897 resultados para Evolutionary transitions
Resumo:
Background: Seed storage proteins are a major source of dietary protein, and the content of such proteins determines both the quantity and quality of crop yield. Significantly, examination of the protein content in the seeds of crop plants shows a distinct difference between monocots and dicots. Thus, it is expected that there are different evolutionary patterns in the genes underlying protein synthesis in the seeds of these two groups of plants. Results: Gene duplication, evolutionary rate and positive selection of a major gene family of seed storage proteins (the 11S globulin genes), were compared in dicots and monocots. The results, obtained from five species in each group, show more gene duplications, a higher evolutionary rate and positive selections of this gene family in dicots, which are rich in 11S globulins, but not in the monocots. Conclusion: Our findings provide evidence to support the suggestion that gene duplication and an accelerated evolutionary rate may be associated with higher protein synthesis in dicots as compared to monocots.
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The effect of irradiation (UV-visible light) on a nematic liquid crystal doped with a photoactive azobenzene derivative was investigated. The selective irradiation results in either an E implies Z or Z implies E isomerization of the azobenzene unit. The effect of the isomerization is to cause a reversible depression of the liquid crystal to isotropic (LC implies l) phase transition temperature of the doped mixture, which can be monitored optically as an isothermal phase transition. This depression also results in a biphasic liquid crystal+isotropic region which is discussed. The authors investigate the cause and magnitude of the phase depression as a function of the amount of doped 4-butyl-4'-methoxyazobenzene (photoactive unit) in 4-cyano-4'-n-pentylbiphenyl (liquid crystal unit), and as a function of the percentage conversion of E implies Z (caused by isomerization) in the azobenzene. The photostationary state of the doped mixtures achieved by Z implies E isomerization is considered and its effect upon the transition temperature of the mixture and response time of the system is discussed. They discuss the implications of the photostationary state with regards to the reversibility of the photo-induced phase transition and hence potential applications.
Resumo:
Starch is the most widespread and abundant storage carbohydrate in crops and its production is critical to both crop yield and quality. As regards the starch content in the seeds of crop plants, there are distinct difference between grasses (Poaceae) and dicots. However, few studies have described the evolutionary pattern of genes in the starch biosynthetic pathway in these two groups of plants. In this study, therefore, an attempt was made to compare the evolutionary rate, gene duplication and selective pattern of the key genes involved in this pathway between the two groups, using five grasses and five dicots as materials. The results showed (i) distinct differences in patterns of gene duplication and loss between grasses and dicots; duplication in grasses mainly occurred prior to the divergence of grasses, whereas duplication mostly occurred in individual species within the dicots; there is less gene loss in grasses than in dicots; (ii) a considerably higher evolutionary rate in grasses than in dicots in most gene families analyzed; (iii) evidence of a different selective pattern between grasses and dicots; positive selection may have occurred asymmetrically in grasses in some gene families, e.g. AGPase small subunit. Therefore, we deduced that gene duplication contributes to, and a higher evolutionary rate is associated with, the higher starch content in grasses. In addition, two novel aspects of the evolution of the starch biosynthetic pathway were observed.
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Evolutionary developmental genetics brings together systematists, morphologists and developmental geneticists; it will therefore impact on each of these component disciplines. The goals and methods of phylogenetic analysis are reviewed here, and the contribution of evolutionary developmental genetics to morphological systematics, in terms of character conceptualisation and primary homology assessment, is discussed. Evolutionary developmental genetics, like its component disciplines phylogenetic systematics and comparative morphology, is concerned with homology concepts. Phylogenetic concepts of homology and their limitations are considered here, and the need for independent homology statements at different levels of biological organisation is evaluated. The role of systematics in evolutionary developmental genetics is outlined. Phylogenetic systematics and comparative morphology will suggest effective sampling strategies to developmental geneticists. Phylogenetic systematics provides hypotheses of character evolution (including parallel evolution and convergence), stimulating investigations into the evolutionary gains and losses of morphologies. Comparative morphology identifies those structures that are not easily amenable to typological categorisation, and that may be of particular interest in terms of developmental genetics. The concepts of latent homology and genetic recall may also prove useful in the evolutionary interpretation of developmental genetic data.
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Why does music pervade our lives and those of all known human beings living today and in the recent past? Why do we feel compelled to engage in musical activity, or at least simply enjoy listening to music even if we choose not to actively participate? I argue that this is because musicality—communication using variations in pitch, rhythm, dynamics and timbre, by a combination of the voice, body (as in dance), and material culture—was essential to the lives of our pre-linguistic hominin ancestors. As a consequence we have inherited a desire to engage with music, even if this has no adaptive benefit for us today as a species whose communication system is dominated by spoken language. In this article I provide a summary of the arguments to support this view.
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The majority of the world’s population now live in cities. This poses great challenges, but also great opportunities in terms of tackling climate change, resource depletion and environmental degradation. Policy agendas have increasingly focused on how to develop and maintain ‘integrated sustainable urban development’, and a number of theoretical conceptualisations of urban transition have been formulated to help our thinking and understanding in both developed and developing countries. Drawing on examples around the world the paper aims to examine the key ‘critical success factors’ that need to be in place for cities to traverse a pathway to a more sustainable future in urban development terms by 2050. The paper explores how important the issues of ‘scale’ is in the context of complexity and fragmentation in the city’s built environment, identifies the lessons that can be learned for future sustainable urban development, and the further research which is needed to address future urban transitions to 2050.
Resumo:
Whole-genome sequencing offers new insights into the evolution of bacterial pathogens and the etiology of bacterial disease. Staph- ylococcus aureus is a major cause of bacteria-associated mortality and invasive disease and is carried asymptomatically by 27% of adults. Eighty percent of bacteremias match the carried strain. How- ever, the role of evolutionary change in the pathogen during the progression from carriage to disease is incompletely understood. Here we use high-throughput genome sequencing to discover the genetic changes that accompany the transition from nasal carriage to fatal bloodstream infection in an individual colonized with meth- icillin-sensitive S. aureus. We found a single, cohesive population exhibiting a repertoire of 30 single-nucleotide polymorphisms and four insertion/deletion variants. Mutations accumulated at a steady rate over a 13-mo period, except for a cluster of mutations preceding the transition to disease. Although bloodstream bacteria differed by just eight mutations from the original nasally carried bacteria, half of those mutations caused truncation of proteins, including a prema- ture stop codon in an AraC-family transcriptional regulator that has been implicated in pathogenicity. Comparison with evolution in two asymptomatic carriers supported the conclusion that clusters of pro- tein-truncating mutations are highly unusual. Our results demon- strate that bacterial diversity in vivo is limited but nonetheless detectable by whole-genome sequencing, enabling the study of evolutionary dynamics within the host. Regulatory or structural changes that occur during carriage may be functionally important for pathogenesis; therefore identifying those changes is a crucial step in understanding the biological causes of invasive bacterial disease.
Resumo:
1. It has been postulated that climate warming may pose the greatest threat species in the tropics, where ectotherms have evolved more thermal specialist physiologies. Although species could rapidly respond to environmental change through adaptation, little is known about the potential for thermal adaptation, especially in tropical species. 2. In the light of the limited empirical evidence available and predictions from mutation-selection theory, we might expect tropical ectotherms to have limited genetic variance to enable adaptation. However, as a consequence of thermodynamic constraints, we might expect this disadvantage to be at least partially offset by a fitness advantage, that is, the ‘hotter-is-better’ hypothesis. 3. Using an established quantitative genetics model and metabolic scaling relationships, we integrate the consequences of the opposing forces of thermal specialization and thermodynamic constraints on adaptive potential by evaluating extinction risk under climate warming. We conclude that the potential advantage of a higher maximal development rate can in theory more than offset the potential disadvantage of lower genetic variance associated with a thermal specialist strategy. 4. Quantitative estimates of extinction risk are fundamentally very sensitive to estimates of generation time and genetic variance. However, our qualitative conclusion that the relative risk of extinction is likely to be lower for tropical species than for temperate species is robust to assumptions regarding the effects of effective population size, mutation rate and birth rate per capita. 5. With a view to improving ecological forecasts, we use this modelling framework to review the sensitivity of our predictions to the model’s underpinning theoretical assumptions and the empirical basis of macroecological patterns that suggest thermal specialization and fitness increase towards the tropics. We conclude by suggesting priority areas for further empirical research.
Resumo:
The coupled δ13C-radiocarbon systematics of threeEuropean stalagmites deposited during the Late Glacial and early Holocene were investigated to understand better how the carbon isotope systematics of speleothems respond to climate transitions. The emphasis is on understanding how speleothems may record climate-driven changes in the proportions of biogenic (soil carbon) and limestone bedrock derived carbon. At two of the three sites, the combined δ13C and 14C data argue against greater inputs of limestone carbon as the sole cause of the observed shift to higher δ13C during the cold Younger Dryas. In these stalagmites (GAR-01 from La Garma cave, N. Spain and So-1 from Sofular cave, Turkey), the combined changes in δ13C and initial 14C activities suggest enhanced decomposition of old stored, more recalcitrant, soil carbon at the onset of the warmer early Holocene. Alternative explanations involving gradual temporal changes between open- and closed-system behaviour during the Late Glacial are difficult to reconcile with observed changes in speleothem δ13C and the growth rates. In contrast, a stalagmite from Pindal cave (N. Spain) indicates an abrupt change in carbon inputs linked to local hydrological and disequilibrium isotope fractionation effects, rather than climate change. For the first time, it is shown that while the initial 14C activities of all three stalagmites broadly follow the contemporaneous atmospheric 14C trends (the Younger Dryas atmospheric 14C anomaly can be clearly discerned), subtle changes in speleothem initial 14C activities are linked to climate-driven changes in soil carbon turnover at a climate transition.
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This chapter provides insight into young people’s caring relations and transitions within what is often considered a particularly ‘troubling’ familial context in both the global North and South: living with HIV. I analyse the findings from two qualitative studies of young people’s caring roles in families affected by HIV in the UK, Tanzania and Uganda from the perspective of a feminist ethics of care, emotion work and life course transitions.
Resumo:
Three new MnIII complexes, {[Mn-2(salen)(2)(OCn)](ClO4)}(n) (1), {[Mn-2(salen)(2)(OPh)](ClO4)}(n) (2) and {[Mn-2(salen)(2)(OBz)](ClO4)}(2) (3) (where salen = N,N'-bis(salicylidene)-1,2-diaminoethane dianion, OCn = cinnamate, OPh = phenylacetate and OBz = benzoate), have been synthesized and characterized structurally and magnetically. The crystal structures reveal that all three structures contain syn-anti carboxylatebridged dimeric [Mn-2(salen)(2)(OOCR)](+) cations (OOCR = bridging carboxylate) that are joined together by weak Mn center dot center dot center dot O(phenoxo) interactions to form infinite alternating chain structures in 1 and 2, but the relatively long Mn center dot center dot center dot O(phenoxo) distance [3.621(2)angstrom] in 3 restricts this structure to tetranuclear units. Magnetic studies showed that 1 and 2 exhibited magnetic long-range order at T-N = 4.0 and 4.6 K (T-N = Neel transition temperature), respectively, to give spin-canted antiferromagnetic structures. Antiferromagnetic coupling was also observed in 3 but no peaks were recorded in the field-cooled magnetization (FCM) or zero-field-cooled magnetization (ZFCM) data, indicating that 3 remained paramagnetic down to 2 K. This dominant antiferromagnetic coupling is attributed to the carboxylate bridges. The ferromagnetic coupling expected due to the Mn-O(phenoxo)center dot center dot center dot Mn bridge plays an auxiliary role in the magnetic chain, but is an essential component of the bulk magnetic properties of the material.
Resumo:
Communities are increasingly empowered with the ability and responsibility of working with national governments to make decisions about marine resources in decentralized co-management arrangements. This transition toward decentralized management represents a changing governance landscape. This paper explores the transition to decentralisation in marine resource management systems in three East African countries. The paper draws upon expert opinion and literature from both political science and linked social-ecological systems fields to guide exploration of five key governance transition concepts in each country: (1) drivers of change; (2) institutional arrangments; (3 institutional fit; (4) actor interactions; and (5) adaptive management. Key findings are that decentralized management in the region was largely donor-driven and only partly tranferred power to local stakeholders. However, increased accountability created a degree of democracy in regards to natural resource governance that was not previously present. Additionally, increased local-level adaptive management has emerged in most systems and, to date, this experimental management has helped to change resource user's views from metaphysical to more scientific cause-and-effect attribution of changes to resource conditions.