DIETARY CHEMISTRY AND ALLOMETRY OF INTESTINAL DISACCHARIDASES IN THE TOAD BUFO-SPINULOSUS

In amphibians, digestive physiological responses to chemical compositi on of food may occur through variations in the interplay between the i ntestinal hydrolysis of dietary substrates and their uptake in respons e to ontogenetic development and body size. In these animals it is exp ected that after metamorphosis, the intestinal hydrolysis of dietary s ubstrates involved in energy supply, rather than in growth requirement s, should decline with body moss (m(b)) due to the higher mass-specifi c energy requirements of small-sized animals (allometric effect). In t he toad Bufo spinulosus we test this hypothesis by measuring the activ ity of the intestinal disaccharidases sucrase, maltase and trehalase a s a function of m(b) and, the response of intestinal sucrase and treha lase by effect of dietary acclimation. We found that large-sized B. sp inulosus feeding on the same dietary items as smaller individuals, exh ibited a decreased activity of intestinal disaccharidases with m(b), p robably due to the higher energetic requirements of smaller individual s, and not to dietary adaptation. Our experiments of dietary acclimati on allow us to conclude that adults are unable to modulate their disac charidase activity in response to dietary chemistry. The lack of labil ity in these digestive enzymes seems to support the hypothesis of dige stive physiological rigidity in adult amphibians and that modulation o f intestine physiological activity can cease to operate during ontogen etic development.