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