Desiccation tolerance commonly found among tardigrades allows them to cope with temporal variation of available water. Although the long-term survival of adults has been demonstrated in several species, desiccation tolerance of eggs and embryos is less well studied, however it is an important aspect from an ecological and evolutionary point of view. For the first time we evaluated the desiccation tolerance and subsequent hatching success of five different developmental stages of the tardigrade species Milnesium tardigradum, when rehydrated following drying at eight different humidity levels (10, 20, 31, 40, 54, 59, 72, 81%). Humidity level and developmental stage are significant factors in determining successful hatch rates. The results showed that the less developed stages were quite sensitive to desiccation. Low humidity levels during the first 3 days of development lead to a decrease in hatch rates following rehydration. Later developmental stages showed higher hatch rates than embryos dried at earlier stages. However, fast drying at low humidity levels resulted in delayed development and lower hatch rates following rehydration. In general, further developed embryos exhibit a better survival capacity compared with younger stages.

Craspedacusta

The

No abstract

With the onset of changing environmental conditions in autumn, the freshwater sponge Spongilla lacustris (Linnaeus, 1759) produces resistant stages (gemmules) which are in the state of quiescence. Gemmules stored at 8 degrees C remained quiescent; however, germination occurred within 24 hr after the water temperature was increased to 22.5 degrees C. Sponges hatched through the micropyle and subsequently built new spicules and a new canal system. The molecular and biochemical mechanisms which enable the gemmules to survive long periods of adverse conditions are not known. For the first time we focused on the role of the stress protein Hsp70 and the expression of hsp70 mRNA in S. lacustris during the development of gemmules in the state of quiescence into growing sponges. The partial sequence of hsp70 seems to be a true hsp gene since transcription could be clearly enhanced by temperature elevation. The results showed a large pool of cellular Hsp70 and hsp70 mRNA in gemmules during the state of quiescence. Within hours after a temperature trigger, the Hsp70 level decreased slowly and reached approximately the level of an adult sponge. Hsp70 presumably allows gemmules to stabilize their proteins and membranes during dormancy from autumn to spring when water temperatures change.