Dietary flexibility in digestive enzyme activity is widespread in vertebrates, but mechanisms are poorly understood. When laboratory rats are switched to higher carbohydrate diet, activity of intestinal sucrase-isomaltase (SI) increases within 6-12 h, mainly by rapid increase in enzyme transcription followed by rapid translation and translocation to the intestine's apical, brush border membrane (BBM). We performed the first unified study of the overall process in birds, relying on activity, proteomic and transcriptomic data from nestling house sparrows (Passer domesticus). They switch naturally from low-starch insect diet to higher-starch seed diet, and SI is responsible for all their intestinal maltase and sucrase activities. Twenty-four hours after a switch to a high-starch diet, SI activity was increased, but not at 12 h post-diet switch. SI was the only hydrolase increased in the BBM, and its relative abundance and activity were positively correlated. Twenty-four hours after a reverse switch back to the lower-starch diet, SI activity was decreased, but not at 12 h post-diet switch. Parallel changes in SI mRNA were associated with the changes in SI activity in both diet switch experiments. This is the first demonstration that birds may rely on rapid increase in abundance of SI and its mRNA when adjusting to high starch diet. Although the mechanisms underlying dietary induction of intestinal enzymes seem similar in nestling house sparrows and laboratory rodents, time course for modulation in nestlings seemed half as fast compared to laboratory rodents. This may be understandable considering differences in ecology and evolution.
The Relative Abundance of Invasive House Sparrows (Passer domesticus) in an Urban Environment in South Africa is Determined by Land Use
