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Search Results: 1 - 10 of 113488 matches for " John W. Grahame "
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Ecological Speciation and the Intertidal Snail Littorina saxatilis
Juan Galindo,John W. Grahame
Advances in Ecology , 2014, DOI: 10.1155/2014/239251
Abstract: In recent decades biologists studying speciation have come to consider that the process does not necessarily require the presence of a geographical barrier. Rather, it now seems to be possible for reproductive barriers to evolve within what was hitherto a single ‘‘species.’’ The intertidal snail Littorina saxatilis has been the focus of a considerable amount of work in this context, and it is now thought of as a good case study of ‘‘ecological speciation.’’ We review some of this work and briefly consider prospects for future developments. 1. Introduction In recent decades, there has been a considerable shift in our view of speciation—ecology has come in [1]. Or rather, it has come back in because the role of ecological processes in diversification dates back to Darwin, although some biologists of the 20th century gave a prominent role in speciation to geographical isolation (allopatry) [2, 3]. This shift of view has been reviewed by Mallet [4]. It is our intention here to give an account of work on Littorina saxatilis (Olivi) over the last three decades, highlighting its contribution and promise to the study of speciation. This marine snail is a species in a small and young genus and is probably the most derived member of the genus Littorina. It is thought to have originated in the eastern North Atlantic about 0.65?Ma?bp [5], rapidly colonizing both sides of the Atlantic. Phylogeographic patterns make it likely that more northern populations have undergone repeated subdivision and recontact as shorelines have been subject to glacial action and concomitant sea level changes. Populations on the northwestern coasts of the Iberian Peninsula appear to be genetically distinct from those elsewhere, suggestive of relatively long isolation [5–7]. L. saxatilis is strictly intertidal, though within the intertidal it has a fairly wide vertical distribution, and is found on rocky shores and in estuaries and salt marshes [8]. There are few published data on longevity. Hughes [9] gives a maximum of about four years. Littorina saxatilis is also highly polymorphic, and this has given rise to a great deal of taxonomic confusion and synonymy. It is part of a species complex, the group of rough periwinkles, with its sister species Littorina compressa (Jeffreys) and Littorina arcana Hannaford Ellis [8]. These latter produce egg masses which are deposited in sheltered crevices on the shore, while L. saxatilis females carry their embryos in a brood pouch in the dorsal mantle cavity until they are released as “crawl aways,” with similar morphology to the adult snails.
Habitat Choice and Speciation
Sophie E. Webster,Juan Galindo,John W. Grahame,Roger K. Butlin
International Journal of Ecology , 2012, DOI: 10.1155/2012/154686
Abstract: The role of habitat choice in reproductive isolation and ecological speciation has often been overlooked, despite acknowledgement of its ability to facilitate local adaptation. It can form part of the speciation process through various evolutionary mechanisms, yet where habitat choice has been included in models of ecological speciation little thought has been given to these underlying mechanisms. Here, we propose and describe three independent criteria underlying ten different evolutionary scenarios in which habitat choice may promote or maintain local adaptation. The scenarios are the result of all possible combinations of the independent criteria, providing a conceptual framework in which to discuss examples which illustrate each scenario. These examples show that the different roles of habitat choice in ecological speciation have rarely been effectively distinguished. Making such distinctions is an important challenge for the future, allowing better experimental design, stronger inferences and more meaningful comparisons among systems. We show some of the practical difficulties involved by reviewing the current evidence for the role of habitat choice in local adaptation and reproductive isolation in the intertidal gastropod Littorina saxatilis, a model system for the study of ecological speciation, assessing whether any of the proposed scenarios can be reliably distinguished, given current research.
Habitat Choice and Speciation
Sophie E. Webster,Juan Galindo,John W. Grahame,Roger K. Butlin
International Journal of Ecology , 2012, DOI: 10.1155/2012/154686
Abstract: The role of habitat choice in reproductive isolation and ecological speciation has often been overlooked, despite acknowledgement of its ability to facilitate local adaptation. It can form part of the speciation process through various evolutionary mechanisms, yet where habitat choice has been included in models of ecological speciation little thought has been given to these underlying mechanisms. Here, we propose and describe three independent criteria underlying ten different evolutionary scenarios in which habitat choice may promote or maintain local adaptation. The scenarios are the result of all possible combinations of the independent criteria, providing a conceptual framework in which to discuss examples which illustrate each scenario. These examples show that the different roles of habitat choice in ecological speciation have rarely been effectively distinguished. Making such distinctions is an important challenge for the future, allowing better experimental design, stronger inferences and more meaningful comparisons among systems. We show some of the practical difficulties involved by reviewing the current evidence for the role of habitat choice in local adaptation and reproductive isolation in the intertidal gastropod Littorina saxatilis, a model system for the study of ecological speciation, assessing whether any of the proposed scenarios can be reliably distinguished, given current research. 1. Introduction The role of divergent natural selection in speciation has been widely studied in recent years [1]. There is now broad acceptance that selection of this type can lead to the evolution of reproductive isolation, even in the face of gene flow [2]. Nevertheless, significant controversy remains. Is “ecological speciation” really distinct from other modes of speciation [3]? Why does reproductive isolation remain incomplete in some cases but not in others [4]? Do chromosomal re-arrangements [5] or divergence hitchhiking [6] help to overcome the antagonism between selection and recombination? What is the role of the so-called “magic traits” [7]? “Habitat isolation” is one part of the ecological barrier to gene exchange between species that includes effects due to local adaptation, competition, and choice [8]. In this paper, we will focus our attention on habitat choice, discussing the nature of its role in ecological speciation and the potential contribution towards reproductive isolation of various forms of habitat choice. We define habitat choice as any behaviour that causes an individual to spend more time in one habitat type than another
Insights into the Ecology and Evolutionary Success of Crocodilians Revealed through Bite-Force and Tooth-Pressure Experimentation
Gregory M. Erickson, Paul M. Gignac, Scott J. Steppan, A. Kristopher Lappin, Kent A. Vliet, John D. Brueggen, Brian D. Inouye, David Kledzik, Grahame J. W. Webb
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0031781
Abstract: Background Crocodilians have dominated predatory niches at the water-land interface for over 85 million years. Like their ancestors, living species show substantial variation in their jaw proportions, dental form and body size. These differences are often assumed to reflect anatomical specialization related to feeding and niche occupation, but quantified data are scant. How these factors relate to biomechanical performance during feeding and their relevance to crocodilian evolutionary success are not known. Methodology/Principal Findings We measured adult bite forces and tooth pressures in all 23 extant crocodilian species and analyzed the results in ecological and phylogenetic contexts. We demonstrate that these reptiles generate the highest bite forces and tooth pressures known for any living animals. Bite forces strongly correlate with body size, and size changes are a major mechanism of feeding evolution in this group. Jaw shape demonstrates surprisingly little correlation to bite force and pressures. Bite forces can now be predicted in fossil crocodilians using the regression equations generated in this research. Conclusions/Significance Critical to crocodilian long-term success was the evolution of a high bite-force generating musculo-skeletal architecture. Once achieved, the relative force capacities of this system went essentially unmodified throughout subsequent diversification. Rampant changes in body size and concurrent changes in bite force served as a mechanism to allow access to differing prey types and sizes. Further access to the diversity of near-shore prey was gained primarily through changes in tooth pressure via the evolution of dental form and distributions of the teeth within the jaws. Rostral proportions changed substantially throughout crocodilian evolution, but not in correspondence with bite forces. The biomechanical and ecological ramifications of such changes need further examination.
Influenza Vaccine Effectiveness against Hospitalisation with Confirmed Influenza in the 2010–11 Seasons: A Test-negative Observational Study
Allen C. Cheng, Mark Holmes, Louis B. Irving, Simon G. A. Brown, Grant W. Waterer, Tony M. Korman, N. Deborah Friedman, Sanjaya Senanayake, Dominic E. Dwyer, Stephen Brady, Grahame Simpson, Richard Wood-Baker, John Upham, David Paterson, Christine Jenkins, Peter Wark, Paul M. Kelly, Tom Kotsimbos
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0068760
Abstract: Immunisation programs are designed to reduce serious morbidity and mortality from influenza, but most evidence supporting the effectiveness of this intervention has focused on disease in the community or in primary care settings. We aimed to examine the effectiveness of influenza vaccination against hospitalisation with confirmed influenza. We compared influenza vaccination status in patients hospitalised with PCR-confirmed influenza with patients hospitalised with influenza-negative respiratory infections in an Australian sentinel surveillance system. Vaccine effectiveness was estimated from the odds ratio of vaccination in cases and controls. We performed both simple multivariate regression and a stratified analysis based on propensity score of vaccination. Vaccination status was ascertained in 333 of 598 patients with confirmed influenza and 785 of 1384 test-negative patients. Overall estimated crude vaccine effectiveness was 57% (41%, 68%). After adjusting for age, chronic comorbidities and pregnancy status, the estimated vaccine effectiveness was 37% (95% CI: 12%, 55%). In an analysis accounting for a propensity score for vaccination, the estimated vaccine effectiveness was 48.3% (95% CI: 30.0, 61.8%). Influenza vaccination was moderately protective against hospitalisation with influenza in the 2010 and 2011 seasons.
(Re-)introducing N Chabani Manganyi
Grahame Hayes
Psychology in Society , 2011,
Abstract: The reprinting of Manganyi's (1997) work, "The violent reverie", is introduced through a contextualisation of the social relations that form the structural and material foundations of violence. To this end the ideas of Zizek on the symbolic and systemic dimensions of violence, and Badiou's account of the "violent history" of democracy, are briefly discussed. The central argument of Manganyi's argument is adumbrated, namely, that the violent reverie has the potential to offer a creative expression to the alienation and anguish of the subordinated racial (black) subject. The article concludes with a brief introduction to Manganyi's impressive oeuvre that incorporates work on psychology, biography, and contemporary politics.
Abstract
Grahame Hayes
Psychology in Society , 2011,
Abstract:
Siyanda Ndlovu
Grahame Hayes
Psychology in Society , 2010,
Abstract:
Editorial
Grahame Hayes
Psychology in Society , 2010,
Abstract:
The Universities: A New Legal Grammar
Grahame Lock
Amsterdam Law Forum , 2010,
Abstract: In recent years the national and internal administration of universities has undergone fundamental change. This change parallels developments in other sectors of public life. It is matter not just of the rise of managerialism and of a takeover of control by the New Public Managers, proxies of other non-academic interests, at the cost of professional autonomy. What we are confronted with is in fact another expression of the substitution of governance for government, and in this connexion of the rise of what is called ‘soft law’. All this is bad news not only for academia but for democracy.
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