SEASONAL-CHANGES IN GUT CAPACITY IN THE WHITE-FOOTED MOUSE (PEROMYSCUS-LEUCOPUS) AND MEADOW VOLE (MICROTUS-PENNSYLVANICUS)

Changes in gut capacity may be important for a species adapting to increased energy requirements or decreased food quality hi a seasonal environment. We conducted a comparative study of seasonal changes in gut capacity in two rodent species with diets of different types. Although the lengths and masses of gut organs differed between species within a season, the species did not differ in the types of gut changes that occurred from summer to winter. All organs except the colon had significantly heavier wet and dry masses in winter than in summer. No significant differences in organ lengths, volumes, or surface areas occurred with season. Increased mass of the small intestine was due to large increases in the mass of the mucosa and smaller increases in the mass of the serosa. In winter, Microtus pennsylvanicus had significantly lower body mass than in summer. Peromyscus leucopus had no change in body mass in winter but may have used torpor as an energy-conservation mechanism. Energy-conservation adaptations in each species may have minimized the need for large changes in the gut organs.