An experimental test of dietary enzyme modulation in pine warblers Dendroica pinus

Modulation of gut function is important in an ecological and evolutionary c ontext because it likely determines what food items an animal can and canno t eat. We examined how diet affects activity of digestive enzymes in an omn ivorous bird, the pine warbler (Dendroica pinus). Pine warblers were fed in sect-based, fruit-based, and seed-based diets for similar to 54 d. We then measured activity of amylase, maltase, sucrase, aminopeptidase-N, trypsin, chymotrypsin, carboxypeptidase A, carboxypeptidase B, pancreatic lipase, an d carboxyl ester lipase. We predicted that carbohydrase activities would be highest in birds fed the diet highest in carbohydrates (fruit based), prot ease activities would be highest in those fed the diet highest in protein ( insect based), and lipase activities would be highest in those fed the diet s highest in lipid (insect based and seed based). Also, we predicted that p ine warblers would exhibit greater dietary modulation of enzyme activity th an reported for a less omnivorous congener, the yellow-rumped warbler (Dend roica coronata). All predictions were upheld, supporting the hypothesis tha t pine warblers modulate the activity of digestive enzymes in proportion to demand from substrates in the diet.