, the MT scenario experienced by the F0 generation did not significantly affect the rm of their offspring. 4. The results will provide new insights into the effects of variable maternal temperature on the individual development and population dynamics of offspring under a global warming scenario.  相似文献   

19.
The maximum quantum yield of photosystem II (as reflected by variable to maximum chlorophyll a fluorescence, Fv/Fm) is regarded as one of the most important photosynthetic parameters. The genetic basis underlying natural variation in Fv/Fm, which shows low level of variations in plants under non‐stress conditions, is not easy to be exploited using the conventional gene cloning approaches. Thus, in order to answer this question, we have followed another strategy: we used genome‐wide association study (GWAS) and transgenic analysis in a rice mini‐core collection. We report here that four single‐nucleotide polymorphisms, located in the promoter region of β‐glucosidase 5 (BGlu‐5), are associated with observed variation in Fv/Fm. Indeed, our transgenic analysis showed a good correlation between BGlu‐5 and Fv/Fm. Thus, our work demonstrates the feasibility of using GWAS to study natural variation in Fv/Fm, suggesting that cis‐element polymorphism, affecting the BGlu‐5 expression level, may, indirectly, contribute to Fv/Fm variation in rice through the gibberellin signaling pathway. Further research is needed to understand the mechanism of our novel observation.  相似文献   

20.
The new salt tolerant cereal, Tritipyrum (2n=6x=42, AABBEbEb) offers potential to introduce desirable characters for wheat improvements. This study was aimed to generate a segregating population from Iranian local wheat cultivars (2n=6x=42, AABBDD) and Tritipyrum crosses, study of the meiotic behaviour in F2 hybrids and identification of Eb chromosomes in F3 individuals. Results showed meiotic abnormalities in F2 plants and different pairing frequency in the meiosis among F2 plants. Genomic in situ hybridization revealed that total and Eb chromosome number of F3 seeds ranged from 39 to 45 and 0 to 10, respectively. A significant prevalence of hyper-aneuploidy was observed among F3 genotypes. C-banding patterns identified Eb chromosomes in Tritipyrum, indicating that it also can be useful to study wheat-Tritipyrum derivatives.  相似文献   

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