The morphology of the gastrointestinal tract and food transit time in the fruit bats Pteropus alecto and P. poliocephalus (Megachiroptera)

The gastrointestinal tract of Pteropus alecto and P. poliocephalus was investigated by dissection and by light and electron microscopy. Food transit time was recorded for a variety of cultivated fruits and roentgenograms were obtained from animals fed with barium-labelled food. Minimum food transit time varied from 12 to 34 min for cultivated fruits but this was extended to 44 min by the addition of barium. There was little variation between the gastrointestinal tracts of the two species. The stomach has an elongated terminal part, and expanded cardiac and fundic regions which display a relatively thick gastric mucosa and abundant parietal cells. These features probably ensure exposure of ingested material to a substantial flow of HC1, perhaps counterbalancing a short exposure to digestive fluids. A caecum and appendix are absent. Well developed villi of the small intestine feature absorptive cells with relatively large microvilli (≤5-7 μm tall), which are probably associated with a rapid rate of absorption. The intestinal mucosa displays many more goblet cells in P. poliocephalus than in P. alecto. The large intestine is short and features prominent longitudinal folds; however, the mucosa undergoes a gradual transition, with number and size of villi decreasing in the distal part of the intestine. Although a distinct rectum cannot be distinguished, the colonic mucosa is restricted to a short segment, slightly shorter in P. poliocephalus than in P. alecto (5-7% and 8-10% of intestinal length respectively).This study highlights several anatomical features of the gastrointestinal tract, which probably allow fruit bats to rapidly process large quantities of food. The advantage of this to a flying mammal is a reduction in bulk carried in the digestive tract, enabling it to reduce the energy expenditure associated with foraging flights