Effects of diet quality on phenotypic flexibility of organ size and digestive function in Mongolian gerbils (Meriones unguiculatus)

In the context of evolution and ecology, there is a trade-off between the benefits of processing food through a digestive system with specific phenotypic attributes and the cost of maintaining and carrying the digestive system. In this study, we tested the hypothesis that digestive modulations at several levels can match each other to meet the energy and nutrient demands of Mongolian gerbils, a small granivorous rodent species, by acclimating them to a high-quality diet diluted with alfalfa powder. Mongolian gerbils on the diluted diet maintained metabolizable energy intake by an integrated processing response (IPR), which included increases in dry matter intake, gut capacity and rate of digesta passage after 2-weeks of acclimation. Down-regulation of hydrolytic enzyme activity in the intestinal brush-border membrane supported the adaptive modulation hypothesis. The absence of up-modulation of summed enzyme hydrolytic capacity on the diluted diet indicated that greater mass of small intestine on a high-fibre diet is not a direct indicator of digestive or absorptive capacity. Changes in mass of vital organs and carcass suggested that the amount of energy allocated to various organs and hence physiological functions was regulated in response to diet shift.