Comparative studies on storage cells in tardigrades during starvation and anhydrobiosis

Abstract

The impact of starvation and anhydrobiosis on the number and size of the storage cells in the tardigrade species Milnesium 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 release 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. Although M. sapiens was raised on green algae, and M. tardigradum and P. tonollii were fed with rotifers and nematodes this difference in nourishment was not reflected in the response of the storage cells to anhydrobiosis.

Mitosis in storage cells of the eutardigradeRichtersius coronifer

“…However, Reuner et al . () did not find a significant decline in storage cell number after starvation for 7 days in Milnesium tardigradum (Doyère, 1849), Macrobiotus sapiens (Binda & Pilato, 1984), and Paramacrobiotus tonollii (Ramazzotti, 1958), and in our own data there is also no tendency towards differences in cell number at different stages of egg development. Therefore, the possibility that mitotic activities in storage cells towards the end of the egg developmental cycle (when moulting also occurs) may have the function of restoring the number of cells after resorption currently has little support.…”

“…These cells belong to the cell category ‘coelomocytes’ (Tahseen, ), and have the role of storage and distribution of energy and nutrition in the body (Kinchin, ). They are single, freely floating cells in the body cavity fluid, with a few hundred up to more than a thousand cells per individual, and with large intraspecific and interspecific variation in numbers (Reuner et al ., ). Storage cells in tardigrades are known to contain stores of lipids and glycogen (May, 1946/1947; Węglarska, ; Szymanska, ), and the presence of tyrosinase activity, reported by Volkmann & Greven (), has indicated immunological functions; however, in general our understanding of the physiological functions of storage cells is still very poor.…”

Body cavity cells of Parachela during their active life

“…Xerobiotus pseudohufelandi primarily accumulated a huge amount of polysaccharides and lipids, and a small amount of proteins. The material that is stored in the body cavity cells is a food reserve that can be used by an animal during extreme environmental conditions such as a period of starvation (Węglarska, ; Szymańska, ; Poprawa, ; Reuner et al ., ).…”

“…Moreover, tardigrades are animals that are able to survive extreme conditions because of their ability to undergo cryptobiosis. The storage cells supply the reserve material that has accumulated in their cytoplasm as the reservoir of energy for entering cryptobiosis and rehydration (Węglarska, ; Jönsson & Rebecchi, ; Reuner et al ., ).…”

“…To date, the storage cell morphology and physiology of some species of tardigrades have been described (Richters, ; Rahm, ; Marcus, ; May, ; Węglarska, , ; Rosati, ; Kinchin, , ; Volkman & Greven, ; Jönsson & Rebecchi, ; Reuner et al ., ). However, only a few papers have described the ultrastructure of these cells, and only two of these have described the alterations that occur in storage cells during the different stages of oogenesis (Szymańska, ; Poprawa, ).…”