The life history response of a clone of Daphnia pulex to nine concentrations of a defined food supply is described and combined with an energy analysis. Three features of this clone were essentially invariant with respect to food level: the length–mass regression, the durations of instars, and the size—specific fractions of net energy intake invested in reproduction. The main response to food limitation was a reduction in size—specific net energy intake and in egg size. Simple mathematical functions are fit to the data on these relationships and combined to produce a model that reconstructs the age—specific patterns of growth and reproduction quite accurately. The energy cost of molting is shown to be a major constraint on the evolution of body size in Daphnia.
Summary By application of the neutral model of phenotypic evolution, quantitative estimates of the rate of input of genetic variance by polygenic mutation can be extracted from divergence experiments as well as from the response of an inbred base population to selection. The analytical methods are illustrated through a survey of data on a diversity of organisms including Drosophila, Tribolium , mice, and several crop species. The mutational rate of introduction of genetic variance ( V m ) scaled by the environmental variance ( V E ) is shown to vary between populations, species, and characters with a range of approximately 10 −4 to 5 × 10 −2 . V m / V E for Drosophila viability is somewhat below this range, while hybrid dysgenesis may temporarily inflate V m / V E beyond 10 −1 . Potential sources of bias and error in the estimation of V m are discussed, as are the practical implications of the observed limits to V m / V E for projecting the long-term response to selection and for testing adaptational hypotheses.
Accounting for income tax is an important and complex area for financial accounting purposes, and it has recently become important for income tax purposes as well. The newly released Schedule UTP (i.e., uncertain tax positions) reflects the heightened interest that the Internal Revenue Service has in taxpayers' financial accounting for income tax. n1 Accounting for income tax is even important to individual taxpayers who do not prepare financial statements.
Abstract Enormous phylogenetic variation exists in the number and sizes of introns in protein‐coding genes. Although some consideration has been given to the underlying role of the population‐genetic environment in defining such patterns, the influence of the intracellular environment remains virtually unexplored. Drawing from observations on interactions between co‐transcriptional processes involved in splicing and mRNA 3′‐end formation, a mechanistic model is proposed for splice‐site recognition that challenges the commonly accepted intron‐ and exon‐definition models. Under the suggested model, splicing factors that outcompete 3′‐end processing factors for access to intronic binding sites concurrently favor the recruitment of 3′‐end processing factors at the pre‐mRNA tail. This hypothesis sheds new light on observations such as the intron‐mediated enhancement of gene expression and the negative correlation between intron length and levels of gene expression.
Cyclical parthenogens are a valuable system in which to empirically test theoretical predictions as to the genetic consequences of sexual reproduction in natural populations, particularly if the frequency of sexual relative to asexual reproduction can be quantified. In this study, we used a series of lake populations of the cyclical parthenogen, Daphnia pulicaria, that vary consistently in their investment in sexual reproduction, to address the questions of whether the ecological variation in investment in sex is detectable at the genetic level, and if so, whether the genetic patterns seen are consistent with theoretical predictions. We show that there is variation in the genetic structure of these populations in a manner consistent with their investment in sexual reproduction. Populations engaging in a high frequency of sex were in Hardy-Weinberg and gametic phase equilibrium, and showed little genotypic differentiation across sampled years. In contrast, populations with a lower frequency of sex deviated widely from equilibrium, had reduced multilocus clonal diversity, and showed significant temporal genotypic deviation.
DNA-fingerprint similarity is being used increasingly to make inferences about levels of genetic variation within and between natural populations. It is shown that the similarity index--the average fraction of shared restriction fragments--provides upwardly biased estimates of population homozygosity but nearly unbiased estimates of the average identity-in-state for random pairs of individuals. A method is suggested for partitioning the DNA-fingerprint dissimilarity into within- and between-population components. Some simple expressions are given for the sampling variances of these estimators.
Significance Owing to internal homeostatic mechanisms, cellular traits may experience long periods of stable selective pressures. Nonetheless, drift and mutation still conspire to generate significant variation in mean phenotypes among phylogenetic lineages. Provided there are classes of mutations with sufficiently small effects, even in the face of constant selection, variation in genetic effective population sizes will result in gradients of mean phenotypes with respect to organism size across the tree of life. Mutation is an important determinant of such patterns, even in the absence of directional bias. Thus, a substantial amount of variation in cellular features may be a simple consequence of lineage-specific differences in the power of drift rather than a reflection of adaptive divergence.
Although observations from biochemistry and cell biology seemingly illustrate hundreds of examples of exquisite molecular adaptations, the fact that experimental manipulation can often result in improvements in cellular infrastructure raises the question as to what ultimately limits the level of molecular perfection achievable by natural selection. Here, it is argued that random genetic drift can impose a strong barrier to the advancement of molecular refinements by adaptive processes. Moreover, although substantial improvements in fitness may sometimes be accomplished via the emergence of novel cellular features that improve on previously established mechanisms, such advances are expected to often be transient, with overall fitness eventually returning to the level before incorporation of the genetic novelty. As a consequence of such changes, increased molecular/cellular complexity can arise by Darwinian processes, while yielding no long-term increase in adaptation and imposing increased energetic and mutational costs.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAnalysis of Structural Characteristics of Chemical Compounds in the Common Data BaseG. W. Adamson, S. E. Creasey, and M. F. LynchCite this: J. Chem. Doc. 1973, 13, 3, 158–162Publication Date (Print):August 1, 1973Publication History Published online1 May 2002Published inissue 1 August 1973https://pubs.acs.org/doi/10.1021/c160050a014https://doi.org/10.1021/c160050a014research-articleACS PublicationsRequest reuse permissionsArticle Views49Altmetric-Citations4LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
The neutral model of phenotypic evolution has yielded several simple predictions about the long-term rates of between-population divergence of polygenic traits and about the equilibrium level of within-population variance when mutation and random genetic drift are the sole evolutionary forces. These conclusions must be modified if populations are only partially isolated. A quantitative model is presented for the development of within- and between-population variance for neutral quantitative characters in pairs of populations with arbitrary effective sizes and migration rates. Both the variance in the base population and subsequent variance generated by mutation are considered, and several dynamical and equilibrium properties are shown to be adequately described by simple approximations. The resultant formulations provide some insight into the sensitivity of measures of morphological distance to gene flow, the necessity of isolation for the accumulation of variation between incipient species, and the consequences of gene flow into captive populations of endangered species.
ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTCompression of Wiswesser Line Notations Using Variety GenerationDavid Cooper and Michael F. LynchCite this: J. Chem. Inf. Comput. Sci. 1979, 19, 3, 165–169Publication Date (Print):August 1, 1979Publication History Published online1 May 2002Published inissue 1 August 1979https://pubs.acs.org/doi/10.1021/ci60019a011https://doi.org/10.1021/ci60019a011research-articleACS PublicationsRequest reuse permissionsArticle Views16Altmetric-Citations7LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InRedditEmail Other access options Get e-Alerts
Many proteins assemble into homomultimeric structures, with a number of subunits that can vary substantially among phylogenetic lineages. As protein-protein interactions require productive encounters among subunits, such variation might partially be explained by variation in cellular protein abundance. Protein abundance in turn depends on the intrinsic rates of production and decay of mRNA and protein molecules, as well as rates of cell growth and division. Using a stochastic framework for prediction of the multimeric state of a protein as a function of these processes and the free energy associated with interface-interface binding, we demonstrate agreement with a wide class of proteins using <i>E. coli</i> proteome data. As such, this platform, which links protein quaternary structure with biochemical rates governing gene expression, protein association and dissociation, and cell growth and division, can be extended to evolutionary models for the emergence and diversification of multimers. While it is tempting to think of multimerization as adaptive, the diversity of multimeric states raises the question of its functional role and impact on fitness. As a force driving selection, we consider the possible increase in enzymatic activity of proteins arising strictly as a consequence of interface-interface binding-namely, enhanced stability to degradation, substrate binding affinity, or catalytic rate of multimers with respect to monomers without invoking further conformational changes, as in allostery. For fixed cost of protein production, we find a benefit conferred by multimers that is dependent on context and can therefore become different in diverging lineages.
SUMMARY A multistate outbreak of Escherichia coli O157:H7 infections occurred in the USA in November–December 2006 in patrons of restaurant chain A. We identified 77 cases with chain A exposure in four states – Delaware, New Jersey, New York, and Pennsylvania. Fifty-one (66%) patients were hospitalized, and seven (9%) developed haemolytic uraemic syndrome; none died. In a matched analysis controlling for age in 31 cases and 55 controls, illness was associated with consumption of shredded iceberg lettuce [matched odds ratio (mOR) 8·0, 95% confidence interval (CI) 1·1–348·1] and shredded cheddar cheese (mOR 6·2, CI 1·7–33·7). Lettuce, an uncooked ingredient, was more commonly consumed (97% of patients) than cheddar cheese (84%) and a single source supplied all affected restaurants. A single source of cheese could not explain the regional distribution of outbreak cases. The outbreak highlights challenges in conducting rapid multistate investigations and the importance of incorporating epidemiological study results with other investigative findings.
