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Metabolic Changes during Estivation in the Common Earthworm Aporrectodea caliginosa
Mark Bayley, Johannes Overgaard, Andrea Sødergaard Høj, Anders Malmendal, Niels C. Nielsen, Martin Holmstrup and Tobias Wang
Physiological and Biochemical Zoology: Ecological and Evolutionary Approaches
Vol. 83, No. 3 (May/June 2010), pp. 541-550
Published by: The University of Chicago Press. Sponsored by the Division of Comparative Physiology and Biochemistry, Society for Integrative and Comparative Biology
Stable URL: http://www.jstor.org/stable/10.1086/651459
Page Count: 10
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Abstract The common earthworm Aporrectodea caliginosa survives drought by forming estivation chambers in the topsoil under even very slight reductions in soil water activity. We induced estivation in a soil of a consistency that allowed the removal of intact soil estivation chambers containing a single worm. These estivation chambers were exposed to 97% relative humidity for 30 d to simulate the effect of a severe summer drought. Gas exchange, body fluid osmolality, water balance, urea, and alanine were quantified, and whole‐body homogenates were screened for changes in small organic molecules via 1H–nuclear magnetic resonance (NMR). Formation of estivation chambers was associated with a dramatic increase in body fluid osmolality, from 175 to 562 mOsm kg−1, accompanied by a 20% increase in water content. Dehydration for 1 mo caused a further increase to 684 mOsm kg−1, while the worms lost 50% of their water content. Gas exchange was depressed by 50% after worms entered estivation and by 80% after a further 30 d of dehydration. Urea concentrations increased from 0.3 to 1 μmol g−1 dry mass during this time. Although 1H‐NMR did not provide the identity of the osmolytes responsible for the initial increase in osmolality after estivation, it showed that alanine increased to more than 80 mmol L−1 in the long‐term‐estivation group. We propose that alanine functions as a nitrogen depot during dehydration and is not an anaerobe product in this case.
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