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Diversification
Kinds of Diversification Terms modified by Diversification Selected AbstractsDIVERSIFICATION OF THE AFRICAN GENUS PROTEA (PROTEACEAE) IN THE CAPE BIODIVERSITY HOTSPOT AND BEYOND: EQUAL RATES IN DIFFERENT BIOMESEVOLUTION, Issue 3 2010Luis M. Valente The Cape region of South Africa is a hotspot of flowering plant biodiversity. However, the reasons why levels of diversity and endemism are so high remain obscure. Here, we reconstructed phylogenetic relationships among species in the genus Protea, which has its center of species richness and endemism in the Cape, but also extends through tropical Africa as far as Eritrea and Angola. Contrary to previous views, the Cape is identified as the ancestral area for the radiation of the extant lineages: most species in subtropical and tropical Africa are derived from a single invasion of that region. Moreover, diversification rates have been similar within and outside the Cape region. Migration out of the Cape has opened up vast areas, but those lineages have not diversified as extensively at fine spatial scales as lineages in the Cape. Therefore, higher net rates of diversification do not explain the high diversity and endemism of Protea in the Cape. Instead, understanding why the Cape is so diverse requires an explanation for how Cape species are able to diverge and persist at such small spatial scales. [source] THE MACROEVOLUTIONARY DYNAMICS OF ANT DIVERSIFICATIONEVOLUTION, Issue 11 2009Marcio R. Pie The availability of increasingly comprehensive phylogenies has provided unprecedented opportunities to assess macroevolutionary patterns, yet studies on invertebrate diversification are few. In particular, despite the ecological and evolutionary importance of ants, little is known about their tempo and mode of diversification. Recent advances in ant phylogenetics can now provide a basis for rigorous analyses of the diversification of ant lineages. The goals of the present study are threefold. First, we demonstrate that a hypothesized disproportionate increase in ant diversification during the angiosperm radiation is largely artifactual. Rather, current evidence points to a fairly constant rate of lineage growth during its history. Moreover, an analysis of diversification patterns across the ant phylogeny indicates considerable rate heterogeneity among lineages. Indeed, and contrary to the expectation if lineages had experienced a single rate of lineage increase, we found no correspondence between genus age and diversity. Finally, we demonstrate a statistically significant phylogenetic signal in ant diversification: closely related genera have diversities that are more similar to one another than one would expect by chance. This suggests that the capacity for diversification may be itself a biological trait that evolved during the radiation of the family Formicidae. [source] PHYTOPHAGOUS INSECT,MICROBE MUTUALISMS AND ADAPTIVE EVOLUTIONARY DIVERSIFICATIONEVOLUTION, Issue 5 2008Eric M. Janson Adaptive diversification is a process intrinsically tied to species interactions. Yet, the influence of most types of interspecific interactions on adaptive evolutionary diversification remains poorly understood. In particular, the role of mutualistic interactions in shaping adaptive radiations has been largely unexplored, despite the ubiquity of mutualisms and increasing evidence of their ecological and evolutionary importance. Our aim here is to encourage empirical inquiry into the relationship between mutualism and evolutionary diversification, using herbivorous insects and their microbial mutualists as exemplars. Phytophagous insects have long been used to test theories of evolutionary diversification; moreover, the diversification of a number of phytophagous insect lineages has been linked to mutualisms with microbes. In this perspective, we examine microbial mutualist mediation of ecological opportunity and ecologically based divergent natural selection for their insect hosts. We also explore the conditions and mechanisms by which microbial mutualists may either facilitate or impede adaptive evolutionary diversification. These include effects on the availability of novel host plants or adaptive zones, modifying host-associated fitness trade-offs during host shifts, creating or reducing enemy-free space, and, overall, shaping the evolution of ecological (host plant) specialization. Although the conceptual framework presented here is built on phytophagous insect,microbe mutualisms, many of the processes and predictions are broadly applicable to other mutualisms in which host ecology is altered by mutualistic interactions. [source] BURNING PHYLOGENIES: FIRE, MOLECULAR EVOLUTIONARY RATES, AND DIVERSIFICATIONEVOLUTION, Issue 9 2007Miguel Verdú Mediterranean-type ecosystems are among the most remarkable plant biodiversity "hot spots" on the earth, and fire has traditionally been invoked as one of the evolutionary forces explaining this exceptional diversity. In these ecosystems, adult plants of some species are able to survive after fire (resprouters), whereas in other species fire kills the adults and populations are only maintained by an effective post-fire recruitment (seeders). Seeders tend to have shorter generation times than resprouters, particularly under short fire return intervals, thus potentially increasing their molecular evolutionary rates and, ultimately, their diversification. We explored whether seeder lineages actually have higher rates of molecular evolution and diversification than resprouters. Molecular evolutionary rates in different DNA regions were compared in 45 phylogenetically paired congeneric taxa from fire-prone Mediterranean-type ecosystems with contrasting seeder and resprouter life histories. Differential diversification was analyzed with both topological and chronological approaches in five genera (Banksia, Daviesia, Lachnaea, Leucadendron, and Thamnochortus) from two fire-prone regions (Australia and South Africa). We found that seeders had neither higher molecular rates nor higher diversification than resprouters. Such lack of differences in molecular rates between seeders and resprouters,which did not agree with theoretical predictions,may occur if (1) the timing of the switch from seeding to resprouting (or vice versa) occurs near the branch tip, so that most of the branch length evolves under the opposite life-history form; (2) resprouters suffer more somatic mutations and therefore counterbalancing the replication-induced mutations of seeders; and (3) the rate of mutations is not related to shorter generation times because plants do not undergo determinate germ-line replication. The absence of differential diversification is to be expected if seeders and resprouters do not differ from each other in their molecular evolutionary rate, which is the fuel for speciation. Although other factors such as the formation of isolated populations may trigger diversification, we can conclude that fire acting as a throttle for diversification is by no means the rule in fire-prone ecosystems [source] THE GEOGRAPHICAL PATTERN OF SPECIATION AND FLORAL DIVERSIFICATION IN THE NEOTROPICS: THE TRIBE SINNINGIEAE (GESNERIACEAE) AS A CASE STUDYEVOLUTION, Issue 7 2007Mathieu Perret The geographical pattern of speciation and the relationship between floral variation and species ranges were investigated in the tribe Sinningieae (Gesneriaceae), which is found mainly in the Atlantic forests of Brazil. Geographical distribution data recorded on a grid system of 0.5 × 0.5 degree intervals and a near-complete species-level phylogenetic tree of Sinningieae inferred from a simultaneous analysis of seven DNA regions were used to address the role of geographical isolation in speciation. Geographical range overlaps between sister lineages were measured across all nodes in the phylogenetic tree and analyzed in relation to relative ages estimated from branch lengths. Although there are several cases of species sympatry in Sinningieae, patterns of sympatry between sister taxa support the predominance of allopatric speciation. The pattern of sympatry between sister taxa is consistent with range shifts following allopatric speciation, except in one clade, in which the overlapping distribution of recent sister species indicates speciation within a restricted geographical area and involving changes in pollinators and habitats. The relationship between floral divergence and regional sympatry was also examined by analyzing floral contrasts, phenological overlap, and the degree of sympatry between sister clades. Morphological contrast between flowers is not increased in sympatry and phenological divergence is more apparent between allopatric clades than between sympatric clades. Therefore, our results failed to indicate a tendency for sympatric taxa to minimize morphological and phenological overlap (geographic exclusion and/or character displacement hypotheses). Instead, they point toward adaptation in phenology to local conditions and buildup of sympatries at random with respect to flower morphology. Additional studies at a lower geographical scale are needed to identify truely coexisting species and the components of their reproductive isolation. [source] SHARED AND UNIQUE FEATURES OF DIVERSIFICATION IN GREATER ANTILLEAN ANOLIS ECOMORPHSEVOLUTION, Issue 2 2006R. Brian Langerhans Abstract Examples of convergent evolution suggest that natural selection can often produce predictable evolutionary outcomes. However, unique histories among species can lead to divergent evolution regardless of their shared selective pressures,and some contend that such historical contingencies produce the dominant features of evolution. A classic example of convergent evolution is the set of Anolis lizard ecomorphs of the Greater Antilles. On each of four islands, anole species partition the structural habitat into at least four categories, exhibiting similar morphologies within each category. We assessed the relative importance of shared selection due to habitat similarity, unique island histories, and unique effects of similar habitats on different islands in the generation of morphological variation in anole ecomorphs. We found that shared features of diversification across habitats were of greatest importance, but island effects on morphology (reflecting either island effects per se or phylogenetic relationships) and unique aspects of habitat diversification on different islands were also important. There were three distinct cases of island-specific habitat diversification, and only one was confounded by phylogenetic relatedness. The other two unique aspects were not related to shared ancestry but might reflect as-yet-unmeasured environmental differences between islands in habitat characteristics. Quantifying the relative importance of shared and unique responses to similar selective regimes provides a more complete understanding of phenotypic diversification, even in this much-studied system [source] STATISTICAL ANALYSIS OF DIVERSIFICATION WITH SPECIES TRAITSEVOLUTION, Issue 1 2005Emmanuel Paradis Abstract Testing whether some species traits have a significant effect on diversification rates is central in the assessment of macroevolutionary theories. However, we still lack a powerful method to tackle this objective. I present a new method for the statistical analysis of diversification with species traits. The required data are observations of the traits on recent species, the phylogenetic tree of these species, and reconstructions of ancestral values of the traits. Several traits, either continuous or discrete, and in some cases their interactions, can be analyzed simultaneously. The parameters are estimated by the method of maximum likelihood. The statistical significance of the effects in a model can be tested with likelihood ratio tests. A simulation study showed that past random extinction events do not affect the Type I error rate of the tests, whereas statistical power is decreased, though some power is still kept if the effect of the simulated trait on speciation is strong. The use of the method is illustrated by the analysis of published data on primates. The analysis of these data showed that the apparent overall positive relationship between body mass and species diversity is actually an artifact due to a clade-specific effect. Within each clade the effect of body mass on speciation rate was in fact negative. The present method allows to take both effects (clade and body mass) into account simultaneously. [source] EVOLUTION OF NICHE WIDTH AND ADAPTIVE DIVERSIFICATIONEVOLUTION, Issue 12 2004Martin Ackermann Abstract Theoretical models suggest that resource competition can lead to the adaptive splitting of consumer populations into diverging lineages, that is, to adaptive diversification. In general, diversification is likely if consumers use only a narrow range of resources and thus have a small niche width. Here we use analytical and numerical methods to study the consequences for diversification if the niche width itself evolves. We found that the evolutionary outcome depends on the inherent costs or benefits of widening the niche. If widening the niche did not have costs in terms of overall resource uptake, then the consumer evolved a niche that was wide enough for disruptive selection on the niche position to vanish; adaptive diversification was no longer observed. However, if widening the niche was costly, then the niche widths remained relatively narrow, allowing for adaptive diversification in niche position. Adaptive diversification and speciation resulting from competition for a broadly distributed resource is thus likely if the niche width is fixed and relatively narrow or free to evolve but subject to costs. These results refine the conditions for adaptive diversification due to competition and formulate them in a way that might be more amenable for experimental investigations. [source] THE ROLE OF SIZE-SPECIFIC PREDATION IN THE EVOLUTION AND DIVERSIFICATION OF PREY LIFE HISTORIESEVOLUTION, Issue 5 2002Troy Day Abstract Some of the best empirical examples of life-history evolution involve responses to predation. Nevertheless, most life-history theory dealing with responses to predation has not been formulated within an explicit dynamic food-web context. In particular, most previous theory does not explicitly consider the coupled population dynamics of the focal species and its predators and resources. Here we present a model of life-history evolution that explores the evolutionary consequences of size-specific predation on small individuals when there is a trade-off between growth and reproduction. The model explicitly describes the population dynamics of a predator, the prey of interest, and its resource. The selective forces that cause life-history evolution in the prey species emerge from the ecological interactions embodied by this model and can involve important elements of frequency dependence. Our results demonstrate that the strength of the coupling between predator and prey in the community determines many aspects of life-history evolution. If the coupling is weak (as is implicitly assumed in many previous models), differences in resource productivity have no effect on the nature of life-history evolution. A single life-history strategy is favored that minimizes the equilibrium resource density (if possible). If the coupling is strong, then higher resource productivities select for faster growth into the predation size refuge. Moreover, under strong coupling it is also possible for natural selection to favor an evolutionary diversification of life histories, possibly resulting in two coexisting species with divergent life-history strategies. [source] OPTIMAL CAPITAL AND RISK TRANSFERS FOR GROUP DIVERSIFICATIONMATHEMATICAL FINANCE, Issue 1 2008Damir Filipovi Diversification is at the core of insurance and other financial business. It constitutes an important issue in the preparation of the new Solvency II framework for the regulation of European insurance undertakings. In this paper, we propose a conceptual framework for a legally enforceable capital and risk transfer which optimally accounts for the designated group diversification benefits. We also provide a consistent valuation principle which is compatible with any prior valuation method. This makes our framework fully flexible and universally applicable. A first simple numerical example illustrates the practicability of our proposal. [source] DEVELOPMENT AND DIVERSIFICATION OF TRUNK PLATES OF THE LOWER CAMBRIAN LOBOPODIANSPALAEONTOLOGY, Issue 2 2007XI-GUANG ZHANG Abstract:, Isolated lobopodian plates are reported from Early Cambrian strata at five localities in southern China. A wide variety of morphologies is represented, reflecting a considerable diversification within the phylum at this time. The new taxon Microdictyon jinshaense is erected and new observations are recorded on established taxa, based on examination of more than 600 well-preserved plates; irregular patterns of node distribution and the presence of large spines are documented on some taxa for the first time. Rare specimens in which two plates are conjoined, with a larger plate underlying a smaller one, are interpreted as showing a new sclerite emerging underneath its predecessor, which has not yet been moulted. These specimens confirm the process of ecdysis in the lobopodians and contribute to a fuller understanding of the ontogeny of these organisms. A functional hypothesis that suggests that the plates were complex visual structures is refuted; it is possible that they were sites of muscle attachment, but a protective role is regarded as more plausible. [source] SOCIALLY RESPONSIBLE INVESTING AND PORTFOLIO DIVERSIFICATIONTHE JOURNAL OF FINANCIAL RESEARCH, Issue 1 2005Zakri Y. Bello Abstract I use a sample of socially responsible stock mutual funds matched to randomly selected conventional funds of similar net assets to investigate differences in characteristics of assets held, portfolio diversification, and variable effects of diversification on investment performance. I find that socially responsible funds do not differ significantly from conventional funds in terms of any of these attributes. Moreover, the effect of diversification on investment performance is not different between the two groups. Both groups underperform the Domini 400 Social Index and S&P 500 during the study period. [source] BANKS' DIVERSIFICATION, CROSS-SELLING AND THE QUALITY OF BANKS' LOANSTHE MANCHESTER SCHOOL, Issue 2009STEFANIA COSCI In this paper we model and empirically test the impact of banks' shift towards financial services on their screening activity and on the quality of their loans. We present a model where it is easier to sell services to positively evaluated loan applicants and we show that the larger the banks' income from services, the lower their optimal screening effort. This prediction is consistent with the empirical evidence based on a panel of European banks and showing that the quality of banks' loans decreases with the share of commission income (a proxy for income from services). [source] HUMAN HEART ,-ADRENOCEPTORS: ,1 -ADRENOCEPTOR DIVERSIFICATION THROUGH ,AFFINITY STATES' AND POLYMORPHISMCLINICAL AND EXPERIMENTAL PHARMACOLOGY AND PHYSIOLOGY, Issue 10 2007P Molenaar SUMMARY 1In atrium and ventricle from failing and non-failing human hearts, activation of ,1 - or ,2 -adrenoceptors causes increases in contractile force, hastening of relaxation, protein kinase A-catalysed phosphorylation of proteins implicated in the hastening of relaxation, phospholamban, troponin I and C-protein, consistent with coupling of both ,1 - and ,2 -adrenoceptors to stimulatory Gsa -protein but not inhibitory Gia -protein. 2Two ,affinity states', namely ,1H and ,1L, of the ,1 -adrenoceptor exist. In human heart, noradrenaline elicits powerful increases in contractile force and hastening of relaxation. These effects are blocked with high affinity by ,-adenoceptor antagonists, including propranolol, (,)-pindolol, (,)-CGP 12177 and carvedilol. Some beta-blockers, typified by (,)-pindolol and (,)-CGP 12177, not only block the receptor, but also activate it, albeit at much higher concentrations (approximately 2 log units) than those required to antagonize the effects of catecholamines. In human heart, both (,)-CGP 12177 and (,)-pindolol increase contractile force and hasten relaxation. However, the involvement of the ,1 -adrenoceptor was not immediately obvious because (,)-pindolol- and (,)-CGP 12177-evoked responses were relatively resistant to blockade by (,)-propranolol. Abrogation of cardiostimulant effects of (,)-CGP 12177 in ,1 -/,2 -adrenoceptor double-knockout mice, but not ,2 -adrenoceptor-knockout mice, revealed an obligatory role of the ,1 -adrenoceptor. On the basis of these results, two ,affinity states' have been designated, the ,1H - and ,1L -adrenoceptor, where the ,1H -adrenoceptor is activated by noradrenaline and blocked with high affinity by beta-blockers and the ,1L -adrenoceptor is activated by drugs such as (,)-CGP 12177 and (,)-pindolol and blocked with low affinity by beta-blockers such as (,)-propranolol. The ,1H - and ,1L -adrenoceptor states are consistent with high- and low-affinity binding sites for (,)-[3H]-CGP 12177 radioligand binding found in cardiac muscle and recombinant ,1 -adrenoceptors. 3There are two common polymorphic locations of the ,1 -adrenoceptor, at amino acids 49 (Ser/Gly) and 389 (Arg/Gly). Their existence has raised several questions, including their role in determining the effectiveness of heart failure treatment with beta-blockers. We have investigated the effect of long-term maximally tolerated carvedilol administration (> 1 year) on left ventricular ejection fraction (LVEF) in patients with non-ischaemic cardiomyopathy (mean left ventricular ejection fraction 23 ± 7%; n = 135 patients). The administration of carvedilol improved LVEF to 37 ± 13% (P < 0.005); however, the improvement was variable, with 32% of patients showing £ 5% improvement. Upon segregation of patients into Arg389Gly-,1 -adrenoceptors, it was found that carvedilol caused a greater increase in left ventricular ejection faction in patients carrying the Arg389 allele with Arg389Arg > Arg389Gly > Gly389Gly. [source] DISCOVERING EXCEPTIONAL DIVERSIFICATIONS AT CONTINENTAL SCALES: THE CASE OF THE ENDEMIC FAMILIES OF NEOTROPICAL SUBOSCINE PASSERINESEVOLUTION, Issue 7 2010Santiago Claramunt The study of continental adaptive radiations has lagged behind research on their island counterparts in part because the mere identification of adaptive radiations is more challenging at continental scales. Here, I demonstrate a new method based on simulations for discovering clades that show exceptionally high phenotypic diversity. The method does not require a phylogeny but accounts for differences in age and species richness among clades and incorporates effects of the phylogenetic structure of data. In addition, I developed a new multivariate measure of phenotypic diversity, which has the advantage over other measures of disparity in that it takes covariation into account. I applied these methods to a clade of endemic Neotropical suboscine passerines, within which the family Furnariidae has been considered an adaptive radiation. I found that the families Thamnophilidae, Furnariidae, and Dendrocolaptidae have experienced a higher rate of cladogenesis than have other clades. Although Thamnophilidae is exceptionally diverse in body size, only Furnariidae and Dendrocolaptidae are exceptionally diverse in shape. The combination of high rates of cladogenesis and high morphometric diversity in traits related to feeding and locomotion suggest that the clade Furnariidae-Dendrocolaptidae represent an authentic continental adaptive radiation. [source] High phenotypic diversity in infecting but not in colonizing Staphylococcus aureus populationsENVIRONMENTAL MICROBIOLOGY, Issue 12 2007Christiane Goerke Summary In hostile environments diversity within a bacterial population may be beneficial for the fitness of the microbial community as a whole. Here we analysed the population diversity of Staphylococcus aureus in infecting and colonizing situations. In the study, performed independently in two German centres, the heterogeneity of the S. aureus population was determined by quantifying the occurrence of phenotypic variants (differences in haemolysis, pigmentation, colony morphology) in primary cultures from nose, oropharyngeal and sputum specimens from cystic fibrosis (CF) patients and in nose swabs from healthy S. aureus carriers. The proportion of heterogeneous samples, the number of clearly distinguishable isolates per sample and the qualitative differences between phenotypes was significantly higher in CF sputum specimens than in the other samples. The heterogeneity of the S. aureus population could be correlated with high bacterial densities in the sputum samples. In patients co-infected with Pseudomonas aeruginosa lower S. aureus bacterial loads and less heterogeneity in the S. aureus population were observed. Typing of all S. aureus isolates from heterogeneous samples by pulsed-field gel electrophoresis or spa typing revealed that the bacteria were polyclonal in 30%, monoclonal with minor genetic alterations in 25% or not distinguishable in 69% of the specimens. Some specimens harboured monoclonal and polyclonal variants simultaneously. Importantly, differences in antibiotic susceptibility were detected in phenotypic S. aureus variants within a single specimen. Diversification of a S. aureus population is highly favoured during chronic CF lung infection, supporting the general hypothesis that maintenance of intrahost diversity can be of adaptive value, increasing the fitness of the bacterial community. [source] Diversification, Ownership and Control of Swedish CorporationsEUROPEAN FINANCIAL MANAGEMENT, Issue 3 2002John A. Doukas We study the short- and long-term valuation effects of Swedish takeovers. Using a sample of 93 bidding firms that acquired 101 targets between 1980 and 1995, we find that diversifying acquisitions lead to a negative market reaction and deterioration of the operating performance of the bidder. Announcement and performance gains in each of the three years following the acquisition occur only when bidders expand their core rather than their peripheral lines of business. Our findings suggest that focused acquisitions lead to greater synergies and operating efficiencies than diversifying acquisitions. Intra-group acquisitions, however, show that bidders do not realise significant gains whether they adopt diversifying or focusing investment strategies by purchasing firms controlled by the Wallenberg and SHB conglomerate groups. Intra-group targets realize significant gains regardless bidder's investment strategy. Finally, the evidence does not support the view that intra-conglomerate acquisitions are associated with expropriation of minority shareholders. However, they appear to enhance the control rights of large shareholders of the bidding firm. [source] Synthesis and Characterisation of Coordination Polymers of CuII and ZnII with 1,3-Bis(1,2,3,4-tetrazol-2-yl)propane , Rotational Freedom of the Donor Group Favours Structural DiversificationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 18 2004Robert Bronisz Abstract The novel bidentate ligand 1,3-bis(1,2,3,4-tetrazol-2-yl)propane (pbtz), which possesses a flexible spacer, was synthesised in order to investigate the influence of the flexibility of ligand molecules on the architecture of coordination polymers. For that purpose the reactions between pbtz and M(ClO4)2·6H2O salts (M = CuII and ZnII) were performed. The complexes [{Cu(pbtz)3}(ClO4)2], and [{Zn(pbtz)3}(ClO4)2·2EtOH], were characterised by IR and UV/Vis spectroscopy and their crystal structures were determined by single-crystal X-ray diffraction measurements. In both compounds the pbtz ligand molecules act as N4,N4, connectors bridging the central atoms, and the 2-substituted tetrazole rings coordinate in a monodentate fashion to the central atoms forming M(tetrazole)6 cores. [{Cu(pbtz)3}(ClO4)2], was isolated as a 1D coordination polymer. The copper(II) ions are triply bridged by ligand molecules, leading to the formation of infinite 1D chains. A highly unusual manner of bridging, with the tethering of two neighbouring central atoms by the same kind of ligand molecules, although possessing different conformations, is observed. In [{Zn(pbtz)3}(ClO4)2·2EtOH], the six-coordinate zinc(II) ions, which are bridged by single ligand molecules, serve as topological nodes, leading to the formation of a 3D ,-polonium-type network. The crystal structure of the ZnII complex contains only one such net solvated by ethanol molecules. A conformational analysis of the ligand molecules in both compounds demonstrates that the flexibility of the pbtz and the ability of the tetrazole rings in particular to adopt various, relative orientations is responsible for the diversity of the architectures of the obtained complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] THE COMBINED EFFECTS OF RIVERS AND REFUGIA GENERATE EXTREME CRYPTIC FRAGMENTATION WITHIN THE COMMON GROUND SKINK (SCINCELLA LATERALIS)EVOLUTION, Issue 2 2010Nathan D. Jackson Rivers can act as both islands of mesic refugia for terrestrial organisms during times of aridification and barriers to gene flow, though evidence for long-term isolation by rivers is mixed. Understanding the extent to which riverine barrier effects can be heightened for populations trapped in mesic refugia can help explain maintenance and generation of diversity in the face of Pleistocene climate change. Herein, we implement phylogenetic and population genetic approaches to investigate the phylogeographic structure and history of the ground skink, Scincella lateralis, using mtDNA and eight nuclear loci. We then test several predictions of a river,refugia model of diversification. We recover 14 well-resolved mtDNA lineages distributed east,west along the Gulf Coast with a subset of lineages extending northward. In contrast, ncDNA exhibits limited phylogenetic structure or congruence among loci. However, multilocus population structure is broadly congruent with mtDNA patterns and suggests that deep coalescence rather than differential gene flow is responsible for mtDNA,ncDNA discordance. The observed patterns suggest that most lineages originated from population vicariance due to riverine barriers strengthened during the Plio,Pleistocene by a climate-induced coastal distribution. Diversification due to rivers is likely a special case, contingent upon other environmental or biological factors that reinforce riverine barrier effects. [source] Diversification of nubbin expression patterns in arthropods: data from an additional spider species, Cupiennius saleiEVOLUTION AND DEVELOPMENT, Issue 4 2005Nikola-Michael Prpic First page of article [source] Evolution of peptidoglycan biosynthesis under the selective pressure of antibiotics in Gram-positive bacteriaFEMS MICROBIOLOGY REVIEWS, Issue 2 2008Jean-Luc Mainardi Abstract Acquisition of resistance to the two classes of antibiotics therapeutically used against Gram-positive bacteria, the glycopeptides and the ,-lactams, has revealed an unexpected flexibility in the peptidoglycan assembly pathway. Glycopeptides select for diversification of the fifth position of stem pentapeptides because replacement of d -Ala by d -lactate or d -Ser at this position prevents binding of the drugs to peptidoglycan precursors. The substitution is generally well tolerated by the classical d,d -transpeptidases belonging to the penicillin-binding protein family, except by low-affinity enzymes. Total elimination of the fifth residue by a d,d -carboxypeptidase requires a novel cross-linking enzyme able to process the resulting tetrapeptide stems. This enzyme, an l,d -transpeptidase, confers cross-resistance to ,-lactams and glycopeptides. Diversification of the side chain of the precursors, presumably in response to the selective pressure of peptidoglycan endopeptidases, is controlled by aminoacyl transferases of the Fem family that redirect specific aminoacyl-tRNAs from translation to peptidoglycan synthesis. Diversification of the side chains has been accompanied by a parallel divergent evolution of the substrate specificity of the l,d -transpeptidases, in contrast to the d,d -transpeptidases, which display an unexpected broad specificity. This review focuses on the role of antibiotics in selecting or counter-selecting diversification of the structure of peptidoglycan precursors and their mode of polymerization. [source] Can Diversification Create Value?FINANCIAL MANAGEMENT, Issue 1 2005Evidence from the Electric Utility Industry Despite SEC and state-level resistance, and contrary to the trend pursued by other firms, many electric utilities have diversified into non-electric and unregulated businesses. Moreover, this failure to focus has been rewarded with higher firm values, again contrary to the discounts documented in the literature for other diversifying firms. Prior literature has questioned whether these premiums (or discounts) can be attributed to diversification per se. Rather, these premiums could arise from the characteristics of the diversifying firms, which have then endogenously chosen to diversify. In a new approach, where regulation can make the diversification decision largely exogenous, we examine the investment policies of the comparable electric-segments in the diversifying and non-diversifying utilities. We find that single-segment electric utilities over-invest compared to diversifying utilities, which explains their diversification premiums and implies that diversification can create value by opening up new investment opportunities. [source] A past and a future for diversification on farms?GEOGRAFISKA ANNALER SERIES B: HUMAN GEOGRAPHY, Issue 1 2003Some evidence from large-scale, commercial farms in South East England Abstract Diversification has been identified as a common response to the agricultural crisis of the 1980s and to the changing ethos of agricultural policy in the closing decade of the twentieth century. In particular, farmers operating large-scale farms have been prominent in adopting this approach, just as they were innovative across a range of farming practices in the expansion and modernisation of their agricultural production in earlier decades. Can we identify serial diversifiers within this sector of the farming community, who are disposed to react in an entrepreneurial fashion to the changing fortunes of agriculture? The paper draws on results from a survey of large-scale commercial farmers in South East England and, by examining the sequence in which various forms of diversification were adopted, identifies a temporal pattern as farmers responded to the fluctuating fortunes of the agricultural industry over the past thirty years. But has the potential for diversification been exhausted? The paper also considers future prospects for diversification within the large-scale, commercially oriented sector of the agricultural industry. [source] Headache Research Funding: The Need for DiversificationHEADACHE, Issue 3 2008John F. Rothrock MD No abstract is available for this article. [source] Putting flesh and polish on autoimmune hepatitis and moving the disease of exclusion to inclusion,HEPATOLOGY, Issue 4 2010Albert J. Czaja Autoimmune hepatitis emerged during an era when concepts of neonatal immune tolerance, clonal selection of lymphocytes, and "forbidden clones" of activated immune cells were forming. The diagnosis had to be deduced from circumstantial evidence and by exclusion of other conditions. The goals of this review are to demonstrate how a clinician nonscientist can contribute to the maturation of autoimmune hepatitis and to illustrate the principles of clinical investigation that can be applied broadly to other projects. Autoimmune hepatitis initially had to be distinguished from other diseases, and improvements in the tests for viral and immune markers were instrumental in this regard. Diversification of the clinical phenotype to accommodate acute severe, asymptomatic, elderly, and variant forms enhanced the pertinence of the disease, and the formation of the International Autoimmune Hepatitis Group standardized the diagnosis, interconnected investigators, and promoted global acceptance of the condition. Subsequent studies refined current corticosteroid-based therapies, identified prognostic markers, assessed genetic predispositions, explored new pharmacological agents, and forecast the emergence of cellular and molecular interventions. Good fortune, stimulating mentors, career dedication, practical goal selection, protocol compliance, compulsive record keeping, personal resilience, and strong collaborations were the bases for progress. Autoimmune hepatitis exemplifies an evolutionary process in the science of autoimmunity and the people committed to its study. Lessons derived from this experience can be far-reaching. (HEPATOLOGY 2010;52:1177-1184) [source] Farmer Initiatives and Livelihood Diversification: From the Collective to a Market Economy in Rural ChinaJOURNAL OF AGRARIAN CHANGE, Issue 2 2009JINGZHONG YE This paper explores how, despite relatively undifferentiated economic, cultural and land tenure conditions, some farmers in a rural area of Hebei Province, north-east China, have managed to devise innovative livelihood activities that provide them with better living standards than the majority of villagers. The research concludes that the dynamics of farmer innovations emerge from a variety of factors: the building of effective social networks and sources of information, ,enlightenment' deriving from small-group interactions, and the construction of trust relations, self-help and cooperation. These factors belong to the sphere of social resources rather than to those of natural, physical, human or financial assets. Hence it is social components that constitute the mobilizers of change in regard to farmers' livelihood development. [source] Structural Diversification of Macrolactones by Substrate-Flexible Cytochrome P450 MonooxygenasesADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 10 2005Kil Lee Abstract The substrate flexibilities of several cytochrome P450 monooxygenases involved in macrolide biosynthesis were investigated to test their potential for the generation of novel macrolides. PikC hydroxylase in the pikromycin producer Streptomyces venezuelae accepted oleandomycin as an alternative substrate and introduced a hydroxy group at the C-4 position, which is different from the intrinsic C-12 hydroxylation position in the natural substrate. This is the first report of C-4 hydroxylation activity of cytochrome P450 monooxygenase involved in the biosynthesis of 14-membered macrolides. EryF hydroxylase from the erythromycin biosynthetic pathway of Saccharopolyspora erythraea and OleP oxidase from the oleandomycin biosynthetic pathway of Streptomyces antibioticus also showed a certain degree of plasticity towards alternative substrates. In particular, EryF and OleP were found to oxidize a 12-membered macrolactone as an alternative substrate. These results demonstrate the potential usefulness of these enzymes to diversify macrolactones by post-PKS oxidations. [source] Diversification in MHC class II invariant chain-like proteins among fishesJOURNAL OF APPLIED ICHTHYOLOGY, Issue 4 2004M. Sakai Summary The major histocompatibility complex (MHC) class II invariant chains are important for an efficient and complete presentation of antigens by MHC class II molecules. Invariant chain-like proteins (Iclp) 1 and 2 were identified by expressed sequence tag analysis from cDNA library of common carp head kidney (HK) stimulated with concanavalin A and lipopolysaccharide. The sequences were 1043 and 1016 bp in length encoding 234 and 198 amino acid proteins, respectively. Based on their predicted structure, the genes harboured transmembrane domain (TMD) and Tg (thyroglobulin) type 1 domains. Expression analysis revealed that both genes were expressed in normal tissues of HK, intestine, brain and gill. By database search, similar homologues were found in Atlantic salmon, fugu and catfish. Phylogenetic and alignment analysis indicate diversity among fish Iclps. [source] Out of the Palaeotropics?JOURNAL OF BIOGEOGRAPHY, Issue 4 2009Historical biogeography, diversification of the cosmopolitan ectomycorrhizal mushroom family Inocybaceae Abstract Aim, The ectomycorrhizal (ECM) mushroom family Inocybaceae is widespread in north temperate regions, but more than 150 species are encountered in the tropics and the Southern Hemisphere. The relative roles of recent and ancient biogeographical processes, relationships with plant hosts, and the timing of divergences that have shaped the current geographic distribution of the family are investigated. Location, Africa, Australia, Neotropics, New Zealand, north temperate zone, Palaeotropics, Southeast Asia, South America, south temperate zone. Methods, We reconstruct a phylogeny of the Inocybaceae with a geological timeline using a relaxed molecular clock. Divergence dates of lineages are estimated statistically to test vicariance-based hypotheses concerning relatedness of disjunct ECM taxa. A series of internal maximum time constraints is used to evaluate two different calibrations. Ancestral state reconstruction is used to infer ancestral areas and ancestral plant partners of the family. Results, The Palaeotropics are unique in containing representatives of all major clades of Inocybaceae. Six of the seven major clades diversified initially during the Cretaceous, with subsequent radiations probably during the early Palaeogene. Vicariance patterns cannot be rejected that involve area relationships for Africa,Australia, Africa,India and southern South America,Australia. Northern and southern South America, Australia and New Zealand are primarily the recipients of immigrant taxa during the Palaeogene or later. Angiosperms were the earliest hosts of Inocybaceae. Transitions to conifers probably occurred no earlier than 65 Ma. Main conclusions, The Inocybaceae initially diversified no later than the Cretaceous in Palaeotropical settings, in association with angiosperms. Diversification within major clades of the family accelerated during the Palaeogene in north and south temperate regions, whereas several relictual lineages persisted in the tropics. Both vicariance and dispersal patterns are detected. Species from Neotropical and south temperate regions are largely derived from immigrant ancestors from north temperate or Palaeotropical regions. Transitions to conifer hosts occurred later, probably during the Palaeogene. [source] A macroevolutionary mosaic: episodic host-switching, geographical colonization and diversification in complex host,parasite systemsJOURNAL OF BIOGEOGRAPHY, Issue 9 2008Eric P. Hoberg Abstract Aim, To integrate ecological fitting, the oscillation hypothesis and the taxon pulse hypothesis into a coherent null model for the evolution of complex host,parasite associations. Location, Global. Methods, This paper reviews and synthesizes literature that focuses on phylogenetic analyses and reciprocal mapping of a model system of hosts and their parasites to determine patterns of host,parasite associations and geographical distributions through time. Results, Host-switching and geographical dispersal of parasites are common phenomena, occurring on many temporal and spatial scales. Diversification involving both co-evolution and colonization explains complex host,parasite associations. Across the expanse of Earth history, the major radiations in host,parasite assemblages have been preceded by ecological disruption, ecological breakdown and host-switching in a context that can be defined by the concept of ecological fitting. This cyclical process sets the stage for co-diversification during periods of relative stability, punctuated by host-switching during episodes of regional to global environmental disruption and climatological change. Main conclusions, Most observed host,parasite associations can be explained by an historical interaction between ecological fitting, oscillation (episodes of increasing host range alternating with isolation on particular hosts) and taxon pulses (cyclical episodes of expansion and isolation in geographical range). Major episodes of environmental change appear to be the main drivers for both the persistence and diversification of host,parasite systems, creating opportunities for host-switching during periods of geographical expansion and allowing for co-evolution and co-speciation during periods of geographical isolation. [source] | |||||||||||||||||||||||||||||||||||||||||||||||||