Maintenance of digestive performance in the turtles Chelydra serpentina, Sternotherus odoratus, and Trachemys scripta

In our continued investigation of the adaptive interplay between feeding ec ology and digestive physiology, we measured postfeeding responses of juveni le Chelydra serpentina, adult Sternotherus odoratus, and subadult Trachemys scripta, three aquatic turtle species that feed at frequent intervals and consume a catholic diet of plants and animals. In this study, we measured O -2 consumption rates from fasting and digesting individuals and compared in testinal nutrient uptake rates and organ masses of turtles fasted for one m onth with turtles sacrificed one day after the ingestion of a meal equivale nt to 5-11% of body mass. O-2 consumption during digestion peaked at rates 3.4, 2.1, and 2.7 times fasting values, respectively, for C.serpentina, S. odoratus, and T. scripta-factors much smaller than those documented previou sly for reptile species that normally consume large meals at long intervals . None of the turtle species experienced significant postfeeding changes in intestinal uptake of amino acids or D-glucose. Ratios of amino acid uptake rates to D-glucose uptake rates were much greater than 1.0 for each specie s, either fasted or fed, a finding characteristic of other carnivores as we ll. Total intestinal capacity to transport the amino acids L-leucine and L- proline and the sugar D-glucose did not change with feeding for any of the turtle species. None of the species experienced significant differences in intestinal mass or enterocyte morphology between fasted and fed individuals . Chelydra serpentina and T. scripta experienced no significant postfeeding changes in organ masses, and the only changes for S. odoratus were 59% and 42% increases in stomach wet and dry masses, respectively, upon feeding. T hus,juvenile C. serpentina, adult S. odoratus, and subadult T. scripta main tain the functional and morphological integrity of their guts during fastin g and exhibit only modest metabolic responses to feeding. We hypothesize th at these are adaptive traits characteristic of species that frequently cons ume and digest small meals.