Meeting Abstract

81.3  Wednesday, Jan. 6  The gastrointestinal tract as a nutrient balancing organ CLISSOLD, Fiona J.*; TEDDER, Benjamin J.; CONIGRAVE, Arthur D.; SIMPSON, Stephen J.; The University of Sydney; The University of Sydney; The University of Sydney; The University of Sydney fiona.clissold@bio.usyd.edu.au

Failure to provision tissues with an appropriate balance of nutrients engenders fitness costs. Maintaining nutrient balance can be achieved by adjusting the selection and consumption of foods, but this may not be possible when the nutritional environment is limiting. Under such circumstances, rebalancing of an imbalanced nutrient intake requires post-ingestive mechanisms. The first stage at which such post-ingestive rebalancing might occur is within the gastrointestinal tract (GIT) by differential release of digestive enzymes; releasing less of those enzymes for nutrients present in excess while maintaining or boosting levels of enzymes for nutrients in deficit. Here we use an insect herbivore, the locust, to show for the first time that such compensatory responses occur within the GIT. In response to precise manipulation of dietary composition that takes account of both the concentration and ratio of macronutrients, we show that proteases and carbohydrases were released differentially. Furthermore, this difference translated into differential extraction of macronutrients from host plants, with locusts sacrificing maximal nutrient assimilation rate for supplying a ratio of protein to carbohydrate that was closer to optimal than in the diet. In contrast to the current view that physiological and structural plasticity in the GIT serves to maximize absorption of all nutrients: our data show that GIT plasticity is integral to maintenance of nutrient homeostasis.