AJP - Regulatory, Integrative and Comparative Physiology, Vol 269, Issue 2 413-R420, Copyright © 1995 by American Physiological Society
Dietary modulation of intestinal hydrolytic enzymes in yellow-rumped warblers
D. Afik, E. C. Vidal, C. Martinez del Rio and W. H. Karasov
Department of Wildlife Ecology, University of Wisconsin-Madison 53706, USA.
Many birds exhibit seasonal switches in diet and thus alter the nutrients
predominating their food intake. We tested for dietary modulation of small
intestine (SI) enzymes in yellow-rumped warblers, a species for which such
diet changes are well documented. Birds were fed three diets formulated
from either fruit, insect, or seed. We predicted that SI carbohydrases and
peptidases would be modulated in direct correlation with relative levels of
dietary carbohydrate and protein, respectively. Aminopeptidase N activity
was about twice as high in birds eating the highest protein content diet.
In contrast, there was no significant dietary effect on any of the
carbohydrase activities. There was a proximal-to-distal decrease in
activities of all the carbohydrases but not aminopeptidase N. The
carbohydrase levels of yellow-rumps are relatively low when compared with
other species in the same family and most similar to lower levels found in
primarily insectivorous birds rather than in primarily granivorous or
nectarivorous species. Considering this and the fact that they do not
exhibit dietary modulation of carbohydrase levels, we conclude that
yellow-rumps are not highly adapted for handling dietary carbohydrates,
especially starch, although they might still efficiently break down and
absorb sucrose and maltose if retention time were sufficiently long.
