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1.
The potential impact of frog diseases on basic research is discussedin practical terms. 相似文献
2.
Bock (1963) showed that in the years 1956-60 early season sprays achieved good control of coffee berry disease (CBD) in East Rift areas of Kenya. In recent years, however, this spray programme has given erratic and often very poor results. In field experiments in 1966 yields of main (late) crop were increased from 151 to 652 kg/ha by early season sprays but in 1967 practically no control of the disease was achieved. Of the fungicides examined captafol was superior to copper; ‘Tuzet’, the best antisporulant, gave the poorest control. Analysis of the data indicates that this large seasonal variation depends on the very different inter-relationships between rainfall, cropping pattern and timing of sprays which obtained in the 2 years. The hypothesis that early-season sprays achieve control of CBD mainly by reducing the sporulating capacity of the maturing bark is questioned. The view is put forward that the protectant action of these sprays has been underestimated. 相似文献
3.
Trimethyloxonium modification of single batrachotoxin-activated sodium channels in planar bilayers. Changes in unit conductance and in block by saxitoxin and calcium 总被引:13,自引:9,他引:4 下载免费PDF全文
Single batrachotoxin-activated sodium channels from rat brain were modified by trimethyloxonium (TMO) after incorporation in planar lipid bilayers. TMO modification eliminated saxitoxin (STX) sensitivity, reduced the single channel conductance by 37%, and reduced calcium block of inward sodium currents. These effects always occurred concomitantly, in an all-or-none fashion. Calcium and STX protected sodium channels from TMO modification with potencies similar to their affinities for block. Calcium inhibited STX binding to rat brain membrane vesicles and relieved toxin block of channels in bilayers, apparently by competing with STX for the toxin binding site. These results suggest that toxins, permeant cations, and blocking cations can interact with a common site on the sodium channel near the extracellular surface. It is likely that permeant cations transiently bind to this superficial site, as the first of several steps in passing inward through the channel. 相似文献
4.
THE USE OF A MULTIPLE-TRANSFER METHOD IN PLANT VIRUS TRANSMISSION STUDIES—SOME STATISTICAL POINTS ARISING IN THE ANALYSIS OF RESULTS 总被引:1,自引:0,他引:1
The frequency of success of attempts to transmit a virus disease from one plant to another has long been used to measure the effects of any of the factors which influence transmission. Samples are taken from the population under test (e.g. vectors, diseased plants, etc.), and usually one sample is tested on each test plant; this is binomial sampling. However, in the procedure we name the 'multiple-transfer method' more than one sample may be tested on each test plant. This increases the number of samples tested without increasing the number of test plants used, and errors due to heterogeneity in the population under test are therefore minimized. Results from experiments using the multiple-transfer method may be evaluated by using the maximum likelihood estimator. The method is particularly reliable when the proportion of infected samples being studied is small, but can lead to considerable over-estimation when the proportion is high. 相似文献
5.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
6.
Snakes are a particularly threatened vertebrate taxon, with distributions of many species and populations becoming increasingly fragmented. At present, little is known about the degree of genetic differentiation that exists between isolated populations even though such information may be critical to their survival and conservation. As an example of how recently developed RAPD genetic markers can be used in conservation genetics, we present preliminary results from a study which used these DNA-based markers to assess population divergence in two threatened Canadian snakes, the black rat snake ( Elaphe o. obsoleta ) and the eastern massasauga rattlesnake ( Sistrurus c. catenatus ). We present information on the levels of variation and reliability of amplification for fragments generated from five primers. We then use a recently developed analytical technique to estimate levels of nucleotide diversity within populations and sequence divergence between populations. Our results show that intrapopulation levels of divergence as estimated by the methods of Clark & Lanigan ( Molecular Biology and Evolution 1993, 10 , 1096–1111) approximate those found for mtDNA in vertebrates and that diversity between snake populations is small and non-significant when tested using randomization procedures. Thus, our study provides an example of how RAPDs can be applied to conservation genetic studies of vertebrates and suggest that the snake populations we examined have only recently become isolated and maybe considered genetically equivalent from a conservation perspective, although this conclusion needs to be confirmed with other DNA-based markers. 相似文献
7.
8.
Variation in heat-shock proteins among species of desert fishes (Poeciliidae, Poeciliopsis) 总被引:4,自引:0,他引:4
Analysis of the heat-shock proteins (hsps) of six closely related species
of Poeciliopsis demonstrated the existence of biochemical diversity in the
hsp100, hsp70, hsp60, and hsp30 protein families among species. Each
species expressed five to seven hsp70-related isoforms. Constitutive 70-kD
isoforms were identical among species, but four different patterns of
heat-inducible isoforms were seen in these six species. Members of the
hsp70 family of molecular chaperones are included among the most highly
conserved proteins known, and the possibility of variation in hsp70 among
closely related species has rarely been addressed. The hsp30 family is
known to be less conserved than the hsp70 family, and, as expected, the
Poeciliopsis hsp30 patterns showed more variation. Most of the hsp30
isoforms characteristic of a particular species were unique to that
species. Hsp100 and hsp60 were identical in five of the species, but
alternate isoforms were found in P. monacha. The small size and limited
geographical distribution of the P. monacha population have probably
contributed to the uniqueness of the monacha pattern. Two of the species
were shown to acquire thermotolerance, the ability to withstand normally
lethal temperatures when subjected to a gradual temperature increase.
Rapid-heating protocols commonly used to establish critical thermal maxima
of organisms do not include this inducible component of thermoresistance
and therefore do not adequately assess an organism's capacity to withstand
thermal stress.
相似文献
9.
Variation in heat shock proteins within tropical and desert species of poeciliid fishes 总被引:8,自引:0,他引:8
Norris CE; diIorio PJ; Schultz RJ; Hightower LE 《Molecular biology and evolution》1995,12(6):1048-1062
The 70-kilodalton heat shock protein (hsp70) family of molecular
chaperones, which contains both stress-inducible and normally abundant
constitutive members, is highly conserved across distantly related taxa.
Analysis of this protein family in individuals from an outbred population
of tropical topminnows, Poeciliopsis gracilis, showed that while
constitutive hsp70 family members showed no variation in protein isoforms,
inducibly synthesized hsp70 was polymorphic. Several species of
Poeciliopsis adapted to desert environments exhibited lower levels of
inducible hsp70 polymorphism than the tropical species, but constitutive
forms were identical to those in P. gracilis, as they were in the
confamilial species Gambusia affinis. These differences suggest that
inducible and constitutive members of this family are under different
evolutionary constraints and may indicate differences in their function
within the cell. Also, northern desert species of Poeciliopsis synthesize a
subset of the inducible hsp70 isoforms seen in tropical species. This
distribution supports the theory that ancestral tropical fish migrated
northward and colonized desert streams; the subsequent decrease in
variation of inducible hsp70 may have been due to genetic drift or a
consequence of adaptation to the desert environment. Higher levels of
variability were found when the 30- kilodalton heat shock protein (hsp30)
family was analyzed within different strains of two desert species of
Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In
both cases the distribution of hsp30 isoform diversity was similar to that
seen previously with allozyme polymorphisms.
相似文献
10.