Desiccation tolerance in embryonic stages of the tardigrade

Abstract

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.

Reproductive traits of Macrobiotus hufelandi during a long-term field study with notes on Paramacrobiotus richtersi and Diphascon pingue (Eutardigrada)

“…Most of such factors finally depend on the mesoclimate, but microclimatic factors (hitherto unknown) also determined by the structure of the habitat (see the discussion in Schuster and Greven, 2007;Schuster et al, 2009) and species-specific factors have to be considered too. It has been shown that also eggs and developmental stages of tardigrades can withstand desiccation and low temperatures (Bertolani et al, 2004;Schill and Fritz, 2008;Guidetti et al, 2011). Hohberg (2006) has documented temperature-dependent development in cultures of P. richtersi with the shortest generation time (43 days) at 20°C, but noted high variability in egg development times.…”

Freeze tolerance, supercooling points and ice formation: comparative studies on the subzero temperature survival of limno-terrestrial tardigrades

“…Many limno-terrestrial tardigrade species are able to tolerate harsh environmental conditions in any developmental stage (Schill and Fritz, 2008) by entering a cryptobiotic state which is induced by desiccation (anhydrobiosis), lack of oxygen (anoxybiosis), osmotic pressure (osmobiosis) or low temperatures (cryobiosis) (Keilin, 1959). In this state metabolism is undetectable and life comes to a reversible standstill until activity is resumed under favourable conditions (Keilin, 1959).…”

Survival and DNA degradation in anhydrobiotic tardigrades

“…They are able to perform anhydrobiosis at any stage of their life cycle, from egg to adult (Bertolani et al, 2004;Schill and Fritz, 2008). Tardigrades are little known and neglected but they are invertebrates present in many environments (sea, freshwater, soil), frequently inhabiting very unstable habitats (e.g.…”