Digestive tract and leaf processing capacity of the stream invertebrateTipula lateralis

Abstract

We investigated the digestive potential of the stream detritivore Tipula lateralis Meigen, 1804 as a tool to understand and predict their ability to adapt to environmental changes, such as the nature of leaf resources reaching streams. The structure of larval digestive tracts and the presence of bacteria were investigated by scanning and transmission electron microscopy. Gut sections were investigated with respect to pH, microbial counts, and ability to digest protein and carbohydrates of unconditioned leaves of Alnus glutinosa (L.) Gaertn. and Eucalyptus globulus Labill. Alkaline conditions prevailed throughout the gut, with the highest values in the middle midgut (pH up to 10.8). An abundant microflora was closely associated with the caecum (~34 × 104colony forming units (cfu)) and hindgut (~50 × 104cfu), whereas the foregut and midgut seemed to be almost devoided of permanent bacteria (~0.45 × 104to ~2.1 × 104cfu). Digestion of T. lateralis seems to be optimized by compartmentalization: proteinase activity was limited to the midgut (0.017 ± 0.0054 change in absorbance units), while the capacity to release reducing substances was almost completely restricted to the caecum and being higher when alder was used as a substratum (0.437 ± 0.153 g glucose·mg–1·h–1). Eucalyptus oils resulted in a 25% reduction in enzymatic capability of gut extracts. Overall, the results suggest that T. lateralis has the enzymatic capability of feeding on recalcitrant leaves, but specific components of leaves such as oils have the potential to interfere with food intake by this leaf consumer. In a more general context, the results help to assess biological changes introduced by eucalyptus plantations in non-native areas.