Dietary modulation of intestinal enzymes of the house sparrow (Passer domesticus): testing an adaptive hypothesis

Insectivorous/frugivorous passerine species studied so far lack the ability to modulate intestinal maltase activity, in contrast to galliformes. We te sted for dietary modulation of small intestine (SI) enzymes including malta se in house sparrows to understand whether the difference between the galli formes on the one hand, and the passerines on the other, reflects a phyloge netic pattern (maltase modulated in galliformes but not passerines), a diet ary pattern (maltase modulated in granivores but not insectivore/frugivores ), some other pattern, or chance. We also tested the prediction that intest inal peptidase activity would be increased on a high protein (HP) diet. Bir ds were fed three diets high in starch, protein, or lipid for 10 days. For birds on the HP diet (60.3% protein) we observed the predicted upward modul ation of aminopeptidase-N activity, as compared with the lower-protein, hig h starch (HS) (12.8% protein) diet. In contrast, birds eating the HS diet h ad similar maltase and sucrase activities, and only slightly higher isomalt ase activity, compared with birds eating the high protein (HP), starch-free diet. Birds eating high lipid (HL) diet had low activities of both carbohy drases and peptidase. Considering that the statistical power of our tests w as adequate, we conclude that house sparrows show little or no increase in carbohydrases in response to elevated dietary carbohydrate. We cannot rejec t the hypothesis that maltase lability among avian species has a phylogenet ic component, or that high dietary fat has a depressing effect on both carb ohydrase and peptidase activities. (C) 2000 Elsevier Science Inc. All right s reserved.