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First published online May 30, 2008
Journal of Experimental Biology 211, 1903-1910 (2008)
Published by The Company of Biologists 2008
doi: 10.1242/jeb.017558
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Slow desiccation improves dehydration tolerance and accumulation of compatible osmolytes in earthworm cocoons (Dendrobaena octaedra Savigny)

Christina R. Petersen1,2, Martin Holmstrup1,*, Anders Malmendal3, Mark Bayley2 and Johannes Overgaard1,2

1 National Environmental Research Institute, University of Aarhus, Department of Terrestrial Ecology, Vejlsøvej 25, 8600 Silkeborg, Denmark
2 Department of Zoophysiology, University of Aarhus, 8000 Aarhus C, Denmark
3 Center for Insoluble Protein Structures (inSPIN), Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Aarhus, 8000 Aarhus C, Denmark


Figure 1
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  		Fig. 1. Upper panels: experimental protocol for gradually (A) and acutely (B) desiccated cocoons of D. octaedra. Arrows, asterisks and circles indicate time points for measurement of survival, water content and osmolytes, respectively. Lower panels: experimental protocol investigating the effects of gradual (C) and acute desiccation (D) on survival and water content after harsh desiccation treatments. Arrows indicate the time for measurement of survival and water content. The key indicates the relative humidity (RH, %).

 

Figure 2
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  		Fig. 2. Water content of D. octaedra cocoons during acute (A) and gradual (B) desiccation. The final desiccation strength was 91% RH for both groups. Water content (C) and survival (D) are shown after 4 and 14 days exposure at the final desiccation strength. Student t-tests were employed to test for differences in water content and survival between gradually and acutely exposed cocoons after both short- and long-term exposure. Values are means ± s.e.m. and asterisks indicate significant differences.

 

Figure 3
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  		Fig. 3. (A) Survival following severe desiccation in D. octaedra cocoons. Cocoons were either exposed acutely (filled circles) or given a 14 day gradual pre-acclimation to desiccation before the final exposure to severe desiccation stress (open circles). Different letters indicate significant differences in survival within each treatment (one-way ANOVA). (B) Water content of acutely and gradually desiccated cocoons following severe desiccation stress. Asterisks indicate a significant difference in water content between pre-acclimated and acutely exposed cocoons (separate t-tests for each desiccation level). (C) Survival versus water content of cocoons exposed acutely (filled circles) and cocoons that were pre-acclimated by gradual desiccation (open circles). All values are means ± s.e.m.

 

Figure 4
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  		Fig. 4. Representative 1H NMR spectra (displaced along the vertical axis to improve clarity) showing the major metabolites in D. octaedra cocoons. The three traces show untreated and fully hydrated cocoons (dotted line), cocoons gradually desiccated over 10 days with a final 4 day exposure to 91% RH (dashed line) and cocoons exposed acutely to 91% RH for 4 days. Well-resolved signals from the metabolites discussed in this study are assigned.

 

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  		Fig. 5. Concentrations of (A) sorbitol and glucose, and (B) alanine, betaine, trehalose and mannitol in D. octaedra cocoons. Samples were taken from untreated controls (0), during a gradual pre-acclimation to desiccation stress at 91% RH (G2–G24) or after a 4 day acute exposure to 91% RH (A4). Samples during the gradual pre-acclimation were taken after 2, 4, 8, 14 and 24 days (see Fig. 1). Asterisks indicate significant difference from day 0 (P<0.05). All values are means ± s.e.m.

 

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© The Company of Biologists Ltd 2008