Factors affecting the volume and macrostructure of gastrointestinal compartments in the tammar wallaby (Macropus eugenii Desmarest)

We explored the factors that govern the length, wet tissue weight and wet digesta content of the gut components of 100 tammar wallabies ( Macropus eugenii Desmarest) shot on the same night, by multivariate (discriminant) analysis and by allometric analyses based on simple linear regression, and on reduced major axis regression. The slope coefficient of the regression describing variation of whole gut content with body weight was not significantly different from isometry. Similarly, stomach length, content and tissue weight scaled isometrically with body weight, as did small intestine tissue weight and content and colon content. Colon tissue weight scaled allometrically with body weight. Length of caecum scaled to body weight was similar to that of browsing species, shorter than that of gazing species and varied with body size like that of larger species. Length of small intestine scaled to body weight was shorter, and length of colon longer, than that of similar-sized grazing species. There was a sexual dimorphism in gut morphology, females having a relatively greater amount of tissue in the stomach and colon, and a relatively longer caecum and colon. There was a reciprocal variation in the weight of digesta in stomach and hindgut, suggesting that hindgut content was evacuated as feeding proceeded. It appears that the hindgut may contribute to overall digestive strategy under conditions when reduction in feeding rate brings about a relative emtpying of the stomach.