1,141,019 research outputs found
Competition-driven evolution of organismal complexity
Non-uniform rates of morphological evolution and evolutionary increases in
organismal complexity, captured in metaphors like "adaptive zones", "punctuated
equilibrium" and "blunderbuss patterns", require more elaborate explanations
than a simple gradual accumulation of mutations. Here we argue that non-uniform
evolutionary increases in phenotypic complexity can be caused by a
threshold-like response to growing ecological pressures resulting from
evolutionary diversification at a given level of complexity. Acquisition of a
new phenotypic feature allows an evolving species to escape this pressure but
can typically be expected to carry significant physiological costs. Therefore,
the ecological pressure should exceed a certain level to make such an
acquisition evolutionarily successful. We present a detailed quantitative
description of this process using a microevolutionary competition model as an
example. The model exhibits sequential increases in phenotypic complexity
driven by diversification at existing levels of complexity and the resulting
increase in competitive pressure, which can push an evolving species over the
barrier of physiological costs of new phenotypic features.Comment: Open PDF with Acrobat to see movies, 22 pages, 9 figure
On the first k moments of the random count of a pattern in a multi-states sequence generated by a Markov source
In this paper, we develop an explicit formula allowing to compute the first k
moments of the random count of a pattern in a multi-states sequence generated
by a Markov source. We derive efficient algorithms allowing to deal both with
low or high complexity patterns and either homogeneous or heterogenous Markov
models. We then apply these results to the distribution of DNA patterns in
genomic sequences where we show that moment-based developments (namely:
Edgeworth's expansion and Gram-Charlier type B series) allow to improve the
reliability of common asymptotic approximations like Gaussian or Poisson
approximations
Computational Complexity and Sour-Grapes-Like Patterns
In this paper, we claim that attested sour-grapes-like patterns of featural and tonal spreading differ meaningfully from what we call the 'true' sour grapes spreading pathology. We propose that the 'false' sour grapes processes attested in some tonal systems are computationally less complex than the unattested true sour grapes pathology, due to the presence of what we refer to as 'zones of predictability' local to potential triggers of spreading. In particular, the false sour grapes spreading patterns can be shown to fall into the class of weakly deterministic mappings, while the true sour grapes spreading pattern does not
Unusual synchronization phenomena during electrodissolution of silicon: the role of nonlinear global coupling
The photoelectrodissolution of n-type silicon constitutes a convenient model
system to study the nonlinear dynamics of oscillatory media. On the silicon
surface, a silicon oxide layer forms. In the lateral direction, the thickness
of this layer is not uniform. Rather, several spatio-temporal patterns in the
oxide layer emerge spontaneously, ranging from cluster patterns and turbulence
to quite peculiar dynamics like chimera states. Introducing a nonlinear global
coupling in the complex Ginzburg-Landau equation allows us to identify this
nonlinear coupling as the essential ingredient to describe the patterns found
in the experiments. The nonlinear global coupling is designed in such a way, as
to capture an important, experimentally observed feature: the spatially
averaged oxide-layer thickness shows nearly harmonic oscillations. Simulations
of the modified complex Ginzburg-Landau equation capture the experimental
dynamics very well.Comment: To appear as a chapter in "Engineering of Chemical Complexity II"
(eds. A.S. Mikhailov and G.Ertl) at World Scientific in Singapor
Sensitive and Precise Quantification of Insulin-Like mRNA Expression in Caenorhabditis elegans
Insulin-like signaling regulates developmental arrest, stress resistance and lifespan in the nematode Caenorhabditis elegans. However, the genome encodes 40 insulin-like peptides, and the regulation and function of individual peptides is largely uncharacterized. We used the nCounter platform to measure mRNA expression of all 40 insulin-like peptides as well as the insulin-like receptor daf-2, its transcriptional effector daf-16, and the daf-16 target gene sod-3. We validated the platform using 53 RNA samples previously characterized by high density oligonucleotide microarray analysis. For this set of genes and the standard nCounter protocol, sensitivity and precision were comparable between the two platforms. We optimized conditions of the nCounter assay by varying the mass of total RNA used for hybridization, thereby increasing sensitivity up to 50-fold and reducing the median coefficient of variation as much as 4-fold. We used deletion mutants to demonstrate specificity of the assay, and we used optimized conditions to assay insulin-like gene expression throughout the C. elegans life cycle. We detected expression for nearly all insulin-like genes and find that they are expressed in a variety of distinct patterns suggesting complexity of regulation and specificity of function. We identified insulin-like genes that are specifically expressed during developmental arrest, larval development, adulthood and embryogenesis. These results demonstrate that the nCounter platform provides a powerful approach to analyzing insulin-like gene expression dynamics, and they suggest hypotheses about the function of individual insulin-like genes
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