Current Zoology 56 (2): 259263, 2010 Received Oct. 27, 2009; accepted Nov. 23, 2009  Corresponding author. E-mail: ralph.schill@bio.uni-stuttgart.de © 2010 Current Zoology Comparative studies on storage cells in tardigrades during starvation and anhydrobiosis Andy REUNER, Steffen HENGHERR, Franz Brümmer, Ralph O. SCHILL * Universität Stuttgart, Biological Institute, Zoology, Pfaffenwaldring 57, 70569 Stuttgart, Germany Abstract The impact of starvation and anhydrobiosis on the number and size of the storage cells in the tardigrade species Mil- nesium tardigradum, Paramacrobiotus tonollii and Macrobiotus sapiens was investigated to gain more insight on the energetic side of anhydrobiosis. Storage cells are free floating cells within the body cavity of tardigrades and are presumed to store and re- lease energy in form of glycogen, protein and fat to maintain a constant nutrient regime for the other tissues. The body size of the animals was not correlated with the size of the storage cells, however, M. tardigradum the largest species analysed also had the largest storage cells. A reduction in the size of the storage cells is apparent in all three species after seven days of starvation. A seven-day period of anhydrobiosis leads to a decrease in cell size in M. tardigradum but not in P. tonollii and M. sapiens. Al- though M. sapiens was raised on green algae, and M. tardigradum and P. tonollii were fed with rotifers and nematodes this dif- ference in nourishment was not reflected in the response of the storage cells to anhydrobiosis [Current Zoology 56 (2): 259–263, 2010]. Key words Tardigrada, cryptobiosis, Milnesium tardigradum, Paramacrobiotus tonollii, Macrobiotus sapiens Tardigrades can be found across all continents and oceans, inhabiting terrestrial, freshwater and marine habitats, from the summit of mountains to lowlands, polar to tropic regions and from coastal to the deep sea (Nelson, 2002). Terrestrial tardigrades are well adapted to extreme environmental changes in their microhabitats and well known for their capabilities to survive for sev- eral years in an anhydrobiotic or cryobiotic state. In the anhydrobiotic state they can endure experimental condi- tions of low or high temperatures as well as immersion in organic solvents, or exposure to high doses of radia- tion and hydrostatic pressure pressure (Westh et al., 1991; Ramløv and Westh, 1992; Westh and Kristensen, 1992; Seki and Toyoshima, 1998; Ramløv and Westh, 2001; Horikawa et al., 2006; Jönsson and Schill, 2007; Jönsson et al., 2008; Ono et al., 2008; Hengherr et al., 2009b). A longevity of 20 years has been reported for the species Echiniscus testudo stored under laboratory conditions (Jørgensen et al., 2007). Under more natural conditions they have the capacity to survive unfavour- able periods by complete desiccation. In this anhydrobi- otic state the tardigrades do not show measurable me- tabolism and form the so-called tun state (Baumann, 1922). The body cavity of tardigrades is filled with storage cells, also called storage bodies. They are seen as the major repository of energy stored in form of lipid, pep- tides and glycogen (May, 1946-1947; Węglarska, 1957; Rosati, 1968; Węglarska, 1975; Szymanska, 1994; Jönsson and Rebecchi, 2002). Electron microscopic work on Macrobiotus richtersi MURRAY 1911 by Szymanska (1994) demonstrated diminishing reserve materials in storage cells during oogenesis which had an impact on the size of the cells, i.e. they became smaller as fat and protein were used for the completion of the egg development. Węglarska (1957) working with Dac- tylobiotus dispar Murray, 1907 (formerly: Macrobiotus dispar) had already noted that cells in starved animals diminish and observed that starvation over a long period lead to the re-absorption of these cells. For Richtersius coronifer RICHTERS 1903 Jönsson and Rebecchi (2002) showed that cell size is a factor affecting survival during anhydrobiosis. The cells furthermore decreased in size implying enhanced energy consumption during entry into and emergence from anhydrobiosis. In this study we explored the storage cell number and size of carnivorous Milnesium tardigradum Doyère 1849 and Paramacrobiotus tonollii Ramazzotti 1958 and the herbivorous Macrobiotus sapiens Binda and Pilato 1984 and compared data on animals fed ad libi- tum with those that had been starved or induced into anhydrobiosis to explore the energetic aspects of anhy-