L'Espècie horitzontal

El concepte d'espècie biològica no ha resolt el problema de la identitat de les espècies perquè la moderna genòmica comparada ha desvetllat que la introgressió és molt més freqüent del que semblava. Per tant, l'aïllament reproductiu no sembla la causa primordial ni de l'origen ni del manteniment de les espècies. El model al·lopàtric d'especiació, considerat com el més general, no explica molts casos d'especiació simpàtrica ben documentats. Més aviat, avui dia el model més afavorit és un escenari en el qual s'intercalen episodis simpàtrics i al·lopàtrics, del qual l'origen dels peixos cíclids és un bon exemple. Però l'intercanvi híbrid de gens, sense duplicació del genoma, és també un punt de partida de noves espècies en moltes plantes i animals. En aquests casos, com el de les espècies híbrides d'Helianthus, la selecció per fertilitat i la selecció ecològica donen suport el paper decisiu de la selecció natural en l'especiació. Finalment, l'intercanvi horitzontal de gens és cada vegada més evident no solament en el món dels procariotes sinó també en el dels eucariotes. Totes aquestes dades obliguen a considerar que l'arbre de la vida és més aviat una xarxa, però el que fan és sobretot reivindicar el paper fonamental que Darwin havia donat a la selecció natural, enfront de l'aïllament, en l'especiació.The biological concept of species has not solved the problem of the species identity because current studies of comparative genomics have revealed a higher than expected frequency of introgression. This evidence casts serious doubts on the prime role of the reproductive isolation in the origin and maintenance of species. The allopatric model of speciation, formerly viewed as the most frequent, fails to explain many well documented cases of sympatric speciation. Rather the allo-sympatric model, in which several allopatric and sympatric episodes are interspersed in time, is currently favoured to explain many speciation study cases such as the origin of cichlid fishes. Moreover, the genic exchange through hybridisation, without whole genome duplication, is often the starting point of new species in many plants and also in animals. In many of these cases, as in the hybrid species of Helianthus, selection for fertility and ecological selection have been documented, bolstering the decisive role of natural selection in speciation. Last but not least, comparative phylogenetic studies have shown that horizontal gene exchange is also a plausible phenomenon both in prokaryote and eukaryote domains of life. Taken together, all this evidence suggests that biodiversity should be pictured rather by a web of life. But, what is most relevant, it vindicates Darwin’s tenet that natural selection, versus reproductive isolation, is the most active mechanism in the origin of species

Fouling of a double pipe heat exchanger

Every single heat exchanger in operation in modern industries is exposed to fouling to a greater or lesser extent depending on the surface temperature, surface condition, material of construction, fluid velocity, flow geometry and fluid composition. The fouling phenomenon is time dependent and will result in a decrease in thermal effectiveness of a heat exchanger. Once the thermal effectiveness decreases to a minimum acceptable level, cleaning of the equipment becomes necessary to restore its performance. This thesis investigates the effects of fouling in a double pipe heat exchanger. The first part consisted of the design and construction of a double pipe heat exchanger that corresponds to our budget and meets our demands. These demands are the possibility of the change in fluid velocity, the ability to use different fluid processes, to have an easy way to get th e inlet and outlet temperatures and to design a double pipe system easy to strip out in order to analyse fouling on the heat transfer surface. The main lines of research are carried out to establish a comparison between the normal development of fouling in a heat exchanger shown in theory books, and the development of fouling in a heat exchanger designed by us. The results of the research also indicate how fouling affects heat transfer, especially heat transfer coefficients and hot and cold fluid outlet temperatures. Dairy products were used as process fluid. Tests were carried out for periods of up to eight hours. The evolution o f temperature, heat transfer, overall h eat transfer coefficient and fouling resistance over time were investigated. The evolution of the temperatures with time and the overall h eat transfer coefficient values are affected by fouling. The evolution o f heat transfer with time occurred according to the different fouling mechanisms. Fouling deposits increased with time until reaching the point where they produced a blockage of the system

Darwinisme, evolució de la forma i especiació

Es dóna una breu introducció als fets de l'evolució: el registre fòssil, els vestigis i el disseny imperfecte, principalment per subratllar l'oportunisme de l'evolució enfront de l'origen independent de les espècies. El concepte d'homologia, derivat de les relacions de descendència entre els éssers vius, ens permet establir la unitat de tipus i la rellevància de la seva interpretació com a unitat de descendència amb modificació. La selecció natural, com a mecanisme bàsic de l'evolució, es relaciona amb el mendelisme per entendre el consens de la síntesi evolutiva. Els avenços recents en el coneixement de l'evolució de la forma ens han permès omplir el buit entre els patrons corporals mitjançant el descobriment de les homologies ancestrals, la qual cosa ha reafirmat el principi darwinista de la unitat de tipus. La genètica evolutiva del desenvolupament ha confirmat també el caràcter unitari dels canvis genètics, fonamentalment en processos reguladors, i com aquests canvis ocorren en els mateixos gens en espècies diferents, encara que de maneres diverses, per generar la biodiversitat. Per entendre aquesta biodiversitat, s'analitza el paper relatiu entre la selecció natural, la deriva genètica i el flux gènic en l'origen i la cohesió de les espècies. En general, l'aïllament reproductiu és un producte, més que una causa de l'especiació, la qual cosa permet entendre els patrons no al·lopàtrics, com són els simpàtrics i d'hibridació, en l'origen de les espècies.We introduce the facts of evolution, namely, the fossil record, the vestiges and the imperfect design, to underline the evolutionary opportunism versus the independent origin of species. The concept of homology, derived from the descent relationships among organisms, allows us to establish the unity of type and its meaning as unity of descent with modification. Natural selection, as a basic evolutionary mechanism, is related with mendelism to understand the consensus of the evolutionary synthesis. Recent advances in the evolution of form allows us to fill the gap between the body plans through the discovery of ancestral homologies, reassessing the Darwinian principle of the unity of type. The evolutionary genetics of development has confirmed also the commonality of the molecular changes, basically in regulatory processes, and how these changes occur in the same genes of different species, even though in different ways, to promote biodiversity. To understand biodiversity, we analyse the relative role of natural selection, genetic drift and gene flow in the origin and cohesion of species. Generally, reproductive isolation is a product rather than a cause of speciation, which allows the understanding of non-allopatric patterns, such as the sympatric and hybrid ones, in the origin of specie

Taxes evolutives i evolució de gens i genomes

S'introdueix el concepte de taxa evolutiva i es discuteix el seu significat, així com també la seva aplicació per determinar l'impacte potencial que poden tenir les alteracions mediambientals provocades per l'acció humana. S'analitzen també els canvis evolutius en seqüències de nucleòtids o d'aminoàcids i la dinàmica de les taxes de substitució. Això permet introduir el concepte de rellotge molecular i caracteritzar la teoria neutralista com una referència estàndard per interpretar les taxes evolutives. S'explica també la utilització de seqüències d'àcids nucleics o de proteïnes per establir les relacions evolutives entre les espècies, amb un exemple de construcció d'un arbre filogenètic i d'un mètode estadístic per determinar-ne la fiabilitat. Tot seguit es consideren els canvis genètics que ens fan diferents del ximpanzé, el nostre parent més proper, i els mecanismes d'evolució de la grandària del genoma mitjançant duplicacions intragèniques, redistribució d'exons, duplicacions de gens complets i duplicacions genòmiques. Finalment, es considera el significat evolutiu dels elements genètics transposables.We introduce the concept of evolutionary rate and discuss its significance and application in the study of systematic human-induced alterations of natural habitats. The evolutionary changes in nucleotide or amino acid sequences and the dynamics of substitution rates are analysed, introducing the concept of molecular clock and the neutral theory as a null hypothesis to interpret evolutionary rates. The use of nucleotide or amino acid sequences to establish evolutionary relationships between species is also discussed, giving an example of the construction of a phylogenetic tree and a statistical method to determine tree reliability. We then proceed to consider those genetic changes that make us different from the chimpanzee, our closest relative, and to discuss the mechanisms responsible of genome-size evolution, in particular intragenic duplication and gene elongation, exon shuffling, gene duplication, and genome duplication. Finally, we discuss the evolutionary significance of transposable genetic elements

Gens amb mobilitat

Els gens mòbils són seqüències d'ADN amb capacitat de moure's i inserir-se en el genoma. Constitueixen més del 50% del genoma humà i el 28% del de la Drosophila (la mosca del vinagre). Degut a la seva mobilitat, són potents productors de mutacions perquè promouen canvis cromosòmics i s'insereixen dins de regions codificadores i reguladores dels gens. Aquest treball es centra en un d'aquests elements transposables a l'espècie Drosophila buzzatii.Los genes móviles son secuencias de ADN con capacidad de moverse e insertarse en el genoma. Constituyen más del 50% del genoma humano y el 28% del de Drosophila (la mosca del vinagre). Debido a su movilidad, son potentes productores de mutaciones porque promueven cambios cromosómicos y se introducen en regiones codificadoras y reguladoras de los genes. Este trabajo se centra en uno de estos elementos transponibles en la especie Drosophila buzzatii

L'Origen de les espècies : 150 anys després de Darwin

Conferència pronunciada a la sala d'actes de les Fac. Biociències i Ciències amb motiu de la celebració de Sant Albert, UAB, 18-11-200

A Genome-Wide Survey of Genetic Instability by Transposition in Drosophila Hybrids

International audienceHybridization between species is a genomic instability factor involved in increasing mutation rate and new chromosomal rearrangements. Evidence of a relationship between interspecific hybridization and transposable element mobilization has been reported in different organisms, but most studies are usually performed with particular TEs and do not discuss the real effect of hybridization on the whole genome. We have therefore studied whole genome instability of Drosophila interspecific hybrids, looking for the presence of new AFLP markers in hybrids. A high percentage (27–90%) of the instability markers detected corresponds to TEs belonging to classes I and II. Moreover, three transposable elements (Osvaldo, Helena and Galileo) representative of different families, showed an overall increase of transposition rate in hybrids compared to parental species. This research confirms the hypothesis that hybridization induces genomic instability by transposition bursts and suggests that genomic stress by transposition could contribute to a relaxation of mechanisms controlling TEs in the Drosophila genome

Distribution of the transposable elements bilbo and gypsy in original and colonizing populations of Drosophila subobscura

Background: Transposable elements (TEs) constitute a substantial amount of all eukaryotic genomes. They induce an important proportion of deleterious mutations by insertion into genes or gene regulatory regions. However, their mutational capabilities are not always adverse but can contribute to the genetic diversity and evolution of organisms. Knowledge of their distribution and activity in the genomes of populations under different environmental and demographic regimes, is important to understand their role in species evolution. In this work we study the chromosomal distribution of two TEs, gypsy and bilbo, in original and colonizing populations of Drosophila subobscura to reveal the putative effect of colonization on their insertion profile. Results: Chromosomal frequency distribution of two TEs in one original and three colonizing populations of D. subobscura, is different. Whereas the original population shows a low insertion frequency in most TE sites, colonizing populations have a mixture of high (frequency ≥ 10%) and low insertion sites for both TEs. Most highly occupied sites are coincident among colonizing populations and some of them are correlated to chromosomal arrangements. Comparisons of TE copy number between the X chromosome and autosomes show that gypsy occupancy seems to be controlled by negative selection, but bilbo one does not. Conclusion: These results are in accordance that TEs in Drosophila subobscura colonizing populations are submitted to a founder effect followed by genetic drift as a consequence of colonization. This would explain the high insertion frequencies of bilbo and gypsy in coincident sites of colonizing populations. High occupancy sites would represent insertion events prior to colonization. Sites of low frequency would be insertions that occurred after colonization and/or copies from the original population whose frequency is decreasing in colonizing populations. This work is a pioneer attempt to explain the chromosomal distribution of TEs in a colonizing species with high inversion polymorphism to reveal the putative effect of arrangements in TE insertion profiles. In general no associations between arrangements and TE have been found, except in a few cases where the association is very strong. Alternatively, founder drift effects, seem to play a leading role in TE genome distribution in colonizing populations

Drosophila Females Undergo Genome Expansion after Interspecific Hybridization

International audienceGenome size (or C-value) can present a wide range of values among eukaryotes. This variation has been attributed to differences in the amplification and deletion of different noncoding repetitive sequences, particularly transposable elements (TEs). TEs can be activated under different stress conditions such as interspecific hybridization events, as described for several species of animals and plants. These massive transposition episodes can lead to considerable genome expansions that could ultimately be involved in hybrid speciation processes. Here, we describe the effects of hybridization and introgression on genome size of Drosophila hybrids. We measured the genome size of two close Drosophila species, Drosophila buzzatii and Drosophila koepferae, their F 1 offspring and the offspring from three generations of backcrossed hybrids; where mobilization of up to 28 different TEs was previously detected. We show that hybrid females indeed present a genome expansion, especially in the first backcross, which could likely be explained by transposition events. Hybrid males, which exhibit more variable C-values among individuals of the same generation, do not present an increased genome size. Thus, we demonstrate that the impact of hybridization on genome size can be detected through flow cytometry and is sex-dependent

High-density hyaluronic acid for the treatment of HIV-related facial lipoatrophy

Facial lipoatrophy is a stigmatizing hallmark of HIV. The injection of facial fillers has an essential role in the treatment of this condition. The objective of our study was to verify the safety and efficacy of a new formulation of high-density hyaluronic acid for the injectable treatment of HIV-related facial lipoatrophy.We treated with high-density hyaluronic acid injections HIV patients affected by moderate to severe facial lipoatrophy and evaluated them at last follow-up, at a minimum of 36 weeks. Physician-related outcomes included pre-and post-treatment ultrasound measurement of the soft-tissue thickness of the cheeks and qualitative assessment of aesthetic results by means of the Global Aesthetic Improvement Scale using pre- and post-treatment photos of the patients. Patient satisfaction outcomes were evaluated with the VAS-face scale and Freiburg test.Fifty-four patients were studied. The median number of treatment sessions was 3 and the median length of treatment was 5.5 months. The thickness of the soft tissues of the cheek increased significantly from 9.45 to 13.12 mm (p<0.0001). On the basis of the Global Aesthetic Improvement Scale, 87.5% of the patients were judged as "much improved" or "improved." Patient satisfaction at 1 year from the end of treatment was proven (VAS-face: 77.9; Freiburg questionnaire: 93.6% of patients were satisfied or very satisfied). Complications were limited to mild redness and swelling in the early postoperative period.Long-term improvement of facial contour and excellent patient satisfaction, in the absence of severe side effects, were obtained by the injection of high-density hyaluronic acid (STYLAGE\uae XL) in HIV patients with facial lipoatrophy