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Journal of Experimental Biology 152,77-92 (1990)
Published by Company of Biologists 1990

Heat Dissipation, Gas Exchange and Acid-Base Status in the Land Snail Oreohelix During Short-Term Estivation

BERNARD B. REES ¹ and STEVEN C. HAND ¹

¹ Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, CO 80309-0334, USA

Within 4 days following entry into estivation, heat dissipation and oxygen consumption by the land snail Oreohelix spp. decreased by 83% compared to standard non-estivating rates. During both non-estivating and estivating conditions, the quantity of heat dissipated per mole of O₂ consumed was indicative of a completely aerobic metabolism. This calorimetric-respirometric (C/R) ratio was -461±12 kJ mol^-1O₂ (S.E.M., N=5) under standard non-estivating conditions and -464±26 kJ mol^-1O₂ (N=4) during estivation. Respiratory exchange ratios reflected a primary dependence upon carbohydrate as a metabolic substrate during both states. Carbon dioxide retention occurred during the first 36h of estivation, resulting in an increase in hemolymph P_COCO2 and a decrease in pH. The respiratory acidosis during short-term estivation was not compensated by elevation of hemolymph [HCO₃^-] above levels predicted from the in vitro nonbicarbonate buffer value of hemolymph. A brief period of rapid CO₂ release, which caused hemolymph P_COCO2 and pH to return to pre-estivation values, preceded the increase in O₂ consumption during arousal. Exposure of nonestivating snails to 4.67 kPa P_COCO2 (1 kPa=7.5 mmHg) caused a rapid and fully reversible 50% suppression of respiration rate. The temporal nature of CO₂ retention and release during entry into and arousal from estivation, and the suppression of O₂ consumption by artificial hypercapnia, support the hypothesis that elevated P_COCO2. or the resultant acidosis may contribute to metabolic suppression during estivation by land snails.

Key words: estivation, dormancy, land snail, calorimetry, oxygen consumption, carbon dioxide retention, acid-base status

Accepted on April 12, 1990

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