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Digestive tract and leaf processing capacity of the stream invertebrate Tipula lateralis

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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× 104 colony forming units (cfu)) and hindgut (~50× 104 cfu), whereas the foregut and midgut seemed to be almost devoided of permanent bacteria (~0.45 × 104 to ~2.1× 104 cfu). 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.

Nous avons déterminé le potentiel digestif du détritivore lotique Tipula lateralis Meigen, 1804 comme outil pour comprendre et prédire la capacité de l’insecte à s’adapter aux changements des facteurs du milieu, tels que la nature des ressources foliaires qui atteignent le cours d’eau. La microscopie électronique à transmission et à balayage nous a permis d’étudier la structure du tube digestif et la présence de bactéries. Des coupes du tube digestif ont servi à déterminer le pH, le nombre de bactéries et la capacité de digérer les protéines et les hydrates de carbone de feuilles non conditionnées d’Alnus glutinosa (L.) Gaertn. et d’Eucalyptus globulus Labill. Les conditions sont alcalines dans l’ensemble du tube digestif avec les valeurs maximales dans le milieu du tube moyen (pH atteignant 10,8). Il y a une abondante microflore intimement associée au caecum (~34 × 104 unités formant colonie (cfu)) et au tube postérieur (~50 × 104 cfu), alors que les tubes antérieur et moyen apparaissent à peu près libres de bactéries permanentes (~0,45 × 104 à ~2.1× 104 cfu). La digestion chez T. lateralis semble être optimisée par la compartimentation: l’activité de la protéinase est limitée au tube digestif moyen (0,017 ± 0,0054 de changement en unités d’absorbance), alors que la capacité de libérer des substances réductrices est presque entièrement confinée au caecum et elle est plus importante lorsque l’aulne est utilisé comme substrat (0,437 ± 0,153 g glucose·mg–1·h–1). Les huiles d’eucalyptus causent une réduction de 25% de la capacité enzymatique des extraits de tube digestif. Dans leur ensemble, nos résultats indiquent que T. lateralis possède la capacité enzymatique de se nourrir de feuilles résistantes; cependant, des composantes particulières des feuilles, telles que les huiles, peuvent perturber l’ingestion de nourriture chez ce consommateur de feuilles. Dans un contexte plus général, ces résultats contribuent à l’évaluation des changements biologiques consécutifs à l’implantation de l’eucalyptus dans les régions où il n’est pas indigène.

Document Type: Research Article

Publication date: August 1, 2006

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  • Published since 1929, this monthly journal reports on primary research contributed by respected international scientists in the broad field of zoology, including behaviour, biochemistry and physiology, developmental biology, ecology, genetics, morphology and ultrastructure, parasitology and pathology, and systematics and evolution. It also invites experts to submit review articles on topics of current interest.
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