Andrés Moya, Cameron Currie y Roderick Mackie presentaron durante el segundo día de la Cumbre Mundial de Evolución 2009 tres charlas sobre uno de los procesos ecológicos más fascinantes: la Simbiosis!"Simbiosis: aprendiendo como vivir juntos" se tituló la charla presentada por el Dr. Andrés Moya de Institut Cavanilles de Biodiversitat i Biologia Evolutiva de la Universitat de València y del Centro de Investigación en Salud Pública y CIBER en Epidemiología y Salud
Pública de España.
"La relevancia biológica de las variadas simbiosis entre procariotas y eucariotas como una fuente de innovacion evolutiva ha sido expuesta con el advenimiento de la era Genómica" dijo Andrés Moya al introducir su tema donde describió los avances en el entendimiento de los procesos que llevan al desarrollo de relaciones simbioticas: "Los mecanismos involucrados en el establecimiento, mantenimiento y evolución de las asociaciones simbióticas puedes ser estudiados gracias a la genómica comparativa, mientras que aproximaciones a los sistemas biológicos en general nos permiten explorar la interdependencia metabólica entre los miembros de los consorcios simbioticos".
El Dr. Cameron Currie del Departmento de Bacteriología de la Universidad de Wisconsin en Madison, EE.UU., presentó una charla sobre uno de los consorcios simbióticos más particulares del mundo animal."La simbiosis ha jugado un rol crítico en la evolución de la diversidad y complejidad biológica. Un ejemplo paradigmático es la simbiosis entre hormigas, hongos y microbios, donde la coevolución estos organismos ha culminado en el desarrollo de uno de los herbivoros dominantes en los trópicos Americanos: las Hormigas Cortadoras de Hojas. Estas hormigas cuidan con esmero sus cultivos de hongos mutualistas, proveyendoles de las condiciones óptimas para su crecimiento; a cambio, el hongos sirve como la principal
fuente de alimento para la colonia. El origen de este mutualismo ocurrió hace más de 45 millones de años atras y la subsecuente historia evolutiva compartida ha generado una significativa diversidad tanto en hormigas como en hongos. Recientes trabajos han demostrado que los jardines de hongos de las hormigas cortadoras de hojas son atacados por un hongo patógeno muy virulento que ha coevolucionado con estos jardines, del género Escovopsis. Para evitar que este patógeno destruya sus cultivos, las hormigas han formado una asociación mutualista con bacterias que viven en el dorso del cuerpo de las hormigas y producen antibióticos que evitan el crecimiento de Escovopsis" describió Cameron Currie.
El Dr. Roderick Mackie del Departamento de Ciencias Animales de la Universidad de Illinois, EE.UU., presentó su charla "Digestión fermentativa en lagartijas herbívoras: analisis de la población bacteriana en el tracto digestivo de Iguanas Marinas (Amblyrynchus cristatus) en el archipiélago de Galápagos". Sus estudios han permitido descubrir que: "las Iguanas Marinas de Galápagos, únicas por ser lagartijas herbívoras marinas, dependen principalmente de la presencia y actividades metabólicas de poblaciones bacterianas con las que han coevolucionado para poder hidrolizar y fermentar los polímeros de las algas de las cuales se alimentan, los mismos que caso contrario serían indigeribles".A continuación presentamos los resúmenes de las charlas de Andres Moya, Cameron Currie y Roderick Mackie:
Symbiosis: learning how to live together by Andres Moya
The biological relevance of the widespread prokaryote-eukaryote symbioses as a source of evolutionary innovation has been unveiled by the advent of the Genomic era, allowing deep knowledge on single or consortia uncultivable species. The establishment and maintenance of symbiosis are complex issues where partners’ fitness determines the evolutionary outcome. Comparative genomics allows to dissect the evolutionary process that begins with host invasion, takes the path from facultative to obligate symbiosis, and ends up in replacement or coexistence with new bacterial symbionts. Whole genomes of several intracellular bacterial symbionts have been sequenced, allowing the comparison among the different evolutionary innovations carried out by these bacteria on their way from free-living to varied stages of integration with their respective hosts. The association and functional interaction of genomes from different species observed during symbiosis can be viewed, like mutation, recombination and other genome rearrangements, as a source of genetic variation, the fuel for evolution. The action of forces such as natural selection and/or random drift will be the responsible of transforming this variation in evolutionary novelties. Host can develop organs to allocate the symbionts, and must modify appropriately its immune response and its growth rate to benefit from having one or more symbionts. The bacterial symbiont experiences dramatic changes on its genome, which can be detected by its comparison with free-living relatives. The mechanisms involved in the establishment, maintenance and evolution of the association can be scrutinized thanks to comparative genomics, while systems biology approaches allow us to explore metabolic interdependences among the members of the symbiotic consortium. Finally, the comparative analyses of reduced symbiont genomes are of relevance in the field of synthetic biology. In-silico studies of metabolic and protein-protein interaction networks performed in simple but natural minimal cells are useful to try to define hypothetical cells with even shorter genomes.
Evolution of ancient agriculture in ants by Cameron R. Currie
Host-microbe symbioses have played a critical role in the evolution of biological diversity and complexity. A paradigmatic example is the fungus-growing ant–microbe symbiosis, where coevolution between ants and their microbial symbionts has culminated into one of the dominate herbivores of the Neotropics: leaf-cutter ants. These ants carefully tend their fungal mutualist, providing optimal conditions for growth; in exchange, the fungus serves as the main food source for the colony. The origin of this mutualism occurred more than 45 million years ago, and the subsequent shared evolutionary history has generated significant diversity in both the ants and their fungi. Recent work has shown that the gardens of fungus-growing ants are host to a specialized, virulent, and coevolved fungal pathogen in the genus Escovopsis. To help deal with this garden pathogen, the ants have formed a mutualistic association with Actinobacteria, which produce antibiotics that suppress the growth of Escovopsis. Actinobacteria are Gram-positive, filamentous bacteria well known for their ability to produce potent antibiotics. Indeed, the majority of antibiotics used pharmaceutically are derived from Actinobacteria. I will present evidence of an ancient association between the ants and their actinobacterial symbionts and explore the dynamics of the potential coevolutionary ‘arms race’ between Escovopsis and the tripartite mutualism of ant, fungus and bacteria. In addition, I will highlight how studies on the evolution of this complex community can help inform on our general understanding of evolutionary theory, such as coevolution, rapid evolution, and stability of cooperative relationships.
Fermentative digestion in herbivorous lizards: bacterial population analysis in the intestinal tract of free-living marine iguanas (Amblyrynchus cristatus) on the Galapagos archipelago by Roderick Mackie, David Nelson, Emily Wheeler, Martin Wikelski and Isaac Cann
Herbivory in lizards is rare. Approximately 2% of all lizard species are truly herbivorous. Activity measurements suggest that herbivorous lizards are capable of high digestive efficiency, but the indigenous microbial community assumed to provide this function has not been directly studied. The Galapagos archipelago harbors two genera of endemic herbivorous iguanas, the marine iguana (Amblyrynchus cristatus) and two species of land iguana (Conolophus subcristatus and C. pallidus). Marine iguanas are uniquely adapted morphologically, physiologically, and behaviorally to feed primarily on soft macrophytic algae growing in the intertidal and subtidal zones. In contrast, land iguanas have a more typical herbivorous diet, feeding entirely on terrestrial plant material. We have applied both cultivation and cultivation-independent approaches to detection, identification and quantification of bacterial populations in free-living land and marine iguanas endemic to the Galapagos Islands. Analysis of the predominant bacterial component of the fecal microbiota by denaturing gradient gel electrophoresis demonstrated 27 bacterial phylotypes in marine iguanas while land iguanas accommodate up to 24 phylotypes. Banding profile comparison showed 17 bands in common between the iguana species. Ten bands were unique to marine iguanas and 7 were unique to land iguanas. Comparative analysis of 16S rDNA sequences was used to determine bacterial and archaeal diversity. Interestingly, almost all bacterial sequences (48/50) from marine iguanas clustered with various clostridial lineages within the low-GC-gram-positive bacterial phylum. Phylogenetic analysis of archeal 16S rDNA sequences revealed that all clones from both species fell into two new clusters related to methanogens. Evidence for horizontal gene transfer within the densely colonized intestine has been obtained using functional genomics approaches. A surprisingly high abundance of salmonella (107 cells/gram of feces) was detected by anaerobic cultivation. Rep-PCR genetic analysis revealed high Salmonella diversity within and between iguana populations. Cluster analysis of Rep-PCR banding patterns shows strong island and species effects on salmonella population similarities, suggesting that this abundant and easily cultivatable species may serve as a model organism for exploring gastrointestinal bacterial biogeography in the Galapagos. Combined, these results strongly support the contention that these unique herbivorous lizards are largely dependent on the presence and metabolic activities of a coevolved bacterial population in order to hydrolyze and ferment algal polymers that are indigestible to the host.
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