Chemical and microbial ecology of thc demosponge Aplysina aerophoba = Ecología química y microbiana de la demosponja Aplysina aerophoba

• Autores: Oriol Sacristán Soriano
• Directores de la Tesis: Cruz Palacín Cabañas (dir. tes.), MIkel A. Becerro (dir. tes.)
• Lectura: En la Universitat de Barcelona ( España ) en 2013
• Idioma: inglés
• Tribunal Calificador de la Tesis: Susanna López-Legentil (presid.), Marta Ribes Llordes (secret.), Oliver P. Thomas (voc.)
• Materias:
  • Ciencias de la vida
    • Biología animal (zoología)
      • Ecología animal
    • Microbiología
      • Mohos
    • Biología vegetal (botánica)
      • Botánica marina
    • Simbiosis
• Enlaces
  • Tesis en acceso abierto en:  TDX  Dipòsit Digital de la UB 
• Resumen

  • Phylum Porifera (Grant, 1836) are sessile metazoans with a differentiated inhalant and exhalant aquiferous system with external pores. Lacking a tissue grade of construction, sponges can reach two well-differentiated regions, the ectosome (external layer free of choanocytes) and the choanosome (internal region with choanocytes). As the most likely primitive metazoans, their challenging structural organization, physiology for biocalcification and trophic requirements allowed sponges to rapidly colonize distinct environments and built important sponge reefs during the Paleozoic and Mesozoic eras, making them an ecologically relevant group principally in marine benthic communities. To date, sponges are still ecologically important among benthic fauna although the role as reef builders in modern coral reefs has changed in favor of scleractinian corals. Nonetheless, sponges have demonstrated a huge capacity to adapt and spread in many habitats contributing to organization and functioning at both community and ecosystem levels. One of the keys of the evolutionary success of this group lies in the close association between sponges and microbes that dates back to the Precambrian era. The need to be defended may have arisen from the lack of motility of sponges and several mechanisms emerged to fulfill their demand including a chemical protection. Many sponges would have taken advantage of associated microbes to use their metabolites as a defense barrier against predators, competitors or foulers. This particular symbiosis has consequently become a key factor in biotic interactions within the sponge research. To date, chemical ecology and microbial ecology are two independent areas of the sponge research with ecological implications that occasionally converge at the same point. We want to analyze the evolution of the sponge chemical and microbial ecology from the very beginning, to quantify their impact on the scientific community, and to compare both research areas. This PhD dissertation has been conceived to study the chemical and microbial ecology of sponges using the demosponge Aplysina aerophoba (Nardo, 1833) as a model species because its secondary chemistry and its associated microbial community are well studied and it is quite abundant in our study area (Northwestern Mediterranean and Canary Islands). Beyond the knowledge achieved about the major chemistry and bacterial assemblages in A. aerophoba, we have been able to explore the variation sources of the natural products and the sponge microbial consortium. Additionally, we have assessed the putative relationships between the host bacterial community and the production of secondary metabolites in this species. We explored changes in the abundance of secondary metabolites and the relative composition of bacterial assemblages in A. aerophoba at multiple spatial (from few centimeters to thousand kilometers) and temporal (months and years) scales. The approach used allowed us to investigate which is the magnitude of the variance attributable to the distinct spatial and temporal scales and the most relevant scale at which the abundance of secondary metabolites and bacterial symbionts varied. We also investigated the relationship between natural products and microbial community structure by assessing whether both parameters covary at multiple scales. Finally, we experimentally addressed whether different light exposures can modify chemical and microbial profiles in the external and internal regions of A. aerophoba. In summary, the production of natural products in sponges and the abundance and phylogenetic composition of the host-associated microbial community mainly depend to a large extent on the sponge-species and the ecological factors with spatial and temporal variations (e.g., light, predation, competition, fouling). The host state (i.e., stress) is also a key factor that may be the main driver of symbiotic shifts causing a breakdown in the sponge health and making the symbiont communities unstable and likely the sponge chemical defense. The combination between abiotic and biotic factors may finally determine the concentration of bioactive compounds and associated microbial diversity as the abiotic environmental context can control the outcomes of biotic interactions, and biotic interactions often moderate the effect of abiotic factors. For that reason, it is not an easy task to actually figure out the factors that limit or enhance chemical and microbial variability. Further experiments and time-series observations are needed to reveal the underlying processes hidden.