DO NORTHERN BOBWHITE QUAIL MODULATE INTESTINAL NUTRIENT ABSORPTION INRESPONSE TO DIETARY CHANGE - A TEST OF AN ADAPTATIONAL HYPOTHESIS

We acclimated northern bobwhite quail (Colinus virginianus) to either chow (high carbohydrate/low protein) or crickets (low carbohydrate/hig h protein) and tested predictions of hypotheses based on the premise o f the economical design of animals. The adaptive modulation hypothesis predicts chat D-glucose uptake would be higher and L-proline uptake l ower in bobwhites acclimated to chow. The spare capacity hypothesis pr edicts that the capacity to absorb D-glucose actively will exceed the estimated nutrient load from daily food intake. There was no significa nt dietary effect on intestinal D-glucose (P = 0.8) and L-proline (P = 0.7) uptake rates measured in vitro using the everted sleeve techniqu e. In chow eaters maximal mediated D-glucose uptake summed along the e ntire length of intestine (53 cm) was far too low (7.2 mmol/d) to expl ain observed rates of glucose absorption in vivo (> 35 mmol/d). Hence, both predictions were falsified. In vitro uptake may not be an approp riate measure of the intestine's absorptive capacity because it does n ot measure possibly important pathways of passive absorption. There is increasing evidence that substantial passive glucose absorption occur s in some birds. If passive absorption predominates the adaptive modul ation hypothesis might not apply.