Diversity and evolutionary history of mygalomorph spiders in the Western Mediterranean and the Canary Islands = La diversidad e historia evolutiva de las arañas migalomorfas en el Mediterráneo Occidental y las Islas Canarias

Abstract

[spa] El infraorden Mygalomorphae es uno de los tres linajes evolutivos principales reconocidos dentro de las arañas, pero su diversidad en el Mediterráneo ha sido en general poco estudiada. Los factores que contribuyen al escaso conocimiento taxonómico del grupo tienen que ver con sus hábitos crípticos y su uniformidad fenotípica. Dicha uniformidad, convierte al grupo en un sistema para testar métodos de delimitación de especies. Por otro lado, el grupo se caracteriza por un baja capacidad de dispersión y elevado sedentarismo, constituyendo un modelo excelente para estudios de biogeografía, ya que sus distribuciones pueden reflejar procesos geológicos tales como la deriva continental. En esta tesis se ha utilizado una metodología integrativa que combina secuencias de DNA de múltiples genes, genotipado mediante AFLPs y modelación de distribución de especies, para abordar una serie de cuestiones relacionadas con la diversidad de este grupo. Mediante el uso de los métodos de análisis filogenéticos, inferencia del marco temporal de la diversificación del grupo y la aplicación de los métodos bayesianos coalescentes para la delimitación de especies se identifican los principales factores que promovieron la diversificación de los migalomorfos en la cuenca mediterránea, se contrastan diferentes escenarios biogeográficos sobre su origen y se investiga su estatus taxonómico. Los resultados de esta tesis mejoran notablemente el conocimiento actual sobre la diversidad críptica, la biogeografía y la filogenia de las familias Ctenizidae, Hexathelidae e Idiopidae que habitan el Mediterráneo e Islas Canarias. En todos los grupos estudiados se han detectado linajes evolutivos independientes que pueden corresponder a especies nuevas. Nuestros resultados ponen en evidencia que los eventos geológicos pasados tales como la desintegración de Gondwana, Laurasia y el Cinturón Herciniano modelaron la distribución actual de los migalomorfos Mediterráneos y que las Islas Canarias fueron colonizadas desde el continente una sola vez. Los resultados de esta tesis también confirman la polifilia de las familias Ctenizidae y Hexathelidae y ponen de manifiesto la necesidad de reevaluar los caracteres morfológicos utilizados en la taxonomía actual.

[eng] The spider infraorder Mygalomorphae, comprising tarantulas, funnel-web spiders and the trap-door spiders, is one of the three main evolutionary lineages recognized within spiders. Its family level phylogenetic relationships are with a few exceptions relatively well solved, but its actual diversity in the Mediterranean region is probably underestimated. Because of the extremely low dispersal capacity, mygalomorph spiders usually show high levels of local endemism and deep population genetic structure, however, closely related species tend to be morphologically conservative. The low vagility and high habitat fidelity of mygalomorphs makes them a perfect model system for biogeographic studies as their distribution ranges are more likely to reflect geological processes such as continental break ups or tectonic plates rearrangements, while their conservative morphology makes them a good system to test species delimiting methods. The present Ph.D. thesis provides insights into the cryptic diversity, distribution patterns and phylogenetic relationships of the species of the families Ctenizidae, Hexathelidae and Idiopidae that inhabit the Western Mediterranean and the Canary Islands. By using a multi-locus approach and state of the art phylogenetic inference methods, the pattern and time frame of the diversification of these groups is inferred. The phylogenetic and temporal information sheds light on the biogeographic scenario and the diversification drivers of the selected families. Molecular based species delimitation approaches are further used to identify species boundaries in morphologically conservative groups. The results of the present study have greatly contributed to improve our current understanding of the diversity, biogeography and phylogeny of the mygalomorph spiders inhabiting the Mediterranean region and the Canary Islands. The existence of the independent evolutionary lineages that may correspond to undescribed species was detected in all studied groups, so far neglected by taxonomists due to their secluded habits and uniform morphology. The study also reveals that the past geological events had a great impact on the present day distribution of Mediterranean mygalomorphs. In the family Ctenizidae, the amphi-Atlantic distribution of Ummidia, traces back to a former Laurasian distribution and the rearrangement of the microplates following the Hercynian Belt break up, drove the diversification of both Cteniza and Ummidia in the Western Mediterranean. Our findings support that the genus Macrothele colonised the Mediterranean region during the Eocene in two independent waves, presumably from Asia, which in turn may have been colonised from Africa by rifting on the Indian subcontinent, following the Gondwana break up. On the other hand, the Canary Islands were colonised once by the genus Titanidiops presumably by passive rafting from the nearby mainland. Finally, the study sheds additional light on the high level phylogeny of mygalomorph spiders. The first ever-molecular phylogeny of the family Ctenizidae that includes representatives of all genera was conducted, revealing that their current higher taxonomic groupings are polyphyletic and failing to retrieve the monophyly of the family as whole, mostly due to the position of Cteniza and Cyrtocarenum. Unfortunately, topology tests could not reject the single origin of the family. Similarly, the results further confirmed the polyphyly of the family Hexathelidae, mostly due to the inclusion of the Atracinae subfamily. Our findings emphasize the need for redefining the limits of the families Ctenizidae and Hexathelidae and re-evaluating the morphological characters used in the current taxonomy of both groups.