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101.
Trevor Price Dolph Schluter 《Evolution; international journal of organic evolution》1991,45(4):853-861
Life-history traits such as longevity and fecundity often show low heritability. This is usually interpreted in terms of Fisher's fundamental theorem to mean that populations are near evolutionary equilibrium and genetic variance in total fitness is low. We develop the causal relationship between metric traits and life-history traits to show that a life-history trait is expected to have a low heritability whether or not the population is at equilibrium. This is because it is subject to all the environmental variation in the metric traits that affect it plus additional environmental variation. There is no simple prediction regarding levels of additive genetic variance in life-history traits, which may be high at equilibrium. Several other patterns in the inheritance of life-history traits are readily predicted from the causal model. These include the strength of genetic correlations between life-history traits, levels of nonadditive genetic variance, and the inevitability of genotype-environment interaction. 相似文献
102.
Martin J. Michaelson H. James Price John R. Ellison J. Spencer Johnston 《American journal of botany》1991,78(2):183-188
An improved procedure is reported for determining DNA amounts of plant nuclei. Nuclei stained with propidium iodide, isolated from chopped plant leaves, were passed through an Ortho Cytofluorograph with a Lexel model 95 argon laser (514 nm) and the fluorescence measured, integrated, and recorded using an Ortho 2140 Data Acquisition computer. All nuclear samples were mixed with nuclei of Sultan barley (2C DNA content = 11.12 pg [picogram]) as an internal standard. DNA contents of ten plant species, ranging from 2C = 1.7 pg to 36.1 pg measured by flow cytometry, correlated strongly (r = 0.99, slope = + 1.00) with DNA contents determined from Feulgen-stained nuclei of the same species using microspectrophotometry. The flow cytometric procedures were sufficiently sensitive to detect differences in DNA content between inbred lines of corn and their F1 hybrids. Our results obtained with improved procedures, specifically using propidium iodide as a fluorochrome and plant nuclei instead of chicken erythrocytes as an internal standard, demonstrate that laser flow cytometry can be a precise, rapid, and reliable method for determining nuclear DNA content of plants. 相似文献
103.
The biology of the arrhenotokous autoparasitoid,Encarsia pergandiella Howard, was studied in the laboratory on the silverleaf whitefly,Bemisia argentifolii Bellows & Perring. Egg to adult development of parasitoid females averaged ca. 14 days at about 25.3+0.2?C regardless of whether the whitefly host was reared on tomato, eggplant or squash. While all instars ofB. argentifolii were accepted for primary parasitization, a greater percentage of third and fourth instars were parasitized. Mortality of whitefly nymphs in the absence of parasitization did not differ among instars and averaged about 35%. Second instar to pupal parasitoid females were accepted for secondary parasitization although a greater percent of pupal females were parasitized. About 40% of immatureE. pergandiella females more than 4 days old died in the absence of secondary parasitization when exposed to adultE. pergandiella females. 相似文献
104.
Net O2 evolution, gross CO2 uptake and net HCO
inf3
su–
uptake during steady-state photosynthesis were investigated by a recently developed mass-spectrometric technique for disequilibrium flux analysis with cells of the marine cyanobacterium Synechococcus PCC7002 grown at different CO2 concentrations. Regardless of the CO2 concentration during growth, all cells had the capacity to transport both CO2 and HCO
inf3
su–
; however, the activity of HCO
inf3
su–
transport was more than twofold higher than CO2 transport even in cyanobacteria grown at high concentration of inorganic carbon (Ci = CO2 + HCO
inf3
su–
). In low-Ci cells, the affinities of CO2 and HCO
inf3
su–
transport for their substrates were about 5 (CO2 uptake) and 10 (HCO
inf3
su–
uptake) times higher than in high-Ci cells, while air-grown cells formed an intermediate state. For the same cells, the intracellular accumulated Ci pool reached 18, 32 and 55 mM in high-Ci, air-grown and low-Ci cells, respectively, when measured at 1 mM external Ci. Photosynthetic O2 evolution, maximal CO2 and HCO
inf3
su–
transport activities, and consequently their relative contribution to photosynthesis, were largely unaffected by the CO2 provided during growth. When the cells were adapted to freshwater medium, results similar to those for artificial seawater were obtained for all CO2 concentrations. Transport studies with high-Ci cells revealed that CO2 and HCO
inf3
su–
uptake were equally inhibited when CO2 fixation was reduced by the addition of glycolaldehyde. In contrast, in low-Ci cells steady-state CO2 transport was preferably reduced by the same inhibitor. The inhibitor of carbonic anhydrase ethoxyzolamide inhibited both CO2 and HCO
inf3
su–
uptake as well as O2 evolution in both cell types. In high-Ci cells, the degree of inhibition was similar for HCO
inf3
su–
transport and O2 evolution with 50% inhibition occurring at around 1 mM ethoxyzolamide. However, the uptake of CO2 was much more sensitive to the inhibitor than HCO
inf3
su–
transport, with an apparent I50 value of around 250 M ethoxyzolamide for CO2 uptake. The implications of our results are discussed with respect to Ci utilisation in the marine Synechococcus strain.Abbreviations Chl
chlorophyll
- Ci
inorganic carbon (CO2 + HCO
inf3
su–
)
- CA
carbonic anhydrase
- CCM
CO2-concentrating mechanism
- EZA
ethoxyzolamide
- GA
glycolaldehyde
- K1/2
concentration required for half-maximal response
- Rubisco
ribulose-1,5,-bisphosphate carboxylase-oxygenase
D.S. is a recipient of a research fellowship from the Deutsche Forschungsgemeinschaft (D.F.G.). In addition, we are grateful to Donald A. Bryant, Department of Molecular and Cell Biology and Center of Biomolecular Structure Function, Pennsylvania State University, USA, for sending us the wild-type strain of Synechococcus PCC7002. 相似文献
105.
Delayed Excitotoxic Neurodegeneration Induced by Excitatory Amino Acid Agonists in Isolated Retina 总被引:2,自引:0,他引:2
Abstract: Evidence from in vitro studies suggests that excitotoxic neuronal degeneration can occur by either an acute or delayed mechanism. Studies of the acute mechanism in isolated chick embryo retina using histological methods indicate that this process is rapidly triggered by activation of glutamate receptors of either the N-methyl-d -aspartate (NMDA) or non-NMDA subtypes. The delayed mechanism, studied primarily in cortical and hippocampal cell cultures prepared from embryonic rodent brain, requires activation of NMDA receptors. In these cell culture systems, stimulation of non-NMDA receptors does not rapidly trigger delayed neuronal degeneration, or does so only indirectly, via activation of NMDA receptors secondary to glutamate release. To provide a more valid basis for comparison of these two mechanisms, we have modified the isolated chick embryo retina model to permit studies of delayed as well as acute excitotoxic neurodegeneration. Retinas maintained for 24 h exhibited no morphological or biochemical signs of damage. Retinal damage was assessed by measuring lactate dehydrogenase (LDH) present in the medium at various times after exposure to agonists and normalized to total LDH in each retina. Glutamate exposure (1 mM, 30 min) did not result in LDH release by the end of the exposure period, but LDH was released over the following 24 h. Briefer periods also led to substantial LDH release. Incubation in the presence of NMDA, or the non-NMDA agonists kainate (KA) or α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA), led rapidly to delayed LDH release. NMDA and AMPA were more potent than glutamate, but high concentrations of glutamate led to more LDH release than high concentrations of these agonists. KA was a powerful excitotoxin, providing more LDH release than glutamate, NMDA, or AMPA at every concentration tested. The delayed LDH release induced by glutamate involved activation of both NMDA and non-NMDA receptors, as a combination of receptor-selective antagonists was necessary to provide complete blockade. These results indicate that glutamate, NMDA, AMPA, and KA all cause delayed as well as acute excitotoxic damage in the retina. It is interesting that brief exposure to the non-NMDA receptor agonists, in relatively low concentrations, led to delayed LDH release. This is different than in other in vitro models of delayed excitotoxic neurodegeneration. 相似文献
106.
Alexander A. Bachmanov Danielle R. Reed Yuro Ninomiya Masashi Inoue Michael G. Tordoff R. Arlen Price Gary K. Beauchamp 《Mammalian genome》1997,8(8):545-548
Individual variability in sucrose consumption is prominent in humans and other species. To investigate the genetic contribution
to this complex behavior, we conducted behavioral, electrophysiological, and genetic studies, using male progeny of two inbred
mouse strains (C57BL/6ByJ [B6] and 129/J [129]) and their F2 hybrids. Two loci on Chromosome (Chr) 4 were responsible for over 50% of the genetic variability in sucrose intake. These
loci apparently modulated intake by altering peripheral neural responses to sucrose. One locus affected the response threshold,
whereas the other affected the response magnitude. These findings suggest that the majority of difference in sucrose intake
between male B6 and 129 mice is due to polymorphisms of two genes that influence receptor or peripheral nervous system activity.
Received: 27 January 1997 / Accepted: 17 March 1997 相似文献
107.
Propylthiouracil Tasting: Determination of Underlying Threshold Distributions using Maximum Likelihood 总被引:2,自引:1,他引:1
Reed Danielle R.; Bartoshuk Linda M.; Duffy Valarie; Marino Susan; Price R. Arlen 《Chemical senses》1995,20(5):529-533
The ability to taste low concentrations of propylthiouracil(PROP) and related bitter compounds is heritable. The currentanalysis determines whether the distribution of PROP taste thresholdsis consistent with an additive or a dominant mode of Mendeliantransmission. To that end, the lowest concentration of PROPdetectable was determined for 1015 subjects and models of bi-or tri-modal distributions of PROP taste thresholds were tested.The model with the greatest likelihood had three distributionsand followed an additive model of PROP taste sensitivity ifthe variances associated with the distributions were assumedto be equal. However, if the taste thresholds were transformedto remove skewness, or if the variances were unequal, then three-or two-distribution models were equally likely. Resolution ofthe mode of inheritance for bitter taste perception awaits additionalfamily studies and the characterization of the molecular basisof taste perception for these bitter compounds. Chem. Senses20: 529533, 1995. 相似文献
108.
Ann-Charlotte E. Granholm Michelle L. Price Michael D. Owen 《Cell and tissue research》1995,280(1):49-57
We have investigated the distribution of tyrosine-hydroxylase-like immunoreactivity in the cerebral ganglia of the American cockroach, Periplaneta americana. Groups of tyrosine-hydroxylase-immunoreactive cell bodies occur in various parts of the three regions of the cerebral ganglia. In the protocerebrum, single large neurons or small groups of neurons are located in the lateral neuropil, adjacent to the calyces, and in the dorsal portion of the pars intercerebralis. Small scattered cell bodies are found in the outer layers of the optic lobe, and clusters of larger cell bodies can be found in the deutocerebrum, medial and lateral to the antennal glomeruli. Thick bundles of tyrosine-hydroxylase-positive nerve fibers traverse the neuropil in the proto- and deutocerebrum and innervate the glomerular and the nonglomerular neuropil with fine varicose terminals. Dense terminal patterns are present in the medulla and lobula of the optic lobe, the pars intercerebralis, the medial tritocerebrum, and the area surrounding the antennal glomeruli, the central body and the mushroom bodies. The pattern of tyrosine-hydroxylase-like immunoreactivity is similar to that previously described for catecholaminergic neurons, but it is distinctly different from the distribution of histaminergic and serotonergic neurons. 相似文献
109.
With so many neutrophins and receptors now known, how is our picture of neurotrophism changing? Recent studies on knockout mice have confirmed our expectations of neurotrophin action in neuronal development. A notable exception is the activation of TrkB, on motor neurons, by an unknown ligand. It is also clear that some neurotrophins have diverse activities and influence early developmental stages. There are interesting new data concerning the role of p75, the low affinity neurotrophin receptor, as a modulator of neurotrophin activity. Even more exciting are new studies on glia-derived neurotrophic factor (GDNF) which demonstrate that this growth factor acts as a potential protector of motor neurons and striatal dopaminergic neurons. 相似文献
110.
Rearing of male farm animals in unisexual groups has been implicated as a factor contributing to the failure of many males to breed as adults. The present study examines the relationship of male-male mounting in yearling dairy goats to subsequent mate preferences and sexual performance.Twenty-four sexually inexperienced male dairy goats, representing the Alpine, LaMancha, Saanen and Toggenburg breeds, were observed for male-male mounting in their home enclosure and then tested for mate choice and sexual performance when exposed to male and female (estrous and diestrous) stimulus animals. Their sexual behavior was compared with 7 adult goats with previous breeding experience.In the mate choice-sexual performance tests, 4 sexually inexperienced goats (17%) were sexually inactive, 6 (25%) mounted both male and female stimulus animals and 14 (58%) mounted only the female stimuli. Mate choice and sexual performance of the 20 sexually active males was not related to the number of male-male mounts initiated or the number of different males mounted in their home enclosure. However, the goats that received the greatest number of mounts in their home pen tended to be bisexual (would mount both male and female stimulus animals) in the mate choice tests. Males that were sexually inactive in mate choice-sexual performance tests repeatedly mounted the same male during home pen observations. Except for ejaculation frequency, the sexual performance of the sexually naive and experienced goats was similar. Goats of the Saanen breed were favored recipients of mounts from other males. There was no relationship between the number of male-male mounts performed and received.It was hypothesized that the reproductive failure of many male farm animals reared in all-male groups may be more closely related to the formation of specific sexual attachments to other males rather than the frequency with which they exhibit homosexual behaviors. 相似文献