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At least 343 records · Page 19Linked to original sources
PubMed1988

Gathering evidence: the case for past life on Mars.

Four billion years ago, the surface of Mars may have been conducive to the origin of life. Scientific evidence suggests that Mars had a biologically favorable atmosphere back then, with warm temperatures and abundant water during its formative years. Many scientists contend that life arose on early Mars but was subsequently wiped out. If Mars was a harbor for past life, why did it become extinct? Where should we, on future Mars missions, look for evidence of past life? Are there analogous biological systems on Earth to study and hypothesize the presence of early Martian life?

Antarctic Regions↗
PubMed2001

Population dynamics with and without selection.

A model describing population dynamics is presented. We study the effect of selection pressure and inbreeding on the time evolution of the population and the chances of survival. We find that the selection is in general beneficial, enabling survival of a population whose size is declining. Inbreeding reduces the survival chances since it leads to clustering of individuals. We have also found, in agreement with biological data, that there is a threshold value of the initial size of the population, as well as of the habitat, below which the population will almost certainly become extinct. We present analytical and computer simulation approaches.

Biological Evolution↗
PubMedDate not supplied

[Biological factors of PTSD: neurotransmitters and neuromodulators].

Subjects with posttraumatic stress disorder exhibit abnormalities in many psychobiological systems. Studies of the effects of stress on learning and memory processes suggest that fear conditioning, behavioural sensitisation, and a failure of extinction may be important in the persistence and reexperiencing of traumatic memories and stress sensitivity. All these symptoms are supported by specific biological mechanisms including NMDA receptors, noradrenergic system, etc. Recent findings show that amino acid transmitters, glutamate and GABA, are intimately involved in the process of factual memory registration, and suggest that amine neurotransmitters, norepinephrine and serotonin, are involved in encoding emotional memory. In addition, research suggests that 5-HT neurones have directs effects on both adrenergic and HPA function. Such findings provide important information that should guide current pharmacological practice and the development of innovative biological therapeutics.

Adaptation, Psychological↗
PubMed2025

PUS7-dependent Ψ reshapes specific synaptic gene exons to facilitate fear extinction memory formation.

RNA modifications serve as dynamic regulators of neural plasticity through their ability to fine-tune transcript stability and splicing. Pseudouridine (Ψ), an evolutionarily conserved RNA modification catalyzed by pseudouridine synthases, plays established roles in neurodevelopment, yet its functional significance in activity-dependent behavioral adaptation remains poorly defined. Here, we investigate Ψ-mediated epitranscriptomic regulation within the infralimbic prefrontal cortex (ILPFC), a brain region requiring precise synaptic remodeling for the clinically relevant form of fear extinction memory. Combining transcriptome-wide pseudouridylation profiling with behavioral analysis in mice, we identified selective Ψ enrichment at exons of synaptic regulatory genes within ILPFC during fear extinction learning. Fear extinction in the ILPFC drives concomitant exonic Ψ deposition and upregulation of synaptogenic transcripts, processes that involve pseudouridine synthase PUS7. Crucially, PUS7 knockdown in the ILPFC selectively impaired fear extinction memory formation without altering baseline fear expression, establishing a causal link between Ψ-dependent RNA processing and activity-dependent synaptic structural remodeling in this microcircuit. Our findings demonstrate that PUS7-mediated Ψ modification spatiotemporally regulates activity-dependent RNA dynamics in the ILPFC, providing the evidence that epitranscriptomic mechanisms precisely coordinate synaptic gene expression within behaviorally defined brain sub-region. This work bridges molecular RNA biology with systems neuroscience, revealing a novel mechanism for activity-dependent regulation of fear extinction in ILPFC.

Animals↗
PubMed2002

The mathematical basis of sexual attraction.

Computer programs have been written to study the dynamic interaction in humans between environmental mutagenesis, the genomic load of deleterious mutations and the probability of zygote survival. The human genome is complex and highly redundant and as a consequence deleterious mutations accumulate. The computer programs are based on a model of the human genome in which deleterious mutations interact synergistically causing impaired performance in individual systems and this leads to a positive correlation between the total number of deleterious mutations in the genome and impaired performance across the whole spectrum of biological capability. This includes performance in intellectual tasks, sporting ability, the ability to fight disease and preserve health and the development of a symmetrical physical form. Sexual reproduction distributes deleterious mutations unequally amongst zygotes and the model predicts that zygote survival will correlate negatively with zygote mutational load. The computer simulation shows that rising environmental mutagenesis will lead to a rise in the human genomic mutational load and to decreased zygote survival, although the full effect would take several generations. If this occurred the health of future generations would suffer and methods to monitor environmental mutagenesis are required. The model also shows that a marked rise in environmental mutagenesis would lead to species extinction if mate choice were random, i.e., unrelated to the genomic mutational load. The biological imperfections caused by mutations, however, in health, intelligence and physical symmetry are all, to varying degrees, related to sexual attraction. The model shows that if mates are chosen in response to sexual attraction the species can be maintained in the presence of high environmental mutagenesis. A polygamous pattern in which females mate with a minority of males has the most marked effect in reducing the number of deleterious mutations in the next generation. The model also shows that as environmental mutagenesis falls the number of eligible males would increase and a species would change from a polygamous to a monogamous pattern of mating. These results imply that we are not attracted by good genes, but by a lack of bad genes. Sexual attraction is a force which counteracts genomic degradation.

Female↗
PubMed2006

Sequencing and analysis of Neanderthal genomic DNA.

Our knowledge of Neanderthals is based on a limited number of remains and artifacts from which we must make inferences about their biology, behavior, and relationship to ourselves. Here, we describe the characterization of these extinct hominids from a new perspective, based on the development of a Neanderthal metagenomic library and its high-throughput sequencing and analysis. Several lines of evidence indicate that the 65,250 base pairs of hominid sequence so far identified in the library are of Neanderthal origin, the strongest being the ascertainment of sequence identities between Neanderthal and chimpanzee at sites where the human genomic sequence is different. These results enabled us to calculate the human-Neanderthal divergence time based on multiple randomly distributed autosomal loci. Our analyses suggest that on average the Neanderthal genomic sequence we obtained and the reference human genome sequence share a most recent common ancestor approximately 706,000 years ago, and that the human and Neanderthal ancestral populations split approximately 370,000 years ago, before the emergence of anatomically modern humans. Our finding that the Neanderthal and human genomes are at least 99.5% identical led us to develop and successfully implement a targeted method for recovering specific ancient DNA sequences from metagenomic libraries. This initial analysis of the Neanderthal genome advances our understanding of the evolutionary relationship of Homo sapiens and Homo neanderthalensis and signifies the dawn of Neanderthal genomics.

Animals↗
PubMed1994

A spectrophotometric assay for the detection of 2-aminophenols in biological samples.

A sensitive and efficient spectrophotometric assay is described for the determination of 2-aminophenols in biological samples. Using ferric ions as a metal catalyst, 2-aminophenol dimerizes in an acidic aqueous environment to 2-hydroxyisophenoxazin-3-one, an intensively colored dye. The newly developed assay is suitable for the detection of 2-aminophenols in the micromolar range. The paper demonstrates that this chemical assay is also applicable for the determination of 2-aminophenols substituted with a halogen at the ortho, meta, or para position of the aromatic ring with respect to the amino moiety, lambda max, and the molar extinction coefficient varying with the substituent pattern. Results obtained for fluorinated 2-aminophenol detection in biological samples by either this new method or 19F NMR are similar. This observation corroborates that the newly developed assay is suitable for detection of 2-aminophenols in biological samples.

Aminophenols↗
PubMed1978

Mathematical theory of group selection: Structure of group selection in founder populations determined from convexity of the extinction operator.

Genetic analysis for group selection is developed for the case of a biallelic locus (A, a) undergoing group selection of founder populations only. By contrast to R. Levins"E = E(x) models, extinction now depends on genetics at the propagule stage but acts uniformly on larger populations. Biological evidence supports this hypothesis, which also allows mathematical treatment at once simpler and biologically more general than the Fokker-Planck partial differential equation formalism adopted by Levins. It is presently possible to handle cytogenetics of both diploid and haplodiploid type. The model is set up as a quasideterministic recursion in the 5-simplex Sigma(5), collapsing both drift and mendelian selection effects into a single parameter u, which is a Fisher-Kimura-Ohta fixation probability. In the analysis, it is shown that the stability of the fixed points is determined by the convexity of the extinction operator acting on propagules, assumed to be of size 2.THUS, [FORMULA: see text] in which E(1) and E(3) are extinction probabilities for phenotypically uniform founder populations and E(2) is the corresponding probability for founder populations of mixed phenotype. Further parameter regions are defined where fixation of the group-selected gene is globally stable, and this is still possible even when extinction pressure acting on carrying capacity populations becomes weak relative to a fixed mendelian selection strength.

Journal Article↗
PubMed2002

Interactions of climate change with biological invasions and land use in the Hawaiian Islands: Modeling the fate of endemic birds using a geographic information system.

The Hawaiian honeycreepers (Drepanidae) represent a superb illustration of evolutionary radiation, with a single colonization event giving rise to 19 extant and at least 10 extinct species [Curnutt, J. & Pimm, S. (2001) Stud. Avian Biol. 22, 15-30]. They also represent a dramatic example of anthropogenic extinction. Crop and pasture land has replaced their forest habitat, and human introductions of predators and diseases, particularly of mosquitoes and avian malaria, has eliminated them from the remaining low- and mid-elevation forests. Landscape analyses of three high-elevation forest refuges show that anthropogenic climate change is likely to combine with past land-use changes and biological invasions to drive several of the remaining species to extinction, especially on the islands of Kauai and Hawaii.

Agriculture↗
PubMed2004

The effect of autocorrelation in environmental variability on the persistence of populations: an experimental test.

Despite its significance regarding the conservation and management of biological resources, the body of theory predicting that the correlation between successive environmental states can profoundly influence extinction has not been empirically validated. Identical clonal populations from a model experimental system based on the collembolan Folsomia candida were used in the present study to investigate the effect of environmental autocorrelation on time to extinction. Environmental variation was imposed by variable implementation (present/absent) of a culling procedure according to treatments that represented six patterns of environmental autocorrelation. The average number of culling events was held constant across treatments but, as environmental autocorrelation increased, longer runs of both favourable and unfavourable culling tended to occur. While no difference was found among the survival functions for the various treatments, the time taken for 50% of the component populations to become extinct decreased significantly with increasing environmental autocorrelation. Similarly, analysis of all extinct populations demonstrated that time to extinction was shortened as environmental autocorrelation increased. However, this acceleration of extinction can be fully offset if sequential introduction is used in place of simultaneous introduction when founding the populations.

Animals↗
PubMed2002

Variation and polymorphism in helminth parasites.

There are strong biological, evolutionary and immunological arguments for predicting extensive polymorphism among helminth parasites, but relatively little data and few instances from which the selective forces acting on parasite diversity can be discerned. The paucity of information on intraspecific variation stands in contrast to the fine detail with which helminth species have been delineated by morphological techniques, accentuating a trend towards considering laboratory strains as representative of a relatively invariant organism. However, in the fast-moving evolutionary race between host and parasite one would predict a monomorphic species would be driven to extinction. We review the arena of intraspecific variation for the major helminth parasites, ranging from biological properties such as host or vector preference, to biochemical and immunological characteristics, as well as molecular markers such as DNA sequence variants. These data are summarized, before focusing in more detail on polymorphisms within protein-coding genes of potential relevance to the host-parasite relationship, such as vaccine candidates. In particular, we discuss the available data on a number of major antigens from the filarial nematode Brugia malayi. Information is currently too sparse to answer the question of whether there is antigenic variation in filariasis, but the indications are that proteins from the blood-borne microfilarial stage show significant intraspecific variability. Future work will define whether polymorphisms in these antigens may be driven by exposure to the host immune response or reflect some other facet of parasite biology.

Animals↗
PubMed1989

Evolution and extinction in the marine realm: some constraints imposed by phytoplankton.

The organic and mineralized remains of planktonic algae provide a rich record of microplankton evolution extending over nearly half of the preserved geological record. In general, Phanerozoic patterns of phytoplankton radiation and extinction parallel those documented for skeletonized marine invertebrates, both augmenting and constraining thought about evolution in the oceans. Rapidly increasing knowledge of Proterozoic plankton is making possible the recognition of additional episodes of diversification and extinction that antedate the Ediacaran radiation of macroscopic animals. In contrast to earlier phytoplankton history, the late Mesozoic and Cainozoic record is documented in sufficient detail to constrain theories of mass extinction in more than a general way. Broad patterns of diversity change in planktonic algae show similarities across the Cretaceous-Tertiary and Eocene-Oligocene boundaries, but detailed comparisons of origination and extinction rates in calcareous nannoplankton, as well as other algae and skeletonized protozoans, suggest that the two episodes were quite distinct. Common causation appears unlikely, casting doubt on monolithic theories of mass extinction, whether periodic or not. Studies of mass extinction highlight a broader class of insights that paleontologists can contribute to evolutionary biology: the evaluation of evolutionary change in the context of evolving Earth-surface environments.

Biological Evolution↗
PubMed1984

Repeatability of taxon longevity in successive foraminifera radiations and a theory of random appearance and extinction.

An analysis of taxonomic longevity for species of the two Cenozoic radiations of Caribbean planktonic foraminifera shows strong similarity in longevity for extinct taxa, though extant species of the latter radiation are biased towards longer-lived forms. In this case, the present is not the key to the past. A simple one-parametric stochastic model predicts generally the shape of the distributions, though there is an excess of species with model longevity and a deficiency of longer-lived forms, relative to the prediction of the model. Although the one parameter may relate to the biology of the group under consideration, the distribution about the mode may reflect random appearance-extinction processes.

Journal Article↗