Variation in Cellulase Activity in Physa heterostropha (Gastropoda) and Other Species of Gastropods in a New England Pond

Cellulase activity in whole animal homogenates of Physa heterostropha (Gastropoda) from White Horn Brook, Rhode Island, was determined from 7 July 1980 to 17 June 1981. Cellulase activity was negatively correlated with air temperature (P<.01). Enzyme from snails acclimated in the laboratory for 6 days at various temperatures also demonstrated this inverse relationship with temperature. Low Q 0 values were observed between 10 and 20 C. Starvation of Physa heterostropha for 48 hr did not result in cellulase activities different from those observed in freshly collected individuals. Starvation of Pseudosuccinea columella for 72 hr did result in significant reduction in cellulase activity. Optimum pH values, using a citric acid/phosphate buffer, for cellulases of Physa heterostropha and Pseudosuccinea columella were 6.5 and 6.95, respectively. The cellulase activities of four gastropod species inhabiting Peckham Farm Pond, Rhode Island, in July 1981, expressed as Ag glucose * min-' * mg protein' and ,ug glucose * min-l * mg snail-' (i 1 SD) were Physa cf. skinneri 93 i 19, 2.75 i 0.26; Pseudosuccinea columella 273 4 26, 6.69 0.52; Gyraulus circumstriatus 204 22, 6.34 + 1.85; Helisoma trivolvis 184 i 20, 3.28 + 0.23. INTRODUCTION Gastropods in low order streams and small ponds are exposed to relatively large amounts of cellulose as allochthonous input. Individuals possessing enzymes with the ability to break B1-4 glycosidic bonds of cellulose to form oligosaccarides could take advantage of this energy source. "Enzymes" used for this purpose are collectively termed cellulase. A good review of the cellulase complex is given by Agnisola et al. (1981). Snails with high cellulase activity can efficiently assimilate Scenedesmus, a green alga with thick cell walls (Calow and Calow, 1975). A positive relationship was observed between the amount of cellulose in the diet of bivalves and their cellulase activity (Crosby and Reid, 1971). The purpose of my study was (1) to determine the variability of the cellulase temperature-activity curves of Physa heterostropha (Physidae: Gastropoda) over time, and (2) to compare the cellulase activities of four species of freshwater snails inhabiting the same small pond. MATERIALS AND METHODS Sampling.-Specimens of Physa heterostropha were collected in a small tributary to White Horn Brook, Kingston, R.I., on 7 July, 1 August, 10 October 1980 and 17 June 1981. Large numbers of Belostoma sp., an aquatic hemipteran, in late June 1981 may have securely depressed the snail population. Belostoma were observed consuming Physa both in the field and laboratory, and snails could not be found where they were abundant 2 weeks earlier. A new sampling site along White Horn Brook was used to collect samples of P. heterostropha on 5 July 1981. Subsequent drying of White Horn Brook precluded additional sampling. Specimens of Gyraulus circumstriatus, Physa cf skinneri, Helisoma trivolvis and Pseudosuccinea columella (previously Lymnaea columella) were collected from a small, tea-colored pond near the University of Rhode Island Peckham Farm in July 1981. Snails were identified by Eileen Jokinen. Cellulase assay. Snails were either assayed for cellulase when fresh from the field or frozen immediately. The snails were ground by hand in a glass-on-glass tissue