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1.
Nat Microbiol ; 4(5): 826-836, 2019 05.
Artigo em Inglês | MEDLINE | ID: mdl-30833731

RESUMO

Human cryptosporidiosis is the leading protozoan cause of diarrhoeal mortality worldwide, and a preponderance of infections is caused by Cryptosporidium hominis and C. parvum. Both species consist of several subtypes with distinct geographical distributions and host preferences (that is, generalist zoonotic and specialist anthroponotic subtypes). The evolutionary processes that drive the adaptation to the human host and the population structures of Cryptosporidium remain unknown. In this study, we analyse 21 whole-genome sequences to elucidate the evolution of anthroponosis. We show that Cryptosporidium parvum splits into two subclades and that the specialist anthroponotic subtype IIc-a shares a subset of loci with C. hominis that is undergoing rapid convergent evolution driven by positive selection. C. parvum subtype IIc-a also has an elevated level of insertion and deletion mutations in the peri-telomeric genes, which is also a characteristic of other specialist subtypes. Genetic exchange between Cryptosporidium subtypes plays a prominent role throughout the evolution of the genus. Interestingly, recombinant regions are enriched for positively selected genes and potential virulence factors, which indicates adaptive introgression. Analysis of 467 gp60 sequences collected from locations across the world shows that the population genetic structure differs markedly between the main zoonotic subtype (isolation-by-distance) and the anthroponotic subtype (admixed population structure). We also show that introgression between the four anthroponotic Cryptosporidium subtypes and species included in this study has occurred recently, probably within the past millennium.


Assuntos
Criptosporidiose/parasitologia , Cryptosporidium/genética , Evolução Molecular , Genoma de Protozoário , Zoonoses/parasitologia , Animais , Criptosporidiose/transmissão , Cryptosporidium/classificação , Cryptosporidium/isolamento & purificação , Cryptosporidium/fisiologia , DNA de Protozoário/genética , Genômica , Genótipo , Humanos , Mutação , Filogenia , Polimorfismo de Nucleotídeo Único , Proteínas de Protozoários/genética , Ruminantes/parasitologia , Zoonoses/transmissão
2.
Proc Natl Acad Sci U S A ; 116(13): 5846-5848, 2019 03 26.
Artigo em Inglês | MEDLINE | ID: mdl-30862733
3.
Plant J ; 98(3): 555-570, 2019 May.
Artigo em Inglês | MEDLINE | ID: mdl-30604470

RESUMO

To optimize shoot growth and structure of cereals, we need to understand the genetic components controlling initiation and elongation. While measuring total shoot growth at high throughput using 2D imaging has progressed, recovering the 3D shoot structure of small grain cereals at a large scale is still challenging. Here, we present a method for measuring defined individual leaves of cereals, such as wheat and barley, using few images. Plant shoot modelling over time was used to measure the initiation and elongation of leaves in a bi-parental barley mapping population under low and high soil salinity. We detected quantitative trait loci (QTL) related to shoot growth per se, using both simple 2D total shoot measurements and our approach of measuring individual leaves. In addition, we detected QTL specific to leaf elongation and not to total shoot size. Of particular importance was the detection of a QTL on chromosome 3H specific to the early responses of leaf elongation to salt stress, a locus that could not be detected without the computer vision tools developed in this study.

4.
New Phytol ; 2018 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-30288743

RESUMO

The oomycete pathogens Phytophthora infestans and P. capsici cause significant crop losses world-wide, threatening food security. In each case, pathogenicity factors, called RXLR effectors, contribute to virulence. Some RXLRs are perceived by resistance proteins to trigger host immunity, but our understanding of the demographic processes and adaptive evolution of pathogen virulence remains poor. Here, we describe PenSeq, a highly efficient enrichment sequencing approach for genes encoding pathogenicity determinants which, as shown for the infamous potato blight pathogen Phytophthora infestans, make up < 1% of the entire genome. PenSeq facilitates the characterization of allelic diversity in pathogen effectors, enabling evolutionary and population genomic analyses of Phytophthora species. Furthermore, PenSeq enables the massively parallel identification of presence/absence variations and sequence polymorphisms in key pathogen genes, which is a prerequisite for the efficient deployment of host resistance genes. PenSeq represents a cost-effective alternative to whole-genome sequencing and addresses crucial limitations of current plant pathogen population studies, which are often based on selectively neutral markers and consequently have limited utility in the analysis of adaptive evolution. The approach can be adapted to diverse microbes and pathogens.

5.
New Phytol ; 2018 Oct 05.
Artigo em Inglês | MEDLINE | ID: mdl-30288750

RESUMO

Physiological races of the oomycete Albugo candida are biotrophic pathogens of diverse plant species, primarily the Brassicaceae, and cause infections that suppress host immunity to other pathogens. However, A. candida race diversity and the consequences of host immunosuppression are poorly understood in the field. We report a method that enables sequencing of DNA of plant pathogens and plant-associated microbes directly from field samples (Pathogen Enrichment Sequencing: PenSeq). We apply this method to explore race diversity in A. candida and to detect A. candida-associated microbes in the field (91 A. candida-infected plants). We show with unprecedented resolution that each host plant species supports colonization by one of 17 distinct phylogenetic lineages, each with an unique repertoire of effector candidate alleles. These data reveal the crucial role of sexual and asexual reproduction, polyploidy and host domestication in A. candida specialization on distinct plant species. Our bait design also enabled phylogenetic assignment of DNA sequences from bacteria and fungi from plants in the field. This paper shows that targeted sequencing has a great potential for the study of pathogen populations while they are colonizing their hosts. This method could be applied to other microbes, especially to those that cannot be cultured.

6.
Nat Ecol Evol ; 2(6): 1000-1008, 2018 Jun.
Artigo em Inglês | MEDLINE | ID: mdl-29686237

RESUMO

Accelerating international trade and climate change make pathogen spread an increasing concern. Hymenoscyphus fraxineus, the causal agent of ash dieback, is a fungal pathogen that has been moving across continents and hosts from Asian to European ash. Most European common ash trees (Fraxinus excelsior) are highly susceptible to H. fraxineus, although a minority (~5%) have partial resistance to dieback. Here, we assemble and annotate a H. fraxineus draft genome, which approaches chromosome scale. Pathogen genetic diversity across Europe and in Japan, reveals a strong bottleneck in Europe, though a signal of adaptive diversity remains in key host interaction genes. We find that the European population was founded by two divergent haploid individuals. Divergence between these haplotypes represents the ancestral polymorphism within a large source population. Subsequent introduction from this source would greatly increase adaptive potential of the pathogen. Thus, further introgression of H. fraxineus into Europe represents a potential threat and Europe-wide biological security measures are needed to manage this disease.

7.
Genome Res ; 28(4): 448-459, 2018 04.
Artigo em Inglês | MEDLINE | ID: mdl-29563166

RESUMO

Understanding the mechanisms driving lineage-specific evolution in both primates and rodents has been hindered by the lack of sister clades with a similar phylogenetic structure having high-quality genome assemblies. Here, we have created chromosome-level assemblies of the Mus caroli and Mus pahari genomes. Together with the Mus musculus and Rattus norvegicus genomes, this set of rodent genomes is similar in divergence times to the Hominidae (human-chimpanzee-gorilla-orangutan). By comparing the evolutionary dynamics between the Muridae and Hominidae, we identified punctate events of chromosome reshuffling that shaped the ancestral karyotype of Mus musculus and Mus caroli between 3 and 6 million yr ago, but that are absent in the Hominidae. Hominidae show between four- and sevenfold lower rates of nucleotide change and feature turnover in both neutral and functional sequences, suggesting an underlying coherence to the Muridae acceleration. Our system of matched, high-quality genome assemblies revealed how specific classes of repeats can play lineage-specific roles in related species. Recent LINE activity has remodeled protein-coding loci to a greater extent across the Muridae than the Hominidae, with functional consequences at the species level such as reproductive isolation. Furthermore, we charted a Muridae-specific retrotransposon expansion at unprecedented resolution, revealing how a single nucleotide mutation transformed a specific SINE element into an active CTCF binding site carrier specifically in Mus caroli, which resulted in thousands of novel, species-specific CTCF binding sites. Our results show that the comparison of matched phylogenetic sets of genomes will be an increasingly powerful strategy for understanding mammalian biology.


Assuntos
Evolução Molecular , Genoma/genética , Muridae/genética , Filogenia , Animais , Sítios de Ligação , Fator de Ligação a CCCTC/genética , Cromossomos/genética , Cariotipagem/métodos , Elementos Nucleotídeos Longos e Dispersos/genética , Camundongos , Retroelementos/genética , Especificidade da Espécie
8.
Nat Commun ; 8(1): 1294, 2017 11 03.
Artigo em Inglês | MEDLINE | ID: mdl-29101318

RESUMO

Red Queen host-parasite co-evolution can drive adaptations of immune genes by positive selection that erodes genetic variation (Red Queen arms race) or results in a balanced polymorphism (Red Queen dynamics) and long-term preservation of genetic variation (trans-species polymorphism). These two Red Queen processes are opposite extremes of the co-evolutionary spectrum. Here we show that both Red Queen processes can operate simultaneously by analysing the major histocompatibility complex (MHC) in guppies (Poecilia reticulata and P. obscura) and swamp guppies (Micropoecilia picta). Sub-functionalisation of MHC alleles into 'supertypes' explains how polymorphisms persist during rapid host-parasite co-evolution. Simulations show the maintenance of supertypes as balanced polymorphisms, consistent with Red Queen dynamics, whereas alleles within supertypes are subject to positive selection in a Red Queen arms race. Building on the divergent allele advantage hypothesis, we show that functional aspects of allelic diversity help to elucidate the evolution of polymorphic genes involved in Red Queen co-evolution.


Assuntos
Ciprinodontiformes/genética , Ciprinodontiformes/imunologia , Evolução Molecular , Complexo Principal de Histocompatibilidade , Poecilia/genética , Poecilia/imunologia , Alelos , Animais , Simulação por Computador , Variação Genética , Genética Populacional , Interações Hospedeiro-Parasita/genética , Interações Hospedeiro-Parasita/imunologia , Desequilíbrio de Ligação , Modelos Genéticos , Modelos Imunológicos , Polimorfismo Genético , Seleção Genética , Especificidade da Espécie
9.
Am Nat ; 190(1): 116-130, 2017 07.
Artigo em Inglês | MEDLINE | ID: mdl-28617645

RESUMO

Models of community assembly have been used to illustrate how the many functionally diverse species that compose plankton food webs can coexist. However, the evolutionary processes leading to the emergence of plankton food webs and their interplay with migratory processes and spatial heterogeneity are yet to be explored. We study the eco-evolutionary dynamics of a modeled plankton community structured in both size and space and physiologically constrained by empirical data. We demonstrate that a complex yet ecologically and evolutionarily stable size-structured food web can emerge from an initial set of two monomorphic phytoplankton and zooplankton populations. We also show that the coupling of spatial heterogeneity and migration results in the emergence of specific biogeographic patterns: (i) the emergence of a source-sink structure of the plankton metacommunities, (ii) changes in size diversity dependent on migratory intensity and on the scale at which diversity is considered (local vs. global), and (iii) the emergence of eco-evolutionary provinces (i.e., a spatial unit characterized by some level of abiotic heterogeneity but of homogenous size composition due to horizontal movements) at spatial scales that increase with the strength of the migratory processes.


Assuntos
Evolução Biológica , Cadeia Alimentar , Plâncton , Animais , Fitoplâncton , Zooplâncton
10.
Nature ; 541(7638): 536-540, 2017 01 26.
Artigo em Inglês | MEDLINE | ID: mdl-28092920

RESUMO

The Southern Ocean houses a diverse and productive community of organisms. Unicellular eukaryotic diatoms are the main primary producers in this environment, where photosynthesis is limited by low concentrations of dissolved iron and large seasonal fluctuations in light, temperature and the extent of sea ice. How diatoms have adapted to this extreme environment is largely unknown. Here we present insights into the genome evolution of a cold-adapted diatom from the Southern Ocean, Fragilariopsis cylindrus, based on a comparison with temperate diatoms. We find that approximately 24.7 per cent of the diploid F. cylindrus genome consists of genetic loci with alleles that are highly divergent (15.1 megabases of the total genome size of 61.1 megabases). These divergent alleles were differentially expressed across environmental conditions, including darkness, low iron, freezing, elevated temperature and increased CO2. Alleles with the largest ratio of non-synonymous to synonymous nucleotide substitutions also show the most pronounced condition-dependent expression, suggesting a correlation between diversifying selection and allelic differentiation. Divergent alleles may be involved in adaptation to environmental fluctuations in the Southern Ocean.


Assuntos
Aclimatação/genética , Temperatura Baixa , Diatomáceas/genética , Evolução Molecular , Genoma/genética , Genômica , Alelos , Dióxido de Carbono/metabolismo , Escuridão , Diatomáceas/metabolismo , Congelamento , Perfilação da Expressão Gênica , Deriva Genética , Camada de Gelo , Ferro/metabolismo , Taxa de Mutação , Oceanos e Mares , Filogenia , Recombinação Genética , Transcriptoma/genética
11.
Am Nat ; 189(2): 170-177, 2017 Feb.
Artigo em Inglês | MEDLINE | ID: mdl-28107051

RESUMO

Rates of metabolism and population growth are often assumed to decrease universally with increasing organism size. Recent observations have shown, however, that maximum population growth rates among phytoplankton smaller than ∼6 µm in diameter tend to increase with organism size. Here we bring together observations and theory to demonstrate that the observed change in slope is attributable to a trade-off between nutrient uptake and the potential rate of internal metabolism. Specifically, we apply an established model of phytoplankton growth to explore a trade-off between the ability of cells to replenish their internal quota (which increases with size) and their ability to synthesize new biomass (which decreases with size). Contrary to the metabolic theory of ecology, these results demonstrate that rates of resource acquisition (rather than metabolism) provide the primary physiological constraint on the growth rates of some of the smallest and most numerically abundant photosynthetic organisms on Earth.


Assuntos
Modelos Biológicos , Fitoplâncton/crescimento & desenvolvimento , Biomassa , Ecologia , Fotossíntese
12.
R Soc Open Sci ; 3(10): 160299, 2016 Oct.
Artigo em Inglês | MEDLINE | ID: mdl-27853546

RESUMO

The relative importance of genetic versus epigenetic changes in adaptive evolution is a hotly debated topic, with studies showing that some species appear to be able to adapt rapidly without significant genetic change. Epigenetic mechanisms may be particularly important for the evolutionary potential of species with long maturation times and low reproductive potential ('K-strategists'), particularly when faced with rapidly changing environmental conditions. Here we study the transcriptome of two populations of the winter skate (Leucoraja ocellata), a typical 'K-strategist', in Atlantic Canada; an endemic population in the southern Gulf of St Lawrence and a large population on the Scotian Shelf. The endemic population has been able to adapt to a 10°C higher water temperature over short evolutionary time (7000 years), dramatically reducing its body size (by 45%) significantly below the minimum maturation size of Scotian Shelf and other populations of winter skate, as well as exhibiting other adaptations in life history and physiology. We demonstrate that the adaptive response to selection has an epigenetic basis, cataloguing 3653 changes in gene expression that may have enabled this species to rapidly respond to the novel environment. We argue that the epigenetic augmentation of species evolutionary potential (its regulation though gene expression) can enable K-strategists to survive and adapt to different environments, and this mechanism may be particularly important for the persistence of sharks, skates and rays in the light of future climate change.

13.
Proc Natl Acad Sci U S A ; 113(11): 2958-63, 2016 Mar 15.
Artigo em Inglês | MEDLINE | ID: mdl-26831076

RESUMO

Mixotrophic plankton, which combine the uptake of inorganic resources and the ingestion of living prey, are ubiquitous in marine ecosystems, but their integrated biogeochemical impacts remain unclear. We address this issue by removing the strict distinction between phytoplankton and zooplankton from a global model of the marine plankton food web. This simplification allows the emergence of a realistic trophic network with increased fidelity to empirical estimates of plankton community structure and elemental stoichiometry, relative to a system in which autotrophy and heterotrophy are mutually exclusive. Mixotrophy enhances the transfer of biomass to larger sizes classes further up the food chain, leading to an approximately threefold increase in global mean organism size and an ∼35% increase in sinking carbon flux.


Assuntos
Processos Autotróficos/fisiologia , Ciclo do Carbono , Cadeia Alimentar , Processos Heterotróficos/fisiologia , Modelos Biológicos , Plâncton/metabolismo , Animais , Organismos Aquáticos/fisiologia , Biomassa , Tamanho Corporal , Clorofila/análise , Clorofila/efeitos da radiação , Clorofila A , Ecossistema , Comportamento Alimentar , Sedimentos Geológicos , Ferro/metabolismo , Ciclo do Nitrogênio , Oceanos e Mares , Fósforo/metabolismo , Fotossíntese , Plâncton/crescimento & desenvolvimento , Plâncton/efeitos da radiação , Comportamento Predatório , Estações do Ano , Luz Solar
14.
Mol Ecol Resour ; 16(2): 534-9, 2016 Mar.
Artigo em Inglês | MEDLINE | ID: mdl-26394708

RESUMO

HYBRIDCHECK is a software package to visualize the recombination signal in large DNA sequence data set, and it can be used to analyse recombination, genetic introgression, hybridization and horizontal gene transfer. It can scan large (multiple kb) contigs and whole-genome sequences of three or more individuals. HYBRIDCHECK is written in the r software for OS X, Linux and Windows operating systems, and it has a simple graphical user interface. In addition, the r code can be readily incorporated in scripts and analysis pipelines. HYBRIDCHECK implements several ABBA-BABA tests and visualizes the effects of hybridization and the resulting mosaic-like genome structure in high-density graphics. The package also reports the following: (i) the breakpoint positions, (ii) the number of mutations in each introgressed block, (iii) the probability that the identified region is not caused by recombination and (iv) the estimated age of each recombination event. The divergence times between the donor and recombinant sequence are calculated using a JC, K80, F81, HKY or GTR correction, and the dating algorithm is exceedingly fast. By estimating the coalescence time of introgressed blocks, it is possible to distinguish between hybridization and incomplete lineage sorting. HYBRIDCHECK is libré software and it and its manual are free to download from http://ward9250.github.io/HybridCheck/.


Assuntos
Biologia Computacional/métodos , Genômica/métodos , Recombinação Genética , Análise de Sequência de DNA/métodos , Software
15.
PLoS One ; 10(8): e0135581, 2015.
Artigo em Inglês | MEDLINE | ID: mdl-26285028

RESUMO

Globally distributed observations of size-fractionated chlorophyll a and temperature were used to incorporate temperature dependence into an existing semi-empirical model of phytoplankton community size structure. The additional temperature-dependent term significantly increased the model's ability to both reproduce and predict observations of chlorophyll a size-fractionation at temperatures below 2°C. The most notable improvements were in the smallest (picoplankton) size-class, for which overall model fit was more than doubled, and predictive skill was increased by approximately 40%. The model was subsequently applied to generate global maps for three phytoplankton size classes, on the basis of satellite-derived estimates of surface chlorophyll a and sea surface temperature. Polar waters were associated with marked decline in the chlorophyll a biomass of the smallest cells, relative to lower latitude waters of equivalent total chlorophyll a. In the same regions a complementary increase was seen in the chlorophyll a biomass of larger size classes. These findings suggest that a warming and stratifying ocean will see a poleward expansion of the habitat range of the smallest phytoplankton, with the possible displacement of some larger groups that currently dominate. There was no evidence of a strong temperature dependence in tropical or sub-tropical regions, suggesting that future direct temperature effects on community structure at lower latitudes may be small.


Assuntos
Biomassa , Clorofila/metabolismo , Modelos Teóricos , Fitoplâncton/crescimento & desenvolvimento , Água do Mar/química , Clorofila A , Ecossistema , Densidade Demográfica , Estações do Ano , Temperatura Ambiente
16.
J Plankton Res ; 37(1): 28-47, 2015 Jan.
Artigo em Inglês | MEDLINE | ID: mdl-25852217

RESUMO

The functional and taxonomic biogeography of marine microbial systems reflects the current state of an evolving system. Current models of marine microbial systems and biogeochemical cycles do not reflect this fundamental organizing principle. Here, we investigate the evolutionary adaptive potential of marine microbial systems under environmental change and introduce explicit Darwinian adaptation into an ocean modelling framework, simulating evolving phytoplankton communities in space and time. To this end, we adopt tools from adaptive dynamics theory, evaluating the fitness of invading mutants over annual timescales, replacing the resident if a fitter mutant arises. Using the evolutionary framework, we examine how community assembly, specifically the emergence of phytoplankton cell size diversity, reflects the combined effects of bottom-up and top-down controls. When compared with a species-selection approach, based on the paradigm that "Everything is everywhere, but the environment selects", we show that (i) the selected optimal trait values are similar; (ii) the patterns emerging from the adaptive model are more robust, but (iii) the two methods lead to different predictions in terms of emergent diversity. We demonstrate that explicitly evolutionary approaches to modelling marine microbial populations and functionality are feasible and practical in time-varying, space-resolving settings and provide a new tool for exploring evolutionary interactions on a range of timescales in the ocean.

17.
Elife ; 42015 Feb 27.
Artigo em Inglês | MEDLINE | ID: mdl-25723966

RESUMO

How generalist parasites with wide host ranges can evolve is a central question in parasite evolution. Albugo candida is an obligate biotrophic parasite that consists of many physiological races that each specialize on distinct Brassicaceae host species. By analyzing genome sequence assemblies of five isolates, we show they represent three races that are genetically diverged by ∼1%. Despite this divergence, their genomes are mosaic-like, with ∼25% being introgressed from other races. Sequential infection experiments show that infection by adapted races enables subsequent infection of hosts by normally non-infecting races. This facilitates introgression and the exchange of effector repertoires, and may enable the evolution of novel races that can undergo clonal population expansion on new hosts. We discuss recent studies on hybridization in other eukaryotes such as yeast, Heliconius butterflies, Darwin's finches, sunflowers and cichlid fishes, and the implications of introgression for pathogen evolution in an agro-ecological environment.


Assuntos
Genoma , Especificidade de Hospedeiro , Imunidade , Oomicetos/genética , Oomicetos/fisiologia , Parasitos/genética , Parasitos/fisiologia , Alelos , Animais , DNA de Plantas/metabolismo , Nucleotídeos/genética , Oomicetos/isolamento & purificação , Oomicetos/patogenicidade , Parasitos/isolamento & purificação , Parasitos/patogenicidade , Filogenia , Reação em Cadeia da Polimerase , Polimorfismo Genético , Recombinação Genética/genética , Alinhamento de Sequência , Virulência/genética
18.
Ecol Lett ; 16(4): 522-34, 2013 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-23360597

RESUMO

Changes in marine plankton communities driven by environmental variability impact the marine food web and global biogeochemical cycles of carbon and other elements. To predict and assess these community shifts and their consequences, ecologists are increasingly investigating how the functional traits of plankton determine their relative fitness along environmental and biological gradients. Laboratory, field and modelling studies are adopting this trait-based approach to map the biogeography of plankton traits that underlies variations in plankton communities. Here, we review progress towards understanding the regulatory roles of several key plankton functional traits, including cell size, N2 -fixation and mixotrophy among phytoplankton, and body size, ontogeny and feeding behaviour for zooplankton. The trait biogeographical approach sheds light on what structures plankton communities in the current ocean, as well as under climate change scenarios, and also allows for finer resolution of community function because community trait composition determines the rates of significant processes, including carbon export. Although understanding of trait biogeography is growing, uncertainties remain that stem, in part, from the paucity of observations describing plankton functional traits. Thus, in addition to recommending widespread adoption of the trait-based approach, we advocate for enhanced collection, standardisation and dissemination of plankton functional trait data.


Assuntos
Plâncton/fisiologia , Animais , Organismos Aquáticos , Tamanho Corporal , Mudança Climática , Ecossistema , Herança Multifatorial , Fixação de Nitrogênio , Fitoplâncton/citologia , Fitoplâncton/fisiologia , Zooplâncton/fisiologia
19.
Water Sci Technol ; 66(11): 2410-7, 2012.
Artigo em Inglês | MEDLINE | ID: mdl-23032772

RESUMO

A unique methodology for the optimal specification of sewer rehabilitation investment is presented in this paper. By accounting for the critical risk of asset failure, this methodology builds on previously successful work which explored the application of multi-objective optimisation tools to assist engineers with the specification of optimal rehabilitation strategies. The conventional sewerage rehabilitation specification process relies on the expertise of professional engineers to manually evaluate CCTV inspection information when determining the nature and extent of the rehabilitation solution. This process is not only tedious and subjective but it has no quantifiable means of identifying optimal solutions or possible combinations of optimal solutions in the delivery of catchment wide rehabilitation programmes. Therefore, the purely manual process of sewer rehabilitation design leaves a number of unanswered questions, such as: (1) Does the solution offer the greatest structural benefit to the network? (2) Is the solution the most cost-effective solution available? (3) Does the solution most greatly reduce the risk of critical asset failure? The application of a multi-objective genetic algorithm optimisation model, coupled with an enhanced critical risk methodology, has successfully answered these questions when applied to a case study data set provided by South West Water (UK).


Assuntos
Drenagem Sanitária , Modelos Teóricos , Medição de Risco
20.
Am Nat ; 178(1): 98-112, 2011 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-21670581

RESUMO

Mixotrophic organisms combine autotrophic and heterotrophic nutrition and are abundant in both freshwater and marine environments. Recent observations indicate that mixotrophs constitute a large fraction of the biomass, bacterivory, and primary production in oligotrophic environments. While mixotrophy allows greater flexibility in terms of resource acquisition, any advantage must be traded off against an associated increase in metabolic costs, which appear to make mixotrophs uncompetitive relative to obligate autotrophs and heterotrophs. Using an idealized model of cell physiology and community competition, we identify one mechanism by which mixotrophs can effectively outcompete specialists for nutrient elements. At low resource concentrations, when the uptake of nutrients is limited by diffusion toward the cell, the investment in cell membrane transporters can be minimized. In this situation, mixotrophs can acquire limiting elements in both organic and inorganic forms, outcompeting their specialist competitors that can utilize only one of these forms. This advantage can be enough to offset as much as a twofold increase in additional metabolic costs incurred by mixotrophs. This mechanism is particularly relevant for the maintenance of mixotrophic populations and productivity in the highly oligotrophic subtropical oceans.


Assuntos
Processos Autotróficos , Metabolismo Energético , Processos Heterotróficos , Modelos Biológicos , Plâncton/fisiologia , Fenômenos Biofísicos , Simulação por Computador , Ecossistema , Dinâmica Populacional
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