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Natural Laboratory (natural + laboratory)
Selected AbstractsINCIPIENT SPECIATION DESPITE LITTLE ASSORTATIVE MATING: THE YELLOW-RUMPED WARBLER HYBRID ZONEEVOLUTION, Issue 12 2009Alan Brelsford Hybrid zones between recently diverged taxa are natural laboratories for speciation research, allowing us to determine whether there is reproductive isolation between divergent forms and the causes of that isolation. We present a study of a classic avian hybrid zone in North America between two subspecies of the yellow-rumped warbler (Dendroica coronata). Although previous work has shown very little differentiation in mitochondrial DNA across this hybrid zone, we identified two nuclear loci (one sex-linked and one autosomal) that show fixed differences across the hybrid zone, in a close concordance with patterns of plumage variation. Temporal stability and limited width of the hybrid zone, along with substantial linkage disequilibrium between these two diagnostic markers in the center of the zone, indicate that there is moderate reproductive isolation between these populations, with an estimated strength of selection maintaining the zone of 18%. Pairing data indicate that assortative mating is either very weak or absent, suggesting that this reproductive isolation is largely due to postmating barriers. Thus, despite extensive hybridization the two forms are distinct evolutionary groups carrying genes for divergent adaptive peaks, and this situation appears relatively stable. [source] Sculpin hybrid zones: natural laboratories for the early stages of speciationMOLECULAR ECOLOGY, Issue 12 2009ANDREA SWEIGART Firmly rooted as we are in the genomic era, it can seem incredible that as recently as 1974, Lewontin declared, ,we know virtually nothing about the genetic changes that occur in species formation'. To the contrary, we now know the genetic architecture of phenotypic differences and reproductive isolation between species for many diverse groups of plants, animals, and fungi. In recent years, detailed genetic analyses have produced a small but growing list of genes that cause reproductive isolation, several of which appear to have diverged by natural selection. Yet, a full accounting of the speciation process requires that we understand the reproductive and ecological properties of natural populations as they begin to diverge genetically, as well as the dynamics of newly evolved barriers to gene flow. One promising approach to this problem is the study of natural hybrid zones, where gene exchange between divergent populations can produce recombinant genotypes in situ. In such individuals, genomic variation might be shaped by introgression at universally adaptive or neutral loci, even as regions associated with local adaptation or reproductive isolation remain divergent. In Nolte et al. (2009), the authors take advantage of two independent, recently formed hybrid zones between sculpin species to investigate genome-wide patterns of reproductive isolation. Using a recently developed genomic clines method, the authors identify marker loci that are associated with isolation, and those that show evidence for adaptive introgression. Remarkably, Nolte et al. (2009) find little similarity between the two hybrid zones in patterns of introgression, a fact that might reflect genetic variation within species or heterogeneous natural selection. In either case, their study system has the potential to provide insight into the early stages of speciation. [source] Evolution on oceanic islands: molecular phylogenetic approaches to understanding pattern and processMOLECULAR ECOLOGY, Issue 6 2002B. C. Emerson Abstract By their very nature oceanic island ecosystems offer great opportunities for the study of evolution and have for a long time been recognized as natural laboratories for studying evolution owing to their discrete geographical nature and diversity of species and habitats. The development of molecular genetic methods for phylogenetic reconstruction has been a significant advance for evolutionary biologists, providing a tool for answering questions about the diversity among the flora and fauna on such islands. These questions relate to both the origin and causes of species diversity both within an archipelago and on individual islands. Within a phylogenetic framework one can answer fundamental questions such as whether ecologically and/or morphologically similar species on different islands are the result of island colonization or convergent evolution. Testing hypotheses about ages of the individual species groups or entire community assemblages is also possible within a phylogenetic framework. Evolutionary biologists and ecologists are increasingly turning to molecular phylogenetics for studying oceanic island plant and animal communities and it is important to review what has been attempted and achieved so far, with some cautionary notes about interpreting phylogeographical pattern on oceanic islands. [source] Plebiscites, Fiscal Policy and the Poor: Learning from US Experience with Direct DemocracyDEVELOPMENT POLICY REVIEW, Issue 5 2005Arthur A. Goldsmith Many countries are contemplating direct political participation as a way of giving marginalised people more say in national fiscal policies. The United States is a natural laboratory for studying how large-scale direct democracy actually works in this regard. Every state allows voters to decide certain ballot questions about how to raise and spend public revenue. The 100-year record shows, however, that state-wide plebiscites fail to produce uniformly equitable or financially sustainable government budgets, or to mobilise low-income groups to defend their economic interests. When called upon to make decisions about state government spending, the electorate is apt to disregard any hardship for poor people. Traditional political parties and advocacy organisations are usually a more promising avenue for promoting anti-poverty budgets. [source] Interseismic Plate coupling and strain partitioning in the Northeastern CaribbeanGEOPHYSICAL JOURNAL INTERNATIONAL, Issue 3 2008D. M. Manaker SUMMARY The northeastern Caribbean provides a natural laboratory to investigate strain partitioning, its causes and its consequences on the stress regime and tectonic evolution of a subduction plate boundary. Here, we use GPS and earthquake slip vector data to produce a present-day kinematic model that accounts for secular block rotation and elastic strain accumulation, with variable interplate coupling, on active faults. We confirm that the oblique convergence between Caribbean and North America in Hispaniola is partitioned between plate boundary parallel motion on the Septentrional and Enriquillo faults in the overriding plate and plate-boundary normal motion at the plate interface on the Northern Hispaniola Fault. To the east, the Caribbean/North America plate motion is accommodated by oblique slip on the faults bounding the Puerto Rico block to the north (Puerto Rico subduction) and to the south (Muertos thrust), with no evidence for partitioning. The spatial correlation between interplate coupling, strain partitioning and the subduction of buoyant oceanic asperities suggests that the latter enhance the transfer of interplate shear stresses to the overriding plate, facilitating strike-slip faulting in the overriding plate. The model slip rate deficit, together with the dates of large historical earthquakes, indicates the potential for a large (Mw7.5 or greater) earthquake on the Septentrional fault in the Dominican Republic. Similarly, the Enriquillo fault in Haiti is currently capable of a Mw7.2 earthquake if the entire elastic strain accumulated since the last major earthquake was released in a single event today. The model results show that the Puerto Rico/Lesser Antilles subduction thrust is only partially coupled, meaning that the plate interface is accumulating elastic strain at rates slower than the total plate motion. This does not preclude the existence of isolated locked patches accumulating elastic strain to be released in future earthquakes, but whose location and geometry are not resolvable with the present data distribution. Slip deficit on faults from this study are used in a companion paper to calculate interseismic stress loading and, together with stress changes due to historical earthquakes, derive the recent stress evolution in the NE Caribbean. [source] Retrospective selection bias (or the benefit of hindsight)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 2 2001Francesco Mulargia SUMMARY The complexity of geophysical systems makes modelling them a formidable task, and in many cases research studies are still in the phenomenological stage. In earthquake physics, long timescales and the lack of any natural laboratory restrict research to retrospective analysis of data. Such ,fishing expedition' approaches lead to optimal selection of data, albeit not always consciously. This introduces significant biases, which are capable of falsely representing simple statistical fluctuations as significant anomalies requiring fundamental explanations. This paper identifies three different strategies for discriminating real issues from artefacts generated retrospectively. The first attempts to identify ab initio each optimal choice and account for it. Unfortunately, a satisfactory solution can only be achieved in particular cases. The second strategy acknowledges this difficulty as well as the unavoidable existence of bias, and classifies all ,anomalous' observations as artefacts unless their retrospective probability of occurrence is exceedingly low (for instance, beyond six standard deviations). However, such a strategy is also likely to reject some scientifically important anomalies. The third strategy relies on two separate steps with learning and validation performed on effectively independent sets of data. This approach appears to be preferable in the case of small samples, such as are frequently encountered in geophysics, but the requirement for forward validation implies long waiting times before credible conclusions can be reached. A practical application to pattern recognition, which is the prototype of retrospective ,fishing expeditions', is presented, illustrating that valid conclusions are hard to find. [source] Introductory perspective on the COREF ProjectISLAND ARC, Issue 4 2006Yasufumi Iryu Abstract Coral reefs are tropic to subtropic, coastal ecosystems comprising very diverse organisms. Late Quaternary reef deposits are fossil archives of environmental, tectonic and eustatic variations that can be used to reconstruct the paleoclimatic and paleoceanographic history of the tropic surface oceans. Reefs located at the latitudinal limits of coral-reef ecosystems (i.e. those at coral-reef fronts) are particularly sensitive to environmental changes , especially those associated with glacial,interglacial changes in climate and sealevel. We propose a land and ocean scientific drilling campaign in the Ryukyu Islands (the Ryukyus) in the northwestern Pacific Ocean to investigate the dynamic response of the corals and coral-reef ecosystems in this region to Late Quaternary climate and sealevel change. Such a drilling campaign, which we call the COREF (coral-reef front) Project, will allow the following three major questions to be evaluated: (i) What are the nature, magnitude and driving mechanisms of coral-reef front migration in the Ryukyus? (ii) What is the ecosystem response of coral reefs in the Ryukyus to Quaternary climate changes? (iii) What is the role of coral reefs in the global carbon cycle? Subsidiary objectives include (i) the timing of coral-reef initiation in the Ryukyus and its causes; (ii) the position of the Kuroshio current during glacial periods and its effects on coral-reef formation; and (iii) early carbonate diagenetic responses as a function of compounded variations in climate, eustacy and depositional mineralogies (subtropic aragonitic to warm-temperate calcitic). The geographic, climatic and oceanographic settings of the Ryukyu Islands provide an ideal natural laboratory to address each of these research questions. [source] Biodiversity and biogeography of the islands of the Kuril ArchipelagoJOURNAL OF BIOGEOGRAPHY, Issue 9 2003Theodore W. Pietsch Abstract Aim Based on seven consecutive seasons of biotic survey and inventory of the terrestrial and freshwater plants and animals of the 30 major islands of the Kuril Archipelago, a description of the biodiversity and an analysis of the biogeography of this previously little known part of the world are provided. Location The Kuril Archipelago, a natural laboratory for investigations into the origin, subsequent evolution, and long-term maintenance of insular populations, forms the eastern boundary of the Okhotsk Sea, extending 1200 km between Hokkaido, Japan, and the Kamchatka Peninsula of Russia. A chain of more than 56 islands, the system is only slightly smaller than the Hawaiian Islands, covering an area of 15,600 km2 and providing 2409 km of coastline. Methods Collections of whole specimens of plants and animals, as well as tissue samples for future molecular studies, were made by teams of scientists from Russia, Japan, and the USA, averaging 34 people for each of the seven annual summer expeditions (1994,2000). Floral and faunal similarities between islands were evaluated by using Sorensen's coefficient of similarity. The similarity matrix resulting from pair-wise calculations was then subjected to UPGMA cluster analysis. Results Despite the relatively small geographical area of all islands combined, the Kuril Island biota is characterized by unusually high taxonomic diversity, yet endemism is very low. An example of a non-relict biota, it originated from two primary sources: a southern source, the Asian mainland by way of Sakhalin and Hokkaido, and a northern source by way of Kamchatka. The contribution of the southern source biota to the species diversity of the Kurils was considerably greater than the northern one. Main conclusion The Bussol Strait, lying between Urup and Simushir in the central Kurils, is the most significant biogeographical boundary within the Archipelago. Of lesser importance are two transitional zones, the De Vries Strait or ,Miyabe Line', which passes between Iturup and Urup in the southern Kurils, and the fourth Kuril Strait, between Onekotan and Paramushir in the northern Kurils. [source] Melting and melt segregation in the aureole of the Glenmore Plug, ArdnamurchanJOURNAL OF METAMORPHIC GEOLOGY, Issue 1 2005M. B. HOLNESS Abstract Contact metamorphism caused by the Glenmore plug in Ardnamurchan, a magma conduit active for 1 month, resulted in partial melting, with melt now preserved as glass. The pristine nature of much of the aureole provides a natural laboratory in which to investigate the distribution of melt. A simple thermal model, based on the first appearance of melt on quartz,feldspar grain boundaries, the first appearance of quartz paramorphs after tridymite and a plausible magma intrusion temperature, provides a time-scale for melting. The onset of melting on quartz,feldspar grain boundaries was initially rapid, with an almost constant further increase in melt rim thickness at an average rate of 0.5,1.0 × 10,9 cm s,1. This rate was most probably controlled by the distribution of limited amounts of H2O on the grain boundaries and in the melt rims. The melt in the inner parts of the aureole formed an interconnected grain-boundary scale network, and there is evidence for only limited melt movement and segregation. Layer-parallel segregations and cross-cutting veins occur within 0.6 m of the contact, where the melt volume exceeded 40%. The coincidence of the first appearance of these signs of the segregation of melt in parts of the aureole that attained the temperature at which melting in the Qtz,Ab,Or system could occur, suggests that internally generated overpressure consequent to fluid-absent melting was instrumental in the onset of melt movement. [source] Evolutionary adaptation to high altitude: A view from in utero,AMERICAN JOURNAL OF HUMAN BIOLOGY, Issue 5 2009Colleen Glyde Julian A primary focus within biological anthropology has been to elucidate the processes of evolutionary adaptation. Frisancho helped to move anthropology towards more mechanistic explanations of human adaptation by drawing attention to the importance of the functional relevance of human variation. Using the natural laboratory of high altitude, he and others asked whether the unique physiology of indigenous high-altitude residents was the result of acclimatization, developmental plasticity, and/or genetic adaptation in response to the high-altitude environment. We approach the question of human adaptation to high altitude from a somewhat unique vantage point; namely, by examining physiological characteristics,pregnancy and pregnancy outcome,which are closely associated with reproductive fitness. Here we review the potent example of high-altitude native population's resistance to hypoxia-associated reductions in birth weight, which is often associated with higher infant morbidity and mortality at high altitude. With the exception of two recent publications, these comparative birth weight studies have utilized surnames, self-identification, and/or linguistic characteristics to assess ancestry, and none have linked ,advantageous' phenotypes to specific genetic variations. Recent advancements in genetic and statistical tools have enabled us to assess individual ancestry with higher resolution, identify the genetic basis of complex phenotypes and to infer the effect of natural selection on specific gene regions. Using these technologies our studies are now directed to determine the genetic variations that underlie the mechanisms by which high-altitude ancestry protects fetal growth and, in turn, to further our understanding of evolutionary processes involved in human adaptation to high altitude. Am. J. Hum. Biol., 2009. © 2009 Wiley-Liss, Inc. [source] Human-information interaction in time-critical settings: Information needs and use in the emergency roomPROCEEDINGS OF THE AMERICAN SOCIETY FOR INFORMATION SCIENCE & TECHNOLOGY (ELECTRONIC), Issue 1 2007Aleksandra Sarcevic Trauma centers are stressful, noisy, and dynamic places, with many people performing complex tasks, and with no technological aids to support their operations. This paper describes research that uses an emergency room as a natural laboratory for investigating information behavior and information sources of trauma team members. Data from interviews, focus groups, and videotaped trauma resuscitations revealed specific information needs in four distinct phases of a trauma event. The most commonly utilized information sources include the patient, vital signs monitor, x-rays images, and other team members. Additionally, data indicated inefficiencies in teamwork and communication. Results from this study can be used to derive system requirements for the design of decision and communication support systems for trauma teams. [source] Optimal Diversification: Reconciling Theory and EvidenceTHE JOURNAL OF FINANCE, Issue 2 2004Joao Gomes ABSTRACT In this paper we show that the main empirical findings about firm diversification and performance are consistent with the maximization of shareholder value. In our model, diversification allows a firm to explore better productive opportunities while taking advantage of synergies. By explicitly linking the diversification strategies of the firm to differences in size and productivity, our model provides a natural laboratory to investigate several aspects of the relationship between diversification and performance. Specifically, we show that our model can rationalize the evidence on the diversification discount (Lang and Stulz (1994)) and the documented relation between diversification and productivity (Schoar (2002)). [source] The political economy of direct legislation: direct democracy and local decision,makingECONOMIC POLICY, Issue 33 2001Lars P Feld Local and regional governments account for an important share of total government spending and, given the decentralization trend in OECD nations, this is likely to increase. How should this spending be governed? This article argues that direct democracy is best suited to organize decision,making at the state and local level. To support this, we present the main theoretical arguments on why and how referenda and initiatives affect fiscal policy outcomes. The basic argument concerns voter control. Under representative democracy, citizens only have direct control at election time. With referenda and initiatives, citizens can selectively control their representatives on specific policies whenever they deviate sufficiently from citizens' preferences. As a result, fiscal policy outcomes are likely to more closely reflect voter preferences. We empirically test this on Swiss data since Switzerland provides a ,natural laboratory' for local governance. The governance structures of Swiss cantons and localities with respect to fiscal issues range from classic parliamentary democracy to pure direct democracy, and an important part of spending and taxation is controlled at these levels. Specifically, we estimate an econometric model of fiscal behaviour using data from 1986 to 1997 for the 26 Swiss cantons, and 1990 data on 134 local communities. It is shown that mandatory referenda on fiscal issues at both levels have a dampening effect on expenditure and revenue, and at the local level also on public debt. Combining this with existing empirical evidence leads to a relatively uncontested result, namely that elements of direct democracy are associated with sounder public finances, better economic performance and higher satisfaction of citizens. [source] | |||||||||||||||||||