Origen y evolución de la fauna marina bentónica antártica: diversidad genética y divergencia molecular entre especies congenéricas de Echinnoidea de Antártica y Sudamérica
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Date
2008-11
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Universidad de Chile
Abstract
La presencia de especies congéneres de invertebrados marinos bentónicos en Antártica y Sudamérica, ha sido históricamente interpretado como el resultado del proceso de vicarianza, consecuencia de la separación de ambos continentes y posterior instalación de la corriente circumpolar Antártica. Sin embargo, pocas evidencias han sido aportadas para validar este modelo. Los géneros Abatus y Sterechinus (Echinidae), son parte importante de la fauna marina bentónica somera de ambos continentes y representan un buen modelo para estudiar los tiempos y modos de especiación entre ambos continentes. De hecho, Sterechinus agrupa especies que se desarrollan a través de una larva planctotrófica de alto poder dispersivo, mientras que las especies del género Abatus no presentan tal estado libre. En este sentido, ambos géneros permitirán contrastar las estimaciones de los tiempos de separación en relación con los distintos modos de desarrollo.
Los marcadores moleculares representan una buena herramienta de trabajo, que nos permiten evaluar el tiempo de separación entre las especies congéneres que habitan estos continentes. El análisis del gen COI (mtDNA) de tres especies de Sterechinus: dos que se encuentran fuera de la convergencia antártica (Argentina y Kerguelen) y una dentro de ésta; y dos especies de Abatus, una de cada continente (Argentina y Antártica) indican que para ambos géneros, los especímenes provenientes de Antártica y Subantártica presentan una clara separación. Asumiendo la hipótesis de reloj molecular, los resultados definen distintos tiempos de divergencia entre la fauna Antártica y Sudamericana para cada género: 5.9 - 4.2 Ma (Sterechinus) y 17 Ma (Abatus). Estos resultados sugieren que la falta de estadio dispersivo en el género Abatus resultó en una separación precoz entre taxa, asociada a la separación física de ambos continentes y a la instalación de una barrera batimétricas entre ellos. En el caso de Sterechinus, el gran potencial de dispersión larval de estas especies podría haber permitido mantener una conectividad muy posterior a los eventos tectónicos y solamente el establecimiento de una barrera oceanográfica efectiva, como la corriente circumpolar antártica (CCA), podría haber iniciado la divergencia entre Antártica y Sudamérica en este género. En el caso de Sterechinus, los patrones filogeofráficos muestran una gran conectividad dentro de cada zona, sugiriendo dos grandes vías de dispersión (modelo de los anillos antárticos y subantárticos).
The presence of congeneric species of marine benthic invertebrates in Antarctica and South America has been historically interpreted as the result of vicariant speciation due to plate tectonics, enhanced by the installation of the Antarctic Circumpolar Current (ACC). Nevertheless, few evidences has been contributed to validate this model. The genera Abatus and Sterechinus (Echinidae) are good examples of this kind of transoceanic distribution and excellent models to study the times and modes of speciation in the Southern Ocean. Actually, Sterechinus have an indirect development mode with a high dispersive planctotrophic larva, while the brood - protecting species of Abatus have a direct development mode. In this regard, both genera constitute good models to determine how the mode of development is related to divergence times. Molecular markers allowed us to evaluate divergence time between congeneric species from Antarctica and South America. We analyzed Cytochome Oxidase subunit I (mtDNA) in three species of Sterechinus from different biogeographic regions, namely S. agassizi (Argentina), S. diadema (Kerguelen Province) and S. neumayeri (Antártica); and two species of Abatus, A. cavernosus (Magellan) and A. agassizii (Antarctica). Our results indicate that both genera show marked genetic differences between species from antarctic and subantarctic regions. Assuming the molecular clock hypothesis, our results indicate different divergence times between the Antarctic and Southamerica fauna of 5.9 - 4.2 Ma (Sterechinus) and 17 Ma (Abatus). These results suggest that the absence of a dispersive stage in Abatus resulted in a ancient separation of the taxa, related to the continental separation. On other hand, the great dispersive potential of Sterechinus species could have allowed to maintain a certain degree of connectivity after tectonic events. In this regard, oly the establishment of an effective oceanographic barrier, a possible intensification of the ACC, could have initiated the diversification of this genus in the Southern Ocean. In Sterechinus, phylogeographic pattern suggests also a great connectivity within each region, which is evidence of two major dispersion routes (Antarctic and subantarctic 2-rings model).
The presence of congeneric species of marine benthic invertebrates in Antarctica and South America has been historically interpreted as the result of vicariant speciation due to plate tectonics, enhanced by the installation of the Antarctic Circumpolar Current (ACC). Nevertheless, few evidences has been contributed to validate this model. The genera Abatus and Sterechinus (Echinidae) are good examples of this kind of transoceanic distribution and excellent models to study the times and modes of speciation in the Southern Ocean. Actually, Sterechinus have an indirect development mode with a high dispersive planctotrophic larva, while the brood - protecting species of Abatus have a direct development mode. In this regard, both genera constitute good models to determine how the mode of development is related to divergence times. Molecular markers allowed us to evaluate divergence time between congeneric species from Antarctica and South America. We analyzed Cytochome Oxidase subunit I (mtDNA) in three species of Sterechinus from different biogeographic regions, namely S. agassizi (Argentina), S. diadema (Kerguelen Province) and S. neumayeri (Antártica); and two species of Abatus, A. cavernosus (Magellan) and A. agassizii (Antarctica). Our results indicate that both genera show marked genetic differences between species from antarctic and subantarctic regions. Assuming the molecular clock hypothesis, our results indicate different divergence times between the Antarctic and Southamerica fauna of 5.9 - 4.2 Ma (Sterechinus) and 17 Ma (Abatus). These results suggest that the absence of a dispersive stage in Abatus resulted in a ancient separation of the taxa, related to the continental separation. On other hand, the great dispersive potential of Sterechinus species could have allowed to maintain a certain degree of connectivity after tectonic events. In this regard, oly the establishment of an effective oceanographic barrier, a possible intensification of the ACC, could have initiated the diversification of this genus in the Southern Ocean. In Sterechinus, phylogeographic pattern suggests also a great connectivity within each region, which is evidence of two major dispersion routes (Antarctic and subantarctic 2-rings model).
Description
Tesis para optar al grado de Magíster en Ciencias Biológicas, mención en Ecología y Biología Evolutiva
Keywords
Fauna marina bentónica, Ciencia, Genética, Echinoidea