We report a study on the presence of the disaccharide trehalose in three desiccation tolerant tardigrades. This
sugar has long been suggested to play a protective role in desiccation tolerant animals. Trehalose was found in all species,
with increased levels in dehydrated specimens of Macrobiotus islandicus, and possibly also in Macrobiotus krynauwi,
both belonging to the family Macrobiotidae. In the third species, Milnesium tardigradum, very low amounts of trehalose
were found, with no increase in the dehydrated state. This species has previously been reported to lack trehalose.
Induction of trehalose has been reported only for species in the family Macrobiotidae, where also the highest levels have
been found. Although the role of trehalose in the desiccation tolerance of tardigrades remains unclear, the diverging
patterns in response to desiccation are interesting. Further studies of higher tardigrade taxa are needed in order to
understand the evolutionary history of trehalose in these invertebrates.