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How Did the Water Bears (Phylum Tardigrada) Evolve Adaptations Allowing Space Survival?

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How Did the Water Bears (Phylum Tardigrada) Evolve Adaptations Allowing Space Survival? Critters in space: How did the water bears (Phylum Tardigrada) evolve adaptations allowing space survival? Supervisor: Davide Pisani Co-Supervisor: Phil Donoghue Supervisors based outside Bristol: Sandra McInness (British Antarctic Survey), Lorena Rebecchi and Roberto Guidetti (University of Modena and Reggio Emilia), Kazuharu Arakawa (Keio University). Tardigrada, the water bears, are microscopic animals that rose to international media attention when it was discovered that they could survive exposure to outer space. Tardigrades do so by entering a state of suspended life called anhydrobiosis, which is initiated through a process of desiccation, where all water evaporate from the animal body. Anhydrobiosis has also allowed tardigrades to colonise Earth’s most extreme environments, including Antarctica. Tardigrada are classi ed in two lineages, the Eutardigrada – which are mostly terrestrial, and the Heterotardigrada – which include marine and terrestrial species. The phylogenetic relationships within the two lineages are unclear. Anhydrobiosis has only been studied in eutardigrades; and the discovery of the factors allowing anhydrobiosis in the eutardigrade Ramazzotius varieornatus were only recently published [1]. In Heterotardigrada, anhydrobiosis is known in the terrestrial Echiniscoididae, and it is almost unknown in marine heterotardigrades (the Arthrotardigrada). This project proposes to use transcriptomic data and cutting edge computational methods[2-4] to clarify the phylogenetic relationships and divergence times within the two tardigrade lineages (Eutardigrada and Heterotardigrada). We shall then use our tardigrade phylogeny as a reference to carry out computational comparative tests and investigate the origin and evolution of genes related to anhydrobiosys in tardigrades. Genes for anydrobiosis were only recently discovered1 and we still do not know when they evolved in tardigrade history, and under what evolutionary pressures. Finally, you will compare Echiniscus (Heterotardigrada, Echiniscidae) species from Italy and Antarctica to test whether signatures of adaptation can be identi ed in genes relating to desiccation from closely related taxa adapted to temperate and polar conditions. The project is ideal for a student with an interest in Evolution and the comparative approach (phylogenetics, molecular clocks and comparative genomics). You will gain a deep knowledge of genomics and the analysis of gene sequences, as well as the reconstruction of phylogenetic trees and mapping the origin and evolution of characters along such trees. You will also learn tardrigrade taxonomy and diversity and spend time working with the British Antarctic Survey in Cambridge, and at the University of Modena and Reggio Emilia in Italy, and Keio University (Japan). 1. Hashimoto Takuma et al. Extremotolerant tardigrade genome and improved radiotolerance of human cultured cells by tardigrade-unique protein Nature Comm. 7, Article: 12808 (2016). 2. Lozano-Fernandez Jesus, Robert Carton, Alastair R. Tanner, Mark N. Puttick, Mark Blaxter, Jakob Vinther, Jørgen Olesen, Gonzalo Giribet, Gregory D. Edgecombe, Davide Pisani. A molecular palaeobiological exploration of arthropod terrestrialisation. Phil. Trans. R. Soc., London. 371: 20150133 (2016). 3. Lahcen I. Campbell, Omar Rota-Stabelli, Gregory D. Edgecombe, Trevor Marchioro, Stuart J. Longhorn, Maximilian J. Telford, Hervé Philippe, Lorena Rebecchi, Kevin J. Peterson, and Davide Pisani. MicroRNAs and phylogenomics resolve the relationships of Tardigrada and suggest that velvet worms are the sister group of Arthropoda. PNAS 108(38):15920–15924 (2011). 4. Rota-Stabelli O., Daley A.C., Pisani D. Molecular Timetrees Reveal a Cambrian Colonization of Land and a New Scenario for Ecdysozoan Evolution. Current Biol. 23(5):392– 398 (2013) . Figure: Antarctic tardigrades (Acutuncus and Macrobiotus). Photos by Sandra McInness .
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