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At least 667 records · Page 37Linked to original sources
PubMed2001

From arctic lemmings to adaptive dynamics: Charles Elton's legacy in population ecology.

We shall examine the impact of Charles S. Elton's 1924 article on periodic fluctuations in animal populations on the development of modern population ecology. We argue that his impact has been substantial and that during the past 75 years of research on multi-annual periodic fluctuations in numbers of voles, lemmings, hares, lynx and game animals he has contributed much to the contemporary understanding of the causes and consequences of population regulation. Elton was convinced that the cause of the regular fluctuations was climatic variation. To support this conclusion, he examined long-term population data then available. Despite his firm belief in a climatic cause of the self-repeating periodic dynamics which many species display, Elton was insightful and far-sighted enough to outline many of the other hypotheses since put forward as an explanation for the enigmatic long-term dynamics of some animal populations. An interesting, but largely neglected aspect in Elton's paper is that it ends with speculation regarding the evolutionary consequences of periodic population fluctuations. The modern understanding of these issues will also be scrutinised here. In population ecology, Elton's 1924 paper has spawned a whole industry of research on populations displaying multi-annual periodicity. Despite the efforts of numerous research teams and individuals focusing on the origins of multi-annual population cycles, and despite the early availability of different explanatory hypotheses, we are still lacking rigorous tests of some of these hypotheses and, consequently, a consensus of the causes of periodic fluctuations in animal populations. Although Elton would have been happy to see so much effort spent on cyclic populations, we also argue that it is unfortunate if this focus on a special case of population dynamics should distract our attention from more general problems in population and community dynamics.

Adaptation, Physiological↗
PubMed1991

Structural features of the human C3 gene: intron/exon organization, transcriptional start site, and promoter region sequence.

The third component of human complement (C3) is a key molecule in the activation of the complement cascade. C3 cDNA fragments were used to identify seven cosmid clones that covered all but 1 kilobase pair (kb) of the C3 gene. The remainder of the gene was cloned by using the polymerase chain reaction. These clones were used to identify the intron/exon boundaries and to map the gene. The C3 gene is 42 kb in length and comprises 41 exons ranging in size from 52 to 213 base pairs (bp). The transcription start site was identified by primer extension, and approximately 1 kb of DNA upstream of this site was sequenced. Putative TATA and CAAT boxes were identified along with a number of regions that shared homology with known regulatory sequences. These include responsive elements for interferon-gamma, interleukin-6, nuclear factor kappa B, estrogen, glucocorticoids and thyroid hormone. Several of these agents have been shown to affect C3 synthesis and mRNA levels. The sizes of the exons in C3 were compared to those of C4 and alpha 2-macroglobulin (alpha 2M). Thirty-nine of 41 exons in C4 were found to be of similar size to the analogous ones in C3, and two-thirds of those in alpha 2M were also similarly sized, supporting the hypothesis that these genes arose from a common ancestor.

Amino Acid Sequence↗
PubMed2004

Design and photochemical characterization of a biomimetic light-driven Z/E switcher.

Protonated Schiff bases (PSBs) of polyenals constitute a class of light-driven switchers selected by biological evolution that provide model compounds for the development of artificial light-driven molecular devices or motors. In the present paper, our primary target is to show, through combined computational and experimental studies, that it is possible to approach the design of artificial PSBs suitable for such applications. Below, we use the methods of computational photochemistry to design and characterize the prototype biomimetic molecular switchers 4-cyclopenten-2'-enylidene-3,4-dihydro-2H-pyrrolinium and its 5,5'-dimethyl derivative both containing the penta-2,4-dieniminium chromophore. To find support for the predicted behavior, we also report the photochemical reaction path of the synthetically accessible compound 4-benzylidene-3,4-dihydro-2H-pyrrolinium. We show that the preparation and photochemical characterization of this compound (together with three different N-methyl derivatives) provide both support for the predicted photoisomerization mechanism and information on its sensitivity to the molecular environment.

Biomimetic Materials↗
PubMed2006

Role of electron-driven proton-transfer processes in the excited-state deactivation of the adenine-thymine base pair.

Exploratory electronic structure calculations have been performed with the CC2 (simplified singles and doubles coupled-cluster) method for two conformers of the adenine (A)-thymine (T) base pair, with emphasis on excited-state proton-transfer reactions. The Watson-Crick conformer and the most stable (in the gas-phase) conformer of the A-T base pair have been considered. The equilibrium geometries of the ground state and of the lowest excited electronic states have been determined with the MP2 (second-order Møller-Plesset) and CC2 methods, respectively. Vertical and adiabatic excitation energies, oscillator strengths, and dipole moments of the excited states are reported. Of particular relevance for the photochemistry of the A-T base pair are optically dark (1)pipi* states of charge-transfer character. Although rather high in energy at the ground-state equilibrium geometry, these states are substantially lowered in energy by the transfer of a proton, which thus neutralizes the charge separation. A remarkable difference of the energetics of the proton-transfer reaction is predicted for the two tautomers of A-T: in the Watson-Crick conformer, but not in the most stable conformer, a sequence of conical intersections connects the UV-absorbing (1)pipi* state in a barrierless manner with the electronic ground state. These conical intersections allow a very fast deactivation of the potentially reactive excited states in the Watson-Crick conformer. The results provide evidence that the specific hydrogen-bonding pattern of the Watson-Crick conformer endows this structure with a greatly enhanced photostability. This property of the Watson-Crick conformer of A-T may have been essential for the selection of this species as carrier of genetic information in early stages of the biological evolution.

Adenine↗
PubMed1997

Darwinism and ethology. The role of natural selection in animals and humans.

The role of behaviour in biological evolution is examined within the context of Darwinism. All Darwinian models are based on the distinction of two mechanisms: one that permits faithful transmission of a feature from one generation to another, and another that differentially regulates the degree of this transmission. Behaviour plays a minimal role as an agent of transmission in the greater part of the animal kingdom; by contrast, the forms it may assume strongly influence the mechanisms of selection regulating the different rates of transmission. We consider the decisive feature of the human species to be the existence of a phenotypical system of cultural coding characterized by precision and reliability which are the distinctive feature of genetic coding in animals. We examine the consequences for the application of the Darwinian model to human history.

Animals↗
PubMed1999

Cloning sulfur assimilation genes of Brassica juncea L.: cadmium differentially affects the expression of a putative low-affinity sulfate transporter and isoforms of ATP sulfurylase and APS reductase.

The heavy-metal accumulator Brassica juncea L. is a high-biomass crop able to extract heavy-metal ions from the soil, a substantial part being translocated from root to shoot. Previous work has shown that Cd accumulation is accompanied by massive formation of phytochelatins (PCs). Rapid de novo synthesis of PCs in roots and leaves requires an increased synthesis of the tripeptide glutathione (GSH), which in turn depends on increased sulfur assimilation. Therefore. we have cloned cDNAs for three enzymes involved in sulfur assimilation, i.e. a putative low-affinity sulfate transporter (LAST) and two isoforms each for ATP sulfurylase (ATPS) and APS reductase (APSR). As degradation of glucosinolates might provide an additional sulfur source under stress, we also cloned a myrosinase (MYR). RNA blot analysis of transcript amounts indicated that upon Cd exposure (25 microM) the expression of ATPS and APSR in roots and leaves of 6-week-old Brassica juncea plants was strongly increased, whereas the expression of MYR was unaffected. LAST transcripts were significantly reduced in the root but remained unchanged in the leaves. Concomitant with Cd induction of ATPS and APSR mRNAs, cysteine concentrations in roots and leaves increased by 81% and 25%, respectively, whereas GSH concentrations decreased in roots and leaves by 39% and 48%, respectively. In agreement with our previous report on Cd induction of gamma-glutamylcysteine synthetase in B. juncea, the results indicate coordinate changes of expression for several sulfur assimilation enzymes in response to an increased demand for cysteine during PC synthesis.

Amino Acid Sequence↗
PubMed2002

Co-opting colleagues: appropriating Dobzhansky's 1936 lectures at Columbia.

This paper clarifies the chronology surrounding the population geneticist Theodosius Dobzhansky's 1937 book, Genetics and the Origin of Species. Most historians assume (a) Dobzhansky's book began as a series of 'Jesup lectures,' sponsored by the Department of Zoology at Columbia University in 1936, and (b) before these lectures were given, Dobzhansky knew he would produce a volume for the Columbia Biological Series (CBS). Archival evidence forces a rejection of both assumptions. Dobzhansky's 1936 Columbia lectures were not Jesup lectures. The book he intended to write from his lectures began as a stand-alone text in evolutionary genetics; the CBS had been defunct since 1910. In May 1937 - seven months after Dobzhansky's Columbia lectures - Leslie Dunn lobbied Columbia University to revive the CBS and the Jesup lecture series. He then quietly back dated, naming Dobzhansky a Jesup lecturer and co-opting his book manuscript as the first volume in the revived CBS. A detailed chronology of this 1936-1937 period is provided. This relocates the CBS and Jesup revivals within the narrow context of zoology at Columbia University. These helped Dunn and colleagues define cutting edges and define themselves as managers and promoters of those edges.

Biological Evolution↗
PubMed2002

Recent philosophy of biology: a review.

Academia is subdivided into separate disciplines, most of which are quite discrete. In this review I trace the interactions between two of these disciplines: biology and philosophy of biology. I concentrate on those topics that have the most extensive biological content: function, species, systematics, selection, reduction and development. In the final section of this paper I touch briefly on those issues that biologists and philosophers have addressed that do not have much in the way of biological content.

Animals↗
PubMed2003

Reflecting on complexity of biological systems: Kant and beyond?

Living organisms are currently most often seen as complex dynamical systems that develop and evolve in relation to complex environments. Reflections on the meaning of the complex dynamical nature of living systems show an overwhelming multiplicity in approaches, descriptions, definitions and methodologies. Instead of sustaining an epistemic pluralism, which often functions as a philosophical armistice in which tolerance and so-called neutrality discharge proponents of the burden to clarify the sources and conditions of agreement and disagreement, this paper aims at analysing: (i) what has been Kant's original conceptualisation of living organisms as natural purposes; (ii) how the current perspectives are to be related to Kant's viewpoint; (iii) what are the main trends in current complexity thinking. One of the basic ideas is that the attention for structure and its epistemological consequences witness to a great extent of Kant's viewpoint, and that the idea of organisational stratification today constitutes a different breeding ground within which complexity issues are raised. The various approaches of complexity in biological systems are captured in terms of two different styles, universalism and (weak and strong) constructivism, between which hybrid forms exist.

Animals↗
PubMed1999

Essentialism revisited: evolutionary theory and the concept of mental disorder.

J. C. Wakefield's (1999) elaboration of his harmful dysfunction analysis (HDA) of mental disorder does little to address previous criticisms (S. O. Lilienfeld & L. Marino, 1995) and instead reveals further conceptual weaknesses in his position. The authors demonstrate that (a) a Roschian analysis can account for the results of all of Wakefield's conceptual experiments and predicts a number of judgments of disorder not predicted by the HDA, (b) the HDA is incapable in many cases of providing a scientifically nonarbitrary distinction between disorder and nondisorder, and (c) the HDA cannot account for failures of cultural ex adaptations, mismatches between evolutionary design and novel environments, or defenses against threat. The authors argue that the HDA has been convincingly falsified and discuss the failure of essentialistic concepts to resolve controversies in other domains of biological science.

Biological Evolution↗
PubMed1999

Nine variations and a coda on the theme of an evolutionary definition of dysfunction.

Nine variations on the theme of J. C. Wakefield's (1999) evolutionary definition of dysfunction show that the concept is not, as he claims, purely causal. It depends also on a teleological element of meaning introduced, in Wakefield's formulation, through an equivocation on the sense in which natural selection explains biological forms. The corollary (presented here briefly as a coda to the theme and variations) is that Wakefield's definition is not, as he also claims, value free. However, contra S. O. Lilienfeld and L. Marino (1995), this does not place diagnostic judgments of dysfunction outside the scope of science.

Biological Evolution↗
PubMed1999

The abduction of disorder in psychiatry.

The evolutionary cornerstone of J. C. Wakefield's (1999) harmful dysfunction thesis is a faulty assumption of comparability between mental and biological processes that overlooks the unique plasticity and openness of the brain's functioning design. This omission leads Wakefield to an idealized concept of natural mental functions, illusory interpretations of mental disorders as harmful dysfunctions, and exaggerated claims for the validity of his explanatory and stipulative proposals. The authors argue that there are numerous ways in which evolutionarily intact mental and psychological processes, combined with striking discontinuities within and between evolutionary and contemporary social/cultural environments, may cause nondysfunction variants of many widely accepted major mental disorders. These examples undermine many of Wakefield's arguments for adopting a harmful dysfunction concept of mental disorder.

Biological Evolution↗