Life without water: An investigation of the mechanisms of anhydrobiosis in nematodes of the Antarctic and short grass steppe

Background/Question/Methods Anhydrobiosis is an adaptive response to desiccation stress, entailing a reversible protective state marked by the cessation of metabolism, and a  reduction in body water. While this survival strategy has been documented in rotifers, tardigrades and some species of nematodes, the mechanisms that mediate this plasticity are not well understood.  The central objective of the current study is to elucidate the mechanisms by comparing anhydrobiosis potential in nematodes isolated from two LTER sites, one dry, McMurdo Dry Valleys LTER (MCM) and one seasonally dry, Short Grass Steppe LTER (SGS).  We hypothesize nematodes from MCM which endure extremely cold and dry soil conditions, will show a greater ability to survive experimentally induced anhydrobiotic conditions than nematodes of Colorado’s SGS.  Additionally, we hypothesized that principal genetic mechanisms, including gene and protein expression and production of protective compounds, would be common to all nematodes capable of desiccation survival.  To investigate these objectives, in the laboratory, cultures of the microbial-feeders Plectus spp. of Antarctica and Acrobeles spp. of the shortgrass steppe were induced to enter the anhydrobiotic state through the manipulation of relative humidity by saturated salts.
Results/Conclusions

This study established that anhydrobiosis is a heritable trait in these species and that genetic variation for anhydrobiotic capacity exists both within and among the species investigated.  The results of this experiment indicate that the suite of traits that mediate the phenotype of anhydrobiosis in these nematodes contains a genetic component that is independent of environmental factors.  Differences in anhydrobiotic survival have also been demonstrated between Plectus spp.  and Acrobeles spp..  These preliminary results indicate that Plectus spp. from the MCM is more tolerant of severe desiccation regimes than Acrobeles spp., and will correspondingly delay response to desiccation and freezing factors.  Plectus spp. exhibits a higher survival rate than Acrobeles spp. under identical experimental desiccation conditions.  Results  reveal common strategies by both species to combat desiccation stress, including the production of disaccharides, specifically trehalose.  Preliminary data show that the amount of these protective compounds can differ based on the species of nematode.  Together, these results suggest that nematodes that utilize anhydrobiosis as a survival strategy to overcome desiccating environmental conditions do so by employing a similar molecular cascade, but the relative anhydrobiotic capacity of these species relates to adaptation to their local environment.