(Table 1) Lead, thorium and uranium isotopic concentration and ages of zircons from Yenisey Ridge metapelites

Reconstruction of the geologic history of the Yenisey Ridge, which developed as an accretionary collision orogen on the western margin of the Siberian craton is essential to understanding the evolution of mobile belts surrounding older cratons, as well as to resolving the recently much debated problem of whether Siberia was part of the supercontinent Rodinia. Available paleotectonic models suggest that this supercontinent was assembled at the Middle-Late Riphean boundary (1100-900 Ma) as a result of the Grenville orogeny, the first long-lived mountain building event which occurred in geosynclinal areas during the Neogaea. However, the character of crustal evolution at that stage is still speculative due to the lack of reliable and conclusive isotope data. In many current geodynamic models, a common underlying assumption is that the Yenisey Ridge showed very little endogenic activity for 1 Gyr, from the time of Tarak granite emplacement (1900-1840 Ma) to the Middle Neoproterozoic (~750 Ma). On the basis of this assumption, several recent studies suggested the absence of Grenvillian collisional events within the Yenisey Ridge. The results of the SHRIMP II U-Pb analysis of rift-related plagiogranites of the Nemtikha Complex, Yenisey Ridge (1380-1360 Ma) suggest an increase in magmatic activity in the Mesoproterozoic. Interpretation of these results in terms of a supercontinent cycle may help find evidence for possible occurrence of the Grenville orogeny on the western margin of the Siberian craton. With this in mind, we attempted to reconstruct using recent geochronological constraints the evolution of metapelitic rocks from the Teya polymetamorphic complex (TPMC), which is a good example of superimposed zoning of low and medium-pressure facies series. High precision age determinations from rock complexes formed in different geodynamic settings under different thermodynamic conditions and geothermal gradients were used to distinguish several major metamorphic events and unravel their time relations with tectonic and magmatic activity in the region.

Ice-rafted debris in ODP Holes 177-1090D and 188-1165B

Constraining the nature of Antarctic Ice Sheet (AIS) response to major past climate changes may provide a window onto future ice response and rates of sea level rise. One approach to tracking AIS dynamics, and differentiating whole system versus potentially heterogeneous ice sheet sector changes, is to integrate multiple climate proxies for a specific time slice across widely distributed locations. This study presents new iceberg-rafted debris (IRD) data across the interval that includes Marine Isotope Stage 31 (MIS 31: 1.081-1.062 Ma, a span of ~19 kyr; Lisiecki and Raymo, 2005), which lies on the cusp of the mid-Brunhes climate transition (as glacial cycles shifted from ~41,000 yr to ~100,000 yr duration). Two sites are studied - distal Ocean Drilling Program (ODP) Leg 177 Site 1090 (Site 1090) in the eastern subantarctic sector of the South Atlantic Ocean, and proximal ODP Leg 188 Site 1165 (Site 1165), near Prydz Bay, in the Indian Ocean sector of the Antarctic margin. At each of these sites, MIS 31 is marked by the presence of the Jaramillo Subchron (0.988-1.072 Ma; Lourens et al., 2004) which provides a time-marker to correlate these two sites with relative precision. At both sites, records of multiple climate proxies are available to aid in interpretation. The presence of IRD in sediments from our study areas, which include garnets indicating a likely East Antarctic Ice Sheet (EAIS) origin, supports the conclusion that although the EAIS apparently withdrew significantly over MIS 31 in the Prydz Bay region and other sectors, some sectors of the EAIS must still have maintained marine margins capable of launching icebergs even through the warmest intervals. Thus, the EAIS did not respond in complete synchrony even to major climate changes such as MIS 31. Further, the record at Site 1090 (supported by records from other subantarctic locations) indicates that the glacial MIS 32 should be reduced to no more than a stadial, and the warm interval of Antarctic ice retreat that includes MIS 31 should be expanded to MIS 33-31. This revised warm interval lasted about 52 kyr, in line with several other interglacials in the benthic d18O records stack of Lisiecki and Raymo (2005), including the super-interglacials MIS 11 (duration of 50 kyr) and MIS 5 (duration of 59 kyr). The record from Antarctica-proximal Site 1165, when interpreted in accord with the record from ANDRILL-1B, indicates that in these southern high latitude sectors, ice sheet retreat and the effects of warming lasted longer than at Site 1090, perhaps until MIS 27. In the current interpretations of the age models of the proximal sites, ice sheet retreat began relatively slowly, and was not really evident until the start of MIS 31. In another somewhat more speculative interpretation, ice sheet retreat began noticeably with MIS 33, and accelerated during MIS 31. Ice sheet inertia (the lag-times in the large-scale responses of major ice sheets to a forcing) likely plays an important part in the timing and scale of these events in vulnerable sectors of the AIS.

Seawater carbonate chemistry, calcification and Zn uptake during experiments with coral Stylophora pistillata, 2011

Many studies have investigated the effect of an increase in pCO2 on coral calcification and photosynthesis but the physiological consequences are still relatively speculative. We investigated the effects of ocean acidification on zinc incorporation and gross calcification in the scleractinian coral Stylophora pistillata. Zn is an essential element for health and growth of corals. Colonies were maintained at normal pHT (8.1) and at two low-pH conditions (7.8 and 7.5) during 5 weeks. Corals were exposed to 65Zn dissolved in seawater to assess uptake rates of this element. After 5 weeks, 65Zn activity measured in the whole coral and in the two compartments: tissue and skeleton, differed significantly between pH conditions with concentration factors higher at pHT 8.1, compared to lower pH. Zn is therefore taken less efficiently by corals at reduced pH. Their gross calcification, as measured by 45Ca incorporation, photosynthesis and photosynthetic efficiency did not change with pH even at the lowest level.

Parallelizing irregular and pointer-based computations automatically: perspectives from logic and constraint programming

Irregular computations pose sorne of the most interesting and challenging problems in automatic parallelization. Irregularity appears in certain kinds of numerical problems and is pervasive in symbolic applications. Such computations often use dynamic data structures, which make heavy use of pointers. This complicates all the steps of a parallelizing compiler, from independence detection to task partitioning and placement. Starting in the mid 80s there has been significant progress in the development of parallelizing compilers for logic pro­gramming (and more recently, constraint programming) resulting in quite capable paralle­lizers. The typical applications of these paradigms frequently involve irregular computations, and make heavy use of dynamic data structures with pointers, since logical variables represent in practice a well-behaved form of pointers. This arguably makes the techniques used in these compilers potentially interesting. In this paper, we introduce in a tutoríal way, sorne of the problems faced by parallelizing compilers for logic and constraint programs and provide pointers to sorne of the significant progress made in the area. In particular, this work has resulted in a series of achievements in the areas of inter-procedural pointer aliasing analysis for independence detection, cost models and cost analysis, cactus-stack memory management, techniques for managing speculative and irregular computations through task granularity control and dynamic task allocation such as work-stealing schedulers), etc.

Non-failure analysis for logic programs

We provide a method whereby, given mode and (upper approximation) type information, we can detect procedures and goals that can be guaranteed to not fail (i.e., to produce at least one solution or not termínate). The technique is based on an intuitively very simple notion, that of a (set of) tests "covering" the type of a set of variables. We show that the problem of determining a covering is undecidable in general, and give decidability and complexity results for the Herbrand and linear arithmetic constraint systems. We give sound algorithms for determining covering that are precise and efiicient in practice. Based on this information, we show how to identify goals and procedures that can be guaranteed to not fail at runtime. Applications of such non-failure information include programming error detection, program transiormations and parallel execution optimization, avoiding speculative parallelism and estimating lower bounds on the computational costs of goals, which can be used for granularity control. Finally, we report on an implementation of our method and show that better results are obtained than with previously proposed approaches.

Automatic parallelization of irregular and pointer-based computations: perspectives from logic and constraint programming

Irregular computations pose some of the most interesting and challenging problems in automatic parallelization. Irregularity appears in certain kinds of numerical problems and is pervasive in symbolic applications. Such computations often use dynamic data structures which make heavy use of pointers. This complicates all the steps of a parallelizing compiler, from independence detection to task partitioning and placement. In the past decade there has been significant progress in the development of parallelizing compilers for logic programming and, more recently, constraint programming. The typical applications of these paradigms frequently involve irregular computations, which arguably makes the techniques used in these compilers potentially interesting. In this paper we introduce in a tutorial way some of the problems faced by parallelizing compilers for logic and constraint programs. These include the need for inter-procedural pointer aliasing analysis for independence detection and having to manage speculative and irregular computations through task granularity control and dynamic task allocation. We also provide pointers to some of the progress made in these áreas. In the associated talk we demónstrate representatives of several generations of these parallelizing compilers.

A simulation study on parallel backtracking with solution memoing for independent and-parallelism

Goal-level Independent and-parallelism (IAP) is exploited by scheduling for simultaneous execution two or more goals which will not interfere with each other at run time. This can be done safely even if such goals can produce multiple answers. The most successful IAP implementations to date have used recomputation of answers and sequentially ordered backtracking. While in principle simplifying the implementation, recomputation can be very inefficient if the granularity of the parallel goals is large enough and they produce several answers, while sequentially ordered backtracking limits parallelism. And, despite the expected simplification, the implementation of the classic schemes has proved to involve complex engineering, with the consequent difficulty for system maintenance and expansion, and still frequently run into the well-known trapped goal and garbage slot problems. This work presents ideas about an alternative parallel backtracking model for IAP and a simulation studio. The model features parallel out-of-order backtracking and relies on answer memoization to reuse and combine answers. Whenever a parallel goal backtracks, its siblings also perform backtracking, but after storing the bindings generated by previous answers. The bindings are then reinstalled when combining answers. In order not to unnecessarily penalize forward execution, non-speculative and-parallel goals which have not been executed yet take precedence over sibling goals which could be backtracked over. Using a simulator, we show that this approach can bring significant performance advantages over classical approaches.

El microclima urbano en los espacios abiertos : estudio de casos en Madrid

El microclima urbano juega un rol importante en el consumo energético de los edificios y en las sensaciones de confort en los espacios exteriores. La urgente necesidad de aumentar la eficiencia energética, reducir las emisiones de los contaminantes y paliar la evidente falta de sostenibilidad que afecta a las ciudades, ha puesto la atención en el urbanismo bioclimático como referente para una propuesta de cambio en la forma de diseñar y vivir la ciudad. Hasta ahora las investigaciones en temas de microclima y eficiencia energética se han concentrado principalmente en como orientar el diseño de nuevos desarrollo. Sin embargo los principales problemas de la insostenibilidad de las actuales conurbaciones son el resultado del modelo de crecimiento especulativo y altamente agotador de recursos que han caracterizado el boom inmobiliario de las últimas décadas. Vemos entonces, tanto en España como en el resto de los Países Europeos, la necesidad de reorientar el sector de la construcción hacía la rehabilitación del espacio construido, como una alternativa capaz de dar una solución más sostenible para el mercado inmobiliario. En este propósito de mejorar la calidad de las ciudades actuales, el espacio público juega un papel fundamental, sobre todo como lugar para el encuentro y la socialización entre los ciudadanos. La sensación térmica condiciona la percepción de un ambiente, así que el microclima puede ser determinante para el éxito o el fracaso de un espacio urbano. Se plantea entonces cómo principal objetivo de la investigación, la definición de estrategias para el diseño bioclimático de los entornos urbanos construidos, fundamentados en las componentes morfotipológica, climática y de los requerimientos de confort para los ciudadanos. Como ulterior elemento de novedad se decide estudiar la rehabilitación de los barrios de construcción de mediado del siglo XX, que en muchos casos constituyen bolsas de degrado en la extendida periferia de las ciudades modernas. La metodología empleada para la investigación se basa en la evaluación de las condiciones climáticas y de confort térmico de diferentes escenarios de proyecto, aplicados a tres casos de estudio situados en un barrio periurbano de la ciudad de Madrid. Para la determinación de los parámetros climáticos se han empleado valores obtenidos con un proceso de simulación computarizada, basados en los principios de fluidodinámica, termodinámica y del intercambio radioactivo en el espacio construido. A través de uso de programas de simulación podemos hacer una previsión de las condiciones microclimáticas de las situaciones actuales y de los efectos de la aplicación de medidas. La gran ventaja en el uso de sistemas de cálculo es que se pueden evaluar diferentes escenarios de proyecto y elegir entre ellos el que asegura mejores prestaciones ambientales. Los resultados obtenidos en los diferentes escenarios han sido comparados con los valores de confort del estado actual, utilizando como indicador de la sensación térmica el índice UTCI. El análisis comparativo ha permitido la realización de una tabla de resumen donde se muestra la evaluación de las diferentes soluciones de rehabilitación. Se ha podido así demostrar que no existe una solución constructiva eficaz para todas las aplicaciones, sino que cada situación debe ser estudiada individualmente, aplicando caso por caso las medidas más oportunas. Si bien los sistemas de simulación computarizada pueden suponer un importante apoyo para la fase de diseño, es responsabilidad del proyectista emplear las herramientas más adecuadas en cada fase y elegir las soluciones más oportunas para cumplir con los objetivos del proyecto. The urban microclimate plays an important role on buildings energy consumption and comfort sensation in exterior spaces. Nowadays, cities need to increase energy efficiency, reduce the pollutants emissions and mitigate the evident lack of sustainability. In reason of this, attention has focused on the bioclimatic urbanism as a reference of change proposal of the way to design and live the city. Hitherto, the researches on microclimate and energy efficiency have mainly concentrated on guiding the design of new constructions. However the main problems of unsustainability of existing conurbations are the result of the growth model highly speculative and responsible of resources depletion that have characterized the real estate boom of recent decades. In Spain and other European countries, become define the need to redirect the construction sector towards urban refurbishment. This alternative is a more sustainable development model and is able to provide a solution for the real estate sector. In order to improve the quality of today's cities, the public space plays a key role, especially in order to provide to citizens places for meeting and socializing. The thermal sensation affects the environment perception, so microclimate conditions can be decisive for the success or failure of urban space. For this reasons, the main objective of this work is focused on the definition of bioclimatic strategies for existing urban spaces, based on the morpho-typological components, climate and comfort requirements for citizens. As novelty element, the regeneration of neighborhoods built in middle of the twentieth century has been studied, because are the major extended in periphery of modern cities and, in many cases, they represent deprived areas. The research methodology is based on the evaluation of climatic conditions and thermal comfort of different project scenarios, applied to three case studies located in a suburban neighborhood of Madrid. The climatic parameters have been obtained by computer simulation process, based on fluid dynamics, thermodynamics and radioactive exchange in urban environment using numerical approach. The great advantage in the use of computing systems is the capacity for evaluate different project scenarios. The results in the different scenarios were compared with the comfort value obtained in the current state, using the UTCI index as indicator of thermal sensation. Finally, an abacus of the thermal comfort improvement obtained by different countermeasures has been performed. One of the major achievement of doctoral work is the demonstration of there are not any design solution suitable for different cases. Each situation should be analyzed and specific design measures should be proposed. Computer simulation systems can be a significant support and help the designer in the decision making phase. However, the election of the most suitable tools and the appropriate solutions for each case is designer responsibility.

La arquitectura en la literatura de ciencia-ficción

En esta Tesis se estudian las Imágenes Arquitectónicas que aparecen descritas en textos literarios de Ciencia Ficción dentro del periodo temporal que limitan los años 1.926 a 1.976. Consta de tres partes fundamentales: En la primera, se plantean las condiciones y objetivos del trabajo y se define el espacio conceptual que ocupa la Arquitectura descrita en Ciencia Ficción. En la segunda, se realizan análisis sobre las formas y temas arquitectónicos, así como de problemas relacionados con ellos que se encuentran en la narrativa fantacientífica, y se desarrollan ideas e hipótesis especulativas, sobre sugerencias referidas a situaciones reales o imaginarias, partiendo de posiciones implícitas en los relatos. En la tercera, se elabora una antología que data y ordena una amplia muestra de textos representativos. SUMMARY. This thesis studies the Architectural Images described in the Science Fiction stories between 1.926 and 1.976. It consist of three main parts: The first one, explains the conditions and objectives of this work and defines the conceptual space of Described Architecture in Science Fiction. The second one, analyses the architectural forms and items, as well as the problems related to the latter, that can be found in the scientific-fantastic narrative. It also develops ideas and speculative hipothesis about suggestions related to real and imaginary situations from implicit positions in the stories. The third one, builds up an anthology, dating and ordering a wide variety of representative excerpts of the S. F. texts o

Reversible Urban Entities. Improving public-to-private continuity.

The aim of this paper is to call into question those typologies conventionally used in developing the post-industrial urban fabric (streets, cityblocks, slabs, etc.), often catering to urban designs based on speculative interests and completely overlooking community interests. By defining the concepts of ?postpublic space? and ?reversible urban entities? and illustrating them with an exemplary case of Spanish residential architecture from the 1960s, we establish one possible way of tackling contemporary urban-residential projects. This alternative approach considers the relationship between residential systems and open space systems and promotes the continuity and/or alternation of scales between house and city in an effort to improve the urban quality of life for residents and external users.

A Comparative Analysis of Hedging in a Corpus of Two Written Legal Discourse Genres

Esta tesis doctoral, que es la culminación de mis estudios de doctorado impartidos por el Departamento de Lingüística Aplicada a la Ciencia y a la Tecnología de la Universidad Politécnica de Madrid, aborda el análisis del uso de la matización (hedging) en el lenguaje legal inglés siguiendo los postulados y principios de la análisis crítica de género (Bhatia, 2004) y empleando las herramientas de análisis de córpora WordSmith Tools versión 6 (Scott, 2014). Como refleja el título, el estudio se centra en la descripción y en el análisis contrastivo de las variedades léxico-sintácticas de los matizadores del discurso (hedges) y las estrategias discursivas que con ellos se llevan a cabo, además de las funciones que éstas desempeñan en un corpus de sentencias del Tribunal Supremo de EE. UU., y de artículos jurídicos de investigación americanos, relacionando, en la medida posible, éstas con los rasgos determinantes de los dos géneros, desde una perspectiva socio-cognitiva. El elemento innovador que ofrece es que, a pesar de los numerosos estudios que se han podido realizar sobre los matizadores del discurso en el inglés general (Lakoff, 1973; Hübler, 1983; Clemen, 1997; Markkanen and Schröder, 1997; Mauranen, 1997; Fetzer 2010; y Finnegan, 2010 entre otros) académico (Crompton, 1997; Meyer, 1997; Skelton, 1997; Martín Butragueňo, 2003) científico (Hyland, 1996a, 1996c, 1998c, 2007; Grabe and Kaplan, 1997; Salager-Meyer, 1997 Varttala, 2001) médico (Prince, 1982; Salager-Meyer, 1994; Skelton, 1997), y, en menor medida el inglés legal (Toska, 2012), no existe ningún tipo de investigación que vincule los distintos usos de la matización a las características genéricas de las comunicaciones profesionales. Dentro del lenguaje legal, la matización confirma su dependencia tanto de las expectativas a macro-nivel de la comunidad de discurso, como de las intenciones a micro-nivel del escritor de la comunicación, variando en función de los propósitos comunicativos del género ya sean éstos educativos, pedagógicos, interpersonales u operativos. El estudio pone de relieve el uso predominante de los verbos modales epistémicos y de los verbos léxicos como matizadores del discurso, estos últimos divididos en cuatro tipos (Hyland 1998c; Palmer 1986, 1990, 2001) especulativos, citativos, deductivos y sensoriales. La realización léxico-sintáctica del matizador puede señalar una de cuatro estrategias discursivas particulares (Namsaraev, 1997; Salager-Meyer, 1994), la indeterminación, la despersonalización, la subjectivisación, o la matización camuflada (camouflage hedging), cuya incidencia y función varia según género. La identificación y cuantificación de los distintos matizadores y estrategias empleados en los diferentes géneros del discurso legal puede tener implicaciones pedagógicos para los estudiantes de derecho no nativos que tienen que demostrar una competencia adecuada en su uso y procesamiento. ABSTRACT This doctoral thesis, which represents the culmination of my doctoral studies undertaken in the Department of Linguistics Applied to Science and Technology of the Universidad Politécnica de Madrid, focusses on the analysis of hedging in legal English following the principles of Critical Genre Analysis (Bhatia, 2004), and using WordSmith Tools version 6 (Scott, 2014) corpus analysis tools. As the title suggests, this study centers on the description and contrastive analysis of lexico-grammatical realizations of hedges and the discourse strategies which they can indicate, as well as the functions they can carry out, in a corpus of U.S. Supreme Court opinions and American law review articles. The study relates realization, incidence and function of hedging to the predominant generic characteristics of the two genres from a socio-cognitive perspective. While there have been numerous studies on hedging in general English (Lakoff, 1973; Hübler, 1983; Clemen, 1997; Markkanen and Schröder, 1997; Mauranen, 1997; Fetzer 2010; and Finnegan, 2010 among others) academic English (Crompton, 1997; Meyer, 1997; Skelton, 1997; Martín Butragueňo, 2003) scientific English (Hyland, 1996a, 1996c, 1998c, 2007; Grabe and Kaplan, 1997; Salager-Meyer, 1997 Varttala, 2001) medical English (Prince, 1982; Salager-Meyer, 1994; Skelton, 1997), and, to a lesser degree, legal English (Toska, 2012), this study is innovative in that it links the different realizations and functions of hedging to the generic characteristics of a particular professional communication. Within legal English, hedging has been found to depend on not only the macro-level expectations of the discourse community for a specific genre, but also on the micro-level intentions of the author of a communication, varying according to the educational, pedagogical, interpersonal or operative purposes the genre may have. The study highlights the predominance of epistemic modal verbs and lexical verbs as hedges, dividing the latter into four types (Hyland, 1998c; Palmer, 1986, 1990, 2001): speculative, quotative, deductive and sensorial. Lexical-grammatical realizations of hedges can signal one of four discourse strategies (Namsaraev, 1997; Salager-Meyer, 1994), indetermination, depersonalization, subjectivization and camouflage hedging, as well as fulfill a variety of functions. The identification and quantification of the different hedges and hedging strategies and functions in the two genres may have pedagogical implications for non-native law students who must demonstrate adequate competence in the production and interpretation of hedged discourse.

Urban microclimate and thermal comfort modelling: strategies for urban renovation

The urban microclimate plays an important role in building energy consumption and thermal comfort in outdoor spaces. Nowadays, cities need to increase energy efficiency, reduce pollutant emissions and mitigate the evident lack of sustainability. In light of this, attention has focused on the bioclimatic concepts use in the urban development. However, the speculative unsustainability of the growth model highlights the need to redirect the construction sector towards urban renovation using a bioclimatic approach. The public space plays a key role in improving the quality of today’s cities, especially in terms of providing places for citizens to meet and socialize in adequate thermal conditions. Thermal comfort affects perception of the environment, so microclimate conditions can be decisive for the success or failure of outdoor urban spaces and the activities held in them. For these reasons, the main focus of this work is on the definition of bioclimatic strategies for existing urban spaces, based on morpho-typological components, urban microclimate conditions and comfort requirements for all kinds of citizens. Two case studies were selected in Madrid, in a social housing neighbourhood constructed in the 1970s based on Rational Architecture style. Several renovation scenarios were performed using a computer simulation process based in ENVI-met and diverse microclimate conditions were compared. In addition, thermal comfort evaluation was carried out using the Universal Thermal Climate Index (UTCI) in order to investigate the relationship between microclimate conditions and thermal comfort perception. This paper introduces the microclimate computer simulation process as a valuable support for decision-making for neighbourhood renovation projects in order to provide new and better solutions according to the thermal quality of public spaces and reducing energy consumption by creating and selecting better microclimate areas.

Considerations of transcriptional control mechanisms: Do TFIID–core promoter complexes recapitulate nucleosome-like functions?

The general transcription initiation factor TFIID was originally identified, purified, and characterized with a biochemical assay in which accurate transcription initiation is reconstituted with multiple, chromatographically separable activities. Biochemical analyses have demonstrated that TFIID is a multiprotein complex that directs preinitiation complex assembly on both TATA box-containing and TATA-less promoters, and some TFIID subunits have been shown to be molecular targets for activation domains in DNA-binding regulatory proteins. These findings have most commonly been interpreted to support the view that transcriptional activation by upstream factors is the result of enhanced TFIID recruitment to the core promoter. Recent insights into the architecture and cell-cycle regulation of the multiprotein TFIID complex prompt both a reassessment of the functional role of TFIID in gene activation and a review of some of the less well-appreciated literature on TFIID. We present a speculative model for diverse functional roles of TFIID in the cell, explore the merits of the model in the context of published data, and suggest experimental approaches to resolve unanswered questions. Finally, we point out how the proposed functional roles of TFIID in eukaryotic class II transcription fit into a model for promoter recognition and activation that applies to both eubacteria and eukaryotes.

Bacteria are different: Observations, interpretations, speculations, and opinions about the mechanisms of adaptive evolution in prokaryotes

To some extent, the genetic theory of adaptive evolution in bacteria is a simple extension of that developed for sexually reproducing eukaryotes. In other, fundamental ways, the process of adaptive evolution in bacteria is quantitatively and qualitatively different from that of organisms for which recombination is an integral part of the reproduction process. In this speculative and opinionated discussion, we explore these differences. In particular, we consider (i) how, as a consequence of the low rates of recombination, “ordinary” chromosomal gene evolution in bacteria is different from that in organisms where recombination is frequent and (ii) the fundamental role of the horizontal transmission of genes and accessory genetic elements as sources of variation in bacteria. We conclude with speculations about the evolution of accessory elements and their role in the adaptive evolution of bacteria.

Meiosis: how could it work?

A physical connection between homologs is required for reductional segregation at the first division of meiosis. This connection is usually provided by one or a few well-spaced crossovers. A speculative overview of processes leading to formation of these crossovers is presented.