Reference: Biol. Bull 191: 385-392. (December, 1996) Metabolism of Gemmules From the Freshwater Sponge Eunapius fragilis During Diapause and Post-Diapause States STEPHEN H. LOOMIS 1 , STEVEN C. HAND : , AND PAUL E. FELL 1 1 Department of Zoology, Connecticut College, New London, Connecticut 06320; and 2 Department ofEPO Biology, University of Colorado, Boulder. Colorado 80309-0334 Abstract. Post-diapause gemmules of the freshwater sponge Eunapius fragilis remained quiescent when maintained at 5C. Germination occurred within 48 to 72 h following warming to 20-23C, culminating with the emergence of a new sponge from the collagenous cap-sule. Both heat dissipation and oxygen consumption climbed steadily during germination and eventually reached 600% of the starting values. By comparison, en-ergy flow was much lower over the same period of time in diapausing gemmules, clearly demonstrating metabolic depression during diapause. The calorimetricrespiro-metric (CR) ratio increased significantly from -354 kJ/ mol O 2 to -541 kJ/mol O 2 between hours 3.5 and 56.5 of germination, with an average value across this period of about -495 kJ/mo!O 2 . The low CR ratio at hour 12.5 (-374 21; 1 SE, H = 3) was statistically below the oxycaloric equivalent, which suggests that gemmules may have experienced hypoxia during the more than 3 months of storage at 5C prior to experiments. The in-crease in metabolism during germination could be blocked by perfusing the gemmules with nitrogen-satu-rated medium (nominally oxygen free). Developing gemmules were able to survive oxygen limitation for sev-eral hours at least; during that time energy flow was de-pressed to 6% of normoxic values. During germination, the range of values was 3.5 to 4.0 nmol/mg protein for ATP, 0.2 to 0.4 nmol/mg protein for ADP, and 0.5 to 0.8 nmol/mg protein for AMP. Because ATP was high even before gemmules were warmed to room tempera-Received 10 October 1 995; accepted 27 September 1996. ture, it is unlikely that levels were severely compromised during the diapause condition. Introduction Gemmules of the sponge Eunapius fragilis are asexu-ally produced reproductive bodies composed of un-differentiated cells surrounded by a complex collagenous capsule. Such bodies serve as the overwintering stage in the life cycle of this sponge. The possession of resting stages in the life cycles of invertebrates is common for organisms inhabiting inconsistent or ephemeral environ-ments and is widespread phylogenetically (Hand, 1 99 1 ). Newly formed gemmules are in an obligate state of de-velopmental (and potentially metabolic) arrest that is termed diapause. Vernalization in the cold for 2-3 months releases the gemmules from diapause and al-lows them to resume development when warmed to 20-23C. The molecular mechanisms of this diapause breakage are unexplained. E. fragilis is well-suited for use in inves-tigating these mechanisms because diapause in its gem-mules is easily manipulated and is quite distinct from quiescence (Fell, 1987), a metabolically arrested condi-tion promoted directly by environmental insult. In other sponges, these two states are apparently intertwined (e.g., Spongilla lacustris, Simpson and Rodan, 1976), and it can be quite difficult to distinguish whether or not gem-mules are in diapause or whether the state has been bro-ken. Other species apparently do not enter diapause at all and exhibit only quiescence (Ephydatia fhiviati/is. Rasmont, 1963, 1965). 385
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