Brian K Hall

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  Available from: Brian K Hall

  Article: A review of Variation: A Central Concept in Biology, edited by

  B Hallgrímsson, B K Hall, Michael J Wade
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  ABSTRACT: Variation: A Central Concept in Biology. B. Hallgrısson and B. K. Hall, 2005, Elsevier Academic Press, New York. 592 pp. ISBN: 0-12-088777-0. Heritable phenotypic variation is essential for evolution by natural selection, limiting both its rate and scope. It is gen-erated by the more or less poorly understood intersection of genes, developmental processes, and the environment. It is not surprising that the features of such a central concept, includ-ing its production, regulation and measurement, remain cur-rent topics of research. This volume is focused on the pro-cesses that generate and constrain phenotypic variation and thereby affect evolution. The majority of the 22 chapters discuss aspects of the creation and regulation of individual variation during development, especially in the face of envi-ronmental stress. The combination of environmental stress, developmental regulation, and phenotypic variation naturally leads many authors to interesting and usefully nuanced dis-cussions of concepts such as ''evolvability,'' ''phenotypic buffering,'' ''modularity,'' ''plasticity,'' and ''canalization.'' Whether these features evolve as by-products or are them-selves adaptations is not resolved, but directions for future research and prescriptions for robust methods are clearly laid out, making this a valuable volume, especially for students planning doctoral research. It is also an excellent volume for discussions of the role of developmental and epigenetic var-iation in evolution. The book is loosely organized into four sections: history, analysis and measurement, developmental origins, and envi-ronmental context. I will mention some of the highlights for me. Bowler's informative history chapter traces the competing views of heredity and variation from Darwin to the Modern Synthesis. This is followed by Van Valen's extremely useful and timely review of statistical methods on the estimation and comparison of univariate and multivariate variation. This chapter is the best summary I have read on this topic. The chapter by Jones and German emphasizes the hierarchical measurement of variation within individuals across a series of developmental stages, among individuals, and among groups and illustrates the analysis with an instructive case study. They show how to reduce a series of measurements taken on a single individual during development to a much smaller number of model parameters by curve fitting to an a priori model of growth and subsequently analyzing variation in the estimated parameters. The possible connection between the developmental buff-ering or canalization of environmental influences on the in-dividual and the genetic response of the population is taken up by Larsen as well as by other chapter authors. He argues for an internalist view of variation wherein phenotypic var-iation, emerging from developmental processes, precedes and is later ''captured by'' genetic changes. Thus, phenotypes occur before the genetic variations that stabilize them, an apparent reversal of the genes first approach of formal evolutionary genetic theory. This is the epigenetic argument that, because some genes, e.g., chaperones like Hsp90, sup-press genetic variation at other genes, the suppressors have not only been selected for this property but also for their property of ''releasing'' hidden variation when needed by the population to meet environmental changes. That is, they are not only ''canalization genes'' but also ''evolutionary capac-itor genes.'' If development is noisy, should the level of noise itself be considered an adaptation? Hoffmann and Mckenzie take up these same or at least very similar questions in a later chapter from a more traditional evolutionary viewpoint. These questions and the different views on them are addressed critically and synthetically in the chapter by Dworkin, which in my opinion is one of the best in the book. He combines
  02/2013; 83:318-319.
• Article: Charles Darwin, embryology, evolution and skeletal plasticity

  B. K. Hall
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  ABSTRACT: Darwin provided us with the theory of evolutionary change through natural selection. Just as important to the science of biology was Darwin’s recognition that all organisms could be classified and were related to one another because they arose from a single common universal ancestor – what we know as the universal tree of life (UtoL). All the features of the skeletal biology of fish therefore can be explained, both in an evolutionary framework (ultimate causation) and in the framework of development, growth and physiology (proximate causation). Neither approach is complete without the other. I will outline the elements of Darwin’s theories on evolution and classification and, as importantly, discuss what was missing from Darwin’s theories. An important class of evidence for evolution used by Darwin came from embryology, both comparative embryology and the existence of vestiges and atavisms. After discussing this evidence I examine some fundamental features of skeletal development and evolution These include: the presence of four skeletal systems in all vertebrates; the existence of two skeletons, one based on cartilage, the other on bone and dentine; the modular nature of skeletal development and evolution; and the plasticity of the skeleton in response to either genetic or environmental changes.
  Journal of Applied Ichthyology 04/2010; 26(2):148 - 151. · 0.87 Impact Factor
• Article: A practical approach for the identification of the many cartilaginous tissues in teleost fish

  P. E. Witten, A. Huysseune, B. K. Hall
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  ABSTRACT: SummaryA classification of teleostean cartilages is essentially an impossible task because of an intergrading of tissues along an almost continuous spectrum of skeletal tissue types. Teleost fish display a spectrum that ranges from cartilage-like connective tissue to bone-like cartilage. In addition, many teleost cartilages cannot be equated with mammalian hyaline cartilage. Existing classifications of teleost cartilage are often disregarded due to the necessarily cumbersome terminology that is used to describe the astounding array of tissue types, a neglect that hampers enhancing our knowledge of the origin and function of teleost cartilage.
  Journal of Applied Ichthyology 03/2010; 26(2):257 - 262. · 0.87 Impact Factor
• Article: Epithelial behaviors and threshold effects in the development and evolution of internal and external cheek pouches in rodents

  P. Brylski, B. K. Hall
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  ABSTRACT: The internal and external cheek pouches found in certain rodents arise early in development by an evagination of the buccal epithelium. Differences in the epithelial evaginations that produce the internal pouches of the Syrian hamster (Mesocricetus auratus) and least chipmunk (Eutamias minimus) are consistent with the view that they evolved independently. The external cheek pouches of rodents of the superfamily Geomyoidea represent a macroevolutionary phenotype when compared to the internal pouches of other rodents. Externalization of an internal pouch rudiment found in the geomyoids Dipodomys and Thomomys can be explained by a simple change early in its development, the effect of which is greatly magnified by facial growth. In this example, the traditional dichotomy between microevolutonary and macroevolutionary theories is bridged by an understunding of developmental dynamics.
  Journal of Zoological Systematics and Evolutionary Research 04/2009; 26(2):144 - 154. · 1.95 Impact Factor
• Article: Bone resorption and bone remodelling in juvenile carp, Cyprinus carpio L.

  P. E. Witten, W. Villwock, N. Peters, B. K. Hall
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  ABSTRACT: The present study considers the important role of bone resorption for bone growth in general, and aims to clarify if and how bone resorption contributes to the skeletal development of carp, Cyprinus carpio L., a teleost species with ‘normal’ osteocyte-containing (cellular) bone. To ensure the identification of osteoclasts and sites of bone resorption independently from the morphology of the bony cells, bones were studied by histological procedures, and by demonstration of the enzymes which serve as osteoclast markers, viz. tartrate resistant acid phosphatase (TRAP), ATPase and a vacuolar proton pump. Two types of bone-resorbing cells were observed in juvenile carp: (1) multinucleated giant cells displaying morphological and biochemical attributes which are known from mammalian osteoclasts; and (b) flat cells which lack a visible ruffled border and for which identification requires the performance of enzyme histochemical procedures. Bone resorption performed by osteoclasts mainly occurs at endosteal bone surfaces. To a lesser extent, bone resorption also takes place at periosteal bone surfaces, but without an apparent connection to bone growth. The latter observation, and the occurrence of bone remodelling, suggest that the endoskeleton of juvenile carp might be involved in mineral metabolism. Morphological differences and biochemical similarities to bone resorption in teleosts with acellular bone are discussed.
  Journal of Applied Ichthyology 07/2008; 16(6):254 - 261. · 0.87 Impact Factor