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PubMed2006

The impacts of different management strategies and environmental forcing in ecological communities.

Understanding the effects of population management on the community a target species belongs to is of key importance for successful management. It is known that the removal or extinction of a single species in a community may lead to extinctions of other community members. In our study, we assess the impacts of population management on competitive communities, studying the response of both locally stable and unstable communities of varying size (between four and 10 species) to three different management strategies; harvesting of a target species, harvesting with non-targeted catch, and stocking of the target species. We also studied the consequences of selecting target species with different relative abundances, as well as the effects of varying environmental conditions. We show here how the effects of management in competitive communities extend far beyond the target population. A crucial role is played by the underlying stability properties of the community under management. In general, locally unstable communities are more vulnerable to perturbation through management. Furthermore, the community response is shown to be sensitive to the relative density of the target species. Of considerable interest is the result that even a small (2.5%) increase in the population size of the target species through stocking may lead to extinction of other community members. These results emphasize the importance of considering and understanding multi-species interactions in population management.

Animals↗
PubMed1998

The context of human genetic evolution.

The debate on modern human origins has often focused on the relationship between genes and fossils. Although more and more genetic evidence has been accumulating in favor of a recent African origin for modern humans, it has been assumed by many that the fossil evidence remains ambiguous. On the contrary, it has been clear for some time that the fossil evidence does not support the multiregional model: Fossils and archeology indicate a pattern of multiple dispersals from and beyond Africa, against which the genetic data can be compared. The continuing value of paleobiology is in complementing genetic information by revealing the context of human evolution: locating the dispersals and extinctions of populations in time and space, correlating these events with the environmental forces that shaped them, and providing an increasingly detailed understanding of the morphology and technology of early humans.

Animals↗
PubMed2007

Resolving the tragedy of the commons: the feedback between intraspecific conflict and population density.

Competition and conflict among individuals can favour exploitative strategies that undermine the common good. Theory suggests that this can lead to a tragedy of the commons and ultimately population extinction, a phenomenon known as evolutionary suicide. Here, I present a model of the evolutionary tragedy of the commons that explicitly considers the population dynamics where individuals invest in individually costly competitive traits. In the simplest form, this supports the notion that selection for high levels of conflict can cause evolutionary suicide. However, as competition comes with survival and fecundity costs, a feedback between the investment in competition and population density can act to reduce the level of conflict and prevent the population from going extinct. This suggests that the interaction between population ecology and the evolution of competition and conflict among individuals may be an important mechanism in resolving the level of competition and conflict among individuals.

Biological Evolution↗
PubMed2002

A novel ultraviolet assay for testing side reactions of carbodiimides.

Carbodiimides possess considerable absorbance in the ultraviolet region; the extinction coefficient of 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide (EDC) in water is epsilon(214) = 6.3. 10(3) L x mol(-1) x cm(-1). It provides a very simple method for testing possible side reactions of carbodiimides. This technique was used to study effects of pH, different buffers, and other components typically present in biological samples on EDC stability. It was shown that the hydrolysis rate in pure water increased from 1.5. 10(-5) to 5. 10(-4) s(-1) by pH decreasing from 7 to 4. A strong increase of the rate of EDC loss was observed in the presence of different components. This effect can be described by the following row of hydrolysis rates: citrate >> acetate approximately phosphate >> SDS. The results can be used to optimize carbodiimide-mediated reactions of peptide bond formation in organic chemistry or peptide synthesis or during immobilization or cross-linking of biological molecules.

Buffers↗
PubMed1992

Stimulus configuration, classical conditioning, and hippocampal function.

Hippocampal participation in classical conditioning is described in terms of a multilayer network that portrays stimulus configuration. The network (a) describes behavior in real time, (b) incorporates a layer of "hidden" units positioned between input and output units, (c) includes inputs that are connected to the output directly as well as indirectly through the hidden-unit layer, and (d) uses a biologically plausible backpropagation procedure to train the hidden-unit layer. Nodes and connections in the neural network are mapped onto regional cerebellar, cortical, and hippocampal circuits, and the effect of lesions of different brain regions is formally studied. Computer simulations of the following classical conditioning paradigms are presented: acquisition of delay and trace conditioning, extinction, acquisition-extinction series of delay conditioning, blocking, over-shadowing, discrimination acquisition, discrimination reversal, feature-positive discrimination, conditioned inhibition, negative patterning, positive patterning, and generalization. The model correctly describes the effect of hippocampal and cortical lesions in many of these paradigms, as well as neural activity in hippocampus and medial septum during classical conditioning. Some of these results might be extended to the description of anterograde amnesia in human patients.

Animals↗
PubMed1975

Absorption spectra and linear dichroism of some amphibian photoreceptors.

Absorption spectra and linear dichroism of dark-adapted, isolated photoreceptors of mudpuppies, larval and adult tiger salamanders, and tropical toads were measured microspectrophotometrically. Spectral half-band width, dichroic ratio, and transverse specific density were determined using averaged polarized absorptance spectra and photomicrographs of seven types of rod outer segments. Two classes of cells were found, one with higher specific density and dichroic ratio, associable with the presence of rhodopsins, the other, lower in both quantities, associable with porphyropsins. Relationships were derived to calculate the product of molar concentration and extinction coefficient (CEmax) from specific density and dichroic ratio. By utilizing the hypothesis of invariance of oscillator strengths and measured half-band widths, Emax values were independently determined, permitting the calculation of C. The pigment concentration for all cells tested was about 3.5 mM. The broadness of green rod pigment spectra is correlated with reduced molar absorptivity and reduced cellular specific density. Estimation of physiological spectral sensitivities is discussed. Based on dichroic ratio considerations, a model is proposed for the orientation of retinals in situ which could account for the apparent degree of alignment of transition moments. In the chosen orientation, the ring portion of conjugation becomes primarily responsible for axial extinction. Reduced dichroism of dehydroretinal-bearing cells can thus result from the extended ring conjugation of chromophores. Some inferences derivable from the model are discussed.

Ambystoma↗
PubMed2005

Small clades at the periphery of passerine morphological space.

Among passerine birds (order Passeriformes), tribe- to family-level clades with five or fewer species are more frequent than one would expect from a homogeneous speciation and extinction process. Previous analyses also suggested that small clades tend to be marginal geographically and/or ecologically. In this study, I use principal component (PC) scores based on eight log-transformed measurements of the wing, tail, leg, and beak to test the hypothesis that small clades (<or=5 species) occupy peripheral positions in morphological space. Species in smaller clades exhibited higher absolute deviations and greater standard deviations on PC axes 4, 6, and 7, reflecting peripheral positions associated with relatively long toes, sometimes in contrast with short legs, and relatively small beaks compared with other birds. These extreme morphological characters are related to foraging on hard substrates, such as rock or bark, or feeding from perched positions or in dense vegetation. The implication that these small clades are protected from extinction at the periphery of morphological and, by inference, ecological space suggests that more detailed studies of the evolution and ecology of species in small clades should be a priority.

Adaptation, Physiological↗
PubMed2006

How do pathogen evolution and host heterogeneity interact in disease emergence?

Heterogeneity in the parameters governing the spread of infectious diseases is a common feature of real-world epidemics. It has been suggested that for pathogens with basic reproductive number R(0)>1, increasing heterogeneity makes extinction of disease more likely during the early rounds of transmission. The basic reproductive number R(0) of the introduced pathogen may, however, be less than 1 after the introduction, and evolutionary changes are then required for R(0) to increase to above 1 and the pathogen to emerge. In this paper, we consider how host heterogeneity influences the emergence of both non-evolving pathogens and those that must undergo adaptive changes to spread in the host population. In contrast to previous results, we find that heterogeneity does not always make extinction more likely and that if adaptation is required for emergence, the effect of host heterogeneity is relatively small. We discuss the application of these ideas to vaccination strategies.

Adaptation, Biological↗
PubMed1998

Effects of residues of deltamethrin in cattle faeces on the development and survival of three species of dung-breeding insect.

OBJECTIVE: To assess the toxicity to insects of drug residues excreted in cattle faeces following treatment with deltamethrin. DESIGN: Bioassays were performed on one species of dung-breeding fly (Musca vetustissima) and two species of dung beetle (Onthophagus binodis and Euoniticellus fulvus). ANIMALS: Cattle on properties near Kangaroo Valley, Canberra and Gundagai were treated with pour-on formulations of deltamethrin. Untreated animals acted as controls. PROCEDURES: Faeces from treated and untreated cattle were inoculated with newly emerged fly larvae or fed to adults of two species of dung beetle. Percentage survival and duration of development provided measures of the toxicity of deltamethrin residues in faeces. RESULTS: Residues of deltamethrin were excreted in concentrations sufficient to inhibit survival of larvae of M vetustissima for 1 to 2 weeks after treatment. Peak concentrations of 0.4 mg deltamethrin/kg dry weight of faeces occurred 3 days after treatment and were sufficient to kill adult beetles for at least twice this period. With one of two formulations tested, there was evidence of a reduction in dung beetle fecundity and an increase in the duration of juvenile development. A model of the effect of deltamethrin on the breeding success of dung beetles in the field suggests that a single treatment, applied when most of the population is in a nonparous condition, may cause up to 75% reduction in beetle activity by the end of the season. Multiple treatments at 10 or 21 day intervals may drive local populations towards extinction. CONCLUSION: Depending on the time and frequency of treatment, the effect of deltamethrin on insects in cattle faeces may range from negligible to catastrophic.

Administration, Topical↗
PubMed1993

Geography of end-Cretaceous marine bivalve extinctions.

Analysis of the end-Cretaceous mass extinction, based on 3514 occurrences of 340 genera of marine bivalves (Mollusca), suggests that extinction intensities were uniformly global; no latitudinal gradients or other geographic patterns are detected. Elevated extinction intensities in some tropical areas are entirely a result of the distribution of one extinct group of highly specialized bivalves, the rudists. When rudists are omitted, intensities at those localities are statistically indistinguishable from those of both the rudist-free tropics and extratropical localities.

Animals↗
PubMed2005

Replicative homeostasis II: influence of polymerase fidelity on RNA virus quasispecies biology: implications for immune recognition, viral autoimmunity and other "virus receptor" diseases.

Much of the worlds' population is in active or imminent danger from established infectious pathogens, while sporadic and pandemic infections by these and emerging agents threaten everyone. RNA polymerases (RNApol) generate enormous genetic and consequent antigenic heterogeneity permitting both viruses and cellular pathogens to evade host defences. Thus, RNApol causes more morbidity and premature mortality than any other molecule. The extraordinary genetic heterogeneity defining viral quasispecies results from RNApol infidelity causing rapid cumulative genomic RNA mutation a process that, if uncontrolled, would cause catastrophic loss of sequence integrity and inexorable quasispecies extinction. Selective replication and replicative homeostasis, an epicyclical regulatory mechanism dynamically linking RNApol fidelity and processivity with quasispecies phenotypic diversity, modulating polymerase fidelity and, hence, controlling quasispecies behaviour, prevents this happening and also mediates immune escape. Perhaps more importantly, ineluctable generation of broad phenotypic diversity after viral RNA is translated to protein quasispecies suggests a mechanism of disease that specifically targets, and functionally disrupts, the host cell surface molecules--including hormone, lipid, cell signalling or neurotransmitter receptors--that viruses co-opt for cell entry. This mechanism--"Viral Receptor Disease (VRD)"--may explain so-called "viral autoimmunity", some classical autoimmune disorders and other diseases, including type II diabetes mellitus, and some forms of obesity. Viral receptor disease is a unifying hypothesis that may also explain some diseases with well-established, but multi-factorial and apparently unrelated aetiologies--like coronary artery and other vascular diseases--in addition to diseases like schizophrenia that are poorly understood and lack plausible, coherent, pathogenic explanations.

Autoimmunity↗
PubMed1979

Diet and status at Chalcatzingo: some empirical and technical aspects of strontium analysis.

Determination of the levels of particular trace elements preserved in bone provides a potential pathway for reconstructing the diet of extinct primate species and archaic human groups. Strontium is one of the most useful trace elements for dietary reconstruction but several empirical properties of strontium must be considered during the interpretation of results. (1) Strontium is distributed unevenly throughout the physical environment. (2) Plants, in general, do not discriminate against strontium. (3) During ionic transfer across biological membranes, strontium is discriminated against by terrestrial vertebrates. (4) It is unlikely that strontium would be selectively removed from bone mineral during diagenesis. A particular difficulty in trace element analysis is caused by interaction between analytical technique and sample matrix. To assess this problem the skeletal population from Chalcatzingo was analyzed by two techniques: atomic absorption spectrometry and neutron activation analysis. The results from the two techniques compared favorably indicating that the pattern of bone strontium levels could be accepted as an accurate reflection of the distribution of bone strontium within the population. After demonstrating the internal accuracy of the results, the bone strontium level and position of social rank within Chalcatzingo were compared. Ethnographic and archaeological evidence on chiefdoms and states indicate that dietary differences in the amount of meat consumed occur between social ranks. The relative social ranks were reconstructed by using a "pattern analysis" of the burial goods accompanying each individual. The individuals accompanied by jade had the lowest mean bone strontium level (X = 532). Those individuals buried with a shallow dish had a slightly higher level (X = 635). A third group, which had no grave goods, had the highest mean bone strontium level (X = 700) which suggests that their diet contained less meat than was available to the rest of the community.

Anthropology, Physical↗
PubMed2005

Solid films of blended poly(vinyl alcohol)/poly(vinyl pyrrolidone) for topical S-nitrosoglutathione and nitric oxide release.

Nitric oxide (NO) is responsible for biological actions in mammals, ranging from the control of arterial pressure to immunological responses. In this study, S-nitrosoglutathione (GSNO), a spontaneous NO donor, was incorporated in solid films of blended poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP) comprising a biomaterial with potential for the local delivery of NO. In dry conditions, the extinction of the absorption bands of GSNO was correlated with the increase of the absorption band of its dimmer, GS-SG, implying NO release through the homolytic cleavage of the S-N bond. Mass spectrometry was used to confirm and to monitor the release of free NO from solid PVA/PVP-GSNO films to the gas phase. Kinetic measurement based on the Griess reaction was used to show that solid PVA/PVP-GSNO films are also capable of releasing both NO and GSNO to aqueous solution trough diffusion. Storage experiments have shown that GSNO is highly stabilized in the dry PVA/PVP matrix. The results indicate that GSNO-containing PVA/PVP films may be used for delivering free NO and/or GSNO topically and controllably.

Administration, Topical↗
PubMed2006

Raman spectroscopy in astrobiology.

Raman spectroscopy is proposed as a valuable analytical technique for planetary exploration because it is sensitive to organic and inorganic compounds and able to unambiguously identify key spectral markers in a mixture of biological and geological components; furthermore, sample manipulation is not required and any size of sample can be studied without chemical or mechanical pretreatment. NASA and ESA are considering the adoption of miniaturised Raman spectrometers for inclusion in suites of analytical instrumentation to be placed on robotic landers on Mars in the near future to search for extinct or extant life signals. In this paper we review the advantages and limitations of Raman spectroscopy for the analysis of complex specimens with relevance to the detection of bio- and geomarkers in extremophilic organisms which are considered to be terrestrial analogues of possible extraterrestial life that could have developed on planetary surfaces.

Biomarkers↗
PubMed2001

[Predictive value of biological species for plant conservation in the Mediterranean area].

The validity of Raunkiaer's biological types (or life-forms) was tested on native Corsican flora, using criteria of altitudinal distribution and rarity. The biological basis of this classification has been widely confirmed. The analysis of floras from Corsica and Provence revealed the major role played by both altitude and human impact, and also demonstrated the importance of the predictive value of life-forms to plant conservation. In Southeastern France, there are no clear proportional relationships between rarity and extinction percentages. With increasing levels of human activity, rarity percentages are seen to increase for nearly all types. Conversely, extinction percentages exhibit a clear progression only for the most threatened life-forms: bulb and tuber geophytes, therophytes, parasites and especially hydrophytes. Thus, priority should be given to the protection of these 4 herbaceous types, which are found at low altitudes and lack visible vegetative organs during the unfavourable season.

Conservation of Natural Resources↗
PubMed1990

Distribution and biology of Ornithodoros erraticus in parts of Spain affected by African swine fever.

Ornithodoros erraticus was found in 30.7 per cent, 35.0 per cent and 71.0 per cent of the pig-pens sampled in the provinces of Salamanca, Badajoz and Huelva in which African swine fever is a problem in the rearing of Iberian pigs. Between 38 and 65 per cent of the pig-pens in these areas are now abandoned and their populations of O erraticus are extinct or becoming so because they can no longer feed on pigs, which in Spain are their main hosts. The abandonment of pig-pens has resulted in the elimination of most soft ticks infected with the virus of African swine fever, and means that the distribution of ticks is now irregular and focal. Another factor affecting their distribution is the kind of soil on which the pig-pens are located. In abandoned pig-pens, the adults and large nymphs survive for about five years or longer when animals occasionally enter them. Hungry tick populations may transmit African swine fever when feeding in winter, whereas the populations that have continuous access to pigs do not feed until the pig-pens reach a temperature of 13 to 15 degrees C. In the latter populations, each stage exhibits a single annual peak of activity, which implies that the development from larva to adult takes two to three years. Pigs may die as a result of the bites, but on no occasion were 100 per cent of the fasting ticks seen to feed, even though they had the opportunity of doing so. This may hinder the eradication of this soft tick from infested pig-pens.

African Swine Fever↗
PubMed2005

Biologically active fluorescent farnesol analogs.

We describe ten polyene analogs of farnesol, typified by 3,7,11-trimethyl-2,4,6,8,10-dodecapentenaldehyde oxime, which preserve the length, cross-section, and approximate hydrophobicity of farnesol. Four of the ten display strong quorum-sensing activity in the human pathogen Candida albicans, with IC(50) values for inhibition of germ-tube formation as low as 10 microM. The polyenes display absorption maxima between 320 and 380 nm, with the extinction coefficients for the oximes approaching 100,000. All but two of the analogs are fluorescent, with excitation maxima varying over the range of 320-370 nm. Oxime anti-4, which can undergo fluorescence excitation at wavelengths beyond 400 nm, is demonstrated to be useful for confocal fluorescence microscopic imaging of fungal cells. The farnesol analogs are also expected to be useful for detection of farnesol binding proteins and in determination of farnesol pharmacokinetics.

Candida albicans↗