PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Experimental evolution”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,333 records · Page 74Linked to original sources

Evolution of translational initiation: new insights from the archaea.

Recent in silico and experimental data have shed new light on the mechanism and components of translational initiation in archaea. The available data about the structure of archaeal mRNAs, mRNA/ribosome interaction and archaeal translation initiation factors are reviewed and analyzed in the conceptual framework of the evolution of translational initiation. A model of the initiation step of translation in the Last Universal Common Ancestor of extant cells is presented and discussed.

Archaea↗

A fitness cost of learning ability in Drosophila melanogaster.

Maintenance of substantial genetic variation for learning ability in many animal populations suggests that learning ability has fitness costs, but there is little empirical evidence for them. In this paper, we demonstrate an evolutionary trade-off between learning ability and competitive ability in Drosophila melanogaster. We show that the evolution of an improved learning ability in replicated experimental fly populations has been consistently associated with a decline of larval competitive ability, compared with replicated control populations. The competitive ability was not affected by crossing of the replicate populations within each selection regime, excluding differential inbreeding as a potential confounding factor. Our results provide evidence for a constitutive fitness cost of learning ability, i.e. one that is paid irrespective of whether or not the learning ability is actually used.

Animals↗

A novel, fully automated rotometer for the study of turning behavior. Comparison of results under different experimental conditions.

The turning or circling activity of the rat is a very useful experimental model for the study of dopaminergic cerebral pathways. Quantification of turning makes it applicable to follow changes of pattern evolution in the same subject or for comparison between animals under different experimental conditions. Automated quantitative evaluation of turning has the advantage of its reliability, eliminates subjective inaccuracies and allows longer periods of observation. Therefore a fully automated rotometer aimed to accomplish these objectives was developed. It consists of a sensor box to transduce the circling movement of animals into computed information to be processed by a microprocessor and a printer for recording of results. The sensor was designed with a 16 holes perforated disc and two infrared receiver/emitter units. Pulses generated in the sensor box are computed and stored by the microprocessor. Reading of results may be made in manual or automated mode from the display or listed through the printer connected on-line. The reliability and validity of the rotometer were tested in animals submitted to different experimental conditions. Rats with unilateral chemical lesions (6-hydroxy-dopamine or kainic acid) of substantia nigra pars compacta rotated vigorously contraversive to lesion side after apomorphine injection (0.5 and 1 mg/kg, s.c.). Electrolytic lesion of the same nucleus made animals rotate ipsiversive to the lesion after apomorphine. To attain significant level of circling activity, the electrolytic lesion should be placed in the external boundaries of substantia nigra (265.8 +/- 53.4 turns/60 min for group with external placed lesion; (n = 5); 97.3 +/- 19.5 for group with internal placed lesion (n = 3); t = 2.31; p less than 0.05). Unilateral striatal lesion with ibotenic acid made animals rotate ipsilaterally with apomorphine as well as with the selective D-2 agonist bromocriptine (10 and 30 mg/kg, i.p.). Qualiquantitative differences in circling were observed between these two dopaminergic agonists. Comparison of circling activity on semispherical and flat surfaces showed a non significant trend to rotate more intensively on spherical surfaces but only in those animals turning greater than or equal to 3 turns/min. The results obtained with the automated rotometer herein described agree with those currently reported in the literature about the subject. They demonstrate also that this apparatus is adequate and reliable for the study of turning behavior under different experimental conditions. Interestingly enough, our observation on the specificity of electrolytic lesions placed in the lateral boundaries of substantia nigra to induce rotation is worth further investigation.

Animals↗

Mathematical model of the evolution of statoconia.

A mathematical model of the evolution of statoconia in statocysts of freshwater snails based on the analysis of experimental data [Wiederhold et al., 1990; Pedrozo et al., 1996; Gao et al., 1997; Gao and Wiederhold, 1997; Wiederhold et al., 1999] is proposed. The growth of statoconia is considered as the process of solution crystallization. The model proposed assumes that two main processes determine the evolution of statoconia in developing snails: the generation of new statoconia and the linear growth of statoconia sizes. The analytical solution of the model and qualitative comparison of theoretical results with the experimental data show: (1) there are at least three periods of statoconia evolution; (2) the generation of new statoconia mainly determines the first period of evolution when the shell diameter of snails D < 4 mm; (3) when D > 6 mm the size distribution of statoconia is determined by the growth of their sizes with a constant rate; (4) on the interval deltaD = 4-6 mm the transformation of size distribution with selective dissolution of statoconia takes place. The model agrees well with the experimental data and makes it possible to estimate some parameters of the statoconia kinetics. Additional experiments, which are necessary for further development of the model, and quantitative estimates of the mechanisms of statoconia evolution are formulated.

Animals↗

A comparison of long-term neurological symptoms after two different focal ischemic models in Mongolian gerbils.

The aim of the present study was to elucidate the relationship between specific tasks and the responsible ischemic lesions after experimentally induced cerebral hemispheric ischemia in Mongolian gerbils. We used the elevated body swing test (EBST) to evaluate asymmetry motor behavior, the bilateral asymmetry test (BAT) to evaluate sensory dysfunction, and the T-maze test to assess cognitive deficit during 4 weeks after either 10-min single unilateral carotid artery occlusion (sCCAO) or 10-min repeated unilateral occlusion (rCCAO). rCCAO produced persistent sensorimotor and severe cognitive deficits. Infarction was confined to the ipsilateral cerebral cortex, hippocampus, dorsolateral nucleus of thalamus and caudate nucleus. sCCAO did not induce sensorimotor abnormalities, but did produce mild cognitive deficits; these animals also showed increased locomotor activity during the early post-ischemic period. In sCCAO, neuronal death was confined to the ipsilateral CA1 sector of the hippocampus. Thus, unilateral CA1 neuronal death was sufficient for evolution of cognitive deficits in this model of experimental focal ischemia. Ischemic lesions extending to the ipsilateral cerebral cortex, basal ganglia, and hippocampus produced persistent and severe sensorimotor impairment accompanying severe cognitive deficits. These findings regarding region-specific behavioral tasks in cerebral ischemia will facilitate improved assessment of stroke therapy.

Animals↗

Insights into the pathogenesis of alcoholic liver necrosis and fibrosis: status report.

The use of the Tsukamoto-French rat model of alcoholic liver disease facilitated pathological, physiological, biochemical and cell biological experiments that examined the validity of some of the existing hypotheses for pathogenesis of alcoholic liver necrosis and fibrosis. Results obtained to date strongly support the contribution of centrilobular hypoxia as a pathogenetic mechanism of alcoholic liver necrosis. The enhanced hepatic lipid peroxidation was not evident at the early stage of ethanol-induced liver necrosis but could be demonstrated at the late stage when the liver damage progressed to liver fibrosis. This suggests that the lipid peroxidation may not be an important mechanism of alcoholic liver necrosis but may be an initiation factor for liver fibrogenesis as recently proposed by others (88). The high-fat diet appears to have promoting effects on both induction of alcoholic liver necrosis and stimulation of liver fibrogenesis. The former may be related to the induction of MEOS by the high-fat diet and consequent centrilobular hypoxia caused by inadequately compensated hepatic overuse of oxygen. The latter can be mediated through sensitization of Ito cells by a high-fat diet. We propose that Kupffer cell-derived TGF beta is, at least in part, responsible for some of phenotypical changes of Ito cells associated with their activation. Our model provides maximal experimental control and induces the discrete stages of alcoholic liver injury that can be reproduced with its pathological evolution telescoped into a short time. Because of these features, replication of the experimental conditions in different laboratories is possible so that results can be validly compared through precise standardization of the experimental protocols. This model requires some training in implantation and maintenance of the gastric catheter. However, the training can be easily attained by anyone who has experience in animal surgery. Another requirement is the initial fund to acquire infusion devices and metabolism cages. Once this equipment is purchased, however, the maintenance cost is low. Even if the initial expenses are included, the cost per animal is relatively inexpensive when compared with the cost involved in the use of larger animals such as baboons or pigs. Since administration of diet and ethanol (or isocaloric glucose solution) is precisely controlled by infusion pumps, this system makes unnecessary the measurement of diet consumption that has to be done daily for each animal with other methods.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

[Accumulation of amino acid substitutions promotes irreversible structural changes in the hemagglutinin of human influenza AH3 virus during evolution].

During protein evolution the amino acid substitutions accumulate with time. However, the effect of accumulation of the amino acid substitutions to structural changes has not been estimated well. We will propose that the discordance of amino acid substitution on the HA protein of influenza A virus is useful for the assessment of structural changes during evolution. Discordance value can be obtained from the experimental data of tolerance or intolerance by introducing site directed mutagenesis at the homologous positions of two HA proteins holding the same amino acid residues. The value of discordance correlated to the number of amino acid differences among proteins. In the H3HA discordance rate was calculated to be 0.45% per one amino acid change. Furthermore, discordance of amino acid substitutions suggests that tolerable amino acid substitutions in different order have a probability of promoting irreversible divergence of the HA protein to different subtypes.

Amino Acid Substitution↗

Treatment of mice bearing a Krebs ascitic tumor by means of a protocol based on radioactive copper (64Cu). IV. Consequences of the nature of cancer: tumor-resistant mice.

In the efficient treatment described (Anticancer Research 9: 941-946, 1989) some compounds (64Cu and thioproline) act against the malignant genomes, and other components (metal ions, amino acids, vitamin D2, thyroxine and chelating substances) act against the functioning of the host cells having the cancer functioning (cancer cells). The experiments described show that this treatment developed with mice injected on day zero with 5 x 10(5) Krebs ascitic cells, is also efficient for mice bearing a spontaneous malignant tumor even if it is not an ascitic tumor. After the decrease in weight due to the loss of the tumor, a typical weight evolution was observed characterized by a second weight increase followed by a decrease leading to normal weight. This last weight remained stable. This typical weight evolution in tumor-free mice (after spontaneous tumor or experimental Krebs ascitic tumor) was related to the age of the tumor at the beginning of the treatment, that is, according to our hypothesis (Anticancer Res 9:955-960, 1989) to the cancer evolution emphasizing the great importance of all physiological phenomena related to this cancer course. To test the consequence of this treatment, some of these tumor-free mice were injected with 5 x 10(5) ascitic cells. No tumor developed in these tumor-free mice meaning that they also were tumor-resistant. This last result is in agreement with the forecast of the systemic analysis on which the efficient treatment was based.

Animals↗

[Larval development of Paricterotaenia porosa (Cestoda: Cyclophyllidea, Dilepididae) in dipterans of the genus Chironomus, experimental hosts. On comparative larval forms of dilepidid flatworms (author's transl)].

The authors describe the larval evolution of Paricterotaenia porosa (Rud., 1810) Fuhrmann (1932) (Cestoda: Cyclophyllidea, Dilepididae) in three species belonging to the genus Chironomus (Diptera, Nematocera) used as experimental hosts. The protoscolex of the infestant larva is retracted into a cystic vesicule, the cysticercoïd is surrounded by a fragmented cercomer and a capsule. P. porosa in contrary to P. paradoxa (Rud., 1802) do not present asexual reproduction in its intermediate host. P. porosa and Anomotaenia constricta (Molin, 1858) Cohn (1900) show a similar evolution, though the cercomer appears sooner in the former. These cysticercoïds are regarded as Monocercus Villot (1883) the characteristics of which are given. The Monocercus is specific to the Dilepididae. The other larval types described in this family i.e. Cercoscolex and Plerocercus (Jackera, 1970) Plerocercoïd (Freeman, 1973) ans Strobilo cysticercoïd (Freeman, 1973) are compared to the larva of other families: Proteocephalidae, Mesocestoididae and Amabiliidae respectively.

Animals↗

Diet-induced atherosclerosis and experimental hypertension in stumptail macaques (Macaca arctoides). Effects of antihypertensive drugs and a non-atherogenic diet in the evolution of lesions.

This study was carried out to determine the evolution of atherosclerotic lesions during a therapeutic period during which regression might be appreciated. We produced aortic and coronary atherosclerosis in 27 young adult stumptail macaques (Macaca arctoides) by feeding a diet supplemented with 2% cholesterol and 25% fat. Hypertension was produced by bilateral or unilateral narrowing of the renal artery. After six months of this regimen, four monkeys were killed (group 1) and 23 monkeys were divided into three groups: group 2 received unsupplemented diet; group 3 received the same diet as group 2 and drug treatment for hypertension; group 4 was continued on the atherogenic diet and received antihypertensive drug treatment. The results indicate that deleting the atherogenic diet leads to a decrease in the lipid content of the lesions and a transformation of the lipid laden atherosclerotic plaques into lipid-poor, fibro-collagenous lesions, with a decrease in the amount of coronary luminal narrowing. Partial control of systolic hypertension by antihypertensive drugs did not accelerate the involution of the atherosclerotic lesions over the relatively short period of this study. No statistically significant correlation by regression analysis was observed between the level of blood pressure elevation, the plasma renin activity, or the degree of the drug response, and the severity and extent of the atherosclerotic lesions. Furthermore, severe arterial hypertension without an atherogenic diet (group 5) produced arteriosclerosis of the aorta, and intensified branch cushions in the coronary arteries, without inducing lipid deposition in either vascular bed.

Animals↗

Streptozotocin induced diabetes as a model of phrenic nerve neuropathy in rats.

Phrenic neuropathies are increasingly recognized in peripheral neuropathies but reports on experimental models of the phrenic nerves diabetic neuropathy are scanty. In the present study, we investigated the phrenic nerve neuropathy, due to experimental diabetes induced by streptozotocin (STZ) and the evolution of this neuropathy in diabetic rats treated with insulin. Proximal and distal segments of the left and right phrenic nerves were morphologically and morphometrically evaluated, from rats rendered diabetic for 12 weeks, by injection of STZ. Control rats received vehicle. Treated rats received a single subcutaneous injection of insulin on a daily basis. The nerves were prepared for light microcopy study by means of conventional techniques. Morphometry was carried out with the aid of computer software. The phrenic nerves of diabetic rats showed smaller myelinated axon diameters compared to controls. The g ratio was significantly smaller for myelinated fibers from diabetic rats compared to controls. Insulin treatment prevented these alterations. Histograms of size distribution for myelinated fibers and axons from control rats were bimodal. For diabetic animals, the myelinated fiber histogram was bimodal while the axon distribution turned to be unimodal. Insulin treatment also prevented these alterations. Our results confirm the phrenic nerve neuropathy in this experimental model of diabetes and suggest that conventional insulin treatment was able to prevent and/or correct the myelinated axon commitment by diabetes.

Animals↗

Experiments investigating cooperative types in humans: a complement to evolutionary theory and simulations.

Unlike other species, humans cooperate in large, distantly related groups, a fact that has long presented a puzzle to biologists. The pathway by which adaptations for large-scale cooperation among nonkin evolved in humans remains a subject of vigorous debate. Results from theoretical analyses and agent-based simulations suggest that evolutionary dynamics need not yield homogeneous populations, but can instead generate a polymorphic population that consists of individuals who vary in their degree of cooperativeness. These results resonate with the recent increasing emphasis on the importance of individual differences in understanding and modeling behavior and dynamics in experimental games and decision problems. Here, we report the results of laboratory experiments that complement both theory and simulation results. We find that our subjects fall into three types, an individual's type is stable, and a group's cooperative outcomes can be remarkably well predicted if one knows its type composition. Reciprocal types, who contribute to the public good as a positive function of their beliefs about others' contributions, constitute the majority (63%) of players; cooperators and free-riders are also present in our subject population. Despite substantial behavioral differences, earnings among types are statistically identical. Our results support the view that our human subject population is in a stable, polymorphic equilibrium of types.

Algorithms↗

The best defence against bioweapons has already been invented by evolution.

Bioweapons are considered from the viewpoint of the mutual evolution of microbe/victim ecological systems. Cases considered include accidental, experimental, and real exploitation of bioweapons as well as other cases in the history of epidemics, and also experimental investigations. It is proposed here that speculations about bioweapon's very high mass annihilating ability are based on over-extrapolation from limited data selected from the ancient history of epidemics and on a false supposition that all people are susceptible to any bioweapon's infectious agent. The history of epidemics, clinical and genetic observations, data from experimental investigations, and results of accidental, experimental, and real exploitation of bioweapons do not confirm the mass annihilating capability of bioweapons. Many people possess constitutional (genetic) immunity presumably formed by natural selection over many human generations. This genetic protection exists in an individual prior to infection. The power of constitutional immunity played an important role during all human evolution. Its protective capability continues to defend humanity from mass annihilation by both epidemics and bioweapons. In this context of constitutional immunity for the majority of individuals, the main goal of modern medicine is to identify and defend the defenseless ones.

Biodiversity↗

Trade-offs between sexual and clonal reproduction in an aquatic plant: experimental manipulations vs. phenotypic correlations.

That trade-offs result from the allocation of limited resources is a central concept of life history evolution. We quantified trade-offs between sexual and clonal reproduction in the aquatic plant, Butomus umbellatus, by experimentally manipulating sexual investment in two distinct nutrient environments. Increasing seed production caused a significant but nonlinear trade-off. Pollinating half of all flowers strongly reduced clonal bulbil production, but pollinating the remaining flowers did not cause any further trade-off. Trade-offs were not stronger under low nutrient conditions that clearly limited plant growth. Experimentally induced trade-offs were not reflected in negative phenotypic correlations between sexual and clonal allocation among plants within eight populations grown in a uniform greenhouse environment. Diminishing effects of increased sexual allocation plus a lack of accord between experimental manipulations and phenotypic correlations suggest that trade-offs between sexual and clonal reproduction are unlikely to constrain the evolution of reproductive strategy in this species.

Analysis of Variance↗

Fitness costs of induced resistance: emerging experimental support for a slippery concept.

Fitness costs can explain the evolution and maintenance of induced resistance in plants. However, the methods currently used to gather evidence for such costs do not allow decreases in fitness to be cleanly attributed to individual traits responsible for induced resistance, because the studies are plagued by multiple confounding responses. Reproductive performance provides an overview of physiological performance and is thus a useful currency to understand the function of induced responses. Integrated molecular, physiological and ecological studies are needed to identify the mechanisms responsible for the decrease in fitness and to evaluate fully the usefulness of the cost paradigm.

Arabidopsis↗

Experimental intra-abdominal abscesses in rats: development of an experimental model.

An animal model has been developed to study the evolution of intra-abdominal abscesses. Gelatin capsules containing pooled colonic contents and barium sulfate were prepared in an anaerobic chamber and implanted into the pelvic region of Wistar rats. The natural course of the ensuing disease was studied in various groups according to the source of the inoculum and sex of the recipient. Colonic contents derived from rats fed a grain diet produced a highly lethal disease with an 80% mortality rate for males and 100% for females. Most deaths occurred within 3 days of implantation, and autopsies showed generalized peritonitis. The addition of blood to the inoculum caused a rapidly fatal peritonitis in all animals. With an inoculum derived from meat-fed rats implanted in male recipients, there was a biphasic disease. Initially, there was peritonitis associated with 43% mortality. All animals that survived this acute period developed discrete intra-abdominal abscesses by the seventh postoperative day. The latter stage was characterized by an indolent course and progressive enlargement of abscesses.

Abdomen↗

Evolution of heart transplantation.

Heart transplantation has evolved from preliminary animal experimentation in the early part of this century to an accepted orthodox therapy for many patients with end-stage cardiac disease in the 1980s. The development of successful heart transplantation is traced from the laboratory to early clinical attempts and the subsequent validation of this therapy, principally by the Stanford group in the 1970s. The dramatic worldwide impact of the use of cyclosporine for immunosuppression in the practice of heart transplantation is reviewed. Resultant changes in the practice of heart transplantation are discussed as well as the future developments of totally implantable circulatory support systems and xenografting.

Age Factors↗

Modeling DNA mutation and recombination for directed evolution experiments.

Directed evolution experiments rely on the cyclical application of mutagenesis, screening and amplification in a test tube. They have led to the creation of novel proteins for a wide range of applications. However, directed evolution currently requires an uncertain, typically large, number of labor intensive and expensive experimental cycles before proteins with improved function are identified. This paper introduces predictive models for quantifying the outcome of the experiments aiding in the setup of directed evolution for maximizing the chances of obtaining DNA sequences encoding enzymes with improved activities. Two methods of DNA manipulation are analysed: error-prone PCR and DNA recombination. Error-prone PCR is a DNA replication process that intentionally introduces copying errors by imposing mutagenic reaction conditions. The proposed model calculates the probability of producing a specific nucleotide sequence after a number of PCR cycles. DNA recombination methods rely on the mixing and concatenation of genetic material from a number of parent sequences. This paper focuses on modeling a specific DNA recombination protocol, DNA shuffling. Three aspects of the DNA shuffling procedure are modeled: the fragment size distribution after random fragmentation by DNase I, the assembly of DNA fragments, and the probability of assembling specific sequences or combinations of mutations. Results obtained with the proposed models compare favorably with experimental data.

Animals↗