BIOCHEMICAL CORRELATES OF ESTIVATION TOLERANCE IN THE MOUNTAINSNAIL OREOHELIX (PULMONATA, OREOHELICIDAE)

Biochemical changes occurring over 7 months of estivation were studied in two species of land snail, Oreohelix strigosa (Gould) and O. subru dis (Reeve), to determine whether differential mortality during estiva tion is related to different energetic strategies. Laboratory-maintain ed snails, which were fed ad libitum prior to estivation, were compare d with snails collected from the field and induced to estivate without augmenting their energy reserves. In all groups, polysaccharide was c atabolized early in estivation, and protein was the primary metabolic substrate after polysaccharide reserves were depleted. Lipid was catab olized at a low rate throughout estivation. Rates of catabolism were l argely statistically equivalent between species. Urea and purine bases accumulated during estivation as a result of protein catabolism, with the former being quantitatively more important. In both laboratory-ma intained and field-collected snails, the rate of urea accumulation was greater in O. subrudis, resulting in higher tissue urea contents in t his species at the end of the 7-month experiment. The tissue concentra tions of urea at 7 months ranged from about 150 to 300 mM and were pos itively correlated (r = 0.99, P = 0.006) with mortality in these snail s. Methylamine compounds, a class of compounds that can offset disrupt ive effects of elevated urea, were measured in one group of O. strigos a at 7 months of estivation and found to be low relative to urea level s. We suggest, therefore, that in the absence of elevated levels of co unteracting compounds, urea may reach toxic levels and may be one fact or limiting the duration of estivation that is survived by these land snails.