Meeting Abstract

81.4  Wednesday, Jan. 6  House sparrow fledglings leave the nest digestively immature but more flexible than adults BRZĘK, P; CAVIEDES-VIDAL, E; KARASOV, W.H.*; Univ. of Białystok, Poland; Univ. of San Luis, Argentina; Univ. of Wisconsin, Madison wkarasov@wisc.edu

Young altricial birds may leave the nest before completion of their development. However, the relative level of their physiological maturity, including digestive function, is almost unknown. In some species, development is also concurrent with gradual change in diet type, e.g. from insect- to seed-dominated diet in House sparrow (Passer domesticus). We compared digestive function and its plasticity in adult House sparrows with those of nestlings about fledging age (12 days). Fledglings had lower intestinal disaccharidase activity and lower glucose absorption rate than adults, which correlates with fledglings’ lower maximal rate of energy assimilation. However, in contrast to adults, nestlings and fledglings were able to modulate tissue-specific activity of intestinal disaccharidases in response to varying diet starch content. We conclude that House sparrow fledglings are still not fully digestively mature, which could limit their ecological performance. On the other hand, nestlings have a capacity for diet-induced modulation of mass-specific activity of intestinal enzymes that is lost sometime between fledging and adulthood. We hypothesize that this ontogenetic decrease in the level of plasticity results from both the lack of necessity (completed diet switch) and presumably from costs involved in maintaining the capacity for such plasticity. Supported by NSF IOS 0615678 to WHK.