Biogeography of sponge-associated bacterial communities and resilence to anthropogenic perturbations = Biogeografía de las comunidades bacterianas asociadas a esponjas y su resiliencia frente a perturbaciones antropogénicas
- Autores: Lucía Pita Galán
- Directores de la Tesis: Patrick M. Erwin (dir. tes.), Susanna López-Legentil (dir. tes.)
- Lectura: En la Universitat de Barcelona ( España ) en 2014
- Idioma: inglés
- Tribunal Calificador de la Tesis: María Jesús Uriz Lespe (presid.), Pierre Galand (secret.), Peter J. Schupp (voc.)
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX Dipòsit Digital de la UB
- Resumen
Marine sponges are a key component of benthic ecosystems in oceans all around the world, from shallow to deep waters, due to their diversity, abundance and influence in the cycle of nutrients. Moreover, the chemical defenses of the sponge against competitors, predators and fouling make the sponge a rich source of novel antitumoral drugs. But the relevance of sponge partially relies on their association with a complex microbial community that expands the metabolism of the host (e.g., via photosynthesis or nitrogen fixation) and takes part of metabolite synthesis. The symbiotic community is dominated by bacteria. One sponge specimen can host hundreds of bacterial taxa that are closely related with other sponge-derived bacteria but rare or absent in the surrounding environment (i.e., seawater and sediments). The sponge-associated bacterial communities are species-specific, but most of the studies are based on samplings at a particular point in time and space; thus, we ignore the potential dynamism of this interaction. The main objective of this PhD thesis was to identify the specificity and persistence of sponge-bacteria symbiosis through spatial and temporal scales. In particular, we used sympatric sponges of the genus Ircinia as a model to distinguish the relative role of environmental-related and host-related factors on the structure of their bacterial communities. In particular, we aimed to assess the effect of currents and spatial heterogeneity of the environment on the bacterial communities associated with sponges from the Bahamas (Ircinia felis and I. strobilina) at a scale of hundreds of kilometers (chapter 1) and confirm if the same pattern is applied to Mediterranean species (I. fasciculata, I. variabilis and I. oros) (chapter 2). Considering the marked seasonality in seawater conditions (i.e., temperature, irradiance, nutrient levels) in the Western Mediterranean Sea, we also investigated the bacterial communities in these sponges through different seasons (chapter 3). Recently, sponges and other filter-feeding invertebrates in the Mediterranean Sea have overcome mass mortality events; thus, we tested in aquaria experiments the potential influence of abnormal environmental changes (drastic increase of temperature and food shortage) in the symbiotic bacterial communities in I. fasciculata and I. oros. Bacterial communities were characterized by transmission electron microscopy and molecular tools (i.e., clone libraries and DNA fingerprinting of 16S rRNA gene sequences). The results derived from this thesis show that host-specific rather than biogeographic factors play a major role in structuring and maintaining sponge-associated bacterial communities. The bacterial communities in Ircinia spp. were species-specific and this specificity were maintained through hundreds of kilometers (chapters 1 and 2) and despite seasonality in seawater conditions (chapter 3). Moreover, stress conditions in aquaria experiments did not significantly affect the symbiotic bacterial communities (chapter 4). These results suggest a tight and stable link between the sponges and their bacterial communities. We proposed that this symbiosis have resulted in a cooperative system where the activity of the bacterial community, together with the homeostasis of the animal host, contribute to the persistence of the interaction under different environmental conditions.
