Digestive Enzymes and Feeding Strategies of Three Stream Invertebrates

Abstract

Gut pH and ability to digest protein and carbohydrates were studied in three steam-dwelling detritivores (Gammarus tigrinus, Hydropsyche betteni and Tipula caloptera). In animals freshly collected from slightly acid streams, gut pH was close to neutrality in Gammarus and Hydropsyche, and moderately alkaline in Tipula. After three weeks in alkaline laboratory water (pH=8.5), gut pH increased significantly in all three invertebrates. Maximum proteinase activity toward Azocoll occurred at a pH higher than that found in freshly collected animals. Only Tipula was able to hydrolyze proteins of unconditioned maple leaves. Ability to digest major plant polysaccharides and to release sugars from unconditioned maple leaves was restricted to Gammarus. All three animals could digest starch and laminarin. Enzymes capable of breaking glycosidic linkages in small molecules, similar to those that might be released during microbial breakdown of leaf polysaccharides, were present in the gut fluids of all three animals. Fungal carbohydrases, ingested with maple leaves, remained active in the guts of Gammarus and Hydropsyche but not in Tipula.