|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Anidrobiosi, radiazioni ultraviolette e riscaldamento globale: adattamenti ecologici, fisiologici, biochimici e molecolari nei tardigradi|
|Titolo in inglese||Anhydrobiosis, ultraviolet radiation and global warming: ecological, physiological, biochemical and molecular adaptations in tardigrades|
|Settore scientifico disciplinare||BIO/05 - ZOOLOGIA|
|Corso di studi||Scuola di D.R. in EARTH SYSTEM SCIENCES: ENVIRONMENT, RESOURCES AND CULTURAL HERITAGE|
|Data inizio appello||2016-03-24|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
Obiettivo del mio progetto di dottorato è stato l’identificazione di strategie adattative di tipo ecologico, fisiologico, biochimico e molecolare evolute dai viventi per tollerare l’essiccamento naturale e l’aumento di temperatura e radiazioni ultraviolette (UV) dovuti ad alterazioni della quantità di ozono troposferico e di CO2.
The aims of my research were the identification of ecological, physiological, biochemical, and molecular defense strategies naturally evolved by animals to tolerate complete desiccation, and increasing UV radiation and temperature due to the alteration of the tropospheric ozone budget and alteration of the CO2 amount. To carry out my research, two species of tardigrades (Acutuncus antarcticus from Antarctic region, and Paramacrobiotus richtersi from temperate region) were used as model animals, and their responses to stress conditions were compared. Tardigrades are microscopic aquatic animals able to colonize terrestrial habitats thanks to their capability to enter anhydrobiosis, a temporary suspension of active life due to the loss up to 97% of body water. They can persist in anhydrobiosis for decades and in this physiological state are able to withstand several physical and chemical extreme stresses. Biochemical analysis performed in experimentally desiccated specimens of P. richtersi demonstrated the accumulation of Reactive Oxygen Species (ROS) during the permanence in the anhydrobiotic state. As a consequence, the activities or accumulation of antioxidant molecules (e.g. scavenging enzymes and glutathione) during the kinetic of anhydrobiosis was evaluated in both model species. In P. richtersi, the catalase activity increased significantly during desiccation process and decreased during rehydration. In A. antarcticus, the activity of superoxide dismutase and the content of glutathione significantly decreased in desiccated animals and increased during rehydration. RNA interference (RNAi) molecular technique was utilized to silence genes enconding to molecules potentially involved in anhydrobiosis (e.g. scavenging enzymes, heat shock proteins, aquaporines, trehalose) in order to fully understand their role in desiccation tolerance of P. richtersi. The results point to the involvement in the desiccation process of at least glutathione peroxidase, a very important antioxidant system in scavenging free radicals. . To evaluate the capability of tardigrades to cope with stress related to global warming, the survival and life history traits of A. antarcticus were analysed on animals and eggs after desiccation and exposition to increasing temperature and UV radiation. The life cycle of A. antarcticus is short and its reproductive output was low, with a short generation time. These traits are advantageous for exploiting the conditions suitable for growth and reproduction during the short Antarctic summer. Hydrated animals of A. antarcticus were able to tolerate increasing temperature values, and both hydrated and desiccated animals showed a good tolerance to increasing UV radiation doses. This tolerance was evaluated also irradiating eggs at different developmental stage and collecting life history traits of two successive generations. All irradiated eggs showed a delay in the hatching time with respect to not irradiated eggs. Moreover, a negative effect on life history traits and newborns with morphological defects were observed. Furthermore, the survivorship of A. antarcticus animals decreased when they were simultaneously exposed to UV radiation and increasing temperatures. These new data on A. antarcticus were compared with those existing and newly produced (tolerance to high temperature) on the temperate species P. richtersi. The data obtained during the PhD project allowed to identify the strategies evolved in tardigrades to withstand stressful environmental conditions, and confirmed tardigrades as a reliable animal model system to improve scientific knowledge on natural defense mechanisms evolved in animals.