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Results for “Extinction, Biological”

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PubMed2004

[Establishment and biological characteristics of orthotopic transplantation tumor model of hepatocellular carcinoma in mice].

OBJECTIVE: To study the feasibility of the establishment of the orthotopic transplantation tumor model of hepatocellular carcinoma in mice and its tumor biological characteristics. METHODS: H22 cells of hepatocellular carcinoma were inoculated to form ectopic transplanted model in mice by subcutaneous injection. Then the subcutaneous tumors were implanted into the liver of mice, and the orthotopic transplantation tumor model of hepatocellular carcinoma was established. RESULTS: The successful rate of the orthotopic transplantation tumor model was 95.6% and the spontaneous metastatic rate was 81.8%, the rate of mass ascites was 40.9% and the natural extinctive rate was 0%. The natural survival time in the orthotopic transplantation tumor model was 28 days and the proliferation of tumor in transplanted model was accelerated after 2 weeks or so. CONCLUSION: The orthotopic transplantation tumor model in mice is an ideal model for studying the metastatic mechanism and screening anti-tumor drugs for liver cancer, just because of its high successful rate and high spontaneous metastatic rate with no natural extinction.

Animals↗

PubMed1979

Non-progressive evolution, the Red Queen hypothesis, and the balance of nature.

The Red Queen hypothesis, or the ability organisms have to control and regulate the available trophic energy, is a recently proposed parameter for measuring fitness. Firstly, this hypothesis is analysed in terms of its heuristic power. Secondly, the claimed causal dependence between this parameter and a, still controversial, law of constant extinction is judged to be unjustified, however reasonable such a claim appears to be. Finally, the ubiquity of competition in nature which is seemingly required by the Red Queen and supposedly realized at the expense of a mutualistic alternative, is deemed to be a questionable assumption.

Biological Evolution↗

PubMed1979

Principles and methods for the quantitative determination of Feulegen stained DNA with the television texture analysis system (TAS).

The television texture analysis system (TAS, Leitz) has been applied to determination of the relative DNA content of Feulgen stained nuclei. The principles of the method are described and comparative measurements are presented. The determination is based on the measurement of areas at preset intervals of transmittance, taking into consideration the necessary correction of extinction values in relation to area and applying a correction for background. The data obtained can be used for the quantitative determination of DNA, and to provide analytical information for quantitation of structure. Comparison of the mean of extinctions as recorded with the scanning photometric method and those recorded with the television texture analysis method, with which 43 nuclei were investigated in transmittance steps of 0.01, revealed a coefficient of correlation of 0.9938.

Amnion↗

PubMed1993

Waves of extinction from sterile insect release.

Employing theoretical models, we show that the sterile insect release method (SIRM) can give rise to traveling waves of fertile insects. The velocity of these waves depends critically upon the density of sterile insects (and thus upon the rate at which sterile individuals are being released into the environment). When the sterile density is sufficiently low, the traveling wave advances, giving rise to an invasion. However, when the sterile density exceeds a critical threshold, the wave reverses direction, thereby retreating and giving rise to local extinction. Both analytical (regular perturbation) methods and numerical methods are used to determine wave velocities and wave profiles. This is the first time traveling wave solutions have been shown for the SIRM.

Animals↗

PubMed2026

Addressing racism as a clinical competence: Robert Wilson, Jr. (1867-1946).

Addressing health inequity is now recognized as a clinical competency in medical education. We examined the career and writings of Robert Wilson Jr. (1867-1946), longtime dean of the Medical College of the State of South Carolina during the Jim Crow Era, using primary and secondary sources within the context of systemic and structural racism, particularly in South Carolina. Wilson used public health data to refute the "Black Extinction Hypothesis" rooted in social Darwinism. He challenged assumptions of inherent Black susceptibility to tuberculosis, linking disease instead to social determinants of health. He also identified disproportionate mortality from kidney and cardiovascular disease among Black populations, anticipating modern health disparities research. Wilson further acknowledged systemic injustice and implicated structural conditions, including housing, in shaping outcomes. In an era of continuing health inequity and racial health disparities, Wilson applied empirical evidence to reject biological determinism, identify outcomes disparities, and advocate for racial justice.

History, 20th Century↗

PubMed2000

Age rank/clade rank metrics--sampling, taxonomy, and the meaning of "stratigraphic consistency".

Paleontologists frequently contrast clade rank (i.e., nodal or patristic distance from the base of a cladogram) with age rank (i.e., relative first known appearances of the analyzed taxa) to measure the degree of congruence between the estimated phylogeny and the fossil record. Although some potential biases of these methods have been examined (e.g., the effect of tree imbalance), other properties of age rank/clade rank (ARCR) comparisons have not been studied in detail. A basic premise of ARCR metrics is that outgroup taxa diverged earlier than ingroups and thus should first appear in older strata. For example, given phylogeny (A,(B,C)), then taxon A should be sampled before either taxon B or taxon C. We examine this premise in the context of (1) phylogenetic theory, (2) taxonomic practice, (3) sampling intensity (R), and (4) factors other than sampling intensity (including cladogram accuracy). Simulations combining clade evolution and sampling over time indicate a poor relationship between ARCR metrics and R when all taxa are apomorphy-based monophyletic groups. However, a good relationship exists when taxa are either stem-based monophyletic groups or if workers include taxa without a priori decisions about monophyly or paraphyly. These results are not surprising because cladograms predict the order in which lineages diverged (which applies to stem-based monophyletic taxa) and the order in which morphologic grades appeared (which applies to paraphyletic taxa relative to derived monophyletic groups). Other factors that increase ARCR metrics when the average R stays the same include high temporal variation in R, budding instead of bifurcating speciation patterns, low extinction rates, cladogram inaccuracy, and (to a much lesser extent) large clade size. These results suggest several plausible explanations for patterned differences in ARCR metrics among clades, thereby compromising their validity as measures of the quality of the fossil record.

Classification↗

PubMed1984

Immunoenzymatic assay of anti-diphtheric toxin antibodies in human serum.

An enzyme-linked immunosorbent assay was developed for measuring immunoglobulin G anti-diphtheric toxin antibodies in human serum. The assay was done in plastic plates coated with purified diphtheric toxoid. Since a straight-line relationship was found between logs of extinction values and of antibody concentrations, with a very constant slope, serum titers could be expressed as log10 of the serum dilution corresponding to a definite optical density, such as 0.5. The assay furnished highly reproducible titers on a continuous range, with coefficients of variation less than 10%. Only one or two serum dilutions were usually sufficient for serum titration. To establish correspondence of the enzyme-linked immunosorbent assay titers with biologically determined antitoxin international units, a regression equation was fitted between the respective values for 112 serum samples titrated in both tests. The enzyme-linked immunosorbent assay titer of 2.38 corresponded to an antitoxin titer of 0.01 U, which is considered as the minimal protective level. Simple to perform, economical, and precise, the immunoenzymatic assay seems to be a very practical procedure for seroepidemiological purposes.

Antibodies, Bacterial↗

PubMed1994

Pigment-cell-specific genes from fibroblasts are transactivated after chromosomal transfer into melanoma cells.

Human and mouse fibroblast chromosomes carrying tyrosinase or b-locus genes were introduced, by microcell hybridization, into pigmented Syrian hamster melanoma cells, and the microcell hybrids were tested for transactivation of the fibroblast tyrosinase and b-locus genes. By using species-specific PCR amplification to distinguish fibroblast and melanoma cDNAs, it was demonstrated that the previously silent fibroblast tyrosinase and b-locus genes were transactivated following chromosomal transfer into pigmented melanoma cells. However, transactivation of the mouse fibroblast tyrosinase gene was unstable in microcell hybrid subclones and possibly dependent on a second fibroblast locus that could have segregated in the subclones. This second locus was not necessary for transactivation of the fibroblast b-locus gene, thus demonstrating noncoordinate transactivation of fibroblast tyrosinase and b-locus genes. Transactivation of the fibroblast tyrosinase gene in microcell hybrids apparently is dependent on the absence of a putative fibroblast extinguisher locus for tyrosinase gene expression, which presumably is responsible for the extinction of pigmentation in hybrids between karyotypically complete fibroblasts and melanoma cells.

Animals↗

PubMed1993

Spectrophotometric determination of mimosine and 3-hydroxy-4-(1H)-pyridone--the toxic principles of Leucaena leucocephala.

A sensitive and selective spectrophotometric method for the estimation of the toxic factors mimosine and 3-hydroxy-4-(1H)-pyridone (DHP) has been developed based on the intense yellow-colored azodye formed with p-nitroaniline which showed a sharp absorption maximum at 400 nm. The method was optimized based on relative sensitivity of the reaction with various aromatic primary amino compounds and under different conditions of pH. Interference from a variety of structurally related compounds and phenols was tested and found insensitive to this method. The molar extinction coefficient at 400 nm for the azodye formed with mimosine was 5.31 x 10(4) M-1 cm-1 and that for DHP was 1.699 x 10(4) M-1 cm-1. The applicability of the method was tested using different plant extracts and recovery was found to be at 100 +/- 0.3%. The method is suitable for accurate estimation of both mimosine and DHP after paper chromatographic separation of extracts of different biological samples.

Azo Compounds↗

PubMed2002

Character release following extinction in a Caribbean reef coral species complex.

The Pleistocene extinction of the widespread organ-pipe Montastraea coral had measurable morphological and ecological effects on surviving lineages of the Montastraea "annularis" species complex. Extinction of the organ-pipe Montastraea occurred after more than 500,000 years of dominance in the shallow-water reef habitat of Barbados. Extinction resulted in a morphological shift of the columnar Montastraea lineage from thick to thin columns in modern reef environments. Pleistocene colonies of the columnar morphotype sympatric with organ-pipe Montastraea showed greater column widths than those in allopatry. We subjected our data to a number of criteria for interpreting the morphological shift as character release following lifting of competitive pressure after extinction. The morphological differences do not appear to be due either to chance or to physical properties of the marine environment. Differential local extinction and recolonization of four members of the species complex did not occur on Barbados, so that the species coexisted and appear to have coevolved between more than 600,000 and 82,000 years ago. The morphological shift is related to coral growth form and growth rate, and thus reflects the acquisition of a primary resource in corals--light. Character release occurred at the same oceanic Caribbean island (Barbados) where environments have fluctuated with similar variance throughout the period of coexistence. Not only has competition among living members of the Montastraea "annularis" species complex been convincingly demonstrated, but trends in relative abundance among fossil members of the species complex strongly suggest that a competitive hierarchy was operating during their Pleistocene coexistence on Barbados. We also observed an ecological analogue to character release on another Caribbean island. Curaçao. The distribution and abundance of living columnar M. annularis s.s. and massive M. faveolata from the leeward reef crest in Curaçao is greater now than in the Pleistocene, when organ-pipe Montastraea dominated this shallow-water reef habitat. Extinction of the faster growing, shallow-water organ-pipe Montastraea resulted in higher abundance of the columnar Montastraea lineage in shallow-water habitats, where it shifted its morphology to one adapted to high light levels. The species extinction released surviving lineages from a competitive network that had resulted in lower rank abundance in the Pleistocene community and enhanced abundance of both columnar M. annularis s.s. and M. faveolata in modern communities. Full validation of our interpretation of character release must await experiments that demonstrate whether phenotypic differences between populations have a genetic basis. However, we believe the results of this study point to the important, yet heretofore neglected, role that biological interactions have played in the evolution of closely related reef coral species.

Animals↗

PubMed1994

Pathogen invasion and host extinction in lattice structured populations.

We examined the propagation of an infectious disease and the eventual extinction of the host population in a lattice-structured population. Both the host colonization and pathogen transmission processes are assumed to be restricted to act between the nearest neighbor sites. The model is analyzed by an improved version of pair approximation (IPA). Pair approximation is a technique to trace the dynamics of the number of nearest neighbor pairs having particular states, and IPA takes account of the clustering property of lattice models more precisely. The results are checked by computer simulations. The analysis shows: (i) in a one-dimensional lattice population, a pathogen cannot invade a host population no matter how large is the transmission rate; (ii) in a two-dimensional lattice population, pathogens will drive the host to extinction if the transmission rate is larger than a threshold. These results indicate that spatially structured population models may give qualitatively different results from conventional population models, such as Lotka-Volterra ones, without spatial structure.

Biometry↗

PubMed2003

Dynamics of nutrient-phytoplankton interaction in the presence of viral infection.

The present paper deals with the problem of a nutrient-phytoplankton (N-P) populations where phytoplankton population is divided into two groups, namely susceptible phytoplankton and infected phytoplankton. Conditions for coexistence or extinction of populations are derived taking into account general nutrient uptake functions and Holling type-II functional response as an example. It is observed that the three component systems persist when the infected phytoplankton population is not able to consume nutrient.

Biological Transport, Active↗

PubMed2000

BLIMP-I mediates extinction of major histocompatibility class II transactivator expression in plasma cells.

Class II transactivator (CIITA), a coactivator required for class II major histocompatibility complex (MHC) transcription, is expressed in B cells but extinguished in plasma cells. This report identifies B lymphocyte-induced maturation protein I (BLIMP-I), a transcriptional repressor that is capable of triggering plasma cell differentiation, as a developmentally regulated repressor of CIITA transcription. BLIMP-I represses the B cell-specific promoter of the human gene that encodes CIITA (MHC2TA) in a binding site-dependent manner. Decreased CIITA correlates with increased BLIMP-I during plasma cell differentiation in cultured cells. Ectopic expression of BLIMP-I represses endogenous mRNA for CIITA and the CIITA targets, class II MHC, invariant chain and H2-DM (the murine equivalent of HLA-DM) in primary splenic B cells as well as 18-81 pre-B cells. Thus, the BLIMP-I program of B cell differentiation includes loss of antigen presentation via extinction of CIITA expression.

Animals↗

PubMed2006

Phanerozoic marine biodiversity dynamics in light of the incompleteness of the fossil record.

Long-term evolutionary dynamics have been approached through quantitative analysis of the fossil record, but without explicitly taking its incompleteness into account. Here we explore the temporal covariance structure of per-genus origination and extinction rates for global marine fossil genera throughout the Phanerozoic, both before and after corrections for the incompleteness of the fossil record. Using uncorrected data based on Sepkoski's compendium, we find significant autocovariance within origination and extinction rates, as well as covariance between extinction and origination, not one, but two, intervals later, corroborating evidence for the unexplained temporal gap found by past studies. However, these effects vanish when the data are corrected for the incompleteness of the fossil record. Instead, we observe significant covariance only between extinction and origination in the immediately following intervals. The gap in the response of the biosphere to extinction in the uncorrected fossil record thus appears to be an artifact of the incompleteness of the fossil record, specifically due to episodic variation in the probability that taxa will be preserved, on time scales comparable to the temporal resolution of Sepkoski's data. Our results also indicate that at that temporal resolution (the stage/substage of duration approximately = 5 million years), changes in origination and extinction do not persist for longer than one interval, except that elevated origination rates immediately after extinction may last for more than a single interval. Thus, although certain individual cases may deviate from the overall pattern, we find that in general the biosphere's response to perturbation is immediate geologically and usually short-lived.

Animals↗

PubMed2002

How many named species are valid?

Estimates of biodiversity in both living and fossil groups depend on raw counts of currently recognized named species, but many of these names eventually will prove to be synonyms or otherwise invalid. This difficult bias can be resolved with a simple "flux ratio" equation that compares historical rates of invalidation and revalidation. Flux ratio analysis of a taxonomic data set of unrivalled completeness for 4,861 North American fossil mammal species shows that 24-31% of currently accepted names eventually will prove invalid, so diversity estimates are inflated by 32-44%. The estimate is conservative compared with one obtained by using an older, more basic method. Although the degree of inflation varies through both historical and evolutionary time, it has a minor impact on previously published background origination and extinction rates. Several lines of evidence suggest that the same bias probably affects more poorly studied, hyperdiverse living groups such as fungi and insects. If so, then current estimates of total global diversity could be revised downwards to as low as 3.5-10.5 million species.

Animals↗

PubMed1990

The interplay of population dynamics and the evolutionary process.

Long-term maintenance of genetic diversity is affected by ecological forces that are driven in turn by current levels of genetic variation. The strength of population regulation and the consequent patterns of population fluctuations determine the likelihood of genetic changes considered pivotal for rapid speciation. However, genetic diversity in the susceptibility to regulatory forces can reduce the magnitude of such fluctuations and minimize the likelihood of genetic revolutions. A group of populations that experiences local extinctions and recolonizations may hold lower levels of genetic diversity than in the absence of such extinctions, but local adaption, which provides enhanced genetic diversity, can reduce the likelihood of local extinctions. Tightly regulated populations experience different selection pressures than poorly regulated populations, although tighter regulation itself can evolve. When genotypic variation affects the outcome of interspecific interactions on a local scale, this effect, coupled with appropriate spatial variation, can enhance the resilience of the interactive system.

Animals↗

PubMed2005

Periodicity of mass extinctions without an extraterrestrial cause.

We study a lattice model of a multispecies prey-predator system. Numerical results show that for a small mutation rate the model develops irregular long-period oscillatory behavior with sizeable changes in a number of species. The periodicity of extinctions on Earth was suggested by Raup and Sepkoski [Proc. Natl. Acad. Sci. 81, 801 (1984)], but thus far is lacking a satisfactory explanation. Our model indicates that this might be a natural consequence of the ecosystem dynamics and not the result of any extraterrestrial cause.

Animals↗

PubMed2006

Global warming and extinctions of endemic species from biodiversity hotspots.

Global warming is a key threat to biodiversity, but few researchers have assessed the magnitude of this threat at the global scale. We used major vegetation types (biomes) as proxies for natural habitats and, based on projected future biome distributions under doubled-CO2 climates, calculated changes in habitat areas and associated extinctions of endemic plant and vertebrate species in biodiversity hotspots. Because of numerous uncertainties in this approach, we undertook a sensitivity analysis of multiple factors that included (1) two global vegetation models, (2) different numbers of biome classes in our biome classification schemes, (3) different assumptions about whether species distributions were biome specific or not, and (4) different migration capabilities. Extinctions were calculated using both species-area and endemic-area relationships. In addition, average required migration rates were calculated for each hotspot assuming a doubled-CO2 climate in 100 years. Projected percent extinctions ranged from <1 to 43% of the endemic biota (average 11.6%), with biome specificity having the greatest influence on the estimates, followed by the global vegetation model and then by migration and biome classification assumptions. Bootstrap comparisons indicated that effects on hotpots as a group were not significantly different from effects on random same-biome collections of grid cells with respect to biome change or migration rates; in some scenarios, however, botspots exhibited relatively high biome change and low migration rates. Especially vulnerable hotspots were the Cape Floristic Region, Caribbean, Indo-Burma, Mediterranean Basin, Southwest Australia, and Tropical Andes, where plant extinctions per hotspot sometimes exceeded 2000 species. Under the assumption that projected habitat changes were attained in 100 years, estimated global-warming-induced rates of species extinctions in tropical hotspots in some cases exceeded those due to deforestation, supporting suggestions that global warming is one of the most serious threats to the planet's biodiversity.

Biodiversity↗