Ancient

Distribution by Scientific Domains
Distribution within Life Sciences

Terms modified by Ancient

  • ancient china
  • ancient dna
  • ancient egypt
  • ancient greece
  • ancient greek
  • ancient history
  • ancient israel
  • ancient lineage
  • ancient near east
  • ancient origin
  • ancient population
  • ancient rome
  • ancient site
  • ancient society
  • ancient time
  • ancient world

  • Selected Abstracts


    CROSSING RELATIONSHIPS AMONG ANCIENT AND EXPERIMENTAL SUNFLOWER HYBRID LINEAGES

    EVOLUTION, Issue 3 2000
    Loren H. Rieseberg
    Abstract., Reproductive barrier formation between newly derived hybrid taxa and their parental species represents a major evolutionary hurdle. Here, I examine the development of a sterility barrier during hybrid speciation by examining the fertility of progeny from all combinations of crosses involving three experimentally synthesized sunflower hybrid lineages, their natural hybrid counterpart, Helianthus anomalus, and their parents, H. annuus and H. petiolaris. Crosses between the parental species and H. anomalus generated almost completely sterile offspring (pollen viability < 5%; seed set < 1%). A fairly strong sterility barrier also has developed between three hybrid lineages and both parental species (pollen viability 11.1,41.6%; seed set 0.84,20.1%). In contrast, the three hybrid lineages are almost fully interfertile (pollen viabilities 83.1,88.6%; seed set 72.1,75.3%), as predicted by molecular mapping studies that indicate they have converged on a similar set of gene combinations and chromosomal rearrangements. A modest decline in compability is observed in crosses between the three hybrid lineages and H. anomalus (pollen viabilities 64.1,70.7%; seed set 37,43%), a result that agrees well with prior data demonstrating significant congruence between the genomes of the natural and experimental hybrid lineages. These observations not only indicate that reproductive isolation can arise as a by-product of fertility selection in hybrid populations, but also testify to the repeatability of this mode of speciation. [source]


    Metagenomic and stable isotopic analyses of modern freshwater microbialites in Cuatro Ciénegas, Mexico

    ENVIRONMENTAL MICROBIOLOGY, Issue 1 2009
    Mya Breitbart
    Summary Ancient biologically mediated sedimentary carbonate deposits, including stromatolites and other microbialites, provide insight into environmental conditions on early Earth. The primary limitation to interpreting these records is our lack of understanding regarding microbial processes and the preservation of geochemical signatures in contemporary microbialite systems. Using a combination of metagenomic sequencing and isotopic analyses, this study describes the identity, metabolic potential and chemical processes of microbial communities from living microbialites from Cuatro Ciénegas, Mexico. Metagenomic sequencing revealed a diverse, redox-dependent microbial community associated with the microbialites. The microbialite community is distinct from other marine and freshwater microbial communities, and demonstrates extensive environmental adaptation. The microbialite metagenomes contain a large number of genes involved in the production of exopolymeric substances and the formation of biofilms, creating a complex, spatially structured environment. In addition to the spatial complexity of the biofilm, microbial activity is tightly controlled by sensory and regulatory systems, which allow for coordination of autotrophic and heterotrophic processes. Isotopic measurements of the intracrystalline organic matter demonstrate the importance of heterotrophic respiration of photoautotrophic biomass in the precipitation of calcium carbonate. The genomic and stable isotopic data presented here significantly enhance our evolving knowledge of contemporary biomineralization processes, and are directly applicable to studies of ancient microbialites. [source]


    Theologizing the Human Jesus: An Ancient (and Modern) Approach to Christology Reassessed

    INTERNATIONAL JOURNAL OF SYSTEMATIC THEOLOGY, Issue 2 2001
    Ivor Davidson
    Many contemporary Christologies, while paying lip-service to the primacy of the human Jesus, devote little attention to the theological status of his humanity. They may be deflected from this task by such factors as preference for experienced-based symbol; the fragmentation of biblical studies and dogmatics; the imperatives of contextual hermeneutics; and the preoccupation with methodology rather than substance. But the human Jesus is only theologically meaningful when viewed on a larger canvas than that of either idealist metaphysics or historical reconstruction. The classical doctrines of the anhypostasis and enhypostasis of Jesus' humanity offer a still useful way of highlighting the primacy of grace, and, contrary to common caricature, do not undermine the density of his human experience. Such an account needs to be supplemented, however, with a robust pneumatology in order to specify the relevance of the human Jesus for revelation, salvation, anthropology, ethics and eschatology. [source]


    Eschatology After Nietzsche: Apollonian, Dionysian or Pauline?

    INTERNATIONAL JOURNAL OF SYSTEMATIC THEOLOGY, Issue 1 2000
    Michael Horton
    Ancient and (post)modern versions of the Greek two-world metaphysics , in both its Platonic (Apollonian) and Hegelian (Dionysian) variations , are explored and contrasted with the Pauline two-age eschatology. This eschatology is shown to be further removed from and more subversive of the metaphysical and epistemological dualisms of modernity than is postmodernism. Reformed federal theology and its biblical theology movement provide a resource for the recovery of the christological and eschatological tension in Pauline theology, enabling Christian theology to reintegrate revelation within the history of redemption and to articulate an eschatology of the pilgrim community. [source]


    Heads of State: Icons, Power, and Politics in the Ancient and Modern Andes.

    JOURNAL OF LATIN AMERICAN & CARIBBEAN ANTHROPOLOGY, Issue 1 2010
    By Denise Y. Arnold, Christine A. Hastorf
    No abstract is available for this article. [source]


    Ancient conserved domain protein-1 binds copper and modifies its retention in cells

    JOURNAL OF NEUROCHEMISTRY, Issue 1 2007
    Alexandra Alderton
    Abstract The ancient conserved domain protein (ACDP) family are a recently identified group of homologous mammalian proteins. Some family members have been suggested to have roles in the metabolism of metals. We investigated the capacity of ACDP-1 to bind metals. Using immobilised metal affinity chromatography and isothermal titration calorimetry we determined that ACDP-1 is a high affinity copper binding protein able to bind copper at nanomolar concentrations. In addition the promoter of ACDP-1 contains metal response elements and the cellular expression of ACDP-1 alters cellular retention of copper. However, cellular expression of ACDP-1 does not alter cellular resistance to the toxicity of copper or other metals. As our findings place the subcellular localisation of ACDP-1 in the cytoplasm it is possible that ACDP-1 represent a novel copper chaperone or storage protein. [source]


    Heads of State: Icons, Power, and Politics in the Ancient and Modern Andes by Denise Y. Arnold and Christine A. Hastorf

    AMERICAN ANTHROPOLOGIST, Issue 3 2009
    JOHN W. VERANO
    No abstract is available for this article. [source]


    Technical note: Terahertz imaging of ancient mummies and bone

    AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY, Issue 3 2010
    Lena Öhrström
    Abstract Ancient mummified soft-tissues are a unique source to study the evolution of disease. Diagnostic imaging of such historic tissues is of foremost interest in paleoanthropology or paleopathology, with conventional x-ray and computed tomography (CT) being the gold-standard. Longer wavelength radiation in the far-infrared or Terahertz region allows diagnostic close-to-surface tissue differentiation of bone morphology while being harmless to human cells. The aim of this study is to show the feasibility and the morpho-diagnostic impact of THz imaging of historic remains. Images of an artificially embalmed ancient Egyptian human mummy hand, an artificially embalmed ancient Egyptian mummified fish and a macerated human lumbar vertebra were obtained by THz-pulse imaging and compared with conventional X-ray and CT images. Although conventional x-ray imaging provides higher spatial resolution, we found that THz-imaging is well-suited for the investigation of ancient mummified soft tissue and embalming-related substances / wrappings. In particular, bone and cartilaginous structures can be well differentiated from surrounding soft-tissues and bandage-wrappings by THz imaging. Furthermore, THz-pulse imaging also measures the time-delay of the pulsed signal when passing through the sample, which provides supplementary information on the optical density of the sample that is not obtained by X-ray and CT. Terahertz radiation provides a completely non-invasive diagnostic imaging modality for historic dry specimens. We anticipate this modality also to be used for detection of hidden objects in historic samples such as funerary amulets still in situ in wrapped mummies, as well as potentially for the identification of spectral signatures from chemical substances, e.g., in embalming essences.. Am J Phys Anthropol, 2010. © 2010 Wiley-Liss, Inc. [source]


    Trustworthiness: Ancient and Modern

    THE POLITICAL QUARTERLY, Issue 3 2008
    JEAN SEATON
    No abstract is available for this article. [source]


    RELATIONSHIP BETWEEN THE COLORATION AND THE FIRING TECHNOLOGY USED TO PRODUCE SUSA GLAZED CERAMICS OF THE END OF THE NEOLITHIC PERIOD*

    ARCHAEOMETRY, Issue 5 2009
    S. LAHLIL
    Ancient decorated potteries from Susa (Mesopotamia) dating from 4200 to 3700 bc, were studied in order to determine the origin and the nature of the raw materials used, and to identify the technological processes applied to make the ceramic bodies and their decorations. Bulk compositions were determined by particle induced X-ray emission (PIXE), while the microstructure and the mineralogical phases were studied using scanning electron microscopy (SEM), energy dispersive X-ray analyses (EDX) and X-ray powder diffraction (XRD). The results showed that the raw materials used to elaborate these potteries were similar for all the ceramic bodies (carbonates and iron and magnesium-rich clays containing sand), and for all the decorations (iron oxides, silica, potassic and alumina sources). The variations of coloration of the ceramics and of their decorations were due to different firing temperatures. The ranges of firing temperatures used by potters were evaluated on the basis of mineral stability domains. [source]


    Somatic Styles of the Early Middle Ages

    GENDER & HISTORY, Issue 3 2008
    Lynda L. Coon
    ,Somatic Styles' examines how classical modes of gender played significant roles in carving out competitive arenas between clerical and lay elites, c.600,900 CE. The paper explores the hermeneutical obstacles standing between the contemporary theorist of gender and the complex nature of the early medieval texts under scrutiny. The analysis reconstructs classicising techniques of gender deployed by early medieval churchmen, and it does so in a way that both challenges the stranglehold of the ,one-sex' model on pre-modern understandings of gender and heals the ,rupture' between the ,Ancient' and the ,Dark Age'. Finally, the essay maps early medieval somatic and gendered styles onto an architectural space where lay and consecrated bodies met , a ninth-century monastic basilica. [source]


    The birth and postnatal development of purinergic signalling

    ACTA PHYSIOLOGICA, Issue 2 2010
    G. Burnstock
    Abstract The purinergic signalling system is one of the most ancient and arguably the most widespread intercellular signalling system in living tissues. In this review we present a detailed account of the early developments and current status of purinergic signalling. We summarize the current knowledge on purinoceptors, their distribution and role in signal transduction in various tissues in physiological and pathophysiological conditions. [source]


    Downstream from calcium signalling: mitochondria, vacuoles and pancreatic acinar cell damage

    ACTA PHYSIOLOGICA, Issue 1 2009
    S. Voronina
    Abstract Ca2+ is one of the most ancient and ubiquitous second messengers. Highly polarized pancreatic acinar cells serve as an important cellular model for studies of Ca2+ signalling and homeostasis. Downstream effects of Ca2+ signalling have been and continue to be an important research avenue. The primary functions regulated by Ca2+ in pancreatic acinar cells , exocytotic secretion and fluid secretion , have been defined and extensively characterized in the second part of the last century. The role of cytosolic Ca2+ in cellular pathology and the related question of the interplay between Ca2+ signalling and bioenergetics are important current research lines in our and other laboratories. Recent findings in these interwoven research areas are discussed in the current review. [source]


    Actin on DNA,An ancient and dynamic relationship,

    CYTOSKELETON, Issue 8 2010
    Kari-Pekka Skarp
    Abstract In the cytoplasm of eukaryotic cells the coordinated assembly of actin filaments drives essential cell biological processes, such as cell migration. The discovery of prokaryotic actin homologues, as well as the appreciation of the existence of nuclear actin, have expanded the scope by which the actin family is utilized in different cell types. In bacteria, actin has been implicated in DNA movement tasks, while the connection with the RNA polymerase machinery appears to exist in both prokaryotes and eukaryotes. Within the nucleus, actin has further been shown to play a role in chromatin remodeling and RNA processing, possibly acting to link these to transcription, thereby facilitating the gene expression process. The molecular mechanism by which actin exerts these newly discovered functions is still unclear, because while polymer formation seems to be required in bacteria, these species lack conventional actin-binding proteins to regulate the process. Furthermore, although the nucleus contains a plethora of actin-regulating factors, the polymerization status of actin within this compartment still remains unclear. General theme, however, seems to be actin's ability to interact with numerous binding partners. A common feature to the novel modes of actin utilization is the connection between actin and DNA, and here we aim to review the recent literature to explore how this connection is exploited in different contexts. [source]


    Plant profilin isovariants are distinctly regulated in vegetative and reproductive tissues

    CYTOSKELETON, Issue 1 2002
    Muthugapatti K. Kandasamy
    Abstract Profilin is a low-molecular weight, actin monomer-binding protein that regulates the organization of actin cytoskeleton in eukaryotes, including higher plants. Unlike the simple human or yeast systems, the model plant Arabidopsis has an ancient and highly divergent multi-gene family encoding five distinct profilin isovariants. Here we compare and characterize the regulation of these profilins in different organs and during microspore development using isovariant-specific monoclonal antibodies. We show that PRF1, PRF2, and PRF3 are constitutive, being strongly expressed in all vegetative tissues at various stages of development. These profilin isovariants are also predominant in ovules and microspores at the early stages of microsporogenesis. In contrast, PRF4 and PRF5 are late pollen-specific and are not detectable in other cell types of the plant body including microspores and root hairs. Immunocytochemical studies at the subcellular level reveal that both the constitutive and pollen-specific profilins are abundant in the cytoplasm. In vegetative cell types, such as root apical cells, profilins showed localization to nuclei in addition to the cytoplasmic staining. The functional diversity of profilin isovariants is discussed in light of their spatio-temporal regulation during vegetative development, pollen maturation, and pollen tube growth. Cell Motil. Cytoskeleton 52:22,32, 2002. © 2002 Wiley-Liss, Inc. [source]


    Fine-needle aspiration of neurilemoma (schwannoma).

    DIAGNOSTIC CYTOPATHOLOGY, Issue 6 2006
    A clinicocytopathologic study of 116 patients
    Abstract The preoperative fine-needle aspiration cytology (FNAC) diagnoses in 116 surgically excised neurilemomas were reviewed and compared with the corresponding histopathologic diagnoses made on surgical specimens and with clinical data. In addition, the utility of adjunctive techniques was analyzed and other spindle-cell lesions in the differential diagnoses were discussed. An unequivocal, benign diagnosis was rendered by FNAC in 80 cases, 67 of which were correctly labelled as neurilemoma in a review of the original cytology reports. There were 6 false-positive malignant diagnoses while 23 smears were considered insufficient and 7 inconclusive as to whether benign or malignant. On reevaluation, the diagnostic smears in most cases contained spindle cells with wavy nuclei embedded in a fibrillar, occasionally collagenous, and/or myxoid matrix and Antoni A/Antoni B tissue fragments. A moderate to abundant admixture of round to oval cells was also frequent. Nuclear palisading was seen in 41 smears with distinctive Verocay bodies in 10. Markedly pleomorphic nuclei were seen in smears from 8 ancient and 6 conventional neurilemomas, and slight to moderate nuclear pleomorphism was observed in 38 additional cases. Thus most neurilemomas have distinct cytomorphologic features that allow correct diagnosis. The major problem in FNAC of neurilemoma is to obtain sufficient material. Furthermore aspirates showing predominantly Antoni A features, nuclear pleomorphism, and/or myxoid changes can easily be confused with other types of benign or malignant soft-tissue tumors. Diagn. Cytopathol. 2006;34:403,412. © 2006 Wiley-Liss, Inc. [source]


    Drilling in the Cathedral

    DIALOG, Issue 3 2003
    Larry Rasmussen
    Abstract Utilitarianism, alienation, consumerism, and oppression are major forces endangering Earth's well-being. Over and against these morally and ecologically destructive forces are practices and ideas rooted and nourished in both ancient and modern religio-moral institutions and traditions. As powerful voices of faith calling the present to account, sacramentalism, mysticism, asceticism, and prophetic liberative practices offer Earth-honoring ways of life that draw from shared wells and deep-running waters. [source]


    Life history and population size variability in a relict plant.

    DIVERSITY AND DISTRIBUTIONS, Issue 1 2008
    Different routes towards long-term persistence
    ABSTRACT A central tenet of conservation biology is that population size affects the persistence of populations. However, many narrow endemic species combine small population ranges and sizes with long persistence, thereby challenging this tenet. I examined the performance of three different-sized populations of Petrocoptis pseudoviscosa (Caryophyllaceae), a palaeoendemic rupicolous herb distributed along a small valley in the Spanish Pyrenees. Reproductive and demographic parameters were recorded over 6 years, and deterministic and stochastic matrix models were constructed to explore population dynamics and extinction risk. Populations differed greatly in structure, fecundity, recruitment, survival rate, and life span. Strong differentiation in life-history parameters and their temporal variability resulted in differential population vulnerability under current conditions and simulated global changes such as habitat fragmentation or higher climatic fluctuations. This study provides insights into the capacity of narrow endemics to survive both at extreme environmental conditions and at small population sizes. When dealing with species conservation, the population size,extinction risk relationship may be too simplistic for ancient, ecologically restricted organisms, and some knowledge of life history may be most important to assess their future. [source]


    Genetic structure of Euphrasia stricta on the Baltic island of Gotland, Sweden

    ECOGRAPHY, Issue 4 2005
    Anna-Karin Kolseth
    Genetic differentiation between and within five varieties of Euphrasia stricta (var. brevipila, var. gotlandica, var. stricta, var. suecica and var. tenuis) on Gotland was investigated, using amplified fragment length polymorphism, AFLP. The varieties are described in the literature by morphology and association to habitat type. We wanted to investigate whether the varieties are locally adapted populations to the typical habitat type for each variety or if they are preadapted to certain habitat types and have colonized Gotland in their present form. A constrained principal coordinate analysis revealed three genetically differentiated subunits within the species. The two early-flowering varieties suecica and tenuis each formed a distinct group, while the three late-flowering varieties brevipila, gotlandica and stricta together formed the third group. A phylogenetic tree confirms the partitioning into three groups. Within the group containing the late-flowering varieties there are populations that pair as each other's closest relatives, but belong to different varieties. These pairs are also geographically adjacent. The phylogenetic tree had a "star-like" appearance indicating a stronger divergence between populations than between varieties. The same pattern was seen in the partitioning of genetic diversity, with a lower amount of genetic variation occurring between varieties, FST=0.14, than between populations within the varieties, FST ranging from 0.26 to 0.60. In Euphrasia stricta the varieties suecica and tenuis and the group containing the varieties stricta/gotlandica/brevipila are likely to have a phylogeographical history outside Gotland, or an ancient and concealed local origin on the island. Within the group stricta/gotlandica/brevipila local evolutionary events seem to determine the variety identity, probably through local adaptation. [source]


    Novel insect-tree associations resulting from accidental and intentional biological ,invasions': a meta-analysis of effects on insect fitness

    ECOLOGY LETTERS, Issue 4 2010
    Coralie Bertheau
    Ecology Letters (2010) 13: 506,515 Abstract The translocation of species beyond their native range is a major threat to biodiversity. Invasions by tree-feeding insects attacking native trees and the colonization of introduced trees by native insects result in new insect,tree relationships. To date there is uncertainty about the key factors that influence the outcome of these novel interactions. We report the results of a meta-analysis of 346 pairwise comparisons of forest insect fitness on novel and ancient host tree species from 31 publications. Host specificity of insects and phylogenetic relatedness between ancient and novel host trees emerged as key factors influencing insect fitness. Overall, fitness was significantly lower on novel host species than on ancient hosts. However, in some cases, fitness increased on novel hosts, mainly in polyphagous insects or when close relatives of ancient host trees were colonized. Our synthesis enables greatly improved impact prediction and risk assessment of biological invasions. [source]


    The wholesale and retail markets of London, 1660,1840

    ECONOMIC HISTORY REVIEW, Issue 1 2002
    Colin Smith
    Markets and marketing are perennial themes in English economic and social history. Yet they remain largely unexplored in relation to London during a period of remarkable growth and change, the long eighteenth century. This article begins to fill that void, by surveying over 70 London produce markets that existed during the period, and identifying patterns in their collective development. It concludes that the physical market place, though ancient in origin, evolved through the ,commercial revolution' as a highly dynamic and diverse institution that played a significant role in London's distribution. [source]


    Transformative Teaching: Restoring the teacher, under erasure

    EDUCATIONAL PHILOSOPHY AND THEORY, Issue 2 2009
    Jenny Steinnes
    Abstract In the large and complex landscape of pedagogy, the focus seems to have turned away from the concept of teaching and towards a stronger emphasis on learning, probably supported by neo-liberal ideology. The teacher is presented more as part of the force of production than as an autonomous performer of a mandate given to him/her by society. He/she is supposed to supply knowledge that is considered useful to a society geared to production and consumption. During the past few decades, enlightenment as a legitimising concept for education has been challenged from different angles, both by a self-critique from within and from external forces. One angle of approach is the questioning of the relationship between the state and education, by way of a critique of modernity. Another approach comes from a critique of knowledge, which has lost most of its universal implications and is left with more pragmatic and utilitarian considerations. Into this landscape of lost legitimisation, I will make an attempt to visualise an impossible/possible position for teaching, featuring ancient, contemporary and phantom-like figures. I am suggesting the concept of transformation as an alternative to development or improvement, which I find to be concepts with a close link to modernity and its linearity. By a careful and conscious use of the word transformation, taking Derrida's intensified focus of language into account, a possible active position might be intimated in spite of the fundamental critique, which has been directed at pedagogy and its imperialistic implications from different angles. [source]


    The neutrophil: understanding ancient and powerful responses in the inflammatory balance

    EQUINE VETERINARY JOURNAL, Issue 1 2003
    A. M. JEFCOAT
    No abstract is available for this article. [source]


    Theories of drug craving, ancient and modern

    ADDICTION, Issue 1 2001
    D. Colin Drummond
    This paper reviews the principal theoretical models of drug craving and provides some directions for future research. The main models are classified broadly into three categories: (1) phenomenological models; based on clinical observation and description; these have been influential in classification systems of addictive disorders and in the development of pharmacological therapies; (2) conditioning models: based on conditioning theory; these have been influential in the development of cue exposure treatments; (3) cognitive theories; based on cognitive social learning theory: these have been influential in the development of cognitive therapies of addiction. It is concluded that no one specific theory provides a complete explanation of the phenomenon of craving. However, theories of craving grounded in general theories of human behaviour offer greatest promise, and generate more specific and testable research hypotheses. Theories that do not require craving to be present for relapse to occur have more empirical support than those that provide simplistic causal explanations. The cue-reactivity model shows promise in the exploration of the relationship between craving and relapse. However, further attention to the phenomenology of craving could help to advise the future measurement and study of drug craving, particularly in the context of research in which drugs are available to human subjects, with adequate ethical safeguards. There is a need for further study of the temporal dynamics of craving and consensus in the field on the most appropriate methods of measurement. Finally, new psychotherapies such as cue exposure and pharmacotherapies that aim to attenuate drinking behaviour, such as naltrexone and acamprosate, provide opportunities to improve understanding of the nature and significance of craving. However, the relatively uncritical assumption that craving is the underlying basis of addiction and represents the most appropriate target for treatment is challenged. [source]


    DETECTING THE HISTORICAL SIGNATURE OF KEY INNOVATIONS USING STOCHASTIC MODELS OF CHARACTER EVOLUTION AND CLADOGENESIS

    EVOLUTION, Issue 2 2005
    Richard H. Ree
    Abstract Phylogenetic evidence for biological traits that increase the net diversification rate of lineages (key innovations) is most commonly drawn from comparisons of clade size. This can work well for ancient, unreversed traits and for correlating multiple trait origins with higher diversification rates, but it is less suitable for unique events, recently evolved innovations, and that exhibit homoplasy. Here I present a new method for detecting the phylogenetic signature of key innovations that tests whethere the evolutionary history of the candidate trait is associated with shorter waiting times between cladogenesis events. The method employs stochastic models of character evolution and cladogenesis and integrates well into a Bayesian framework in which uncertainty in historical inferences (such as phylogenetic relationships) is allowed. Applied to a well-known example in plants, nectar spurs in columbines, the method gives much stronger support to the key innovation hypothesis than previous tests. [source]


    PHYLOGEOGRAPHIC STRUCTURE AND CRYPTIC SPECIATION IN THE TRANS-ANTARCTIC MOSS PYRRHOBRYUM MNIOIDES

    EVOLUTION, Issue 2 2003
    Stuart F. McDaniel
    Abstract Many bryophyte species have distributions that span multiple continents. The hypotheses historically advanced to explain such distributions rely on either long-distance spore dispersal or slow rates of morphological evolution following ancient continental vicariance events. We use phylogenetic analyses of DNA sequence variation at three chloroplast loci (atpB-rbcL spacer, rps4 gene, and trnL intron and 3,spacer) to examine these two hypotheses in the trans-Antarctic moss Pyrrhobryum mnioides. We find: (1) reciprocal monophyly of Australasian and South American populations, indicating a lack of intercontinental dispersal; (2) shared haplotypes between Australia and New Zealand, suggesting recent or ongoing migration across the Tasman Sea; and (3) reciprocal monophyly among Patagonian and neotropical populations, suggesting no recent migration along the Andes. These results corroborate experimental work suggesting that spore features may be critical determinants of species range. We use the mid-Miocene development of the Atacama Desert, 14 million years ago, to calibrate a molecular clock for the tree. The age of the trans-Antarctic disjunction is estimated to be 80 million years ago, consistent with Gondwanan vicariance, making it among the most ancient documented cases of cryptic speciation. These data are in accord with niche conservatism, but whether the morphological stasis is a product of stabilizing selection or phylogenetic constraint is unknown. [source]


    Generality of vertebrate developmental patterns: evidence for a dermomyotome in fish

    EVOLUTION AND DEVELOPMENT, Issue 1 2006
    S. H. Devoto
    SUMMARY The somitic compartment that gives rise to trunk muscle and dermis in amniotes is an epithelial sheet on the external surface of the somite, and is known as the dermomyotome. However, despite its central role in the development of the trunk and limbs, the evolutionary history of the dermomyotome and its role in nonamniotes is poorly understood. We have tested whether a tissue with the morphological and molecular characteristics of a dermomyotome exists in nonamniotes. We show that representatives of the agnathans and of all major clades of gnathostomes each have a layer of cells on the surface of the somite, external to the embryonic myotome. These external cells do not show any signs of terminal myogenic or dermogenic differentiation. Moreover, in the embryos of bony fishes as diverse as sturgeons (Chondrostei) and zebrafish (Teleostei) this layer of cells expresses the pax3 and pax7 genes that mark myogenic precursors. Some of the pax7- expressing cells also express the differentiation-promoting myogenic regulatory factor Myogenin and appear to enter into the myotome. We therefore suggest that the dermomyotome is an ancient and conserved structure that evolved prior to the last common ancestor of all vertebrates. The identification of a dermomyotome in fish makes it possible to apply the powerful cellular and genetic approaches available in zebrafish to the understanding of this key developmental structure. [source]


    Expression of Pax258 in the gastropod statocyst: insights into the antiquity of metazoan geosensory organs

    EVOLUTION AND DEVELOPMENT, Issue 6 2003
    Elizabeth K. O'brien
    Summary Most animals have sensory systems that allow them to balance and orient relative to the pull of gravity. Structures responsible for these functions range from very simple statocysts found in many aquatic invertebrates to the complex inner ear of mammals. Previous studies suggest that the specialized mechanosensory structures responsible for balance in vertebrates and insects may be homologous based on the requirement and expression of group II Pax genes (i.e., Pax-2/5/8 genes). Here we report the expression of a Pax-258 gene in the statocysts and other chemosensory and mechanosensory cells during the development of the gastropod mollusk Haliotis asinina, a member of the Lophotrochozoa. Based on the phylogenetic distribution of geo-sensory systems and the consistent expression of Pax-258 in the cells that form these systems, we propose that Pax-258, along with POU-III and -IV genes, has an ancient and conserved role in the formation of structures responsible for balance and geotaxis in eumetazoans. [source]


    Evolution of the echinoderm Hox gene cluster

    EVOLUTION AND DEVELOPMENT, Issue 5 2001
    Suzanne Long
    SUMMARY Extant echinoderms are members of an ancient and highly derived deuterostome phylum. The composition and arrangement of their Hox gene clusters are consequently of interest not only from the perspective of evolution of development, but also in terms of metazoan phylogeny and body plan evolution. Over the last decade numerous workers have reported partial Hox gene sequences from a variety of echinoderms. In this paper we used a combined methods approach to analyze phylogenetic relationships between 68 echinoderm Hox homeodomain fragments, from species of five extant classes,two asteroids, one crinoid, one ophiuroid, one holothuroid, and three echinoids. This analysis strengthens Mito and Endo's (2000) proposition that the ancestral echinoderm's Hox gene cluster contained at least eleven genes, including at least four posterior paralogous group genes. However, representatives of all paralogous groups are not known from all echinoderm classes. In particular, these data suggest that echinoids may have lost a posterior group Hox gene subsequent to the divergence of the echinoderm classes. Evolution of the highly derived echinoderm body plan may have been accompanied by class-specific duplication, diversification and loss of Hox genes. [source]


    Hypoxia-inducible factor as a physiological regulator

    EXPERIMENTAL PHYSIOLOGY, Issue 6 2005
    Patrick H. Maxwell
    Hypoxia-inducible factor (HIF) is a transcription complex which responds to changes in oxygen, providing cells with a master regulator that coordinates changes in gene transcription. HIF operates in all mammalian cell types and is ancient in evolutionary terms, being conserved in C. elegans and D. melanogaster. This review summarizes recent insights into the molecular events that link reduced oxygenation to HIF activation and emerging insights into the extensive role of HIF in a broad range of physiological processes. [source]