Publication: Interacciones parásito-hospedador y especiación en peces cíclidos de lagunas cratéricas neotropicales
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2017-12-04
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Universidad Complutense de Madrid
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Abstract
Desde que Darwin lo propuso por primera vez en 1859, la selección natural ha sido considerada como el principal motor de la diversificación. Sin embargo, a pesar de ello, la especiación se ha considerado como el resultado de procesos aleatorios, en los que la deriva genética juega un papel importante. Sólo en las últimas décadas se ha llegado al consenso de que hay que invertir los esfuerzos en la identificación de los mecanismos responsables de la evolución del aislamiento reproductivo, especialmente en casos donde el flujo de genes no tiene barreras físicas (i.e., la especiación simpátrica). Este cambio ha dado lugar a un renovado reconocimiento del papel de la selección como una poderosa fuerza de especiación, especialmente en la interacción parasito-hospedador. Los peces cíclidos son la familia más rica de vertebrados, se distribuyen en los ríos y lagos de África, Madagascar, India y sur y centro América. Los cíclidos representan un sistema ideal para el estudio de la evolución, debido a sus sorprendentes ejemplos de radiación adaptativa, su diversidad morfológica, y varias ocurrencias de paralelismo evolutivo. Los Cíclidos Neotropicales de lagunas crátericas son idóneos para estudiar los procesos de evolución ya que muestran uno de los ejemplos más convincentes de especiación simpátrica. El Complejo Mayor de Histocompatibilidad (MHC) es el componente clave del sistema inmune adaptativo de todos los vertebrados, y consiste en los genes más polimórficos conocidos. Debido a su complejidad el MHC aún no ha sido caracterizado en muchas especies, incluyendo los cíclidos Neotropicales. En este trabajo caracterizamos los genes del MHC de clase IIB del complejo del cíclido de Midas (Amphilophus cf. citrinellus). Para ello diseñamos cebadores específicos, y con ellos caracterizamos la conformación de intrones y exones, y la expresión alélica. Creamos modelos 3D de estructura molecular para cada alelo de MHC e identificamos sus claves componentes estructurales...
Since Darwin first proposed it in 1859, natural selection has been considered the main driver of diversification. Yet for the most part, speciation has been mainly viewed as a result of random processes, where genetic drift plays an important role. Only in the last decades has the consensus view of speciation shifted towards identifying the mechanisms responsible for the evolution of reproductive isolation, especially when gene flow is present during the process (i.e. sympatric speciation). This shift has resulted in a renewed recognition of the role of selection as a powerful cause of speciation, especially ecologically driven selection such as host-parasite interactions. Cichlid fish are the most species-rich families in vertebrates, distributed in rivers and lakes of Africa, Madagascar, India, and Southern and Central America. Cichlids represent a model system for the study of evolution due to their striking cases of adaptive radiation, morphological diversity, and frequent occurrence of evolutionary parallelism. Neotropical crater lake cichlids are especially ideal as they display one of the most convincing examples of sympatric speciation. The Major Histocompatibility Complex (MHC) is the key component of the adaptive immune system of all vertebrates and consists of the most polymorphic genes known to date. Due to this complexity, however, MHC remains to be characterized in many species including any Neotropical cichlid fish. In this work, we characterized the genes of MHC class IIB chain of the Midas cichlid species complex (Amphilophus cf. citrinellus). We designed new specific primers for PCR amplification, characterized the intron-exon conformation, and evaluated allele expression. We then created models of protein structure homology for each allele, and identified their key structural components. Using phylogenetic analysis, we identified one group of putative non-classical MHC and eleven groups of classical MHC which are under positive selection. We used Next Generation Sequencing to sequence the antigen binding site (exon 2) of MHCIIB and describe the population level variation among six Nicaraguan lakes. We report a striking case of parallel speciation in two of the volcanic crater lakes (Xiloá and Apoyo) where at least three ecologically and morphologically equivalent species of Midas cichlids have evolved independently in each of two lakes...
Since Darwin first proposed it in 1859, natural selection has been considered the main driver of diversification. Yet for the most part, speciation has been mainly viewed as a result of random processes, where genetic drift plays an important role. Only in the last decades has the consensus view of speciation shifted towards identifying the mechanisms responsible for the evolution of reproductive isolation, especially when gene flow is present during the process (i.e. sympatric speciation). This shift has resulted in a renewed recognition of the role of selection as a powerful cause of speciation, especially ecologically driven selection such as host-parasite interactions. Cichlid fish are the most species-rich families in vertebrates, distributed in rivers and lakes of Africa, Madagascar, India, and Southern and Central America. Cichlids represent a model system for the study of evolution due to their striking cases of adaptive radiation, morphological diversity, and frequent occurrence of evolutionary parallelism. Neotropical crater lake cichlids are especially ideal as they display one of the most convincing examples of sympatric speciation. The Major Histocompatibility Complex (MHC) is the key component of the adaptive immune system of all vertebrates and consists of the most polymorphic genes known to date. Due to this complexity, however, MHC remains to be characterized in many species including any Neotropical cichlid fish. In this work, we characterized the genes of MHC class IIB chain of the Midas cichlid species complex (Amphilophus cf. citrinellus). We designed new specific primers for PCR amplification, characterized the intron-exon conformation, and evaluated allele expression. We then created models of protein structure homology for each allele, and identified their key structural components. Using phylogenetic analysis, we identified one group of putative non-classical MHC and eleven groups of classical MHC which are under positive selection. We used Next Generation Sequencing to sequence the antigen binding site (exon 2) of MHCIIB and describe the population level variation among six Nicaraguan lakes. We report a striking case of parallel speciation in two of the volcanic crater lakes (Xiloá and Apoyo) where at least three ecologically and morphologically equivalent species of Midas cichlids have evolved independently in each of two lakes...
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Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Biológicas, leída el 10-07-2017