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PubMed2004

Rapid recovery from the Late Ordovician mass extinction.

Understanding the evolutionary role of mass extinctions requires detailed knowledge of postextinction recoveries. However, most models of recovery hinge on a direct reading of the fossil record, and several recent studies have suggested that the fossil record is especially incomplete for recovery intervals immediately after mass extinctions. Here, we analyze a database of genus occurrences for the paleocontinent of Laurentia to determine the effects of regional processes on recovery and the effects of variations in preservation and sampling intensity on perceived diversity trends and taxonomic rates during the Late Ordovician mass extinction and Early Silurian recovery. After accounting for variation in sampling intensity, we find that marine benthic diversity in Laurentia recovered to preextinction levels within 5 million years, which is nearly 15 million years sooner than suggested by global compilations. The rapid turnover in Laurentia suggests that processes such as immigration may have been particularly important in the recovery of regional ecosystems from environmental perturbations. However, additional regional studies and a global analysis of the Late Ordovician mass extinction that accounts for variations in sampling intensity are necessary to confirm this pattern. Because the record of Phanerozoic mass extinctions and postextinction recoveries may be compromised by variations in preservation and sampling intensity, all should be reevaluated with sampling-standardized analyses if the evolutionary role of mass extinctions is to be fully understood.

Biodiversity↗
PubMed1999

Late quaternary extinction of a tree species in eastern North America.

Widespread species- and genus-level extinctions of mammals in North America and Europe occurred during the last deglaciation [16,000-9,000 yr B.P. (by (14)C)], a period of rapid and often abrupt climatic and vegetational change. These extinctions are variously ascribed to environmental change and overkill by human hunters. By contrast, plant extinctions since the Middle Pleistocene are undocumented, suggesting that plant species have been able to respond to environmental changes of the past several glacial/interglacial cycles by migration. We provide evidence from morphological studies of fossil cones and anatomical studies of fossil needles that a now-extinct species of spruce (Picea critchfieldii sp. nov.) was widespread in eastern North America during the Last Glacial Maximum. P. critchfieldii was dominant in vegetation of the Lower Mississippi Valley, and extended at least as far east as western Georgia. P. critchfieldii disappeared during the last deglaciation, and its extinction is not directly attributable to human activities. Similarly widespread plant species may be at risk of extinction in the face of future climate change.

Biological Evolution↗
PubMed2003

Exploring developmental modes in a fossil arthropod: growth and trunk segmentation of the trilobite Aulacopleura konincki.

Trilobites offer the opportunity to explore postembryonic development within the fossil record of arthropod evolution. In contrast to most trilobites, the Silurian proetid Aulacopleura konincki from the Czech Republic exhibits marked variation in the mature number of thoracic segments, with five morphs with 18-22 thoracic segments. The combination of abundant articulated specimens available from a narrow stratigraphic interval and segmental intraspecific variation makes this trilobite singularly useful for studying postembryonic growth and segmentation. Trunk segmentation followed a hemianamorphic pattern, as seen in other arthropods and as characteristic of the Trilobita; during a first anamorphic phase, segments were accreted, while in the subsequent epimorphic phase, segmentation did not proceed further despite continued growth. Size increment during the anamorphic phase was targeted and followed Dyar's rule, a geometric progression typical of many arthropods. We consider alternative hypotheses for the control of the switch from anamorphic to epimorphic phases of development. Our analysis favors a scenario in which the mature number of thoracic segments was determined quite early in development rather than at a late stage in association with a critical size threshold. This study demonstrates that hypotheses concerning developmental pattern and control can be tested in organisms belonging to an extinct clade.

Animals↗
PubMed1988

Planetary environments and the conditions of life.

Life arose on Earth within a billion years (1 Ga) after planetary accretion and core formation. The geological record, which begins 3.8 Ga BP, indicates environmental conditions much like today's, except for the absence of oxygen. By 3.5 Ga BP microbial ecosystems were already colonizing shallow marine hydrothermal environments along shorelines of volcanic islands. Although similar environments could have existed more than 3.8 Ga BP, they may not have been the spawning grounds of life. Geophysical models of the first 600 Ma of Earth history following accretion and core formation point to a period of great environmental disequilibrium. In such an environment the passage of energy from Earth's interior and from the Sun through gas-liquid-solid domains and their boundaries with each other generated a dynamically interacting, complex hierarchy of self-organized structures, ranging from bubbles at the sea-air interface to tectonic plates. Nested within this hierarchy were the precursors of living systems. The ability of a planet to produce such a hierarchy is speculated to be a prerequisite for the origin and sustenance of life. Application of this criterion to Mars, which apparently experienced no plate tectonism, argues against the origin of martian life. Because only further geological and biogeochemical exploration of the planet can place these qualitative speculations on firm ground, the search for evidence of extinct life on Mars continues to be of highest scientific priority.

Biological Evolution↗
PubMed1999

Diversity and extinction in a lattice model of a population with fluctuating environment.

I study a lattice stochastic model of a mutating population sensitive to the influence of a fluctuating environment. The dynamics of the population stressed by linear and periodic disturbances is investigated. In agreement with previous studies of nonspatial models, I find a critical rate of change in the environmental variable beyond which the population becomes extinct, and I show explicitly that the presence of space in the model can affect the critical rate. Further, I study the diversity defined as the total number of different cell types present in the lattice as a function of intensity and frequency of the environmental disturbance. If the disturbance becomes fast and intense the population becomes extinct. Interestingly, I find that for moderate stresses the diversity increases with the intensity and frequency of disturbance. The transition between large diversity and extinction is sharp, implying that the populations with high diversity are generally the ones closest to the extinction threshold. When subjected to colored noise of increasing intensity the system grows in diversity but at the same time is more likely to become extinct.

Biophysical Phenomena↗
PubMed1987

Environmental trends in extinction during the Paleozoic.

Extinction intensities calculated from 505 Paleozoic marine assemblages divided among six environmental zones and 40 stratigraphic intervals indicate that whole communities exhibit increasing extinction offshore but that genera within individual taxonomic classes tend to have their highest extinction onshore. The offshore trend at the community level results from a concentration of genera in classes with low characteristic extinction rates in nearshore environments. This finding is consistent with the ecologic expectation that organisms inhabiting unpredictably fluctuating environments should suffer more extinction than counterparts living under more predictably equitable conditions.

Animals↗
PubMed2002

Akodon sex reversed females: the never ending story.

The existence of fertile A. azarae females with a chromosome sex pair indistinguishable from that of males was reported more than 35 years ago. These heterogametic females were initially thought to occur due to an extreme process of dosage compensation in which X inactivation was restricted to Xp and complemented by a deletion of Xq (Xx females). Later on, a C-banding analysis of A. mollis variant females showed that these specimens were in fact XY* sex reversed and not Xx females. The finding of positive testing for Zfy and Sry multiple-copy genes in Akodon males and heterogametic females confirmed the XY* assumption. At the present time, XY* sex reversed females have been found to exist in nine Akodon species. Akodon heterogametic females produce X and Y* oocytes, which upon sperm fertilization give rise to viable XX (female), XY* (female), and XY (male) embryos, and to non-viable Y*Y zygotes. Heterozygous females exhibit a better reproductive performance than XX females in order to compensate the Y*Y zygote wastage. XY* sex reversed females are assumed to occur due to a deficient Sry expression resulting in the development of ovaries instead of testes. Moreover, the appearance of Y* elements is a highly recurrent event. It is proposed that homozygosity for an autosomal or pseudoautosomal recessive mutation (s-) inhibits Sry expression giving rise to XY* embryos with ovary development. Location of the Y* chromosome in the female germ cell lineage produces an ovary-specific imprinting of the Sry* gene maintaining its defective expression through generations independently from the presence or absence of s- homozygosity. By escaping the ovary-specific methylation some Y* chromosomes turn back to normal Ys producing Y oocytes capable of generating normal male embryos when fertilized by an X sperm. Fluctuations in the rate of variant females in field populations and in laboratory colonies of Akodon depend on the balance between the appearance of new variant females (s-/s-, XY* specimens) and the extinction of sex reversed specimens due to imprinting escape.

Animals↗
PubMed1993

The pharmacology of pain signalling.

Recent advances in pain research illustrate the analytical power of modern neurosciences in a field previously accessible only to methods of systems biology. Novel molecular and cellular biological techniques have changed the face of pain research by detailing the multiplicity of pain transducing and pain suppressive systems which involve neuronal and hormonal systems acting in concert to help the individual to cope with pain. The introduction of concepts of neuronal plasticity in this field has led to important therapeutical consequences. Novel compounds and new regimens for drug treatment to prevent activity-dependent long-term changes or to facilitate extinction in pain-related systems are emerging.

Analgesics↗
PubMed2005

Species diversity can drive speciation.

A fundamental question in evolutionary ecology and conservation biology is: why do some areas contain greater species diversity than others? Island biogeographic theory has identified the roles of immigration and extinction in relation to area size and proximity to source areas, and the role of speciation is also recognized as an important factor. However, one as yet unexplored possibility is that species diversity itself might help to promote speciation, and indeed the central tenets of island biogeographic theory support such a prediction. Here we use data for plants and arthropods of the volcanic archipelagos of the Canary and Hawaiian Islands to address whether there is a positive relationship between species diversity and rate of diversification. Our index of diversification for each island is the proportion of species that are endemic, and we test our prediction that this increases with increasing species number. We show that even after controlling for several important physical features of islands, diversification is strongly related to species number.

Animals↗
PubMed1987

Purification and characterization of human recombinant interleukin-1 beta.

A human interleukin-1 (IL-1) beta cDNA was cloned, and the region coding for the mature protein was expressed in Escherichia coli. The 17-kDa biologically active product was purified in 40% yield to apparent homogeneity, without chaotropes, from the soluble fraction of sonicated cell lysates. The recombinant IL-1 beta was characterized by amino acid analysis, NH2- and COOH-terminal sequence analysis, sodium dodecyl sulfate-polyacrylamide gel electrophoresis, spectroscopy, and biological assay. Specific biological activity was 4.6 X 10(8) units/mg in a co-mitogenic IL-2 induction assay using cultured EL-4 T-lymphocytes. The molar extinction coefficient was determined to be 10,300 cm-1 M-1 at 280 nm. NH2-terminal sequence analysis revealed that 70% of the product begins with the Ala corresponding to the NH2 terminus of the natural protein, while 30% begins with the following Pro. No initiator Met was observed. Both of the sulfhydryl groups are reactive to Ellman's reagent and to iodoacetamide under nonreducing conditions, indicating that the Cys residues do not form disulfide bonds. S-Carboxamidomethyl-Cys-rIL-1 beta retained biological activity in the IL-2 induction assay. Circular dichroism suggested an extensive beta sheet structure for rIL-1 beta.

Amino Acid Sequence↗
PubMed1984

An optimized continuous assay for cAMP phosphodiesterase and calmodulin.

A continuous spectrophotometric assay for cAMP phosphodiesterase has been optimized and adopted for assaying calmodulin in biological samples. This method utilizes the coupled enzyme reactions of myokinase, pyruvate kinase, and lactic acid dehydrogenase. The effective molar extinction coefficient for this method is 1.25 X 10(4) at 340 nm. A point-assay method capable of handling a large number of samples has also been established. This same procedure can also be adopted for the assay of calcineurin and other calmodulin-binding proteins.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed2000

Approaches towards the quantitative analysis of peptides and proteins by reversed-phase high-performance liquid chromatography in the absence of a pure reference sample.

A reversed-phase HPLC protocol for the quantitative analysis of peptides and proteins is presented. It is applicable to purified samples and potentially to crude biological extracts. The key feature is that an analytically pure reference sample of the analyte is not required because the extinction coefficient for the UV absorbance at 280 nm can be accurately estimated from the amino acid sequence. The concentration of a protein can therefore be calculated from the peak area relative to an internal standard. Sources of error and limitations of the method are systematically considered. Tryptophan containing peptides gave closer agreement to expected values than those with only tyrosine. It was found that analogous, previously used methods could not be directly applied to lower wavelengths.

Chromatography, High Pressure Liquid↗
PubMed1978

[Immersion: From mental anorexia to behavioral therapeutics].

The flooding is an extinction process of an emotion or a pulsion through a mechanism of Pavlov of conditioned inhibition. The author does here an experimental study of this process. This study allows to explain the exact flooding mechanism. So we can better understand and better introduce the practical flooding applications in therapeutic as well as in psychopathology.

Animals↗
PubMed1982

[Human pharmacokinetics of different i.v. doses of azapropazone (HPLC-determination) (author's transl)].

The pharmacokinetic profile of azapropazone (Prolixan), sodium salt of 5-dimethylamino-9,5-dimethylamine-9-methyl-5-propyl-1H-pyrazolol[1,2-a][1,2,4]benzotriazine-1,3(2H)-dione, was established. Six healthy, adult volunteers received a single dose of either 600 mg or 1200 mg azapropazone as sodium salt intravenously. The drug was selectively separated from its metabolites and other plasmatic compounds and it was quantified by measurement of extinction at 254 nm. The kinetic parameters of azapropazone were independent of the applied dose (600 mg and 1200 mg): Biological half-life (t0.5): 16.8 +/- 2.95 h and 17.2 +/- 3.0 h; Total clearance (Cltot): 10.2 +/- 2.1 ml min-1 (both doses); Central volume of distribution (Vc): 3.7 +/- 0.71 and 3.9 +/- 0.91; Apparent volume of distribution (Vd): 12.5 +/- 2.91 and 14.4 +/- 2.41. Initial serum concentrations were 170 +/- 41.5 micrograms ml-1 and 326.3 +/- 84.5 micrograms ml-1, determined by extrapolation (C0 at time t0). The areas under the plasma concentration curves (AUC0 infinity) were calculated to amount 1052.5 +/- 217.4 micrograms ml-1h-1 and 2078.4 +/- 515.9 micrograms ml-1h-1. Three rate constants associated with the elimination of the drug could be calculated.

Adult↗
PubMed2001

Intein spread and extinction in evolution.

Inteins are selfish DNA elements found within coding regions. They are translated with their host protein, but then catalyze their own excision and the formation of a peptide bond between their flanking protein regions. Understanding what drives and selects inteins is relevant for assessing whether they have unidentified biological functions and whether they can invade and become established in new genes and organisms. Inteins are suggested to have been present and more common in the progenitors of eukaryotes and prokaryotes. In these cells, inteins had some beneficial function or had evolved from an unknown beneficial protein. Since then, this putative benefit has been lost and inteins are gradually becoming extinct. The proteins in which inteins are currently found are proposed to be proteins vital for the survival of the organism, where intein removal is most difficult.

Archaea↗