1,721,008 research outputs found
Evolutionary consequences of growth-from plasticity in a red seaweed.
Full text linkEvolutionary processes in any population depend upon patterns of phenotypic variation available to selection and their underlying heritability. In this thesis, I used the filamentous red seaweed Asparagopsis armata, with particular focus on its modularity, to test several key questions underlying its growth-form evolution in heterogeneous environments. I established that experimental manipulations of light quantity and quality mimicking variation in underwater light due to shading or depth induce growthform plasticity in A. armata that may be evolutionarily significant given its variability among clones. Current patterns of plasticity displayed by A. armata appear adaptive, moreover, given that a reciprocal transplant of phenotypes between light environments found densely-branched (phalanx-like) phenotypes to have higher relative growth rates than sparsely-branched (guerrilla-like) phenotypes in well-lit patches, but lower relative growth rates than the latter in shaded patches. Using the capacity for rapid growth as a proxy for fitness, multivariate selection analyses identified environment-dependent patterns of directional selection on single traits coupled with linear and nonlinear selection on multi-trait combinations that shape growth-form variation within patches of differing light intensity, thereby reinforcing plasticity across light environments. Quantitative genetic analyses, however, suggest that the modular iteration of genes in morphogenesis may limit further growth-form evolution in A. armata populations exposed to spatial heterogeneity in light by constraining thallus responses to environment-dependent selection. Last, heritable responses to artificial selection on growth-form variation among clonal cell-lineages revealed the surprising capacity for A.armata to circumvent genetic constraints inherent to its development by adapting to environmental change in the absence of sexually-generated variance among clones
Environmental effects on genetic variance are likely to constrain adaptation in novel environments
Full text linkLay Summary: The potential for populations to adapt rapidly to new environments will depend on the amount of genetic variation in multiple traits that make up a multidimensional phenotype. If traits are tightly correlated at the genetic level, then selection will change all traits together and adaptation will be forced into directions determined by the genetic architecture of the traits. However, genotypes can produce different phenotypes in different environments, known as plasticity. If genotypes vary in their responses to the environment, then plasticity in a novel environment could determine how much genetic variation lies in the direction of selection, and therefore the potential for rapid adaptation. We focus on two closely related sister species of Sicilian daisy (Senecio) that are native to low and high elevations on Mt. Etna. We generated and then reciprocally planted seeds of both species at four elevations on Mt. Etna, including their native habitats and two intermediate elevations. We tested how genetic variation in ecologically important leaf traits changed across elevations, and whether such changes should help or hinder rapid adaptation at the edge of species’ native ranges, and in novel environments beyond their existing ranges. We found that genetic variance in leaf traits changed less between species than across elevations. Genetic variance in the high-elevation species changed most across elevations, which occurred in ways that would be likely to prevent adaptation to low elevations and, by extension, the warmer conditions being created by climate change. Genetic variance in the low-elevation species changed least across elevations and showed more potential to aid adaptation to high-elevation habitats. Together, our results show that two sister species vary in their phenotypic and genotypic responses to the environment, which suggests that closely related species can differ greatly in their potential to persist and then adapt to novel environments
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Data from: Faster isn't always better: selection on growth rate fluctuates across the life history and environments
No full textGrowth rate is increasingly recognised as a key life-history trait that may affect fitness directly, rather than evolving as a by-product of selection on size or age. An ongoing challenge is to explain the abundant levels of phenotypic and genetic variation in growth rates often seen in natural populations, despite what is expected to be consistently strong selection on this trait. Such a paradox suggests limits to how contemporary growth rates evolve. We explored limits arising from variation in selection, based on selection differentials for age-specific growth rates expressed under different ecological conditions. We present results from a field experiment that measured growth rates and reproductive output in wild individuals of a colonial marine invertebrate (Hippopodina iririkiensis), replicated within and across the natural range of succession in its local community. Colony growth rates varied phenotypically throughout this range, but not all such variation was available for selection, nor was it always targeted by selection as expected. While the maintenance of both phenotypic and genetic variation in growth rate is often attributed to costs of growing rapidly, our study highlights the potential for fluctuating selection pressures throughout the life history and across environments to play an important role in this process
Data from: Unravelling anisogamy: egg size and ejaculate size mediate selection on morphology in free-swimming sperm
No full textGamete dimorphism (anisogamy) defines the sexes in most multicellular organisms. Theoretical explanations for its maintenance usually emphasize the size-related selection pressures of sperm competition and zygote survival, assuming that fertilization of all eggs precludes selection for phenotypes that enhance fertility. In external fertilizers, however, fertilization is often incomplete due to sperm limitation, and the risk of polyspermy weakens the advantage of high sperm numbers that is predicted to limit sperm size, allowing alternative selection pressures to target free-swimming sperm. We asked whether egg size and ejaculate size mediate selection on the free-swimming sperm of Galeolaria caespitosa, a marine tubeworm with external fertilization, by comparing relationships between sperm morphology and male fertility across manipulations of egg size and sperm density. Our results suggest that selection pressures exerted by these factors may aid the maintenance of anisogamy in external fertilizers by limiting the adaptive value of larger sperm in the absence of competition. In doing so, our study offers a more complete explanation for the stability of anisogamy across the range of sperm environments typical of this mating system and identifies new potential for the sexes to coevolve via mutual selection pressures exerted by gametes at fertilization
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
Faster is not always better: selection on growth rate fluctuates across life history and environments
Full text linkGrowth rate is increasingly recognized as a key life-history trait that may affect fitness directly rather than evolve as a by-product of selection on size or age. An ongoing challenge is to explain the abundant levels of phenotypic and genetic variation in growth rates often seen in natural populations, despite what is expected to be consistently strong selection on this trait. Such a paradox suggests limits to how contemporary growth rates evolve. We explored limits arising from variation in selection, based on selection differentials for age-specific growth rates expressed under different ecological conditions. We present results from a field experiment that measured growth rates and reproductive output in wild individuals of a colonial marine invertebrate (Hippopodina iririkiensis), replicated within and across the natural range of succession in its local community. Colony growth rates varied phenotypically throughout this range, but not all such variation was available for selection, nor was it always targeted by selection as expected. While the maintenance of both phenotypic and genetic variation in growth rate is often attributed to costs of growing rapidly, our study highlights the potential for fluctuating selection pressures throughout the life history and across environments to play an important role in this process
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