Js. Clegg, EMBRYOS OF ARTEMIA-FRANCISCANA SURVIVE 4 YEARS OF CONTINUOUS ANOXIA -THE CASE FOR COMPLETE METABOLIC-RATE DEPRESSION, Journal of Experimental Biology, 200(3), 1997, pp. 467-475
Encysted gastrula embryos of the crustacean Artemia franciscana have a
cquired an array of adaptations that enable them to survive a wide var
iety of environmental extremes. The present paper shows that at least
60% survive 4 years of continuous anoxia at physiological temperatures
(20-23 degrees C) when fully hydrated, Although these embryos appear
to carry on a metabolism during the first day of anoxia, no evidence f
or a continuing metabolism throughout the subsequent 4 years was obtai
ned, During this period, there were no measurable changes in the level
s of their stored, mobilizable carbohydrates (trehalose, glycogen, gly
cerol), Calculations indicate that, if these carbohydrates are being u
tilized at all during anoxia, the rate is at the least 50 000 times lo
wer than the aerobic rate (lower limit of detection), Indications of p
roteolysis during prolonged anoxia were sought but not found, Under st
arvation conditions, the life span of larvae produced from embryos tha
t had undergone 4 years of anoxia was not significantly different from
that of larvae produced by embryos that had not experienced anoxia, T
hus, all substrates and other metabolites required to support embryoni
c development to the nauplius, as well as endogenous (unfed) larval gr
owth and molting, are retained during 4 years of anoxia, It is not pos
sible to prove experimentally the absence of a metabolic rate in anoxi
c embryos under physiological conditions of hydration and temperature,
Nevertheless, on the basis of the results presented here, I will make
the case that the anoxic embryo brings its metabolism to a reversible
standstill, Such a conclusion requires that these embryos maintain th
eir structural integrity in the absence of measurable biosynthesis and
free energy flow and are thus an exception to a major biological gene
rality, Potential mechanisms involved in their stability are discussed
.